Control of appetite. Personal and departmental recollections

Appetite xxx (2012) xxx–xxx

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Research review

Control of appetite. Personal and departmental recollections q G.R. Hervey Department of Physiology, University of Leeds, UK Garth House, Beryl Lane, WELLS, Somerset, BA5 2XQ, UK.

a r t i c l e

i n f o

Article history: Received 21 July 2012 Received in revised form 21 September 2012 Accepted 10 October 2012 Available online xxxx Keywords: Parabiosis Ventromedial hypothalamic obesity Body fat Negative feedback Control mechanisms Lipostatic hypothesis Liporegulatory substance exchanged in parabiosis Department of Experimental Medicine R.A. McCance G.C. Kennedy

a b s t r a c t This paper is partly a brief academic autobiography. It begins in 1942 when I volunteered for lifesaving research for the Royal Navy. This brought me to a Department headed by a very unusual Professor, R.A. McCance, an eccentric and a polymath. I have tried to say something about him and the Department. After the war, McCance gave me the Ph.D. project: The Effect of Ventromedial Lesions in the Hypothalamus in Rats in Parabiosis. It had recently been discovered that such lesions cause obesity, and energy balance was an active field. Parabiosis dates to the nineteenth century but had not previously been used in this context. The results were uniform and dramatic. I have briefly presented them, with a review of my own and others’ subsequent work. This leads to a picture of a negative feedback system, which regulates food intake to maintain a near-constant proportion of fat in the body, and maintains energy balance with increasing precision as time progresses. The parabiotic effect strongly suggests that there must be a blood-borne link between body fat and the hypothalamus. I have tried to make the case as strongly as I can for further work to identify this link, which has obvious scientific and clinical importance. Ó 2012 Elsevier Ltd. All rights reserved.

Contents Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Research for the Navy, begun in wartime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Professor R.A. McCance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Department of Experimental Medicine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gordon Kennedy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The start of my work on the control of food intake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . My Ph.D. project (1953–1956). Ventromedial hypothalamic lesions in rats in parabiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Subsequent work on parabiosis with obese and lean partners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Parabiosis in mice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Obesity from lateral hypothalamic stimulation in rats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Obesity from tube-feeding in rats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Obesity in Zucker rats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Denials of ‘the signal’s’ existence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . My subsequent physiological career . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Negative feedback control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The concept of negative feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Application of control system thinking to energy balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Energy expenditure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Our last experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Retirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The nature of the ‘signal’ from fat to food intake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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q This is the second paper in the Special Part-Issue of Appetite entitled ‘‘Hervey, Harris and the parabiotic search for lipostatic signals,’’ guest edited by Gerard P. Smith and David A. Booth. Acknowledgements: The author acknowledges much support from Prof. Gerard Smith and Prof. Ruth Harris in writing this paper. E-mail address: [email protected]

0195-6663/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.appet.2012.10.008

Please cite this article in press as: Hervey, G. R. Control of appetite. Personal and departmental recollections. Appetite (2012), http://dx.doi.org/10.1016/ j.appet.2012.10.008

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G.R. Hervey / Appetite xxx (2012) xxx–xxx

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Introduction

Professor R.A. McCance

Part of this paper, written at the age of 88, is based on personal recollection. It is partly autobiographical, and says something about research in the UK during and after the Second World War, and some of the personalities involved. It reviews work on a physiological effect that I believe I was the first to describe, in 1957, and research that followed. I believe this area has been neglected, relative to its scientific interest and potential clinical importance. I very much hope that this review will stimulate others to carry on work in this field and find it rewarding.

I first met Professor McCance when I responded to the appeal for volunteers for research for the Navy. In the First World War McCance served with great bravery in the Royal Navy as a pilot in the earliest days of flying off warships. He first made his name as a nutritionist, carrying out vast numbers of analyses of foods – in those days by the laborious techniques of ‘wet’ chemistry – initially to establish the types and amounts of the many kinds of carbohydrates in foodstuffs, in the interests of better control of diabetes. He was a founder member of the Nutrition Society. His work in the field of diabetes, mainly at King’s College Hospital, also led to him becoming a pioneer in the UK on the clinical physiology of sodium, and thus to a better understanding of body fluid physiology. This led to his election as Fellow of the Royal Society and the creation for him of the Department of Experimental Medicine at Cambridge. He insisted on the Department’s name in honour of Claude Bernard, whom he greatly admired. Dr. Elsie Widdowson wrote an excellent short biography of McCance in an Obituary Notice (Widdowson, 1993), though she says nothing about her part in his scientific life. McCance met Widdowson at King’s College Hospital, beginning a life-long partnership in research. One of the first fruits of this was the still current handbook, The Chemical Composition of Foods. In the early days of the Second World War McCance, Widdowson and the Department team made an important contribution by their advice to the Government on food rations. Their recommendations were not just theoretical. McCance, Widdowson and others from the Department spent 6 weeks doing strenuous mountain walking in the English Lake District, living entirely off the suggested rations. These would seem extremely meagre to modern mouths, but the team’s members emerged fitter than ever. It has been said that the British population has never been fitter than when it had to live on McCance’s suggested rations. Fortunately one of McCance’s many eccentricities was not included in the recommendations. He only ate once in the day – ‘‘like a dog’’ as his wife once said. This could cause embarrassment at formal dinners: where vegetables were offered in turn to guests, McCance might take the entire tureen of potatoes! After the war McCance and a number of colleagues spent many months in Germany studying the effects of severe malnutrition, particularly in children, and the best means of facilitating recovery. The colleagues included Lois Thrussell (now Strangeways), to the best of my knowledge at 90 the only other member of the Department in my time who is still with us. McCance’s research was always based on accurate measurement of all the relevant physiological variables, but I think he preferred investigating situations where there were large changes. His clinical reputation was enhanced by some spectacular successes. One was Daphne, who became his devoted Secretary. From an early age she had become increasingly crippled by multiple deformities. Her condition appeared to be severe rickets but treatment with Vitamin D in conventional dose had no effect. McCance gave her 250,000 units per day – and she was cured (though still requiring much work by orthopaedic surgeons). The biochemistry of D in this rare condition was unravelled later.

