CIGARETTE SMOKING INHIBITS PROSTACYCLIN FORMATION

1248 tion between body weight and blood pressurel2 may partly explain the association of blood pressure with dietary sodium. This study does not rule out the second hypothesis, that offspring may respond differently to high sodium intake. Several studies support this hypothesis. For example, Pietinen et al13 reported a regression slope of 0.07 mm Hg/mmol Na of systolic pressure on sodium excretion in the normotensive offspring of hypertensive parents, but no association in the offspring of normotensive parents. However, these findings have been criticised because of, amongst other things, small numbers and failure to measure parental blood pressure. 2,14 Other authors have found differences in sodium-handling at a cellular level between the offspring of hypertensive and .normotensive parents.15,16 In view of the crude methods used to select offspring in these studies their findings are remarkable, for they suggest that much larger differences should be found between more carefully defined groups of offspring. However, in the absence of data on sodium intake, we do not know to what extent these findings reflect a true variation in susceptibility, or merely a different response to variation in dietary sodium intake. We are currently testing the hypothesis that offspring differ in their response to high sodium intake, by using a study design17 which compares blood pressure at two levels of sodium intake in high/high and low/low offspring. This work was supported by the British Heart Foundation and the Medical Research Council. We thank Mair Boast, Catherine Edwards, Mary Hart, Angela Hughes, Evelyn Thomas, and Pam Walton of our research team; Mr Tony Thomas and Dr Tony Ames of Neath General Hospital for urine analyses; Dr David Gordon of St Mary’s Hospital Medical School, London, for estimations of plasma renin activity; and colleagues at the MRC Epidemiology and Medical Care Unit, Northwick Park, for their advice in the planning stage of this study.

Correspondence should be addressed to G. C. M. W., WHO Monica Project, Royal Infirmary, 10 Alexandra Parade, Glasgow G31 2ER.

CIGARETTE SMOKING INHIBITS PROSTACYCLIN FORMATION

JERRY L. NADLER

JOSEFINA S. VELASCO

RICHARD HORTON Section of Endocrinology, Department of Medicine, University of Southern California School of Medicine, Los Angeles, California, USA

Urinary prostacyclin (PGI2) was

measured in 12 chronic smokers and 12 non-smokers after inhalation of smoke from nicotine-containing and nicotine-free cigarettes. In a separate study a pressor dose of noradrenaline, which increases PGI2, was given to smokers and non-smokers. PGI2 was measured as the stable metabolite, 6-keto-PGF1&agr; in 4 h urine samples by radioimmunoassay after chromatography on LH-20 ’Sephadex’. Smoking of nicotine-free cigarettes had no effect on PGI2 release in either smokers or non-smokers. In nonsmokers inhalation of nicotine-containing tobacco smoke increased heart-rate, blood-pressure, and urine osmolality, but did not affect urinary 6-keto-PGF1&agr;. In contrast, when chronic smokers used nicotine-containing cigarettes there was a highly significant reduction in excretion of 6-ketoPGF1&agr; (192±20 to 138±17 ng/g creatinine). Noradrenaline increased PGI2 in non-smokers (181±16 to 348±56) but not in smokers. Smoking of nicotine-containing tobacco abolished the PGI2 response to noradrenaline. These observations suggest that inhalation of nicotine-containing tobacco smoke reduces vascular PGI2 production; this may be a factor in the development of accelerated cardiovascular disease.

Summary

Introduction THE

mechanism

of tobacco-smoke-induced vascular

disease’,’ is unknown. Smoking is associated with release of REFERENCES 1. Editorial. Cells, ions, and blood pressure. Lancet 1982; ii: 965-67. 2. Watt GCM, Foy CJW. Dietary sodium and arterial pressure: Problems of studies within a single population J Epidemiol Comm Hlth 1982; 36: 197-201. 3. Higgins MW, Keller JB, Metzner HL, Moore FE, Ostrander LD. Studies of blood pressure in Tecumseh, Michigan II. Antecedents in childhood of high blood pressure in young adults Hypertension 1980; 2 (suppl 1): 117-23. 4. Cooper R, Soltero I, Liu K, Berkson D, Levinson S, Stamler J. The association between urinary sodium excretion and blood pressure in children. Circulation 1980; 62: 97-104. 5 Watson RL, Langford HG, Abernethy J, Barnes TY, Watson MJ. Urinary electrolytes, body weight and blood pressure Pooled cross-sectional results among four groups of adolescent females. Hypertension 1980; 2 (suppl 1) 93-98. 6 Hart JT. Semicontinuous screening of a whole community for hypertension. Lancet

