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The central neuropeptides ACTH and α-MSH in fever control
J. therm. Biol. Vol. 9, No. I/2. pp. 139--143, 1984 Printed in G r e a t Britain. All rights reserved
0306-4565/84 $3.00 + 0 . 0 0 Copyright ,~ 1984 Pergamon Press Ltd
THE CENTRAL NEUROPEPTIDES ACTH AND ct-MSH IN FEVER CONTROL J. M. LIPTON,L2 J. R. GLYN-BALLINGER,I M. T. MURPHY,1 J . A . Z I M M E R , I G . B E R N A R D I N I I and W. K. SAMSON* ~Physiology and 2Anesthesiology Departments, University of Texas Health Science Center at Dallas. Dallas, TX 75235, U.S.A.
Abstract--The chain of evidence that the endogenous neuropeptides ACTH and ct-MSH have a role in central mediation of thermoregulation is reviewed. It is concluded that one or both of these peptides is important to the limitation of maximal fever. Key Word Index--ACTH; :~-MSH; fever; thermoregulation; CNS peptides; antipyresis; squirrel
monkeys.
INTRODUCTION
ACTH and n-MSH (ACTH 1-13) are derived from a common precursor, propiomelanocortin, and share a common amino acid sequence. These peptides, which were first isolated from pituitary tissue, are now known to be widely distributed within the brain (Krieger and Martin, 1981; O'Donahue and Jacobowitz, 1980). Pituitary ACTH and ~-MSH have been implicated in adrenal cortical stimulation and melanocyte stimulation, but their functional significance in extrapituitary sites is unknown. However, there is speculation that these peptides may have neurotransmitter or neuromodulator functions based on the findings that: both peptides are located in cell bodies within the arcuate nucleus and are distributed via fibres which enter hypothalamic, limbic and other CNS regions; ~t-MSH is present within (Barnea et al., 1977; Parker and Porter, 1979) and released from synaptosomes (Warberg et al., 1977).
was no effect of the high dose of either peptide on body temperature in a hot environment (30°C). This pattern of response is not consistent with lowering of the central set-point of temperature control by either peptide. In experiments on the hyperthermic effects of prostaglandin E2 and amphetamine, the peptides inhibited both heat conservation and heat production. These findings account for the lack of effect of the high dose of either peptide in a hot environment in which the level of heat production and conservation was already minimal. While screening batches of ACTH for pyrogen contamination, Douglas and Paton (1952) had previously noted that this peptide caused hypothermia in rabbits after intravenous (IV) injection. Posterior pituitary hormonal contamination of the ACTH samples was not responsible for the hypothermias since injections of posterior pituitary extract did not induce hypothermia. Although intracisternal administration of approx. 500-600/~g ACTH to rabbits did not reduce
EFFECT OF CENTRAL ADMINISTRATION OF ACTH AND .,-MSH ON NORMAL BODY TEMPERATURE
TABLE I EFFECTS OF ICV ADMINISTRATION OF PEP'rIDES ON BODY TEMPERATURE OF RABBITS IN A 23*C ENVIRONMENT
That these peptides might have physiological roles in CNS mediation of temperature control was initially suggested by the results of experiments in which 16 peptides were tested for effects upon body temperature (Lipton and Glyn, 1980; Table 1). In these experiments ACTH 1-24 and ~-MSH 1-13 were the only peptides that reliably decreased temperature when injected into the cerebral ventricles (ICV) of rabbits in a thermoneutral environment. 1.25-5.0/zg of these peptides evoked dose-related hypothermias with a maximum decrease of approx. I°C. ACTH 1-10 and, in further experiments (Lipton et al., 198 i ), corticotropin-like intermediate lobe peptide (CLIP 18-39) did not alter body temperature, suggesting that the 11-13 fragment may be of primary importance to the hypothermic effect (Lipton et al., 1981). The dose-related hypothermias that were produced by these peptides in a thermoneutral environment were augmented in the cold (10°C), but there
Pepiide
Dose Ipmoles)
Mean max A T I~CI
Time to max A T (hr}
,~-MSH ACTH( 1-241
3.08 1.42
- 1.0 -0.9
1.67 I. 17
7 7
Oxytocin
5.51
0.4
1.0
10
Vasopre,sin Glucagon ACTHI I- I01 Bombesin Cholecy,,Iokinin
5.08 1.41 3.85 3.20 4.70
0.3
0.33 1.33 1.0 2.0 0.17
12 15 7 7 7
9.99
0.3
2.33
7
0.40 0.44
0.17 3.0
7 7
2.33
7
10.30 4.16
0.3 - 0.2 0.3 t). I 0,1
0.5 1.5
7 7
2.99 7.71
0.3 0. I
0.67 0.83
7 7
0.3
0.2 0.6 0. I
N
Conlracep!ive
tetrapeplidc Gastrin Insulin Inlerleron l.cupeptin "LHRH Panhibin
(Somato,,tatinl Proctolin
139
0.25
J. M. LIPTONet aL
140
A N T I P Y R E T I C E F F E C T OF C E N T R A L A N D IV A D M I N I S T R A T I O N O F A C T H AFTER ADRENALECTOMY
their temperature (Ferrari et al., 1963), the positive findings after peripheral and central injection of the peptide described above suggest that the ACTH given by the intracisternal route may not reach the essential site of action.
