Effect of administration of adrenocorticotropic hormone on plasma concentrations of testosterone, luteinizing hormone, follicle stimulating hormone and cortisol in stallions

EFFECT OF ADMINISTRATION OF ADRENOCORTICOTROPIC HORMONE ON PLASMA CONCENTRATIONS OF TESTOSTERONE, LUTEINIZING HORMONE, FOLLICLE STIMULATING HORMONE AND CORTISOL IN STALLIONS

James J. Wiest, MS, Donald L. Thompson, Jr., PhD, Deborah R. McNeill-Wiest, MS, Frank Garza, Jr., MS, Pamela S. Mitchell, MS

SUMMARY

In boars and rabbits, administration of adrenocorticotropic hormone (ACTH) results in a testis-dependent, shortterm increase in concentrations of testosterone in peripheral plasma. This experiment was designed to assess the shortterm effects of a single ACTH injection on plasma concentrations of testosterone, luteinizing hormone (LH), follicle stimulating hormone (FSH) and cortisol in stallions. Eight light horse and two pony stallions were paired by age and weight and then one of each pair was randomly assigned to the treatment (ACTH, .2 IU/kg of body weight) or control (vehicle) group. Injection of ACTH increased (P<.01) plasma concentrations of cortisol by approximately twofold in the first 60 minutes; control stallions showed no change (P>.10) in concentrations ofcortisol during the blood sampling period. Control stallions exhibited a midday increase (P<.05) in concentrations of testosterone similar to that reported previously; ACTH treatment prevented or delayed this increase such that concentrations of testosterone in treated stallions were lower (P<.05) than in controls 4 to 5 hours after injection of ACTH. Treatment with ACTH had no effect (P<.10) on plasma concentrations of LH or FSH up to 12 hours after injection. INTRODUCTION

Administration of adrenocorticotropic hormone (ACTH) to boars 6a'9 and rabbits 4,n increased plasma concentrations of testosterone within 60 to 120 minutes. The testosterone secreted in response to ACTH in boars originated from the testes, because administration of ACTH to barrows did not Authors' address: Departmentof Animal Science,LouisianaAgricultural ExperimentStation,LouisianaState UniversityAgriculturalCenter,Baton Rouge,LA70803-4210.Addressreprintrequeststo D.L.Thompson,Jr. Mr. Wiest's presentaddress is: Horse Scetion,Depaamentof Animal Science, Texas A&M Univ., CollegeStation,TX 77843. Acknowledgement:Approvedfor publicationby the Directorof the Louisiana AgriculturalExperimentStationas manuscriptnumber87-11-1551. 168

alter plasma concentrations of testosterone.6 Exposure of stallions to mares for teasing or breeding increased plasma concentrations of cortisol. 16Corticosteroids have been implicated in the inhibition of luteinizing hormone (LH) secretion in primates 3 and horses) In addition, it has been reported that corticosteroids reduce the LH response to gonadotropin releasing hormone (GnRH) in cows and primates, 3~," but not in rats TM or mares) ° The present experiment was designed to determine if ACTH administration causes a short-term increase in testosterone secretion in stallions as it does in boars and rabbits. In addition, plasmaconcentrations of LH and follicle stimulating hormone (FSH) were measured to determine if ACTH administration affects plasma concentrations of these hormones. MATERIALS AND METHODS

Eight light-horse and two pony stallions aged 3 to 20 years were used. All stallions were in good body condition and were fed a maintenance diet of hay and commercial grain mix. Stallions were paired according to similarities in age and body weight, and then one of each pair was randomly assigned to the control or treatment group. Treated stallions received ACTH (Acthar) a intravenously at .2 IU/kg of body weight in aqueous 16% gelatin and .5% phenol (pH = 7.2). Control stallions were injected with an equivalent amount of vehicle. For withdrawal of blood samples, a 14-gauge catheter was inserted into one jugular vein of each stallion at approximately 0700. Blood samples were drawn at -60, -30, -15 and -.5 minutes relative to treatment injection. After treatment injection, blood samples were drawn at 15-minute intervals through 90 minutes, every 30 minutes until 360 minutes and then hourly until 12 hours after treatment injection. Blood samples were placed into heparinized tubes and were kept on ice. Plasma was harvested by centrifugation and was stored at -15°C. Concentrations of gonadotropins and testosterone were aArmour PharmaceuticalsCo., Kankakne,IL 60901