Research for the Navy, begun in wartime My research career started in wartime, working for the Royal Navy. As soon as I had come up to Cambridge in 1942 to study medicine, an appeal went out for students to work in Professor McCance’s Department of Experimental Medicine as subjects for research on the problems of survival after ships had sunk. Two thirds of Naval casualties had died in the water and not in action, mostly in cold climates and with little prospect of early rescue. The major outcome was the tented inflatable life-raft. In 1950, under the late Eric Glaser and while a Temporary Acting Surgeon Lieutenant and ship’s doctor on the minesweeper HMS True Love (I was engaged at the time!), I was responsible for physiological measurements on subjects in the life-raft: in Arctic and Tropical waters, in mid-Atlantic, and later in a controlled environment in Cambridge. The life-raft is now standard equipment world-wide. The work on survival in McCance’s Department led to fundamental knowledge. We confirmed with precise measurements J.L. Gamble’s suggestion that taking 100 g glucose daily saves more than twice its weight of water, through reducing protein catabolism and thus excretion of urea, which is extravagant of water. So 100 g/day glucose should always be included in survival rations. In the course of investigating the effects of drinking sea water – a very bad thing to do – we discovered osmotic diuresis, and came close to discovering the hyper-osmolarity of the renal medulla. I was also much involved in drug treatment of motion sickness, and devised an early crossed-over design for comparing remedies. A little later I began working with Frank Golden in the Institute of Naval Medicine, which possesses a refrigerated swimming pool. This research included the relationship between body composition and the rate of body cooling in cold water, and the explanation of the ‘after-drop’ in central body temperature that occurs after rescue from cold water. Although Frank was a serving Naval officer, I was able to persuade the Navy to allow him to spend time on research: he gained a Ph.D., reached the rank of Surgeon Rear Admiral and became a world authority on survival in cold water. The research on survival started my own interest in control mechanisms. The work for the Navy – and for all involved in disasters at sea – continued in McCance’s Department for 20 years after the war: I feel very privileged to have had a part in this, and continued to have some involvement until – and even after – I retired. The association also helped my teaching. For 20 years I took students annually for a week’s course at the Institute of Naval Medicine. I remained involved in Naval research until my retirement, becoming a Consultant in Physiology to the Royal Naval Medical Service and succeeding Professor McCance as Chairman of a Medical Research Council Survival at Sea Committee.

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G.R. Hervey / Appetite xxx (2012) xxx–xxx

Another triumph was Peter. Since radiotherapy for a brain tumour Peter had come to weigh about twice his age in stones: when first seen at age 21 he weighed 260 kg and was helpless in bed. Over 18 months as McCance’s patient, with the assistance only of the hospital dietetic department, his weight fell to 70-odd kg. I last saw him, still well, in 1993 at the Memorial Service for Professor McCance in Sidney Sussex College Chapel. On a lighter note, McCance practised a sort of ‘Lifemanship’. He attended meetings of nutritionists, physiologists, paediatricians, endocrinologists and other experts. If, say, he was among endocrinologists he would call himself a paediatrician, and so on. In this way he always had ‘something extra’ – and worthwhile – to say on the subject under discussion. The Department of Experimental Medicine I think I can say that McCance’s Department was like no other, making it hard to describe. I was based there from 1942 to 1957, with breaks for clinical studies and Naval Service. It was jointly funded by the University and the Medical Research Council. For some of this time I was McCance’s Senior House Officer, looking after and investigating his patients in his nine beds in Addenbrooke’s Hospital. My impression was that McCance did not do much work in the laboratory, but wrote papers in his office. He also worked with pigs at his home and farm in Bartlow. Elsie Widdowson and technicians working under her did the chemical analytical work. The partnership with Dr. Widdowson was also critical to the successful running of the Department. McCance was not a ‘difficult’ or unkind person, but he was an eccentric and entirely absorbed in his research. When misunderstandings arose, Elsie was always there to help, and always seemed to resolve the difficulty. The Department occupied part of the ground floor of the University Pathology building, with access to a mechanical workshop, and animal accommodation in the top floor. There was a large central area that served for meetings, dining-room, kitchen and general purposes, surrounded by variously sized offices and laboratories. We were required to meet there every day for lunch (since it was wartime often based on pork from McCance’s farm). He used to cycle the 14 miles from his home to the Department and back every day (supposedly composing his next day’s paper in his head and ignoring any traffic). His own lunch was an apple (he was a connoisseur of English apples) and a cup of black coffee. These lunches provided an opportunity for members of the Department such as myself to meet distinguished scientific visitors from all over the world. One of my assignments, stimulated by McCance’s patients, was to work with Paul Fourman on potassium deficiency. Six weeks of a potassium-deficient diet with everything possible accurately measured was a good experience in do-it-on-yourself physiology. Perhaps it qualified me to arrange weekly practical classes in McCance’s Department for final year students from the Cambridge Department of Physiology in which they ran experiments on themselves. I continued such classes in my subsequent teaching career. Very sadly, Paul Fourman died early, as it happened in my Department in Leeds. McCance and Widdowson both worked into their nineties and died virtually in harness. Elsie was a few years younger than Mac.

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UK of making lesions in the ventromedial hypothalamic nuclei of rats (Kennedy, 1950). Also of particular interest to me, he interpreted the results in terms of a negative feedback control system controlling food intake in normal animals; and hypothesized that the amount of fat in the body provided the information for the feedback signal. I can not recall the exact dates, but I think he arrived at the Department about a year after I had begun my parabiotic– hypothalamic experiments. Very tragically, while I was still in the Department, he caught a virus encephalitis while on an academic visit overseas. On return he attempted to resume his work, devotedly supported by his wife Minnie, but this could not continue for long. The death of such a fine experimenter and powerful thinker was a great loss to the field of energy balance and appetite. Gordon must have been older than I, and since he had not taken a medical degree would have had more scientific experience. He was also a very different personality. So I may have had some worries when he arrived in the Department. However, Gordon never used parabiosis, and the parabiotic/ hypothalamic experiment was my Ph.D. project. Neither Gordon nor McCance ever suggested that Gordon and I should collaborate. I never knew what attracted Gordon to move from the presumably excellent facilities of the National Institute to the comparatively primitive conditions in the Department. Perhaps it was just the attractions of Cambridge. Nor, of course, do I know of any plans McCance may have had for Gordon, who would certainly have been an asset to any research department. He had an office in the Department, and the use of the animal facilities; before he died he was working on endocrine factors affecting body composition in rats (as I did later in my career). I think I can say that Gordon and I became good friends. I can remember good discussions with him, in his office and at the Eagle (the local hostelry, serving much of the Downing Street scientific community at Cambridge). We certainly shared enthusiasm for looking at biological systems in terms of feedback control.

The start of my work on the control of food intake After coming out of the uniformed Navy in 1952, I continued with Naval-related research in McCance’s Department for the next year or so. In late 1953, as I recall, McCance suggested that I should study for a Ph.D. He suggested that the subject should be the effects of obesity-producing lesions in the ventromedial hypothalamus in

Gordon Kennedy Since Gordon Kennedy worked in the Department of Experimental Medicine while I did, and laid the foundations in the UK of the field I was to work in, I am anxious to pay him an adequate tribute. He had a first-class mind. While in his previous post at the MRC National Institute for Medical Research, he was the pioneer in

Fig. 1. Normal pair of young adult parabiotic rats (Hervey (1959) with permission).