1970; ii: 223-26. JT. Hypertension. London: Churchill Livingstone, 1980. 8. Cummins RO, Shaper AG, Walker M. Methodological problems with estimation of salt intake. Lancet 1981; i: 1373-74. 9. Liu K, Cooper R, McKeever J, et al. Assessment of the association between habitual 7. Hart

salt intake and

high blood

pressure:

methodological problems.

Am

J Epidemiol

1979; 110: 219-26. 10. Clegg G, Morgan DB, Davidson C. The heterogeneity of essential hypertension: relation between lithium efflux and sodium content of erythrocytes and a family history of hypertension. Lancet 1982; ii. 891-94. 11. Heagerty AM, Milner M, Bing RF, Thurston H, Swales JD. Leucocyte membrane sodium transport in normotensive populations: dissociation of abnormalities of sodium efflux from raised blood pressure. Lancet 1982, ii 894-96. 12 Chiang BW, Perlman LV, Epstein FH Overweight and hypertension: a review. Circulation 1969; 39: 403-21. 13. Pietinen PI, Wong O, Altschul AM. Electrolyte output, blood pressure and family history of hypertension. Am J Clin Nutr 1979; 32: 997-1005. 14. Cooper R, Liu K. Correlations between salt intake, blood pressure and family history of hypertension. Am J Clin Nutr 1980; 33: 2218-20. 15. Meyer P, Garay RP, Nazaet C, et al. Inheritance of abnormal erythrocyte cation transport in essential hypertension. Br Med J 1981; 282: 1114-17. 16. Woods KL, Beevers DG, West M Familial abnormality of erythrocyte cation transport in essential hypertension. Br Med J 1981; 282: 1186-88 17. MacGregor GA, Markandu MD, Best FE, et al Double-blind randomised crossover trial of moderate sodium restriction in essential hypertension Lancet 1982; i: 351-54.

catecholamines,3 cortisot,4 and vasopressin,s and with changes in blood clotting activity. Other studies suggest that nicotine or carbon monoxide has a direct toxic effect.’,8 In healthy vessels there seems to be a balance between vessel-wall production of prostacyclin (PGI2) and various platelet functions including release of thromboxane.9 A disturbance in this relation could be a feature of several diseases of both the vessels and the platelets. We therefore studied the effect of smoking high-nicotine cigarettes on production of PGI2. Because a-adrenergic stimulation increases PGI2 excretion in man, 10 we compared the effect of a pressor dose of noradrenaline (NA) on the excretion rate of PGI2 in smokers and non-smokers.

Patients and Methods We studied normal healthy smokers (>20 cigarettes daily) and non-smokers not on any medication. All were maintained ona normal sodium and potassium diet. Chronic smokers abstained from cigarettes for 12 h before each study period. 12 subjects m both groups had 4 high-nicotine (>1 mg) cigarettes over a 4 h period. smoking one an hour. On another day they smoked 4 non-rucotmecontaining cigarettes (,Free’, cocoa-bean based). Smokers and nonsmokers were instructed to and observed to inhale in a similafashion and the protocol was reversed. Because we had found tha: NA increases the PGI2 excretion rate, we infused a pressor dose (NA 01 µg/kg/min) over 4 h during both non-smoking and smoking periods in a separate study. Protocols and consent forms were approved by our institutional research committee. Urine samples were collected on separate days between 8 AM jnd noon during non-smoking, smoking, and NA mfusion studies

1249 Urine volume, osmolality, sodium, and creatinine were measured by standard techniques. PGI2 production was estimated by measuring the excretion rate of the PGI2 stable metabolite, 6-keto-PGF,. Details of this