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determined by radioimmunoassay as described previously. 17lg Concentrations of cortisol were determined for selected samples by radioimmunoassay as previously described?3 Hormonal data were analyzed by analysis of variance that took into account the repetitive nature of the sampling (splitplot design)?'~5 Significance of differences between groups for each time period was assessed by LSD test?5

RESULTS Concentrations of cortisol increased (P<.01) in ACTHtreated stallions within 60 minutes after injection, whereas they remained constant in control animals during the same period of time (Figure 1). Concentrations of cortisol remained elevated in ACTH-treated stallions through 240 minutes. However, concentrations of cortisol in treated stallions were lower (P<.05) than in control stallions by 300 minutes after injection of ACTH and remained depressed through 12 hours after treatment. Concentrations of testosterone in control and ACTHtreated stallions are presented in Figure 2. There was a suppressive effect (P<.05) of ACTH administration on concentrations of testosterone between 4 and 5 hours after treatment. Testosterone concentrations increased (P<.05) in control stallions during midday, but decreased (P<.05) in ACTHtreated stallions during this time. Concentrations of LH and FSH remained constant in both groups of stallions throughout the blood sampling period and were not affected (P>.10) by ACTH administration (data not shown).

DISCUSSION Administration of ACTH increased plasma concentra100

tions of cortisol in these stallions, whereas concentrations of testosterone were decreased. Thus, the stallion differs from the boar and rabbit, in which ACTH administration produces a short-term, testis-dependent increase in concentrations of testosterone. 6,7,9In other species, an increase in testosterone secretion is preceded by an increase in LH concentrations. However, Juniewicz and Johnson6observed no increase in LH concentrations in boars administered ACTH, even though concentrations of testosterone were stimulated. Thus, a direct effect on the testes was implicated. In the present experiment, the decrease in concentrations of testosterone was not preceded or accompanied by a decreas~ in concentrations of LH, which may also indicate a direct effect on the testes by either ACTH or the corticosteroids secreted in response to ACTH. The control stallions in the present experiment exhibited a midday rise in concentrations of testosterone similar to that reported previously.TMAdministration of ACTH at approximately 0800 prevented this rise, although concentrations of testosterone in ACTH-treated stallions did appear to rebound later in the day. Similarly, Doerr and Pirke2 reported that cortisol treatment of adult men caused a decrease in the nocturnal rise in concentrations of testosterone. As in our previous report, TM the variations in testosterone secretion during the day were not associated with any specific pattern of LH secretion. Thus, it appears that short-term testosterone secretion in the stallion is affected by factors other than LH acting at the level of the testes. In heifers, ACTH treatment decreased the LH response to exogenous GnRH.s It was showns,l~ by in vitro studies that ACTH itself has no effect on the LH response to GnRH treatment, whereas cortisol has a direct suppressive effect on the bovine pituitary. There was no change in plasma concentrations of LH or FSH in the present experiment, even though 1.0

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Figure 1. Mean concentrations of cortlsol in plasma of control (C) and ACTH-treated (T) stallions. Injections of ACTH or vehicle were given at time 0. Means for ACTH-treated stallions that differ (P<.05) from controls are indicated by asterisks. Pooled SE from analysis of variance was 5.0 ng/ml. Volume 8, Humber 2, 1988

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Figure 2. Mean concentrations of testosterone in plasma of control (C) and ACTH-treated (T) stallions. Injections of ACTH or vehicle were given at time 0. Means for ACTHtreated stallions that differ (P<.05) from controls are indicated by the asterisks. Pooled SE from the analysis of variance was .13 ng/ml. 169