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G.R. Hervey / Appetite xxx (2012) xxx–xxx

one of a pair of rats joined in parabiosis, and investigate the effects on its partner. McCance’s interests had long included food intake and body composition. He would have been well aware that earlier investigators such as Adolph (1947) had shown that animals such as rats adjusted their food intake to balance their energy requirements. He must have been excited by the discovery that damage to the ventromedial nuclei of the hypothalamus caused hyperphagia and obesity: it was a ‘hot topic’. One of the foundations of endocrinology had been the observation that, in a pair of human conjoined twins, the conjoined twin of a mother who was lactating also lactated. This strongly suggested that lactation is controlled by something circulating in the blood. Rats united in parabiosis had subsequently thrown light on several physiological systems that involve blood-borne signals, such as the control by the pituitary of the adrenal glands and gonads. I do not recall any specific discussion between McCance and myself as to what outcome we might expect from the suggested experiment, but in view of the already known effects of ventromedial hypothalamic lesions in single animals I think we both expected obesity – if there was any effect – in the partners of animals made obese by ventromedial lesions. As to practicalities, I do not know whether funding had become a problem for the Department, or whether my facilities reflected McCance’s disregard for the necessities of laboratory research. I had a laboratory to myself (but not an office), but it took 3 years to get a sink put in. With the aid of the workshop I designed and had built a simple stereotaxic machine, using parts from old brass microscopes. It seemed obvious that the pairs of rats should be genetically uniform. In the first experiments I used a hooded strain from the Lister Institute, but subsequently was fortunate that the Compton Institute for Animal Pathology could offer two strains which had been inbred for many generations: one hooded (PVG/C) and one albino (WAG/C). I used first generation hybrids between these in all subsequent experiments. These are still genetically uniform but show hybrid vigour. The Institute for Animal Pathology was closed during Mrs. Thatcher’s regime of ‘cuts’, but I maintained my breeding colony until I retired. It is not essential to use rats of this degree of genetic uniformity, but the success rate of parabiosis with the F1 hybrids – about 90% in my hands – falls progressively with less genetic uniformity. I think it is also very important that animals need to be ‘happy’ if long-term experiments are to be successful. (When I moved to another Department I found that breeding success was not as good as it had been in McCance’s Department. I had a Victorian house with

Fig. 2. Under surface of rat’s brain post-mortem, showing effective hypothalamic lesions. Traced from a colour photograph (Hervey (1959) with permission).

Fig. 3. Parabiotic pair with hypothalamic lesions in one member (the left as seen in the photograph), after spontaneous death of its unoperated partner, approximately 2 months after the lesions in the left member had been made (Hervey (1959) with permission).

a large kitchen and I moved the breeding colony to this, where the rats became my four childrens’ pets. Breeding has never been so successful! The minimum requirement is an animal technician sympathetic to rats; a transistor radio also helps.) There was a good description of the operative procedure for parabiosis in the literature (Bunster & Meyer, 1933), which I modified to give a better and more stable long-term union. The two rats in an otherwise untreated parabiotic pair have identical appearance (Fig. 1). I measured the exchange of blood by using Evans Blue. (We had used Evans Blue extensively in human work on survival at sea. I was not then aware that its use in parabiotic rats and the calculation of blood exchange had been described earlier). In my experiments it averaged 1% of one rat’s blood volume exchanged in each direction per minute. The value of the parabiotic preparation is that, in principle, the otherwise untreated partner of an animal that has been treated in some way is exposed to any changes the treatment may have caused in the composition of the treated animal’s blood. The time-course of these changes, however, is critical since the rate of exchange of blood is relatively fixed. The technique for making lesions in the ventromedial hypothalamus had been developed by previous workers. The site of effective lesions (Fig. 2) can be checked by the naked eye post-mortem. (Figs. 1–4 are from my original photographs or drawings included in my 1959 paper.) I measured body fat by removing intestinal contents and shredding and drying the carcasses, getting water content; and then extracting fat by repeated changes of petroleum ether in large beakers and drying again. I think the accuracy was quite good, and as it turned out the changes were large.

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Fig. 4. Growth curves and post-mortem body weights of a group of two parabiotic pairs and one single rat. All were males and litter-mates. At approximately 5 months old, lesions were made in the hypothalamus of the right-hand member of one pair. The left-hand member of this pair appeared to be moribund approximately 2½ months later; all the animals were then killed. The solid lines are half the weight of each of the pairs during life. The dot-and-dash line is the weight of the single untreated rat. The closely dashed lines are the presumed weights of the individual rats in the pair in which lesions were made in the right-hand member, from the time of making the lesions to death. The solid circles are the individual body weights after death and separation of the parabiotic pairs (Hervey (1959) with permission).

My Ph.D. project (1953–1956). Ventromedial hypothalamic lesions in rats in parabiosis As expected the lesioned animals rapidly gained weight after the lesions had been made and became obviously obese (Fig. 3). Their partners, however, lost weight and some died, apparently from starvation. They showed no interest in food: even when it was offered by hand, they did not eat but simply looked away. There was no evidence that any changed behaviour by the lesioned animals was interfering with their partners’ feeding. The abdominal viscera of the rat with hypothalamic lesions contained visibly much larger amounts of fat than the viscera of otherwise untreated parabiotic pairs. The parabiotic partners of the obese rats had lost all visible fat in the viscera (Hervey, 1957, 1959). This seems as clear-cut a result as one could wish for. Provided that the operative techniques – parabiosis and ventromedial hypothalamic lesions – were successful (around 90% in each case), I have never experienced any contrary results. A typical course of body weight changes in one group of five litter-mate male rats is shown in Fig. 4. At approximately 1 month old, two pairs were joined in parabiosis. At 5 months ventromedial hypothalamic lesions were made in the right-hand animal of one of these pairs. All were killed at 7½ months when the weight curves were beginning to flatten out. The weights at post-mortem were: the untreated single rat 363 g; the otherwise untreated pair of rats in parabiosis 281 and 287 g; the parabiotic rat with lesions 596 g; its parabiotic partner 236 g. At the end of the experiment the percentage fat contents (means of all rats in this experiment) were as follows: untreated single rats (mean of 14), 12.4%; in otherwise untreated rats in parabiosis, the means of the left and right in five pairs were 6.7% and

6.4%; the mean of eight comparable rats not in parabiosis but which had received ventromedial hypothalamic lesions was 49.4%; the mean of eight rats in parabiosis which had received ventromedial hypothalamic lesions was 48.5%; the mean fat content of their unlesioned partners was 1.6%. I also found that, in otherwise untreated parabiotic pairs, the fat contents of each partner were just over half those seen in rats not in parabiosis. Subsequent work on parabiosis with obese and lean partners Parabiosis in mice Haessler and Crawford (1967), in the course of work on the fatty acid composition of body fat in obesity caused by ventromedial hypothalamic lesions, reported that when lesioned mice were reduced to normal weight by restricted feeding and then joined in parabiosis with normal mice and allowed to feed freely, they rapidly gained weight; their partners with intact brains became emaciated. The authors pointed out that this replicated my experiments with rats. No evidence was found for changes in fat composition. (The success rate reported makes me wonder whether mice available to experimenters may be more genetically uniform than rats.) Coleman and Hummel (1969), working in the context of diabetes, found that congenitally diabetic mice became grossly obese. When they were joined in parabiosis with non-diabetic mice, there were no great changes in diabetic status in either partner, which implied that any exchanges of insulin or glucose do not over-ride existing metabolism. The non-diabetic partners, however, died before the diabetic partners in 11 of 12 pairs. Their blood glucose steadily decreased before death (even though glucose might cross