TABLE II-EFFECT OF HIGH NICOTINE

(N-FREE),

AND NA

+

(HIGH N), NICOTINE FREE + S) ON URINE

HIGH NICOTINE SMOKING (NA

VOLUME. OSMOLALITY, AND CREATININE IN CHRONIC SMOKERS

radioimmunoassay (RIA) have been provided elsewhere. 10 Briefly,

acidified urine sample with authentic tritiated standard for correction is extracted with ethyl acetate and chromatographed on a LH 20 (1 - 5 x 60 cm) ’Sephadex’ column. The appropriate fraction is then dried and the compound measured by RIA with an antiserum generated in a rabbit by repeated injection of6-keto- PGF I" coupled to thyroglobulin. Bound and free ligand were separated by a second antibody technique. Recoveries are 60± 1007o with sensitivity, calculated from both variation in assay curve intercept and the non-specific blank of the assay (6±2 pg), of 10 pg. Accuracy was calculated by addition of known amounts of 6-keto-PGFta (r=0-96) and precision is <10% (SD). There was no significant change in sample values after further thin-layer or highpressure liquid chromatography. All urine samples were immediately frozen at -30°C and, within a few days, sets of samples were measured in a single assay. Control and experimental samples were run in the same assay. Student’s t test for paired and unpaired values was used. All results are reported as the mean ±SE in nanograms per gram of creatinine (ng/g creat.). Each subject was used as his or her own control. an

recovery

Results

Smoking of nicotine-free cigarettes had no effect on 6-ketoPGF1" excretion rate in either non-smokers or chronic smokers (fig 1, table I). Non-smokers inhaling nicotinecontaining cigarette smoke had increased heart-rate (17±3 beats/min) and blood-pressure (12:i:2mm Hg systolic) but no

i

Values given

are

i

mean±SEM. TV total volume.

in urinary 6-keto-PGFIa (table I). However, when chronic smokers used 4 nicotine-containing cigarettes, there was a highly significant reduction in the excretion rate of the prostacyclin metabolite (fig 1). 6-keto-PGFj values fell from 192±20 to 138± 17 ng/g creat. (p<0 02). Repeat studies were performed on a few of the subjects during a second identical protocol and the same results were obtained. No changes in sodium or creatinine were observed (tables I and II). In nonsmokers only, urine volume decreased (from 301 ±66 to and osmolality increased (from 225±68 ml/4 h, p<0’05) 515±108 to 795±123 mosmol/kg, p<0-05) during exposure

change

high-nicotine cigarettes (table I). given in a pressor dose (22±2 mm Hg rise) increased PGI2 metabolite excretion rate in chronic smokers who abstained from cigarettes (181±16 to 348±56, p<0’01). However, the same dose and pressor response in chronic smokers inhaling tobacco smoke had no effect on 6-ketoPGFI, excretion (fig 2). This lack of response was also seen, over the 4 h period, in the smoking non-smokers (table I). to

NA

1-Effect of smoking high nicotine (high N, hatched bar) and nicotine free (N-free, clear bar) cigarettes on urinary 6-keto-PGFla excretion in chronic smokers.

Fig

Mean±SE values

are

shown.

High N vs control, p<0

TABLE I-EFFECT OF HIGH NICOTINE

(N-FREE),

02.

(HIGH N), NICOTINE FREE (NA+S) ON

AND NORADRENALINE + HIGH-NICOTINE SMOKING

URINE

VOLUME, OSMOLALITY, CREATININE SODIUM, AND

6-KETO-PGF, IN NON-SMOKERS

2-Effect of pressor NA infusion on urinary chronic smokers who were abstaining (stippled

Fig

6-keto-PGFla in or smoking

bar)

high-nicotine cigarettes (hatched bar). Mean±SE values

are

shown. *NA

vs

control, p<0-OL

Discussion

PGI2

is

a

potent vasodilator and

platelet antiaggregatory

agent which is mainly synthesised by endothelial cells of vessels present in most or all organs including the lung, aorta,

Values

given are mean±SEM.

TV=total volume.