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concentrations of cortisol were increased more than twofold. In fact, the approximate twofold elevation of concentrations of cortisol produced by ACTH administration was similar in magnitude to the elevation produced by sexual excitement in stallions? 6 This lack of effect of cortisol on gonadotropin concentrations may be due to the relatively short period that concentrations of cortisol were elevated, because others ~,~0 reported that longer-term dexamethasone treatment suppressed the secretion of LH but not FSH in mares. In conclusion, treatment of stallions with ACTH increased concentrations ofcortisol in plasma and prevented the expected midday increase in testosterone secretion. However, the transient increase in cortisol secretion did not affect plasma concentrations of LH or FSH up to 12 hours after ACTH injection. REFERENCES 1. Asa CS, Ginther OJ: Giueocortieoid suppression of oestrus, follicles, LH and ovulation in the mare. J Reprod Fert Supp132:247-251, 1982. 2. Doerr P, Pirke KM: Cortisol-induced suppression of plasma testosterone in normal adult males. J Clin Endacrlnol Metab 43:622-629, 1976. 3. Dubey AK, Plant TM: A suppression ofgonadotropin secretion by cortisol in castrated male rlaesus monkeys (Maccaca mulatta) mediated by the interruption of hypothalamie gonadotropin-releasing hormone release. Biol Reprod 33:423-431, 1985. 4. Fanlbom KW, Fenske M, Pitzel L, Konig A: Effects of an intravenous injection of tetraeosactid on plasma eorticosteroid and testosterone levels in unstressed male rabbits. Acta Endocrino191:511-518, 1979. 5. Gill JL, Hafs HD: Analysis of repeated measurements of animals. J Anita Sci 33:331-335, 1971. 6. Juniewicz PE, Johnson BH: Influence of adrenal steroids upon testosterone secretion by the boar testis. Biol Reprod 25:725-733, 1981. 7. Juniewiez PE, Johnson BH: Ability of eortisol and progesterone to

mediate the stimulatory effect of adrenocortieotropic hormone upon testosterone production by the porcine testis. Biol Reprod 30:134-142, 1984. 8. Li PS, Wagner WC: In vivo and in vitro studies on the effect of adrenoco~cotropic hormone or cortisol on the pituitary response to gonadotropin releasing hormone. BiolReprod 29:25-37, 1983. 9. Liptrap RM, Raeside JI: Increase in plasma testosterone concentration after injection of adrenoco~cotrophin into the boar. J Endocrinol 66:123-131, 1975. 10. McNeiU DR: Dexamethasone and progesterone effects on gonadotropin secretion in pony mares. MS Thesis, Louisiana State Univ., Baton Rouge, 1986. 11. Padmanabhan V, Keech C, Convey EM: Cortisol inhibits and adrenoco~eotropin has no effect on luteinizing hormone-releasing hormone-induced release of luteinizin'g hormone from bovine pituitary cells in vitro. Endocrinology 112:1782-1787, 1983. 12. Pitzel L, Kendoff T, Fenske M, Koniz A: Increase of testicular testosterone release after ACTH injection into male rabbits. Acta Endocrinol 96(Suppl 240):107-108, 1981. (Abstr.) 13. Reimers TJ, Cowen RG, Davidson HP, Colby ED: Validation of radioimmunoassays for triiodothyronine, thyroxine, and hydroco~isone (cortisol) in canine, feline and equine sera. Amer J Vet Res 42:2016-2021, 1981. 14. Suter DE, Schwartz NB: Effects ofglucoeorticoids on secretion of luteinizing hormone and follicle-stimulatinghormone by female rat pituitary cells in vitro. Endocrinology 117:849-854, 1985. 15. Steel RGD, Torrie JH: Principles and Procedures of Statistics: a Biometrical Approach (2nd edition), McGraw-Hill, Inc., New York, 1980. 16. Tamanini C, Giordano N, Chiesa F, Seren F: Plasma cortisol variations induced in the stallion by mating. Acta Endocrin 102:447-450, 1983. 17. Thompson DL Jr, Godke RA, Squires EL: Testosterone effects on mares during synchronization with altrenogest: FSH, LH, estrous duration and pregnancy rate. dAnim Sci 56:678-686, 1983. 18. Thompson DL Jr, ReviUe-Moroz SI, Walker MP, Derrick DJ, Papkoff H: Testosterone administration to mares during estrus: Duration of estrus and diestms and concentrations of LH and FSH in plasma. JAnim Sci 56:911-918, 1983. 19. Thompson DLJr, St George RL, Jones LS, Garza F Jr: Patterns of secretion of luteinizing hormone, follicle stimulating hormone and testosterone in stallions during the summer and winter. JAnim Sci 60:741-748, 1985.

Salmonella Typhimurium

CROSS PROTECTIVE ANTISERUM Gram negative endotoxemia in horses of all ages and corrects FPT (failure of pasaive transfer) in foals. Contains high levels of both IgG(t) and total IgG.

FORAGE • FEEDSTUFF ° W A T E R ° S O I L • M A N U R E

ANALYSIS An important too/in montoring relationships between trace and major minerals

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