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Fig. 5. Body weights and food intakes before and during lateral hypothalamic stimulation. Means of two groups of six parabiotic pairs. In the body weight graph the solid circles are means for the rats in the group not subjected to stimulation; the open circles are means for the stimulated group, before and after the period of lateral hypothalamic stimulation of one rat (shown below the graph). The dashed lines show the presumed weight changes over the stimulation period for these pairs in which one partner received stimulation and the other did not. The solid circles at the end of the experiment are the mean weights for all rats after separating the pairs and weighing post-mortem. In the food intake graph, before the period of stimulation the vertical columns are means for all rats in the experiment. During stimulation, the dashed columns are the mean food intakes of the stimulated rats as stimulation progressed; the solid columns are the mean food intakes of their non-stimulated partners. The dashed horizontal line shows the food intakes before the stimulation period for comparison. (Hervey et al. (1977) with permission).

from the diabetic partner); their stomachs were empty of food; the pancreas and liver were very small; their bodies contained little or no adipose tissue. They had evidently ceased to eat significantly. The authors suggested that this was a result of the obesity of the congenitally diabetic partner, due to the circulating ‘satiety factor’ I had reported in rats. Obesity from lateral hypothalamic stimulation in rats The background to this investigation was that Parameswaran – a very bright student – had registered for a Ph.D. in my department, and I had shown him the technique of parabiosis. Some time earlier – I think at a gathering in Lausanne – I had met Prof. L. De Ruiter, whose Department in the Netherlands had developed the technique of long-term electrical stimulation of the lateral hypothalamus in rats, something I had never attempted. De Ruiter readily agreed to Parameswaran visiting Groningen to learn the technique and apply it to rats in parabiosis, adding some investigation of the nature of the circulating factor. I have to say that De Ruiter and I were only among the authors of the resulting papers as the respective Heads of Department and originators and organisers of the project. I think this would be improper by modern standards, but I wanted Parameswaran’s work to be part of our group’s. He made a first-class job of his project, and it was good that he headed the list of authors in the full paper. Hervey, Parameswaran, and Steffens (1977) and Parameswaran, Steffens, Hervey, and De Ruiter (1977) reported that in parabiotic pairs made as in my 1959 paper, electrical stimulation of the lateral hypothalamus in one rat caused that rat to overeat and become obese, very much as after lesions in the ventromedial hypothalamus; and that, as the overeating in the stimulated rat continued, food intake in the partner was progressively reduced (Fig. 5). The authors attributed this effect to the transmission of a relatively long-lived ‘humoral satiety factor’ through the parabiotic union. They tentatively concluded that this could not be insulin, glucagon or a circulating nutrient. Obesity from tube-feeding in rats Nishizawa and Bray (1980) were concerned to resolve the conflict: between the positive findings I had reported in 1959 and Parameswaran and colleagues had reported in 1977, and the negative

findings reported by Han and colleagues in 1963 and Fleming in 1969 (see below). They employed over-feeding by stomach tube to induce obesity in one rat of a parabiotic pair, avoiding disturbing the hypothalamus. They checked the existence of a crosscirculation with Evans Blue at four half-hour intervals: the mean was 0.7% of each rat’s blood volume exchanged per minute. Their results confirmed our group’s positive findings. When the food intake of the tube-fed partner was increased (on a high fat or high-carbohydrate diet) it became obese; the partner feeding freely substantially reduced its food intake and lost weight and fat (fat content was calculated from the weight of specified fat pads). Candidates for the blood-borne factor were discussed. Several known peptide hormones had been suggested, but these generally have too short a half-life. The paper concludes ‘‘Although the nature of this circulating ergostatic or lipostatic factor is unknown, its identification will add significantly to the understanding of the regulation of body fat.’’ Interestingly, ‘‘ergostatic or lipostatic’’ implies that the authors regarded regulation of body fat content as the means of regulating energy balance. Harris and Martin (1984, 1986) also used tube-feeding. Exchange of blood through the parabiotic union averaged 1.6% of blood volume. Doubling the food intake by tube-feeding immediately and totally suppressed feeding by the tube-fed rat and produced the expected obesity. The partner’s food intake decreased, but this was doubtfully significant. In my experience it is difficult to estimate the effect on the food intake of a parabiotic partner to a treated rat without specialized caging. The percentage of fat in the partner’s body was markedly reduced. In the experiment in the first paper the fat content of the free-feeding parabiotic partners averaged 8.1%; in the tube-fed rats in parabiotic pairs it was 40.3% and in their partners it was 3.4%. In the second paper the figures were 10.0%, 38.5% and 6.1% respectively. It took 23 days of over-feeding of the tubefed rats for the effect of the ‘lipid-depleting agent’ to appear in the partners; by 39 days the partners’ fat content was halved. The investigators examined in some detail known hormones which might be the lipid-depleting factor, but concluded that it had yet to be identified. In earlier work with ventromedial hypothalamic lesions the partner ceased to eat with a timing that suggested a response to the fat content of the treated rat, rather than to its excessive food intake. Parabiosis might cause reduction of fat stores through decreased fat synthesis or increased catabolism.

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Obesity in Zucker rats Ruth Harris was a Ph.D. student at Leeds with the studies of Zucker rats her project. She joined congenitally obese Zucker rats in parabiosis with lean rats, usually littermates (Harris, Hervey, Hervey, & Tobin, 1987). (As with Parameswaran’s project, my name was included as a courtesy.) The success rate was only 37% of 112 pairs made. This was attributed to disharmony due to the lower genetic uniformity among the rats of this strain, causing immune reactions when blood exchange developed. Among the survivors the plasma exchange rates were very uniform at about 1.3% of one animal’s blood volume exchanged per minute. The results for successful pairs (in the same order as the PVG/C and WAG/C results above) were: Male rats: post-mortem weights: non-obese single rats 378 g; non-obese rats in parabiotic pairs 252 g; obese rats not in parabiosis 485 g; obese rats in parabiosis with non-obese rats 413 g; their non-obese partners 212 g. Percentage fat contents: untreated non-obese single rats 12%; otherwise untreated non-obese rats in parabiotic pairs 7.5%; obese rats not in parabiosis 45%; obese rats in parabiosis with non-obese rats 43%; their non-obese partners 4%. Female rats: post-mortem weights: non-obese single rats 228 g; non-obese rats in parabiotic pairs 188 g; obese rats not in parabiosis 481 g; obese rats in parabiosis with non-obese rats 347 g; their non-obese partners 152 g. Percentage fat contents: untreated non-obese single rats 12%; otherwise untreated non-obese rats in parabiotic pairs 7.5%; obese rats not in parabiosis 53%; obese rats in parabiosis with non-obese rats 48%; their non-obese partners 3%. These show a similar picture to the results of the experiments with PVG/C and WAG/C rats. They imply that the genetic abnormality of the obese rats interferes with the regulation of food intake exerted by the ventromedial hypothalamus, in much the same way as ventromedial lesions do. If there is a blood-borne signal that indicates the amount of fat in the body, in Zucker rats the hypothalamus apparently does not respond to it. But evidently Zucker rats produce ‘the signal’ as other strains in similar circumstances do; and it circulates in the blood, since it affects the nonobese parabiotic partners. So it may be the same as ‘the signal’ demonstrated in Hervey’s (1959) and others’ experiments. Its nature remains obscure. The authors raise a possibility that oestrogens may play a part in the story. In view of its potential importance, it is remarkable that there seems to have been relatively little interest in identifying the blood-borne ‘signal’ which has shown up in a number of contexts. I shall return to Hervey and Tobin’s recent work later.

