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Dehydroepiandrosterone and Exercise in Golden Hamsters
Physiology & Behavior, Vol. 67, No. 4, pp. 607–610, 1999 © 1999 Elsevier Science Inc. Printed in the USA. All rights reserved 0031-9384/99/$–see front matter
PII S0031-9384(99)00108-0
Dehydroepiandrosterone and Exercise in Golden Hamsters DAVID R. PIEPER,1 CATHERINE A. LOBOCKI, EDWARD M. LICHTEN AND JADWIGA MALACZYNSKI Providence Hospital, Southfield, MI 48037 Received 9 March 1999; Accepted 24 May 1999 PIEPER, D. R., C. A. LOBOCKI, E. M. LICHTEN AND J. MALACZYNSKI. Dehydroepiandrosterone and exercise in golden hamsters. PHYSIOL BEHAV 67(4) 607–610, 1999.—Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) are adrenal androgens that have been associated with a sense of well-being in humans. We describe two experiments done to test the hypothesis that an increase in DHEA or DHEAS secretion is associated with the inclination to exercise using a hamster model. In the first experiment, morning blood samples were obtained from adult male golden hamsters at various intervals after being placed in cages with (EX group) or without (SED group) access to running wheels. The EX group had lower DHEA (6, 12, and 14 weeks; p , 0.05) and DHEAS (13 and 16 weeks; p , 0.01) levels than the SED hamsters. In the second experiment, the number of wheel revolutions was monitored in castrated adult male hamsters implanted with Silastic capsules containing no hormone (blank control group), testosterone, or DHEA. The number of wheel revolutions in the group receiving DHEA was not significantly different than the blank control group, whereas testosterone increased wheel running at 4, 5, and 7 weeks (p , 0.05). These results indicate that DHEA and DHEAS levels decrease with exercise in male golden hamsters and that exogenous DHEA does not enhance the tendency to run on wheels. © Elsevier Science Inc. Dehydroepiandrosterone
Adrenal
Testosterone
Exercise
Hamsters DHEA
DHEAS
In one approach to test this hypothesis, serum from exercising and sedentary male hamsters was assayed to see if exercise increases DHEA secretion. In a second study, silastic capsules of DHEA or testosterone were implanted in castrated male hamsters to determine the effect on wheel running activity.
DEHYDROEPIANDROSTERONE (DHEA) and dehydroepiandrosterone sulfate (DHEAS) are adrenal androgens that circulate in human blood in high concentrations, but the physiological role of these hormones is poorly understood (6,14,18,19). Although laboratory rats have little circulating DHEA or DHEAS, golden hamsters, like humans, secrete cortisol as a major glucocorticoid, as well as measurable quantities of DHEA and DHEAS (2,3,10,21). The hamster DHEA apparently is in large part derived from the adrenal gland, and, as in humans, reaches peak circulating levels in young adults, and then gradually declines with age (21). Treatment of elderly men and women with low doses of DHEA markedly increased their sense of well-being (16,29). Exercise may increase DHEA levels of humans (4,5,13,27,28), but there are also reports of no effect (9,15). If golden hamsters are housed in cages with running wheels, they voluntarily run in the device, averaging 10 km per 24 h (1,22). We hypothesized that voluntary exercise in hamsters is correlated with a chronic increase in the DHEA secretion, which then tends to increase their inclination to run in the wheels.
MATERIALS AND METHODS
Protocol: Experiment 1 Eighteen 9-week-old male Golden hamsters (Mesocricetus auratus, LAK:LVG) were obtained from Charles River Laboratories. Within several days of arrival, one-half of the animals were singly housed in cages equipped with a running wheel (EX group), whereas the other half were singly housed in similar cages without access to a wheel (SED group). The exercise cages were equipped with a vertical wheel that was 14 inches in diameter and 4.5 inches wide (LC-34, Lafayette Instrument, Lafayette, IN). All hamsters were maintained on long photoperiod (14:10 h light:dark cycle, lights on 0600– 2000 hr) for the entire study. This is a standard photoperiod
1To whom requests for reprints should be addressed at St. John Hospital, Department of Medical Education, 22101 Moross Rd., Detroit, MI 48236. E-mail: [email protected]
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608
PIEPER ET AL.
known to maintain reproductive function in Golden hamsters under normal circumstances. All animals were fed ad lib throughout the study. Blood samples were obtained from each animal before transferring to EX or SED groups and 4, 8, 11, 13, and 16 weeks following transfer. Samples (0.5 mL) were obtained from the retro-orbital sinus under light CO2 anesthesia between 0800 and 1000 h. Samples were obtained within 1 min of contact with the animal, so that the serum hormone levels would not be affected by the stress of handling or anesthesia.