ACTH was first implicated in fever control when Hench et al. (1949) pointed out that peripheral administration of this peptide reduces fever and other symptoms of rheumatoid arthritis. Amplitude and duration of fevers induced by systemic injection of pyrogens in humans and rabbits were reduced by prior intramuscular administration of ACTH (Kass and Finland, 1950). Judging from increases in circulating corticosteroids, ACTH release is induced by peripheral pyrogens (Bassoe, 1969) so that limitation of fever by this peptide may occur naturally. Corticosteroids also reduce fever when injected into the preoptic/anterior hypothalamic region (POAH; Chowers et al., 1968; Willies and Woolf, 1980) and, although it appears more likely that central injection of ACTH acts directly at sites within the brain to cause antipyresis, the possibility remained that the fever reduction occurred indirectly via release of corticosteroids from the adrenal gland and their subsequent action on CNS temperature controls. To test this idea ACTH was injected ICV in bilaterallyadrenalectomized rabbits made febrile by IV injections of LP. Central administration of 0.25/~ g ACTH reduced fever when given simultaneously with the pyrogen in one group of adrenalectomized rabbits (2-3 kg) and when given 30 min after the pyrogen in another (3--4 kg) group. In smaller adrenalectomized rabbits progressively smaller ICV doses of ACTH were given until doses were found that had no effect on afebrile temperatures of individual rabbits but that still reduced fever. The doses varied between 25-75 ng and caused significant reduction of fever in these adrenalectomized animals. These results demonstrate that defervescence produced by centrallyadministered ACTH does not depend upon the release of corticosteroids and their subsequent action on the brain, and that only a small amount of ACTH is required to inhibit fever in these adrenalectomized rabbits. It has been reported that only small amounts of peripherally-administered ACTH enter the brain (Mezey et al., 1978; Verhoef and Witter, 1976). Since corticosteroids reduce fever and readily enter the brain (Abelson et al., 1955; Christy and Fishman, 1961; Cranny and Kelley, 1958; Sandberg et al., 1954), peripheral ACTH may reduce fever indirectly
R E D U C T I O N O F F E V E R BY C E N T R A L ADMINISTRATION OF ACTH AND ~-MSH
Both ACTH 1-24 and ~-MSH 1-13 reduced fever when injected centrally in rabbits (Glyn and Lipton, 1981). Five microgrammes of ACTH 1-24 reversed vasoconstriction during the chill phase of fever and reduced rises in temperature after IV or ICV injections of leukocytic pyrogen (LP). Fever was also reduced by 5 pg of ~t-MSH, but the antipyretic effect was less than that produced by ACTH. However, as described above, this dose of either peptide lowered temperature in afebrile rabbits so that the peptides may have produced antipyresis by virtue of a physiological antagonism. The hypothermia produced by this dose may be, as we now suspect, an exaggeration of a naturally-occurring inhibition of heat production and conservation by these peptides. However, in subsequent experiments, a non-hypothermic dose of 0.25 pg ACTH and a similar amount of ~-MSH also reversed vasoconstriction and reduced fever caused by IV injection of LP. These findings indicate that small doses of the peptides are antipyretic in the same sense as aspirin-like drugs. That is, the peptides can reduce fever in doses that do not alter normal body temperature. The influence on heat conservation supports the possibility that inhibition of central pathways that control vasoconstriction may be one of the actions of these peptides in normal limitation of fever. It has been noted previously that there are marked differences among species in temperature response to central administration of putative neurotransmitters (Biigh, 1980). To test the generality of the antipyretic effect of ACTH, the squirrel monkey (Saimiri sciureus), a primate model that reliably develops fever after injection of bacterial endotoxin and animal (Lipton and Fossler, 1974) and human (Lipton et al.. 1979) LP, was used. In experiments on three monkeys, ICV injections of non-hypothermic doses of ACTH reduced fever (Fig. 1). These findings demonstrate that ACTH can act as a central antipyretic in a primate species as well as in lagomorphs.
• --.--e ENOOTOXiN (IV) o.---o Ir NOOTOXIN (IV') 4. ACTH (ICY)
+1
M63
z! O,
M64
+1
O~
O,
-2
-2
M65
~W Z~
°,~ er
-2 I t
I 2
! 3
I t
HOURS AFTER
I 2 ACTH
I 3
I t
I 2
I 3
INJECTION
Fig. 1. Antipyretic effect of ACTH (1-24) injected 1CV in 3 squirrel monkeys made febrile by IV administration of Salmonella typhosa endotoxin. ACTH (0.6-2.5 #g) given at peak fevers. O indicates fever after ACTH; • indicates control fever course after peak in each monkey.