Denials of ‘the signal’s’ existence The general criticism has been made that the effects in otherwise untreated partners in parabiosis could be ‘non-specific’. It is difficult to see what ‘non-specific’ could mean when specific effects occur whenever parabiosis is properly carried out. If a particular outcome always, or nearly always, follows a particular procedure, presumably there must be some mechanism connecting the outcome with the procedure. The next step should be to identify this mechanism. Effective parabiosis requires, for example, that the pairs of scapulae and femora are scraped to expose raw bone and are then firmly stitched together; (I also stitched the muscles of the peritoneal cavity together, but found it better not to open the peritoneal cavities.) If the operation is not correctly carried out, my experience is that the shared length of the bodies becomes progressively

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shorter; one morning you find two perfectly normal, separate rats in the cage! For that reason it is important to measure the cross-circulation in every pair to be used in subsequent experiments. The whole point of the procedure is to obtain exchange of blood: the interpretation hinges on this. I found the rate of exchange varies between pairs, but over the range I encountered this did not seem to affect the results. I do not remember ever finding no or minimum exchange if the parabiosis had been done as I have described. I know of only two reports of experiments that contradict my findings. Han, Mu, and Lepkovsky (1963) studied food intake of rats in divided cages. Their paper surprised me because Lepkovsky invited me to visit his laboratory in the Berkeley campus for a few weeks in (I think) 1965, and I do not recall that he ever mentioned that he had worked with hypothalamic lesions in parabiotic rats, or what his findings were. He did not ask me to repeat my experiments in his department. There would in any case have been major difficulties about this: I was not there for long enough; there was no evidence that the rats maintained in the department were genetically uniform; they were evidently unused to humans, and I found them impossible to handle. I do not know where, when or by which author the experiments reported by Han et al. were carried out. I think that in their experiments the divided cages, limited feeding times, water restrictions, and the fact that the two peritoneal cavities communicated widely may all have led to the rats with ventromedial hypothalamic lesions gaining little fat. From my point of view this would be a crucial factor. In fact a non-significant decrease in the food intake of the partners was reported. Fleming (1969) reported a variety of studies of food intake in parabiotic rats. The section in ‘hypothalamic hyperphagia in parabiotic rats’ in this paper is something of a tailpiece in a paper largely concerned with other matters. The section starts with the statement that the relevant data were reported by the author in 1957, but there does not appear to be an exact reference to this. Data presented in his Fig. 12 suggest that, after hypothalamic lesions in one partner, both partners stopped gaining weight relative to a control group. Neither of these papers reports measurements of the cross-circulation in the parabiotic animals. I think this measurement is essential: in my view its omission alone is sufficient to invalidate the negative findings.

My subsequent physiological career My Ph.D. was completed by 1957. I had the offer of a junior post in the prestigious Cambridge University Department of Physiology: but my research interests were different from the predominant electrophysiology of that Department, and I doubted whether I would fit in. I did not know whether I could continue my rat experiments. The salary of the post was poor. I felt I belonged in the North. I had started my family. Sheffield University Department of Physiology offered a Lecturership which I was successful in getting. It was a busy teaching Department and I was happy there. There was a good Medical Sciences Club where one could meet clinicians and discuss the interface between physiology and medicine. There was still a post-war climate in UK, and I spent a lot of time building equipment for neurophysiology from surplus radar components. I also built up teaching of endocrinology. I had brought my rat colony and continued to use the rather primitive methods I had used in Cambridge. I tried to devise a method for measuring food intake of individual rats in parabiotic pairs, but without success. Five years later I had a brief spell in Edinburgh University as a Senior Lecturer. My teaching job was ideal: I had sole responsibility

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for teaching physiology relevant to medicine and surgery to students working for their first examination leading to qualification as surgeons. But my research did not fit into the Department, whose interests, like Cambridge, were neurophysiological. I did, however, get to know and kept in touch with Reg Passmore, the doyen of human energy physiology in the UK. He was one of a few who accepted my interpretation of the parabiotic experiments, and the way these demonstrated a mechanism for regulation of energy balance (Passmore & Eastwood, 1986, chap. 9). I soon moved to the Department of Physiology at Marischal College, Aberdeen. This was a small Department with a remarkable range of interests. I had a spacious laboratory, good animal accommodation on the College roof and good technician services. I was fortunate in getting a grant from the United States that provided proper carcass and food analysis equipment, which I used for the rest of my career. I joined Frank Hytten of the Department of Obstetrics and Jonathan Jeffery of the Department of Biochemistry to study the weight gain and body composition changes of pregnancy, using rats as the model. My late wife, Elizabeth Hervey, also took part. We did a lot of work on the effects of steroids, particularly using our body composition methods (and startling the Chemistry Department, who owned an Elliott 803 computer, by putting ‘rats’ on it). This work raised in my mind the possibility that steroids might be involved in signalling fat content in the context of energy balance. In 1967 I became Professor and Head of the Department of Physiology at the University of Leeds. This was initially very much in the traditional UK style of such a Chair, with the Department housed with Anatomy in a separate building adjacent to Leeds General Hospital. I had to set up a good relationship with a research unit, well supported by the British Heart Foundation but theoretically within my Department, headed by the very able Professor Ron Linden, who sadly has since died. In my 22 years there, there were huge changes in the country and its universities. There was a long period of expansion, reorganisation, and then poverty. I had to move the Department to new buildings twice. By the time I retired it had become part of a School of Biological Studies, in a huge concrete building, with no established Chair and ‘multi-disciplinary’ laboratories much less suitable for physiology. Medical students now spend less time on physiology, and there is no longer financial support for medical students wanting to take a third (‘Part 2’) year to study physiology or other medical science in more depth. When I arrived at Leeds, as a ‘honeymoon grant’ the University bought a Linc-8 computer for the Department. This was 5 foot high, had a 4 Kb memory (expandable at unaffordable cost to 32 Kb), used paper tape input and output, and could be connected to physiological equipment. Having some experience with computing (prior to Aberdeen, I actually operated the EDSAC-1 computer in Cambridge), I wrote Symbolic Assembly and Fortran systems for the Linc-8 using magnetic tapes, and used it for all subsequent work. I remember being in a minority of one in a Senate debate in which I argued for every department acquiring a computer, against the wishes of the Computer Sciences Department who believed all departments should be connected to their central computer.

of my career was increasingly concerned with applying this mode of thinking to the problems of energy balance and food intake, here is a short account of it, and some of the terms used. The simplest feedback control system depends on information about the present state of a ‘controlled quantity’ being ‘fed back’, by a suitable ‘receptor’ and ‘afferent pathway’, to a ‘control centre’. The control centre can change, via an ‘efferent pathway’, an ‘effector’. The effector changes the state of the controlled quantity, in a direction that opposes the change the receptor detected, and so reduces the change. Hence the feedback loop is said to have a ‘negative’ effect. Such a system can never bring the controlled quantity fully back to its previous state. There is always a difference, known as ‘load error’. The control system is characterized by ‘gain’, which measures the extent to which it reduces changes in the controlled quantity. To reduce the change to zero would require infinite gain. In Hervey and Duggan (1990) I have used diagrams to help explain the application of the concept of negative feedback to physiological control of appetite. Data from the Naval life-raft trials in the Arctic demonstrate ‘load error’ in human thermoregulation (Hervey, 1988, chap. 41) (Fig. 6). More complex biological control systems which may exist are described in a review by Hardy (1961).