CA) as previously described (22,24,25). The sensitivity of the testosterone assay was 40 pg/mL. The intraassay coefficient of variation was 6.4%. Total serum corticosterone was assessed using a doubleantibody RIA kit for rats and mice from ICN Biomedicals, Inc. (Costa Mesa, CA). Serum samples were diluted 1:20 with the steroid diluent provided in the kit. The percent crossreactivity with desoxycorticosterone, testosterone, and cortisol was 0.34, 0.10, and 0.05%, respectively. The intraassay coefficient of variation was 5.2%, and the sensitivity was 25 pg/mL.
Protocol Experiment 2
Statistics
Thirty Golden hamsters, 9 weeks old on arrival, were received from Charles River as above, and were maintained under similar standard environmental conditions. Within 1 week of arrival, all animals were anesthetized with sodium pentobarbital (35 mg/kg i.p.) and castrated. All animals were implanted with a subcutaneous Silastic capsule (No. 602-305, Dow Corning, Midland, MI) as previously described (22,26). Ten hamsters received blank capsules (no hormone), 10 received capsules containing 10 mm testosterone (Sigma), and 10 received capsules containing 20 mm DHEA (Sigma).
All sequential data were analyzed by multivariate analysis of variance for repeated measures. Where significance was indicated using this test, the data from each week were analyzed post hoc with Duncan’s multiple range test to determine which groups differed. Data of Table 1 were analyzed with one-way analysis of variance and post hoc Duncan’s multiple range test.
Hormone Levels Serum DHEA levels were assessed using a double antibody RIA kit from Diagnostic Systems Laboratories, Inc (Webster, TX). The sensitivity (minimal detectable level) was 9 pg/mL, and the intraassay coefficient of variation was 6.6%. All samples were done in one assay. The crossreactivity with DHEAS, isoandrosterone, and androstenedione was 0.02, 0.73, and 0.46%, respectively. DHEAS was assessed using a Coat-A-Count RIA kit from Diagnostic Products Corporation (Los Angeles, CA). The lowest standard in the kit was diluted 1:2 to obtain a 2.5 mg/dL calibrator (z87% binding). The sensitivity was 1.1 mg/dL, and the intraassay coefficient of variation was 6.9%. The crossreactivity with DHEA, estrone-3-sulfate, testosterone, and androstenedione was 0.08, 0.56, 0.10, and 0.12%, respectively. Total serum testosterone was assessed using a Coat-ACount direct RIA kit (Diagnostic Products, Los Angeles,
RESULTS
Experiment 1 Mean serum DHEAS levels in Experiment 1 were lower in the exercising hamsters throughout the study, and the difference was significant at weeks 13 and 16 p , 0.01 (Fig. 1). Serum DHEA was also significantly lower in the exercising than sedentary hamsters at 6, 11, and 13 weeks (p , 0.05; Fig. 1). Serum testosterone was higher in the exercising than sedentary hamsters at 5 (p , 0.05), 11 (p , 0.01), and 13 (p , 0.01) weeks (Fig. 1). There was no consistent effect of exercise on serum corticosterone levels (Fig. 1). The EX and SED hamsters had similar body weights at the end of the study. Experiment 2 Serum was obtained on Week 6 at 0800 h, and Week 7 at 2000 h. Serum DHEA and DHEAS were both significantly higher in the DHEA-treated hamsters at both time points than the blank group or testosterone groups, whereas serum testosterone was very high in the testosterone-treated hamsters compared to the control or DHEA-treated hamsters at both sampling times (Table 1). The testosterone-treated hamsters ran significantly more than the animals with blank implants, starting 4 weeks after initiation of the study, whereas animals with DHEA implants were generally intermediate between the blank and testosterone-treated hamsters but were not significantly different than either of those groups (Fig. 2). TABLE 1 HORMONE LEVELS AT 0800 AND 2000 H IN EXPERIMENT 2 Treatment Group
FIG. 1. Basal serum dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), testosterone, and corticosterone levels in hamsters with access to running wheels (EX) or sedentary controls (SED). Values represent mean 6 SE. *p , 0.05, **p , 0.01 compared to other group at same time point. There were seven to nine animals per group at each time point.