141
ACTH, ~t-MSH and fever via stimulation of corticosteroid release. To learn whether peripheral ACTH itself is antipyretic it was given IV to adrenalectomized rabbits made febrile by IV LP injections. ACTH (2.5 pg total dose, less than 1 p g k g -I) reduced fever when given simultaneously with LP and when given 30 min after LP injection and had no effect on afebrile body temperature. In tests on 10 rabbits IV ACTH (2.5 pg) also reduced fever after ICV injection of LP. These results are much like those after ICV injections of ACTH and suggest that: (1) adrenal cortical activity is not required for the antipyresis caused by IV ACTH; (2) this peptide must be able to enter the brain in sufficient amounts to act on central temperature controls and thereby reduce fever. From the combined results it may be that ACTH, and perhaps the smaller ~-MSH fragment acts as a brake to limit the amplitude of fever. Thus these peptides may have a role in the central mechanism of the upper fever limit first proposed by DuBois (1949). CENTRAL AND P E R I P H E R A L a-MSH IN F E V E R C O N T R O L
If these central peptides are important to the limitation of maximal fever there should be a change in central concentration or turnover of one or both of the peptides at fever peak. Using a sensitive radioimmunoassay we established the presence of immunoreactive ~-MSH (i.r. u-MSH) in discrete CNS sites within the rabbit brain (Samson et aL, 1981). The concentration of i.r. ~-MSH within the septal region increased significantly during fever (Tr, > 41-0°C) compared to the concentration in afebrile matched (weight and previous response to pyrogen) controls killed at the same time (Table 2). The concentration of i.r. ~-MSH within the arcuate nucleus, the presumed origin of ~-MSH found in the septal region, decreased though not significantly in animals with fever. Fever did not alter the concentration of the peptide within the POAH region or within the other brain regions sampled. These results suggest that the septum may be the central site of action in production of antipyresis by centrally- and peripherally-administered ~-MSH. There are abundant efferent pathways from the septal region to the
TABLE 2
a-MSH CONTENT ( ~ Area Septum Paraventr/cular hypothalamus Median Eminence
Midbrain Arcuate nucleus Preoptic/Anterior hypothalamus
Pituitary *p<0.01 t-test.
TB 9,'1-2--]
PROTEIN (Mean ± SEM)I
Pyrosen Injected (n=9}
Control In= 171
0.81 "*" 0.I0"
0.54 ± 0.04
2.94 5.41 2.46 7.15
_ ± ± *-_
0.42 0.S2 0.28 1.07
3.13 4.90 2.32 10.33
- 0.40 _* 0.63 ± 0.19 ± 1.29
6.36 _~ 0.76 6.78 ± 0.93 7.87 ± 1.95 7.71 ± 1.26 ng~p.g protein 86.5 ± I0.0 89.5 ~- 11.9
e.-.-e n,40 LP+a-ldSH OF.ql o--.o n,40 LP÷a-MSH 4F.g
p_.,
t0
8'E 2 ~ 0.5 (J"6 {:Z:
o
o
t
2
3
4
5
TIME AFTER INJECTION (hrs)
Fig. 2. Antipyretic effect of I pg a-MSH (1-13) injected bilaterally in the septal region of rabbits made febrile by IV injection of LP. primary temperature control in the POAH region (Powell, 1963; Raisman, 1966) which may represent the anatomical substrate for limbic modulation of thermoregulation. The idea that the peptide concentration within the septum is important to fever control was strengthened in experiments in which ~-MSH was injected bilaterally into the septal region of rabbits made febrile by IV injections of LP. One microgramme of :t-MSH inhibited fever, whereas control injections of the peptide given when the animals were afebrile did not alter body temperature (Fig. 2). The febrile response is reduced in aged rabbits (Lipton and Ticknor, 19791, squirrel monkeys (Clark et al., 1980) and man (Petersdorf, 1974). The precise nature of the change with ageing that is responsible for reduced fever capacity is not known, but alterations in central controls of body temperature or a reduction in central sensitivity to endogenous pyrogens with ageing may be responsible (Lipton and Ticknor, 1979; Clark et al., 19801. From the data described above it may be that an enhanced central sensitivity to endogenous antipyretic peptides could also account for the results. This idea was supported when it was noted that the antipyretic effect of ~t-MSH increased with age (Murphy and Lipton, 19821. A dose of 25 ng ct-MSH given ICV had a greater fever-reducing effect in older (3-4 yr) than in younger ( < 2 yr) rabbits. In addition, this peptide when given IV (2.5 pg) to animals made febrile by LP reduced fever by 58.8% over 1.5 h post-injection in the older rabbits, whereas over a similar time period fever was reduced by 26% in younger rabbits. A dose of 5 mg of acetaminophen, a 2000-fold greater dose by weight, had no effect on fever in either age group, so that the peptide is comparatively a much more potent antipyretic. IV injection of 2.5pg ~t-MSH reduced fever caused by ICV injection of LP in the older but not in the younger rabbits. These results indicate that the peptide can readily antagonize fever caused by LP within the brain and that older rabbits are more sensitive to this antipyretic action of :t-MSH. Further, intragastric administration of 2.5 mg a-MSH reduced fever caused by IV LP. The reduction was 40.9% over 2 h in younger animals and 57~o in older rabbits. This finding indicates that ~t-MSH or some active fragment is absorbed from the gut into the blood stream and enters the brain. Although the half-life of ~t-MSH in blood is short (Kastin et al., 1976), it seems that MSH enters the brain in quantities sufficient to exert marked and
142
J.M. LIPTOr~et al.