Application of control system thinking to energy balance Higher animals require energy, obtained from food, to maintain their elaborate structure and functions. They also store energy in their bodies, primarily in the form of fat, which frees them from the need to feed continuously. Fat, of course, also has specific functions: assisting to maintain body temperature, protecting internal structures and, in humans, creating good looks. Although severe deviations eventually become life-threatening, the store of fat in the body can vary substantially without disturbing other functions. Control of body fat content thus provides a good means of maintaining energy balance. Experiments such as those by attributed to Adolph (Hervey, 1969) (Fig. 7) showed effects in rats of changing the concentration of energy in a freely available diet. If the energy concentration was decreased, the rats’ consumption of the food increased; and vice versa. In both cases the rats’ intake of energy changed by much less than it would have done if they had continued to eat the same weight of food as before the change in the food’s energy concentration. These early experiments beautifully demonstrate control of energy balance.

Negative feedback control The concept of negative feedback Even as a student at King’s College Hospital, I can remember being asked to explain negative feedback. By my early years of research this approach had become very popular. Since the last part

Fig. 6. Load error in a human experiment. The upper line shows mean rectal temperatures of eight subjects who lived in a tented, inflatable life-raft on Tromsø Fjord in the Norwegian Arctic for the days shown. Although rectal temperature was maintained during the test, it was significantly lower than before or after. The lower line, showing finger-tip temperature, shows that the subjects were vasoconstricted during the test, but not maximally. They shivered for about 10% of the time (Hervey (1988) with permission).

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as shown by the level of the signal in the common blood-stream. Each rat’s hypothalamus, as it were, ‘sees’ the fat in both bodies. Energy expenditure

Fig. 7. Changes in weight of food eaten and in energy intake per day in adult female rats (A) on reducing the energy content per unit weight of diet, and (B) on increasing it. Solid line: weight of food eaten daily; dashed line: energy content of food eaten, expressed in terms of equivalent weight of diet supplied in the initial period; horizontal dashed line: mean food intake in the initial period (experiment attributed to E.F. Adolph; from Hervey, 1969) with permission.

The obesity produced by ventromedial hypothalamic lesions suggests that the ventromedial hypothalamus contains a control centre which governs food intake by regulating the fat store in the body, and so maintains energy balance – of course with some load error. The efferent pathway for this control can reasonably be presumed to be in the brain, via neurones that connect the ventromedial nuclei to appropriate appetite and motor systems. The afferent pathway is still a mystery. When the ventromedial hypothalamus is damaged and attractive food is available the animal becomes obese. The hypothalamus has evidently lost its response to the obesity that follows excessive food intake. Food intake is controlled only by the availability and attractiveness of food. When, however, an animal with ventromedial hypothalamic lesions is joined in parabiotic union with a partner with an undamaged hypothalamus (and cross-circulation has been confirmed), the partner’s food intake falls: it becomes very thin and may die, apparently of starvation. This is a key observation. It strongly suggests that in an intact animal a signal from body fat content via the blood stream informs the hypothalamic centres how to adjust food intake. A parabiotic partner also receives the signal and acts on it. Cross-circulation rates show that the ‘signal’ has a relatively long persistence in the circulation, not surprisingly if it is generated by fat. My guess is that it is unlikely to be any presently known hormone or metabolite. I guess that it may be a steroid. The high solubility partition coefficient between fat and water of many steroids might make one a suitable candidate. In parabiotic pairs without hypothalamic lesions in either partner, I found at post-mortem that the fat content of each was consistently about half the fat content found in normal litter-mates not in parabiosis. I interpreted this on the basis that the common blood-stream carries the signal arising from the total fat content of both rats’ bodies to the hypothalamus of each. Each responds to it, and adjusts feeding to maintain an appropriate total fat content,

When we made the second move to a new building the University gave me a rat room with close control of air temperature and humidity and uniform air movement. I formed a close collaboration with Graham Tobin, a Lecturer in the Department. The facility gave us ideal conditions for pursuing experiments on energy balance in rats with the accuracy we believe is necessary. (Grants were another matter.) We built a system which measured oxygen consumption and carbon dioxide production in up to five cages, each containing differently treated groups of one to four rats, or one parabiotic pair with access to separate, measured, food and water supplies for each partner. A PDP-12 mini-computer controlled the system, recording gas analyses minute by minute and checking the analysers hourly. We could measure the food intake and collect excreta of the rats in the cages. Carcasses were analysed at the end of the experiments. Energy content of the food, excreta, and post-mortem bodies were measured by bomb calorimetry. Thus we could measure all three components of energy balance – intake, output and storage – at intermediate stages of an experiment, and check the accuracy of our balances at the end. We were able, for example, to measure the substantial energy cost of storing energy as fat (Hervey & Tobin, 1983). The first use of this equipment, however, took up a lot of valuable time and I believe should never have been necessary. It concerned the effector for energy balance. My colleagues and I have always believed that control of food intake is the major effector. Rothwell and Stock (1979), however, advocated a theory that brown fat is a main regulator of energy balance. Brown fat is a tissue in young mammals known to be capable of being ‘switched on’ in cold conditions to produce heat, as a rather ‘last ditch‘ mechanism of thermoregulation. The concept that it can also regulate energy balance by dissipating excess energy intake is not a new one: it was originally called ‘luxuskonsumption’ or ‘thermogenesis’. Rothwell and Stock attempted to revive it. They claimed that in adult rats (of some strains), and also in humans, brown fat regulates energy balance by increasing energy expenditure in response to over-feeding. They popularised this idea in a ‘Horizon’ television program. Their paper appears to claim that when the energy intake of a group of six rats was increased by 80% by ‘cafeteria’ feeding (i.e. giving the rats a choice of attractive foods), and compared with a control group of six rats, thermogenesis dissipated 90% of the excess energy intake. This proposition, however, depended on indirect measurement of energy expenditure from estimates of energy intake and storage. When, later, responding to criticisms, Rothwell and Stock claimed that they had checked energy expenditure by simultaneous measurement of oxygen consumption, we were not convinced. Fortunately the arguments have been set out in full. The journal Clinical Science asked both groups of researchers to present their arguments in ‘Controversies in Medicine’ (Hervey & Tobin, 1983; Rothwell & Stock, 1983). I believe the brown fat theory of energy balance has largely disappeared, though no doubt there are still adherents. But a great deal of our time was wasted. Our last experiments Graham Tobin and I tried to get an MRC grant to continue work with our powerful system for studying energy balance. Our proposal included recruiting a biochemist with the skills to tackle the problem of the chemical nature of the ‘signal’ that travelled