*,fp<0-05

(paired).

and kidney.ll-’3 It is a rapidly inactivated prostaglandin which probably acts locally at the vessel-plasma interface. Blood levels are too low for it to be measured either as the parent compound or as metabolites.14 However, nanogram amounts of the stable metabolite 6-keto-PGFla are present in

1250

human urine. Evidence suggests that most PGF] arises from renal vessels;15 however,

extrarenally.16The decrease

urinary 6-ketosome

may arise

urinary 6-keto-PGFIa levels in chronic smokers inhaling high-nicotine tobacco is of interest whatever the vascular origin of prostacyclin. Evidence suggests that prostaglandin formation is affected by smoking and nicotine. In the dog, aspirin or phentolamine reversed the tendency to thrombus formation and reduced coronary perfusion induced by smoking or nicotine administration.17 Formation and release of prostacyclin by coronary arteries in perfused rabbit hearts is reduced by nicotine. 18 More direct studies with kidney cell microsomes, indicate inhibition ofPGI2 at an early stageofbiosynthesis. 19 In contrast, nicotine apparently has little effect on platelet thromboxane-A2 formation and release.20 Bradykinin is a vasodilator which may act in part by PGI2 release. Nicotine and aspirin reduce the vasodilatory action of bradykinin in guineapig and rabbit coronary vessels.21 An in-vitro study suggested that umbilical arteries from smoking mothers release significantly less prostacyclin than those from controls.22 The changes in PGI2 metabolite in

found in chronic smokers suggest that nicotine-containing cigarettes inhibits prostacyclin production. This phenomenon is not seen in non-smokers, perhaps because they produce more PGI2 in response to alpha-adrenergic stimulation. In contrast, chronic smokers may lose their sensitivity to the adrenergic effects of nicotine and smoking, so that they show greater inhibition ofPGI2 than do novice smokers. The increase in PGI2 excretion rate in non-smoking controls in response to NA infusion and the elimination of this NA effect in both smokers and non-smokers using nicotine-containing cigarettes accords with this suggestion. These studies suggest that cigarette smoke acts as a vascular toxin by altering PGI2 formation and excretion. excretion that smoking of

we

These studies were supported by grants to ProfR. Horton from the National Institutes of Health HL 21112. Dr J Nadler was the recipient of a fellowship from an NIH training grant. These studies were performed in a clinical research centre funded by the US Public Health Service Grant. We thank Mrs Susan Bitolas for her excellent secretarial assistance. REFERENCES

GD, Petitti DB, Bawol RD, Siegelaub AB. Mortality in cigarette smokers and quitters N Engl J Med 1981; 304: 1404-10. 2. Ball K, Turner R Smoking and the host: the basis for action. Lancet 1974; ii: 822-26. 3. Cryer PE, Haymond MW, Santiago JV, Shah SD. Norepinephrine and epinephrine release and adrenergic mediation of smoking-associated hemodynamic and metabolic events. N Engl J Med 1976, 295: 573-77. 4. Winternitz WW, Quillen D Acute hormonal response to smoking. J Clin Pharm 1977; 1. Friedman

17: 384-97. 5. Hussain MK, Frantz AG, Ciarochi F, Robinson AG. Nicotine stimulated release of neurophysin and vasopressin in humans. J Clin Endocrinol Metab 1975; 41: 1113-17. 6. Hawkins P. Smoking, platelets and thrombosis Nature 1972; 236: 450-02. 7. Shimamoto T. Damage to silicon-like properties of vascular endothelial cells and prevention by monoamine oxidase inhibitor Nialamide. Astan Med J 1960; 3: 479-84. 8. Davies RF, Topping DL, Turner DM. The effect of intermittent carbon monoxide exposure on experimental artherosclerosis in the rabbit. Atherosclerosis 1976; 24: 572-86. 9. Moncada S, Vane JR. Arachidonic acid metabolites and the interaction between platelets and blood vessel walls. N EnglJ Med 1979; 300: 1142-47. 10. Nadler JL, Zipser RD, Coleman R, Horton R Stimulation of renal prostaglandins by pressor hormones in man comparison of PGE2 and I2 (6 keto PGF1&agr;). J Clin Endocrinol Metab 1983; 56: 1260-65. 11. Moncada S, Gryglewski R, Bunting R, Vane JR An enzyme isolated from arteries transforms prostaglandin endoperoxides to an unstable substance that inhibits platelet aggregation Nature 1976; 263: 663-65. 12. Johnson R, Morton D, Kinner J, Gormon R, McGuire J, Sun F, Whittiker N, Bunting S, Salmon J, Moncada S, Vane JR. The chemical nature of prostaglandin X (prostacyclin) Prostaglandins 1976; 12: 915-28. 13. Ubatuba F, Moncada S, Vane JR. The effect of prostacyclin (PGI2) on platelet behaviour, thrombus formation in vivo and bleeding time. Thromb Haemostas 1979; 41: 425-35.