prolonged antipyretic actions. The enhanced sensitivity to ct-MSH with ageing may contribute to reduction in, or disappearance of, fever responses in elderly homeotherms. The potency of peripherally-administered ~-MSH in reducing fever raises the possibility that this peptide might be useful clinically for fever control. ACTH also reduces fever but the undesirable side effects of repeated administration (Cushing's syndrome) and the fact that it must be given parenterally has limited the use of the peptide tbr its antipyretic properties. ~t-MSH does not induce the release of corticosteroids, and it has been found not to cause untoward psychological or physiological changes in man (Kastin et al., 1971). The potent antipyretic action and the relative safety of this peptide suggest that it could be a useful clinical medication. SUMMARY
The evidence reviewed above suggests that ACTH and the shorter molecule ~t-MSH have roles in physiological control of body temperature. It appears that small quantities of these peptides are antipyretic without altering afebrile body temperature. The evi. dence suggests that naturally occurring release of ACTH during fever may be important to fever control by virtue of an action of the peptide on central temperature control. The data also suggest that the concentration of ~t-MSH within the septal region is important to central modulation of fever. Antipyretic effects produced by peripheral administration of low doses of each peptide raise the possibility that the peptides may have clinical value. ~-MSH may be especially useful for controlling fever in man since this peptide, unlike ACTH, does not induce steroid release. Acknowledgementa--Research described in this paper was supported by Grant NS 10046 from the National Institute of Neurological and Communicative Disorder and Stroke and by Grant AG 00109 from the National Institute on Aging. The authors are grateful to Pamela Langdon for secretarial assistance. REFERENCES
Abelson D., Baron D. N. and Toakley J. G. (1955) Studies of cercbrospinsl fluid following oral administration of cortisone acetate or hydrocortisone. J. Endocr. 12, 87-92. Bamea A., Oliver C. and Porter J. C. (1977) Subcellular localization of a-melanocyte-stimulating hormone in the rat hypothalamus. J. Neurochem. 29, 619--624. Basset H. H. (1969) Adrenal function in fever. Scand. J. infect. D/s. l, 197-211. Blish J. (1980) Central neurology of homcothermy and fever. In Fever (Edited by Lipton J. M.), pp. 81-90. Raven Press, New York. Chowers I., Conforti N. and Feldman S. (1968) Local effect of cortisol in the preoptic area on temperature regulation. Am. J. Physiol. 214, 538-542. Christy N. P. mad Fishman R. A. (1961) Studies of the biood--cerebrospinalfluid barrier to cortisol in the dog, J. din. Invest. 40, 1997-2006. Clark S. M., Ocan J. T. and Lipton J. M. (1980) Reduced febrile responses to peripheral and central administration ofpyrogen in aged squirrel monkeys. Neurobiol. Aging 1, 175-180. Cranny R. L. and Kelley V. C. (1958) The use of hydro-
cortisone in the treatment of tuberculous meningitis. A study of steroid concentrations in cerebrospinal fluid. J. Dis. Childh. 96, 165-168. Douglas W. W. and Paton W. D. M. (1952) The hypothermic and antipyretic effect of preparations of ACTH. Lancet 134, 342-345. DuBois E. F. (1949) Why are temperatures over 106:F rare? Am. J. reed. Sci. 217, 361-368. Ferrari W., Gessa G. L. and Vario L. (1963) Behavioral effects induced by intracisternally injected ACTH and MSH. Am. N.Y. Acad. Sci. 104, 330--345. Glyn J. R. and Lipton J. M. (1981) Hypothermic and antipyretic effects of centrally administered ACTH (1-24) and ~t-melanotropin. Peptides 2, 177-187. Hench P. S., Kendall E. C., SIocumb C. H. and Policy H. F. (1949) The effect of a hormone of the adrenal cortex (17-hydroxy-ll-dehydrocorticosterone: compound E) and of pituitary adrenocorticotropic hormone on rheumatoid arthritis. Proc. Staff Meet. Mayo Clin. 24, 181-197. Kass E. H. and Finland M. (1950) Effects of ACTH on induced fever. New Engl. J. Med. 2,t3, 693-695. Kastin A. J., Miller L. H., Gonzalez-Barcena D., Hawley W. D., Dyster-Aas K., Schally A. V., Velasco de Parra M. L. and Velasco M. (1971) Psyehophysiologiccorrelates of MSH activity in man. Physiol. Behat,. 7, 893-896. Kastin A. J., Nissen C., Nikolis K., Medzihradszky K., Coy D. H., Teplan I. and Schally A. V. 0976) Distribution of 3H-a-MSH in rat brain. Brain Res. Bull. 1, 19-26. Krieger D. T. and Martin J. B. (1981) Brain peptides. New Engl. J. Med. 304, 876-885; 944-951. Lipton J. M. and Fossler D. E. (1974) Fever produced in the squirrel monkey by intravenous and intracerebral endotoxin. Am. J. Physiol. 