0800–h Sample DHEA (ng/ml) DHEAS (mg/dL) Testosterone (ng/mL) 2000–h Sample DHEA (ng/mL) DHEAS (mg/dL) Testosterone (ng/ML)
Blank Implant
Testosterone Implant
DHEA Implant
0.58 6 0.037 7.63 6 0.88 ND
0.56 6 0.046 6.35 6 0.65 1.11 6 0.18*
4.26 6 0.69* 12.0 6 0.93* ND
0.95 6 0.03 11.0 6 1.1 ND
0.98 6 0.064 7.49 6 1.08* 9.64 6 0.71 15.7 6 1.1* 1.07 6 0.085* ND
*p , 0.05 compared to blank implant group.
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609
FIG. 2. Body weight and number of wheel revolutions per day in castrated hamsters implanted with silastic capsules containing no hormone (blank), testosterone, or DHEA. Values represent mean 6 SE. *p , 0.05 compared to the blank group at the same time point. There were 10 animals per group at each time point.
Testosterone suppressed the rate of body weight gain at 4 and 5 weeks, but DHEA had no effect (Fig. 2). DISCUSSION
The decrease in DHEAS and DHEA with exercise is clearly not consistent with our hypothesis that exercise increased these levels and affected a hamster’s inclination to
run. It is possible that there is an increase in DHEA or DHEAS levels at another time of the day or in response to the acute nocturnal activity of these animals. In a separate study we have found a diurnal rhythm in the secretion of these hormones in hamsters with peak levels in the evening (21). The present study assessed basal 0800-h levels. The exercising animals had similar corticosterone levels as the sedentary group (Fig. 1), suggesting that running is not stressful to the hamsters. The regulation of adrenal DHEA secretion in humans is poorly understood, but may be regulated at least in part by ACTH (8,11,18,20). It is possible that the effect of exercise on DHEA levels reported in the present study (Fig. 1) is related to an exercise-induced alteration in metabolism of DHEA and/or DHEAS, but it is also possible that the exercise effect is mediated through the hypothalamo–hypophyseal axis, or that there is a more direct effect of exercise on adrenal gland function. The corticosterone data of the present study (Fig. 1) are not consistent with an exercise-mediated decrease in ACTH stimulation as a cause of the decrease in DHEA or DHEAS. There was an increase in serum testosterone levels with exercise at 6, 10, and 12 weeks, and it is possible that some of the decrease in serum DHEA may be related to an increased conversion to testosterone (12). We do not know why exercise increases (4,5,13,27,28), or has no effect (9,15) on serum DHEA and DHEAS levels in humans but decreases it in hamsters. One possibility is that exercise is more stressful in humans than hamsters. It is also possible that some of the differences between the human studies and the results reported here are related to the time when the blood samples were drawn in relation to the time of day the exercise occurred. Our study was concentrated on the effect of long-term exercise on basal DHEA and DHEAS levels where the blood samples were taken at 0800–1000 h, which is 4–6 h after the time when these animals stop wheel running activity (17,23). Giving exogenous DHEA to hamsters did not significantly increase running wheel activity, whereas testosterone did (Fig. 2). The effect of testosterone to increase running wheel activity in hamsters has been previously reported (1,7,22). However, the lack of effect of DHEA is further evidence that it is not involved in the inclination for hamsters to run on wheels. In summary, exercising hamsters tend to have lower basal serum DHEA and DHEAS levels than animals without access to running wheels, and exogenous treatment with DHEA had no effect on locomotor activity.
REFERENCES 1. Borer, K. T.: Regulation of energy balance in the golden hamster. In: Siegel, H. I., ed. The hamster: Reproduction and behavior. New York: Plenum Press; 1985:363–408. 2. Cloutier, M.; Fleury, A.; Courtemanche, J.; Ducharme, L.; Mason, J.; Lehoux, J.-G.: Cloning and expression of hamster adrenal cytochrome P450C17 cDNA. In: Bellino, F. L.; Daynes, R. A.; Hornsby, P. J.; Lavrin, D. H.; Nestler, J. E., eds. Dehydroepiandrosterone and aging. New York: New York Academy of Sciences; 1995. 3. Cloutier, M.; Fleury, A.; Courtemanche, J.; Ducharme, L.; Mason, J.; Lehoux, J.-G.: Characterization of the adrenal cytochrome P450C17 in the hamsters, a small animal model for the study of adrenal dehydroepiandrosterone biosynthesis. DNA Cell Biol. 16:357–368; 1997. 4. Cumming, D. C.; Brunsting, L. A., III; Strich, G.; et al.: Reproductive hormone increases in response to acute exercise in men. Med. Sci. Sports Exerc. 18:369–373; 1986.