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Fig. 8. Evidence for feedback control of body fat content. In parabiotic pairs of rats, the body fat content of a free-feeding partner is shown to depend, negatively, upon the fat content of its partner which is being over-fed by stomach tube. Four matched parabiotic pairs of rats in continuous flow calorimeter. Each point is the mean of three test runs for each pair during life. Fat contents were estimated during life from body weights, food intakes and calorimetric data, and later checked by post-mortem analysis. Horizontal axis: mean body fat content of one partner, fed by intragastric tube at 1.0, 1.25 and 1.5 times voluntary food intake. Vertical axis: body energy content (equivalent to fat content) of the other partner, which was allowed to feed freely (Hervey & Duggan (1990) with permission).

in the blood crossing between rats in parabiosis, thus elucidating what we believe to be an important mechanism for controlling food intake and so maintaining energy balance. Perhaps because we had spent so much time developing the system and the experiments were long-term, we had few papers to present; these were difficult times; the application was unsuccessful. I think it is also true that the whole research support system in UK was changing, away from supporting individual workers in university departments and towards supporting larger groups working full-time in research institutes. We did, however, perform one important experiment in the calorimeter system. In each of four parabiotic pairs, one rat was overfed by stomach tube, while the other could feed freely. The primary measurements were the changes in the energy content of the tubefed partners as it progressed during the experiment, and the food intake and energy content of their voluntary-feeding partners. This enabled us to relate the amount of the disturbance of energy balance produced in the tube-fed partner to the food intake and energy balance of the free-feeding partner, at three points in time as the experiment progressed: thus indicating the ‘gain’ of the energy balance control system on our hypothesis (Fig. 8). Fig. 8 shows the means of three experimental runs with four matched parabiotic pairs. The levels of feeding in the tube-fed rats supplied 1.0, 1.25 and 1.5 times the rats’ previous free-feeding energy intake. There was a near-linear, negative relationship between the body fat content of the tube-fed rats and the body energy content (effectively fat content) of their free-feeding partners. There were differences among the individual pairs in the slope of this relationship, i.e. in its gain or precision. This experiment has only been presented briefly in Hervey and Duggan’s (1990) review of the feedback control of body fat content. The finding of such a clear relationship, however, seems to confirm that whatever is transmitted through the parabiotic union could be the afferent pathway of a physiological control system, which controls the amount of body fat, and therefore maintains approximate energy balance.

The project then suffered a disaster when Graham Tobin resigned from the University. I am sure this was not for any personal reasons. I think his main reason was that he, like other academically first-class people, was frustrated by the University system. Without external research funding, the establishments of University Departments were jealously guarded, increasingly so as University funding became tighter. Promotion within a department – in his case to Senior Lecturer – had to wait for ‘empty shoes’, and then was competitive. Graham joined the food industry. I recall him visiting in his new BMW. I much regret that I did not write up properly the experiments we managed to do in the calorimeter system. My only excuse is that I never found the time. As well as teaching and running a Department I was still involved in work for the Navy: including a lengthy process of sending an academic from Leeds to New Orleans to work with Channing Ewing on the treatment of motion sickness; and I cannot write papers quickly. I was grateful for the invitation from J.M. Forbes to join him as an editor and contribute the chapter in the Forbes and Hervey (1990) book, but I imagine this has not been widely read. John Duggan had given excellent assistance in the experiments as a Research Assistant, and since Graham Tobin had left, it seemed right to make him a co-author. Retirement I had to retire from my departmental post in 1989 due to an obligatory age rule. The University would have allowed me to continue research in the Department of Animal Physiology (a relic of a flourishing School of Agriculture when I first came), with an office and animal technician support. I was, however, unsuccessful with a grant application for a Research Assistant. Sacrificing the rat colony that had served me so well was a bitter experience. The Navy also ended my Consultant appointment, though I continued to advise the Merchant Navy on life-raft rations. The nature of the ‘signal’ from fat to food intake In February 1996 I attended a joint meeting in London of the Nutrition Society and the Association for the Study of Obesity. This was to celebrate the isolation of leptin, which was presented as the provider of the feedback that regulates food intake, and thus body fat content. Both the Chairman in his initial address and the first speaker showed photographs of parabiotic rats from my 1959 paper (without mentioning me). These would at any rate have reminded the audience of the dramatic effects a feedback system can have. Leptin had been identified by parabiotic studies, in obese diabetic (db/db) and obese (ob/ob) mice (Coleman, 1973; Coleman & Hummel, 1969). Its identification was clearly a major advance. There was a feeling that a Nobel prize was near. I am delighted that Ruth Harris is reviewing leptin in the next article in this collection. There is now a large and confusing literature on leptin. There seem to me to be at least three obvious initial questions. Perhaps the answers are already available. (1) Are there any species or strain differences in leptin’s actions? (2) What is its lifetime in the circulation in each case? (3) Can administering leptin at an appropriate rate replicate the effects on animals of parabiosis with an obese partner? Regarding the first question, I recall Professor Edholm opening a meeting on obesity with a portentous declaration: ‘‘Man is not a rat’’. One might expect that such a fundamental process as maintaining energy balance would be the same at least among mammals; but aspects such as the chemical nature of a feedback signalling substance might vary. My group have used rats in all experiments, as the pioneers studying energy balance mostly did. Rats show quite close

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regulation of energy balance. If the interest is in human obesity, the choice of rats can also be defended on the grounds that they are also omnivores and, as users of cafeteria feeding can attest, show remarkably human-like preferences among foods – chocolate chip cookies, cheesy flavoured snacks and so forth. Furthermore, laboratory strains of rat are co-operative if handled kindly and learn to tolerate protracted experimental treatments remarkably well. Apart from parabiosis, total genetic uniformity may be no advantage in research relating to the high body fat contents prevalent across human populations. Bearing in mind how much work has been done with mice as test animals without so far coming up with a solution for human obesity, I suggest that more work should be done using rats – most importantly, with care and kindness. Regarding question (2), since the early days of parabiosis it has been appreciated that, because of the limit to the rate at which blood is exchanged between the individuals in a parabiotic pair, any substance that can effectively cross between the individuals – and thus fulfill the function of what I have called the ‘signal’ – must have a relatively long half-life in the circulation. I think it has been claimed that leptin passes this test. Nishizawa and Bray (1980), however, expressed the opinion that peptides – of which they listed a number known at the time as possible ‘ergostatic factors’ – have too short a half-life in the circulation to be candidates. As to question (3), I have yet to see news headlines that leptin in physiological concentrations in the circulation consistently produces the severe reduction in food intake seen every time in parabiotic partners of obese animals (provided there is a checked crosscirculation). Hence I continue to wonder whether a steroid could serve as the ‘signal’. Many steroids have a long half-life in the circulation and fulfil diverse functions, including rôles in energy metabolism. During work on the effects of progesterone on energy balance in the 1960s (Hervey & Hervey, 1967), it occurred to me that a steroid with a high fat:water partition coefficient (similar to that of progesterone though not progesterone itself) might provide a means of measuring the amount of fat in the body (Hervey, 1969).