226, 1022-1027. Lipton J. M. and Glyn J. R. (1980) Central administration of peptides alters thermoregulation in the rabbit. Peptides 1, 15-18. Lipton J. M. and Ticknor C. B. (1979) Influence of sex and age on febrile responses to peripheral and central administration of pyrogens in the rabbit. J. Physiol., Lond. 295, 263-272. Lipton J. M., Dinarello C. A. and Kenhedy J. I. (1979) Fever produced in the squirrel monkey by human leukocytic pyrogen. Proc. Soc. exp. Biol. Med. 160, 426-428. Lipton J. M., Glyn J. R. and Zimmer J. A. (1981) ACTH and ~-melanotropin in central temperature control. Fedn Proc. 40, 2760-2764. Mezey E., Palkovits M., Kloet E. R. de, Verhoef J. and Wied D. de (1978) Evidence for pituitary-brain transport of a behaviorally potent ACTH analog. Life Sci. 22, 831-838. Murphy M. T. and Lipton J. M. (1982) Peripheral administration of ~-MSH reduces fever in older and younger rabbits. Peptides, 3, 775-779. O'Donohue T. L. and Jacobowitz D. M. (1980) Studies on ~t-melanotropin in the central nervous system. In Polypeptide Hormones (Edited by Beers R. F. Jr and Bassett E. G.), pp. 203-222. Raven Press, New York. Parker C, R. and Porter J. C. (1979) Subcellular localization of immunoreactive :t-melanocyte stimulating hormone in human brain. Brain Res. Bull. 4, 535-538. Petersdorf R. G. (1974) Chills and fever. In Harrison's Principles of Internal Medicine (Edited by Wintrobe M. W., Thorne G. W., Adams R. D., Braunwald E., lsselbacher K. and Petersdorf R. G.), pp. 50. McGraw-Hill, New York. Powell E. W. (1963) Septal effects revealed by axonal degeneration in the rat. Expl Neurol. 8, 406--422. Raisman G. (1961) The eonnexions of the septum. Brain 89, 317-348. Samson W. K., Lipton J, M., Zimmer J. A. and Glyn J. R. (1981) The effect of fever on central :t-MSH concentrations in the rabbit. Peptides 2, 419-423.
ACTH, :t-MSH and fever Sandberg A. A., Eik-Nes K., Nelson D. H. and Tyler F. H. (1954) Levels of 17-hydroxycorticosteroids in body fluids. d. Lab. clin. Med. 43, 874-879. Verhoef J. and Witter A. (1976) The in vivo fate of a behaviorally active ACTH 4-9 analog in rats after systemic administration. Pharmac. Biochem. Behav. 4, 583-590. Warberg J., Oliver C., Eskay R. L., Parker C. R. Jr, Barnea A. and Porter J. C. (1977) Release of a-MSH
143
from a synaptosome-enriched fraction prepared from rat hypothalamic tissue. In Melanocyte Stimulating Hormone: Control, Chemistry and Effects (Edited by Tilders F. J. H., Swaab D. F. and Wimersma Greidanus Tj. B. van), pp. 167-169. Karger, New York. Willies G. H. and Woolf C. J. (1980) The site of action of corticosteroid antipyresis in the rabbit. J. Physiol., Lond. 300, 1-6.
0306-4565/84 $3.00 + 0 . 0 0 Copyright ,~ 1984 Pergamon Press Ltd
THE CENTRAL NEUROPEPTIDES ACTH AND ct-MSH IN FEVER CONTROL J. M. LIPTON,L2 J. R. GLYN-BALLINGER,I M. T. MURPHY,1 J . A . Z I M M E R , I G . B E R N A R D I N I I and W. K. SAMSON* ~Physiology and 2Anesthesiology Departments, University of Texas Health Science Center at Dallas. Dallas, TX 75235, U.S.A.
Abstract--The chain of evidence that the endogenous neuropeptides ACTH and ct-MSH have a role in central mediation of thermoregulation is reviewed. It is concluded that one or both of these peptides is important to the limitation of maximal fever. Key Word Index--ACTH; :~-MSH; fever; thermoregulation; CNS peptides; antipyresis; squirrel
monkeys.
INTRODUCTION
ACTH and n-MSH (ACTH 1-13) are derived from a common precursor, propiomelanocortin, and share a common amino acid sequence. These peptides, which were first isolated from pituitary tissue, are now known to be widely distributed within the brain (Krieger and Martin, 1981; O'Donahue and Jacobowitz, 1980). Pituitary ACTH and ~-MSH have been implicated in adrenal cortical stimulation and melanocyte stimulation, but their functional significance in extrapituitary sites is unknown. However, there is speculation that these peptides may have neurotransmitter or neuromodulator functions based on the findings that: both peptides are located in cell bodies within the arcuate nucleus and are distributed via fibres which enter hypothalamic, limbic and other CNS regions; ~t-MSH is present within (Barnea et al., 1977; Parker and Porter, 1979) and released from synaptosomes (Warberg et al., 1977).