5. Diamond, P.; Brisson, G. R.; Candas, B.; Peronnet, F.: Trait anxiety, submaximal physical exercise and blood androgens. Eur. J. Appl. Physiol. 58:699–704; 1989. 6. Ebeling, P.; Koivisto, V. A.: Physiological importance of dehydroepiandrosterone. Lancet 343:1479–1481; 1994. 7. Ellis, G. B.; Turek, F. W.: Testosterone and photoperiod interact to regulate locomotor activity in male hamsters. Hormones Behav. 17:66–75; 1983. 8. Hornsby, P. J.: Biosynthesis of DHEAS by the human adrenal cortex and its age-related decline. In: Bellino, F. L.; Daynes, R. A.; Hornsby, P. J.; Lavrin, D. H.; Nestler, J. E., eds. Dehydroepiandrosterone and aging. New York: New York Academy of Sciences; 1995:29–46. 9. Houmard, J.; McCulley, C.; Shinebarger, M.; Bruno, N.: Effects of exercise training on plasma androgens in men. Horm. Metab. Res. 26:297–300; 1993.
610 10. Lehoux, J.-G.; Lefebvre, A.: De Novo synthesis of corticosteroids in hamster adrenal glands. J. Steroid Biochem. 12:479–485; 1980. 11. Lejeune–Lenain, C.; Van Cauter, E.; Desir, D.; Beyloos, M.; Franckson, J. R.: Control of circadian and episodic variations of adrenal androgen secretion in man. J. Endocrinol. Invest. 10:267– 276; 1987. 12. Longcope, C.: Metabolism of dehydroepiandrosterone. In: Bellino, F. L.; Daynes, R. A.; Hornsby, P. J.; Lavrin, D. H.; Nestler, J. E., eds. Dehydroepiandrosterone and aging. New York: New York Academy of Sciences; 1995:143–148. 13. Lopez, S. A.; Wingo, C.; Hebert, J. A.: Total serum cholesterol and urinary dehydroepiandrosterone in humans. Atherosclerosis 24:471–481; 1976. 14. Meikle, A. W.; Daynes, R. A.; Araneo, B. A.: Adrenal androgen secretion and biological effects. Endocrinol. Metab. Clin. North Am. 20:381–400; 1991. 15. Milani, R. V.; Lavie, C. J.; Barbee, R. W.; Littman, A. B.: Lack of effect of exercise training on dehydroepiandrosterone-sulfate. Am. J. Med. Sci. 310:242–246; 1995. 16. Morales, A. J.; Nolan, J. J.; Nelson, J. C.: Effects of replacement dose of dehydroepiandrosterone in men and women of advancing age. J. Clin. Endocrinol. Metab. 78:1360–1367; 1994. 17. Morin, L. P.: Biological rhythms. In: Siegel, H. I., ed. The hamster: Reproduction and behavior. New York: Plenum Press; 1985: 123–361. 18. Nafziger, A. N.; Herrington, D. M.; Bush, T. L.: Dehydroepiandrosterone and dehydroepiandrosterone sulfate: Their relation to cardiovascular disease. Epidemiol. Rev. 13:267–293; 1991. 19. Nestler, J.: Advances in understanding the regulation and biologic actions of dehydroepiandrosterone. Curr. Opin. Endocrinol. Diabetes 3:202–211; 1996. 20. Odell, W. D.; Parker, L. N.: Control of adrenal androgen production. Endocr. Res. 10:617–630; 1985.