Preliminary

Communication

BROMOCRIPTINE LOWERS INTRAOCULAR PRESSURE WITHOUT AFFECTING BLOOD PRESSURE

QAIS A.

SALIM M. HASSAN MEKKI PAUL TURNER

Department of Clinical Pharmacology, St Bartholomew’s Hospital Medical College, London EC1 Oral bromocriptine (1·25 mg) was given to 8 healthy volunteers in a double-blind placebo controlled cross-over study. 3 and 4 h after taking the tablet there was a significant reduction in intraocular pressure but no change in pupil diameter. There were no changes in heart rate, blood pressure, and systolic time intervals in 6 other healthy volunteers within 3 h of being given 1·25 mg bromocriptine. These results suggest that dopamine receptors may be involved in the control of intraocular pressure.

Summary

INTRODUCTION

application of bromocriptine in rabbits’ eyes dose and time related reduction of intraocular produced Such an effect of bromocriptine has not yet been pressure. in A man. reported systemic hypotensive action has been reported in normotensive and hypertensive patients during treatment with bromocriptine.2,3 This study was designed to investigate the ocular and cardiovascular effects of oral bromocriptine in healthy volunteers. TOPICAL

a

SUBJECTS AND METHODS 14 healthy volunteers (age 20-22 years) gave informed consent to participate in the study. Each attended on two occasions, at least one week apart, at the same time of the day, to receive either I25mg bromocriptine or a matched placebo tablet in a double-blind crossover manner.

In one group (3 males and 5 females), intraocular pressure and pupil diameter were measured before and at 3 and 4 h after taking the tablet. Intraocular pressure was measured by non-contact tonometry.4 The average of three successive readings on each eye was recorded. Pupil diameters were measured by a pupil gauge (Smith and Nephew Pharmaceuticals Ltd). In the other group (41 males and 2 females), the volunteers arrived after an overnight fast and rested while supine. Blood pressure, pulse rate and systolic timc

14. Blair I, Barrow S, Waddell K, Lewis P, Dollery C Prostacyclin is not a circulating hormone in man Prostaglandins 1982; 23: 579-89 15. Patrono C, Pugliese F, Clabattoni G, Patrignani P, Maseri A, Chierchia S, Peskar B A Cinotti GA, Simonetti BM, Pierucci A. Evidence for a direct stimulatory effect of prostacyclin on renin release in man J Clin Invest 1982, 69: 231-39 16. Zipser RD, Martin K. Urinary excretion of arterial blood prostaglandins in man Am J Physiol 1982; 242: E171-77. 17. Folts JD, Bonebrake FC The effect of cigarette smoke and nicotine on platele thrombus formation in stenosed dog coronary arteries· inhibition with phentolamine. Circulation 1982; 65: 465-70 18 Wennmalm A Nicotine inhibits hypoxia and arachidonic acid induced release of prostacyclin-like activity in rabbit hearts. Br J Pharmacol 1980, 69: 545-49 19. Alster P, Wennmalm A. Effect of nicotine on the formation of prostaglandins in the rabbit kidney. Clin Physiol 1981, 1: 105 20. Wennmalm A Interaction of nicotine and prostaglandins in the cariovascular system Prostaglandins 1982, 23: 139-44. 21. TurKer RK, Ercan ZS, Ersoy A, Zengil H. Inhibition by nicotine of the vasodilator effect of bradykinin: evidence for a prostacyclin-dependent mechanism. Arch Int Pharmacody 1982, 257: 94-103 22. Dadak CH, Leithner CH, Sinzinger H, Silberbauer K Diminished prostacyclin formation in umbilical arteries of babies born to women who smoke Lancet 94.