was no effect of the high dose of either peptide on body temperature in a hot environment (30°C). This pattern of response is not consistent with lowering of the central set-point of temperature control by either peptide. In experiments on the hyperthermic effects of prostaglandin E2 and amphetamine, the peptides inhibited both heat conservation and heat production. These findings account for the lack of effect of the high dose of either peptide in a hot environment in which the level of heat production and conservation was already minimal. While screening batches of ACTH for pyrogen contamination, Douglas and Paton (1952) had previously noted that this peptide caused hypothermia in rabbits after intravenous (IV) injection. Posterior pituitary hormonal contamination of the ACTH samples was not responsible for the hypothermias since injections of posterior pituitary extract did not induce hypothermia. Although intracisternal administration of approx. 500-600/~g ACTH to rabbits did not reduce
EFFECT OF CENTRAL ADMINISTRATION OF ACTH AND .,-MSH ON NORMAL BODY TEMPERATURE
TABLE I EFFECTS OF ICV ADMINISTRATION OF PEP'rIDES ON BODY TEMPERATURE OF RABBITS IN A 23*C ENVIRONMENT
That these peptides might have physiological roles in CNS mediation of temperature control was initially suggested by the results of experiments in which 16 peptides were tested for effects upon body temperature (Lipton and Glyn, 1980; Table 1). In these experiments ACTH 1-24 and ~-MSH 1-13 were the only peptides that reliably decreased temperature when injected into the cerebral ventricles (ICV) of rabbits in a thermoneutral environment. 1.25-5.0/zg of these peptides evoked dose-related hypothermias with a maximum decrease of approx. I°C. ACTH 1-10 and, in further experiments (Lipton et al., 198 i ), corticotropin-like intermediate lobe peptide (CLIP 18-39) did not alter body temperature, suggesting that the 11-13 fragment may be of primary importance to the hypothermic effect (Lipton et al., 1981). The dose-related hypothermias that were produced by these peptides in a thermoneutral environment were augmented in the cold (10°C), but there
Pepiide
Dose Ipmoles)
Mean max A T I~CI
Time to max A T (hr}
,~-MSH ACTH( 1-241
3.08 1.42
- 1.0 -0.9
1.67 I. 17
7 7
Oxytocin
5.51
0.4
1.0
10
Vasopre,sin Glucagon ACTHI I- I01 Bombesin Cholecy,,Iokinin
5.08 1.41 3.85 3.20 4.70
0.3
0.33 1.33 1.0 2.0 0.17
12 15 7 7 7
9.99
0.3
2.33
7
0.40 0.44
0.17 3.0
7 7
2.33
7
10.30 4.16
0.3 - 0.2 0.3 t). I 0,1
0.5 1.5
7 7
2.99 7.71
0.3 0. I
0.67 0.83
7 7
0.3
0.2 0.6 0. I
N
Conlracep!ive
tetrapeplidc Gastrin Insulin Inlerleron l.cupeptin "LHRH Panhibin
(Somato,,tatinl Proctolin
139
0.25
J. M. LIPTONet aL
140
A N T I P Y R E T I C E F F E C T OF C E N T R A L A N D IV A D M I N I S T R A T I O N O F A C T H AFTER ADRENALECTOMY
their temperature (Ferrari et al., 1963), the positive findings after peripheral and central injection of the peptide described above suggest that the ACTH given by the intracisternal route may not reach the essential site of action.
ACTH was first implicated in fever control when Hench et al. (1949) pointed out that peripheral administration of this peptide reduces fever and other symptoms of rheumatoid arthritis. Amplitude and duration of fevers induced by systemic injection of pyrogens in humans and rabbits were reduced by prior intramuscular administration of ACTH (Kass and Finland, 1950). Judging from increases in circulating corticosteroids, ACTH release is induced by peripheral pyrogens (Bassoe, 1969) so that limitation of fever by this peptide may occur naturally. Corticosteroids also reduce fever when injected into the preoptic/anterior hypothalamic region (POAH; Chowers et al., 1968; Willies and Woolf, 1980) and, although it appears more likely that central injection of ACTH acts directly at sites within the brain to cause antipyresis, the possibility remained that the fever reduction occurred indirectly via release of corticosteroids from the adrenal gland and their subsequent action on CNS temperature controls. To test this idea ACTH was injected ICV in bilaterallyadrenalectomized rabbits made febrile by IV injections of LP. Central administration of 0.25/~ g ACTH reduced fever when given simultaneously with the pyrogen in one group of adrenalectomized rabbits (2-3 kg) and when given 30 min after the pyrogen in another (3--4 kg) group. In smaller adrenalectomized rabbits progressively smaller ICV doses of ACTH were given until doses were found that had no effect on afebrile temperatures of individual rabbits but that still reduced fever. The doses varied between 25-75 ng and caused significant reduction of fever in these adrenalectomized animals. These results demonstrate that defervescence produced by centrallyadministered ACTH does not depend upon the release of corticosteroids and their subsequent action on the brain, and that only a small amount of ACTH is required to inhibit fever in these adrenalectomized rabbits. It has been reported that only small amounts of peripherally-administered ACTH enter the brain (Mezey et al., 1978; Verhoef and Witter, 1976). Since corticosteroids reduce fever and readily enter the brain (Abelson et al., 1955; Christy and Fishman, 1961; Cranny and Kelley, 1958; Sandberg et al., 1954), peripheral ACTH may reduce fever indirectly