PIEPER ET AL. 21. Pieper, D.; Lobocki, C.: Characterization of serum dehydroepiandrosterone secretion in hamsters. 80th Annual Meeting of Endocrine Society P1-385–200; 1998. 22. Pieper, D. R.; Ali, H. Y.; Benson, L.; Shows, M.; Lobocki, C. A.; Subramanian, M. G.: Voluntary exercise increases gonadotropin secretion in male golden hamsters. Am. J. Physiol. 269:R179– R185; 1995. 23. Pieper, D. R.; Lobocki, C. A.: Olfactory bulbectomy lengthens circadian period of locomotor activity in golden hamsters. Am. J. Physiol. 261:R973–R978; 1991. 24. Pieper, D. R.; Lobocki, C. A.; Karo, K.: Olfactory bulbectomy counteracts the inhibitory effect of food restriction on reproductive function. Am. J. Physiol. 35:R1891–R1895; 1994. 25. Pieper, D. R.; Lobocki, C. A.; Thompson, M.; Subramanian, M.: The olfactory bulbs tonically inhibit serum gonadotropin and prolactin levels in male hamsters on long or short photoperiod. J. Neuroendocrinol. 2:707–715; 1990. 26. Pieper, D. R.; Unthank, P. D.; Shuttie, D. A.; Lobocki, C. A.: The olfactory bulbs influence testosterone feedback on gonadotropin secretion in male hamsters on long or short photoperiod. Neuroendocrinology 46:318–323; 1987. 27. Ponjee, G. A. E.; DeRooy, H. A. M.; Vader, H. L.: Androgen turnover during marathon running. Med. Sci. Sports Exerc. 26:1274–1277; 1994. 28. Velardo, A.; Pantaleoni, M.; Valerio, L.; Barini, A.; Marrama, P.: Influence of exercise on dehydroepiandrosterone sulphate and androstenedione plasma levels in man. Exp. Clin. Endocrinol. 97:99–101; 1991. 29. Yen, S. S. C.; Morales, A. J.; Khorram, O.: Replacement of DHEA in aging men and women, potential remedial effects. In: Bellino, F. L.; Daynes, R. A.; Hornsby, P. J.; Lavrin, D. H.; Nestler, J. E., eds. Dehydroepiandrosterone and aging. New York: New York Academy of Sciences; 1995:128–142.
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Dehydroepiandrosterone and Exercise in Golden Hamsters DAVID R. PIEPER,1 CATHERINE A. LOBOCKI, EDWARD M. LICHTEN AND JADWIGA MALACZYNSKI Providence Hospital, Southfield, MI 48037 Received 9 March 1999; Accepted 24 May 1999 PIEPER, D. R., C. A. LOBOCKI, E. M. LICHTEN AND J. MALACZYNSKI. Dehydroepiandrosterone and exercise in golden hamsters. PHYSIOL BEHAV 67(4) 607–610, 1999.—Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) are adrenal androgens that have been associated with a sense of well-being in humans. We describe two experiments done to test the hypothesis that an increase in DHEA or DHEAS secretion is associated with the inclination to exercise using a hamster model. In the first experiment, morning blood samples were obtained from adult male golden hamsters at various intervals after being placed in cages with (EX group) or without (SED group) access to running wheels. The EX group had lower DHEA (6, 12, and 14 weeks; p , 0.05) and DHEAS (13 and 16 weeks; p , 0.01) levels than the SED hamsters. In the second experiment, the number of wheel revolutions was monitored in castrated adult male hamsters implanted with Silastic capsules containing no hormone (blank control group), testosterone, or DHEA. The number of wheel revolutions in the group receiving DHEA was not significantly different than the blank control group, whereas testosterone increased wheel running at 4, 5, and 7 weeks (p , 0.05). These results indicate that DHEA and DHEAS levels decrease with exercise in male golden hamsters and that exogenous DHEA does not enhance the tendency to run on wheels. © Elsevier Science Inc. Dehydroepiandrosterone
Adrenal
Testosterone
Exercise
Hamsters DHEA
DHEAS
In one approach to test this hypothesis, serum from exercising and sedentary male hamsters was assayed to see if exercise increases DHEA secretion. In a second study, silastic capsules of DHEA or testosterone were implanted in castrated male hamsters to determine the effect on wheel running activity.