Conclusion The parabiotic preparation with one partner made obese by any of a variety of methods – always with the proviso that exchange of blood through the parabiotic union has been verified – still seems to be the only situation in which a normal rat with free access to food and water will reduce its intake of food to the point of starving to death. Even if neither partner is obese, the parabiotic exchange approximately halves the fat content of each partner. My colleagues and I interpret our findings as demonstrating a feedback control of the amount of fat in the body, which maintains approximate energy balance. We believe there is substantial evidence to support this. The concept does, however, depend on the idea that a still hypothetical ‘signal’ indicating the amount of fat in the body travels in the blood-stream to the ventromedial nuclei of the hypothalamus. In a parabiotic pair this information reaches the brain of each partner, signalling the total amount of fat present in the two bodies. If correct, this is an interesting physiological finding. It will be a useful finding only if and when the existence of the ‘signal’ in the circulation has not just been demonstrated, but the ‘signal’ has been identified. As we and others have shown, administration of progesterone, oestrogens and some analogues change body weight and fat content, in rats and probably in humans (Hervey & Hervey, 1967). There is no proof, but it seems reasonable to suggest that these agents act upon the central regulation of body fat content and thus energy balance. Although the steroids so far investigated are clearly not the ‘signal’ for regulation of body fat content envisaged

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in this paper, they may provide a clue as to its nature. The differential solubility of steroids in fat and water might provide a mechanism for measuring body fat content. In 1969 I suggested looking for a steroid (Hervey, 1969). Most of this story – at least in rats – has been known for 50 years. There have been huge advances in biochemical techniques meantime, but we still do not know the nature of the ‘signal’, (I am assuming it is not leptin: see Harris, 2012). Assuming that the ‘signal’ is a chemical substance, there must be a difference in its concentration in the blood between underfed and overfed states. I personally wonder whether purely chemical techniques, investigating steroids – and the use of rats, which are larger than mice and in which I think the feedback control of energy balance has been better demonstrated – might be helpful on the practical problem of identifying the ‘signal’. I wish good luck to anyone who tries this approach. References Adolph, E. F. (1947). Urges to eat and drink in rats. American Journal of Physiology, 151, 110–125. Bunster, E., & Meyer, R. K. (1933). An improved method of parabiosis. Anatomical Record, 57, 339–343. Coleman, D. L. (1973). Effects of parabiosis of obese with diabetes and normal mice. Diabetologia, 9, 294–298. Coleman, D. L., & Hummel, K. P. (1969). Effects of parabiosis of normal with genetically diabetic mice. American Journal of Physiology, 217, 1298–1304. Fleming, D. G. (1969). Humoral and metabolic factors in the regulation of food and water intake. Food intake studies in parabiotic rats. Annals of the New York Academy of Science, 157, 985–1003. Forbes, J. M., & Hervey, G. R. (1990). The control of body fat content. London: SmithGordon. Haessler, H. A., & Crawford, J. D. (1967). Alterations in the fatty acid composition of depot fat associated with obesity. Annals of the New York Academy of Science, 131, 476–484. Han, P. W., Mu, J., & Lepkovsky, S. (1963). Food intake of parabiotic rats. American Journal of Physiology, 205, 1139–1143. Hardy, J. D. (1961). Physiology of temperature regulation. Physiological Reviews, 41, 521–606. Harris, R. B. S. (2012). Identification of leptin as the parabiotic ‘‘satiety’’ factor. Past and present interpretations. Appetite. Harris, R. B. S., Hervey, E., Hervey, G. R., & Tobin, G. (1987). Body composition of lean and obese Zucker rats in parabiosis. International Journal of Obesity, 11, 275–283. Harris, R. B. S., & Martin, R. J. (1984). Specific depletion of body fat in parabiotic partners of tube-fed obese rats. American Journal of Physiology, 247, R380–R386. Harris, R. B. S., & Martin, R. J. (1986). Metabolic response to a specific lipid-depleting factor in parabiotic rats. American Journal of Physiology, 250, R276–R286. Hervey, G. R. (1957). Hypothalamic lesions in parabiotic rats. Journal of Physiology (London), 138, 15–16P. Hervey, G. R. (1959). The effects of lesions in the hypothalamus in parabiotic rats. Journal of Physiology (London), 145, 336–352. Hervey, G. R. (1969). Regulation of energy balance. Nature, 223, 629–631. Hervey, G. R., & Duggan, J. P. (1990). The concept of feedback control of body fat content and the evidence for it. In J. M. Forbes & G. R. Hervey (Eds.), The control of body fat content (pp. 1–18). London: Smith-Gordon. Hervey, G. R. (1988). Thermoregulation. In D. Emslie-Smith & G. H. Bell (Eds.), Textbook of physiology (BDS). London: Churchill Livingstone. Hervey, E., & Hervey, G. R. (1967). The effects of progesterone on body weight and composition in the rat. Journal of Endocrinology, 37, 361–384. Hervey, G. R., Parameswaran, S. V., & Steffens, A. B. (1977). The effects of lateral hypothalamic stimulation in parabiotic rats. Journal of Physiology (London), 266, 64–65P. Hervey, G. R., & Tobin, G. (1983). Luxuskonsumption, diet-induced thermogenesis and brown fat: a critical review. Clinical Science, 64, 7–18. Kennedy, G. C. (1950). The hypothalamic control of food intake in rats. Proceedings of the Royal Society B, 137, 535–549. Nishizawa, Y., & Bray, G. A. (1980). Evidence for a circulating ergostatic factor. Studies on parabiotic rats. American Journal of Physiology, 239, R344–R351. Parameswaran, S. V., Steffens, A. B., Hervey, G. R., & De Ruiter, L. (1977). Involvement of a humoral factor in regulation of body weight in parabiotic rats. American Journal of Physiology, 232, R150–R157. Passmore, R., & Eastwood, M. A. (1986). Energy balance and the regulation of body weight. In Davidson & Passmore (Eds.), Human nutrition and dietetics (8th ed.. London: Churchill Livingstone, p. 91. Rothwell, N. J., & Stock, M. J. (1979). A role for brown adipose tissue in diet-induced thermogenesis. Nature, 281, 31–35. Rothwell, N. J., & Stock, M. J. (1983). Luxuskonsumption, diet-induced thermogenesis and brown fat: the case in favour. Clinical Science, 64, 19–23. Widdowson, E. M. (1993). Obituary notice. Proceedings of the Nutrition Society, 52, 383–386.

Please cite this article in press as: Hervey, G. R. Control of appetite. Personal and departmental recollections. Appetite (2012), http://dx.doi.org/10.1016/ j.appet.2012.10.008