R E D U C T I O N O F F E V E R BY C E N T R A L ADMINISTRATION OF ACTH AND ~-MSH
Both ACTH 1-24 and ~-MSH 1-13 reduced fever when injected centrally in rabbits (Glyn and Lipton, 1981). Five microgrammes of ACTH 1-24 reversed vasoconstriction during the chill phase of fever and reduced rises in temperature after IV or ICV injections of leukocytic pyrogen (LP). Fever was also reduced by 5 pg of ~t-MSH, but the antipyretic effect was less than that produced by ACTH. However, as described above, this dose of either peptide lowered temperature in afebrile rabbits so that the peptides may have produced antipyresis by virtue of a physiological antagonism. The hypothermia produced by this dose may be, as we now suspect, an exaggeration of a naturally-occurring inhibition of heat production and conservation by these peptides. However, in subsequent experiments, a non-hypothermic dose of 0.25 pg ACTH and a similar amount of ~-MSH also reversed vasoconstriction and reduced fever caused by IV injection of LP. These findings indicate that small doses of the peptides are antipyretic in the same sense as aspirin-like drugs. That is, the peptides can reduce fever in doses that do not alter normal body temperature. The influence on heat conservation supports the possibility that inhibition of central pathways that control vasoconstriction may be one of the actions of these peptides in normal limitation of fever. It has been noted previously that there are marked differences among species in temperature response to central administration of putative neurotransmitters (Biigh, 1980). To test the generality of the antipyretic effect of ACTH, the squirrel monkey (Saimiri sciureus), a primate model that reliably develops fever after injection of bacterial endotoxin and animal (Lipton and Fossler, 1974) and human (Lipton et al.. 1979) LP, was used. In experiments on three monkeys, ICV injections of non-hypothermic doses of ACTH reduced fever (Fig. 1). These findings demonstrate that ACTH can act as a central antipyretic in a primate species as well as in lagomorphs.
• --.--e ENOOTOXiN (IV) o.---o Ir NOOTOXIN (IV') 4. ACTH (ICY)
+1
M63
z! O,
M64
+1
O~
O,
-2
-2
M65
~W Z~
°,~ er
-2 I t
I 2
! 3
I t
HOURS AFTER
I 2 ACTH
I 3
I t
I 2
I 3
INJECTION
Fig. 1. Antipyretic effect of ACTH (1-24) injected 1CV in 3 squirrel monkeys made febrile by IV administration of Salmonella typhosa endotoxin. ACTH (0.6-2.5 #g) given at peak fevers. O indicates fever after ACTH; • indicates control fever course after peak in each monkey.
141
ACTH, ~t-MSH and fever via stimulation of corticosteroid release. To learn whether peripheral ACTH itself is antipyretic it was given IV to adrenalectomized rabbits made febrile by IV LP injections. ACTH (2.5 pg total dose, less than 1 p g k g -I) reduced fever when given simultaneously with LP and when given 30 min after LP injection and had no effect on afebrile body temperature. In tests on 10 rabbits IV ACTH (2.5 pg) also reduced fever after ICV injection of LP. These results are much like those after ICV injections of ACTH and suggest that: (1) adrenal cortical activity is not required for the antipyresis caused by IV ACTH; (2) this peptide must be able to enter the brain in sufficient amounts to act on central temperature controls and thereby reduce fever. From the combined results it may be that ACTH, and perhaps the smaller ~-MSH fragment acts as a brake to limit the amplitude of fever. Thus these peptides may have a role in the central mechanism of the upper fever limit first proposed by DuBois (1949). CENTRAL AND P E R I P H E R A L a-MSH IN F E V E R C O N T R O L
If these central peptides are important to the limitation of maximal fever there should be a change in central concentration or turnover of one or both of the peptides at fever peak. Using a sensitive radioimmunoassay we established the presence of immunoreactive ~-MSH (i.r. u-MSH) in discrete CNS sites within the rabbit brain (Samson et aL, 1981). The concentration of i.r. ~-MSH within the septal region increased significantly during fever (Tr, > 41-0°C) compared to the concentration in afebrile matched (weight and previous response to pyrogen) controls killed at the same time (Table 2). The concentration of i.r. ~-MSH within the arcuate nucleus, the presumed origin of ~-MSH found in the septal region, decreased though not significantly in animals with fever. Fever did not alter the concentration of the peptide within the POAH region or within the other brain regions sampled. These results suggest that the septum may be the central site of action in production of antipyresis by centrally- and peripherally-administered ~-MSH. There are abundant efferent pathways from the septal region to the
TABLE 2
a-MSH CONTENT ( ~ Area Septum Paraventr/cular hypothalamus Median Eminence
Midbrain Arcuate nucleus Preoptic/Anterior hypothalamus
Pituitary *p<0.01 t-test.