DEHYDROEPIANDROSTERONE (DHEA) and dehydroepiandrosterone sulfate (DHEAS) are adrenal androgens that circulate in human blood in high concentrations, but the physiological role of these hormones is poorly understood (6,14,18,19). Although laboratory rats have little circulating DHEA or DHEAS, golden hamsters, like humans, secrete cortisol as a major glucocorticoid, as well as measurable quantities of DHEA and DHEAS (2,3,10,21). The hamster DHEA apparently is in large part derived from the adrenal gland, and, as in humans, reaches peak circulating levels in young adults, and then gradually declines with age (21). Treatment of elderly men and women with low doses of DHEA markedly increased their sense of well-being (16,29). Exercise may increase DHEA levels of humans (4,5,13,27,28), but there are also reports of no effect (9,15). If golden hamsters are housed in cages with running wheels, they voluntarily run in the device, averaging 10 km per 24 h (1,22). We hypothesized that voluntary exercise in hamsters is correlated with a chronic increase in the DHEA secretion, which then tends to increase their inclination to run in the wheels.
MATERIALS AND METHODS
Protocol: Experiment 1 Eighteen 9-week-old male Golden hamsters (Mesocricetus auratus, LAK:LVG) were obtained from Charles River Laboratories. Within several days of arrival, one-half of the animals were singly housed in cages equipped with a running wheel (EX group), whereas the other half were singly housed in similar cages without access to a wheel (SED group). The exercise cages were equipped with a vertical wheel that was 14 inches in diameter and 4.5 inches wide (LC-34, Lafayette Instrument, Lafayette, IN). All hamsters were maintained on long photoperiod (14:10 h light:dark cycle, lights on 0600– 2000 hr) for the entire study. This is a standard photoperiod
1To whom requests for reprints should be addressed at St. John Hospital, Department of Medical Education, 22101 Moross Rd., Detroit, MI 48236. E-mail: [email protected]
607
608
PIEPER ET AL.
known to maintain reproductive function in Golden hamsters under normal circumstances. All animals were fed ad lib throughout the study. Blood samples were obtained from each animal before transferring to EX or SED groups and 4, 8, 11, 13, and 16 weeks following transfer. Samples (0.5 mL) were obtained from the retro-orbital sinus under light CO2 anesthesia between 0800 and 1000 h. Samples were obtained within 1 min of contact with the animal, so that the serum hormone levels would not be affected by the stress of handling or anesthesia.
CA) as previously described (22,24,25). The sensitivity of the testosterone assay was 40 pg/mL. The intraassay coefficient of variation was 6.4%. Total serum corticosterone was assessed using a doubleantibody RIA kit for rats and mice from ICN Biomedicals, Inc. (Costa Mesa, CA). Serum samples were diluted 1:20 with the steroid diluent provided in the kit. The percent crossreactivity with desoxycorticosterone, testosterone, and cortisol was 0.34, 0.10, and 0.05%, respectively. The intraassay coefficient of variation was 5.2%, and the sensitivity was 25 pg/mL.
Protocol Experiment 2
Statistics
Thirty Golden hamsters, 9 weeks old on arrival, were received from Charles River as above, and were maintained under similar standard environmental conditions. Within 1 week of arrival, all animals were anesthetized with sodium pentobarbital (35 mg/kg i.p.) and castrated. All animals were implanted with a subcutaneous Silastic capsule (No. 602-305, Dow Corning, Midland, MI) as previously described (22,26). Ten hamsters received blank capsules (no hormone), 10 received capsules containing 10 mm testosterone (Sigma), and 10 received capsules containing 20 mm DHEA (Sigma).
All sequential data were analyzed by multivariate analysis of variance for repeated measures. Where significance was indicated using this test, the data from each week were analyzed post hoc with Duncan’s multiple range test to determine which groups differed. Data of Table 1 were analyzed with one-way analysis of variance and post hoc Duncan’s multiple range test.