TB 9,'1-2--]
PROTEIN (Mean ± SEM)I
Pyrosen Injected (n=9}
Control In= 171
0.81 "*" 0.I0"
0.54 ± 0.04
2.94 5.41 2.46 7.15
_ ± ± *-_
0.42 0.S2 0.28 1.07
3.13 4.90 2.32 10.33
- 0.40 _* 0.63 ± 0.19 ± 1.29
6.36 _~ 0.76 6.78 ± 0.93 7.87 ± 1.95 7.71 ± 1.26 ng~p.g protein 86.5 ± I0.0 89.5 ~- 11.9
e.-.-e n,40 LP+a-ldSH OF.ql o--.o n,40 LP÷a-MSH 4F.g
p_.,
t0
8'E 2 ~ 0.5 (J"6 {:Z:
o
o
t
2
3
4
5
TIME AFTER INJECTION (hrs)
Fig. 2. Antipyretic effect of I pg a-MSH (1-13) injected bilaterally in the septal region of rabbits made febrile by IV injection of LP. primary temperature control in the POAH region (Powell, 1963; Raisman, 1966) which may represent the anatomical substrate for limbic modulation of thermoregulation. The idea that the peptide concentration within the septum is important to fever control was strengthened in experiments in which ~-MSH was injected bilaterally into the septal region of rabbits made febrile by IV injections of LP. One microgramme of :t-MSH inhibited fever, whereas control injections of the peptide given when the animals were afebrile did not alter body temperature (Fig. 2). The febrile response is reduced in aged rabbits (Lipton and Ticknor, 19791, squirrel monkeys (Clark et al., 1980) and man (Petersdorf, 1974). The precise nature of the change with ageing that is responsible for reduced fever capacity is not known, but alterations in central controls of body temperature or a reduction in central sensitivity to endogenous pyrogens with ageing may be responsible (Lipton and Ticknor, 1979; Clark et al., 19801. From the data described above it may be that an enhanced central sensitivity to endogenous antipyretic peptides could also account for the results. This idea was supported when it was noted that the antipyretic effect of ~t-MSH increased with age (Murphy and Lipton, 19821. A dose of 25 ng ct-MSH given ICV had a greater fever-reducing effect in older (3-4 yr) than in younger ( < 2 yr) rabbits. In addition, this peptide when given IV (2.5 pg) to animals made febrile by LP reduced fever by 58.8% over 1.5 h post-injection in the older rabbits, whereas over a similar time period fever was reduced by 26% in younger rabbits. A dose of 5 mg of acetaminophen, a 2000-fold greater dose by weight, had no effect on fever in either age group, so that the peptide is comparatively a much more potent antipyretic. IV injection of 2.5pg ~t-MSH reduced fever caused by ICV injection of LP in the older but not in the younger rabbits. These results indicate that the peptide can readily antagonize fever caused by LP within the brain and that older rabbits are more sensitive to this antipyretic action of :t-MSH. Further, intragastric administration of 2.5 mg a-MSH reduced fever caused by IV LP. The reduction was 40.9% over 2 h in younger animals and 57~o in older rabbits. This finding indicates that ~t-MSH or some active fragment is absorbed from the gut into the blood stream and enters the brain. Although the half-life of ~t-MSH in blood is short (Kastin et al., 1976), it seems that MSH enters the brain in quantities sufficient to exert marked and
142
J.M. LIPTOr~et al.
prolonged antipyretic actions. The enhanced sensitivity to ct-MSH with ageing may contribute to reduction in, or disappearance of, fever responses in elderly homeotherms. The potency of peripherally-administered ~-MSH in reducing fever raises the possibility that this peptide might be useful clinically for fever control. ACTH also reduces fever but the undesirable side effects of repeated administration (Cushing's syndrome) and the fact that it must be given parenterally has limited the use of the peptide tbr its antipyretic properties. ~t-MSH does not induce the release of corticosteroids, and it has been found not to cause untoward psychological or physiological changes in man (Kastin et al., 1971). The potent antipyretic action and the relative safety of this peptide suggest that it could be a useful clinical medication. SUMMARY
The evidence reviewed above suggests that ACTH and the shorter molecule ~t-MSH have roles in physiological control of body temperature. It appears that small quantities of these peptides are antipyretic without altering afebrile body temperature. The evi. dence suggests that naturally occurring release of ACTH during fever may be important to fever control by virtue of an action of the peptide on central temperature control. The data also suggest that the concentration of ~t-MSH within the septal region is important to central modulation of fever. Antipyretic effects produced by peripheral administration of low doses of each peptide raise the possibility that the peptides may have clinical value. ~-MSH may be especially useful for controlling fever in man since this peptide, unlike ACTH, does not induce steroid release. Acknowledgementa--Research described in this paper was supported by Grant NS 10046 from the National Institute of Neurological and Communicative Disorder and Stroke and by Grant AG 00109 from the National Institute on Aging. The authors are grateful to Pamela Langdon for secretarial assistance. REFERENCES
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