Hormone Levels Serum DHEA levels were assessed using a double antibody RIA kit from Diagnostic Systems Laboratories, Inc (Webster, TX). The sensitivity (minimal detectable level) was 9 pg/mL, and the intraassay coefficient of variation was 6.6%. All samples were done in one assay. The crossreactivity with DHEAS, isoandrosterone, and androstenedione was 0.02, 0.73, and 0.46%, respectively. DHEAS was assessed using a Coat-A-Count RIA kit from Diagnostic Products Corporation (Los Angeles, CA). The lowest standard in the kit was diluted 1:2 to obtain a 2.5 mg/dL calibrator (z87% binding). The sensitivity was 1.1 mg/dL, and the intraassay coefficient of variation was 6.9%. The crossreactivity with DHEA, estrone-3-sulfate, testosterone, and androstenedione was 0.08, 0.56, 0.10, and 0.12%, respectively. Total serum testosterone was assessed using a Coat-ACount direct RIA kit (Diagnostic Products, Los Angeles,
RESULTS
Experiment 1 Mean serum DHEAS levels in Experiment 1 were lower in the exercising hamsters throughout the study, and the difference was significant at weeks 13 and 16 p , 0.01 (Fig. 1). Serum DHEA was also significantly lower in the exercising than sedentary hamsters at 6, 11, and 13 weeks (p , 0.05; Fig. 1). Serum testosterone was higher in the exercising than sedentary hamsters at 5 (p , 0.05), 11 (p , 0.01), and 13 (p , 0.01) weeks (Fig. 1). There was no consistent effect of exercise on serum corticosterone levels (Fig. 1). The EX and SED hamsters had similar body weights at the end of the study. Experiment 2 Serum was obtained on Week 6 at 0800 h, and Week 7 at 2000 h. Serum DHEA and DHEAS were both significantly higher in the DHEA-treated hamsters at both time points than the blank group or testosterone groups, whereas serum testosterone was very high in the testosterone-treated hamsters compared to the control or DHEA-treated hamsters at both sampling times (Table 1). The testosterone-treated hamsters ran significantly more than the animals with blank implants, starting 4 weeks after initiation of the study, whereas animals with DHEA implants were generally intermediate between the blank and testosterone-treated hamsters but were not significantly different than either of those groups (Fig. 2). TABLE 1 HORMONE LEVELS AT 0800 AND 2000 H IN EXPERIMENT 2 Treatment Group
FIG. 1. Basal serum dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), testosterone, and corticosterone levels in hamsters with access to running wheels (EX) or sedentary controls (SED). Values represent mean 6 SE. *p , 0.05, **p , 0.01 compared to other group at same time point. There were seven to nine animals per group at each time point.
0800–h Sample DHEA (ng/ml) DHEAS (mg/dL) Testosterone (ng/mL) 2000–h Sample DHEA (ng/mL) DHEAS (mg/dL) Testosterone (ng/ML)
Blank Implant
Testosterone Implant
DHEA Implant
0.58 6 0.037 7.63 6 0.88 ND
0.56 6 0.046 6.35 6 0.65 1.11 6 0.18*
4.26 6 0.69* 12.0 6 0.93* ND
0.95 6 0.03 11.0 6 1.1 ND
0.98 6 0.064 7.49 6 1.08* 9.64 6 0.71 15.7 6 1.1* 1.07 6 0.085* ND
*p , 0.05 compared to blank implant group.
DHEA AND EXERCISE IN HAMSTERS
609
FIG. 2. Body weight and number of wheel revolutions per day in castrated hamsters implanted with silastic capsules containing no hormone (blank), testosterone, or DHEA. Values represent mean 6 SE. *p , 0.05 compared to the blank group at the same time point. There were 10 animals per group at each time point.
Testosterone suppressed the rate of body weight gain at 4 and 5 weeks, but DHEA had no effect (Fig. 2). DISCUSSION
The decrease in DHEAS and DHEA with exercise is clearly not consistent with our hypothesis that exercise increased these levels and affected a hamster’s inclination to
run. It is possible that there is an increase in DHEA or DHEAS levels at another time of the day or in response to the acute nocturnal activity of these animals. In a separate study we have found a diurnal rhythm in the secretion of these hormones in hamsters with peak levels in the evening (21). The present study assessed basal 0800-h levels. The exercising animals had similar corticosterone levels as the sedentary group (Fig. 1), suggesting that running is not stressful to the hamsters. The regulation of adrenal DHEA secretion in humans is poorly understood, but may be regulated at least in part by ACTH (8,11,18,20). It is possible that the effect of exercise on DHEA levels reported in the present study (Fig. 1) is related to an exercise-induced alteration in metabolism of DHEA and/or DHEAS, but it is also possible that the exercise effect is mediated through the hypothalamo–hypophyseal axis, or that there is a more direct effect of exercise on adrenal gland function. The corticosterone data of the present study (Fig. 1) are not consistent with an exercise-mediated decrease in ACTH stimulation as a cause of the decrease in DHEA or DHEAS. There was an increase in serum testosterone levels with exercise at 6, 10, and 12 weeks, and it is possible that some of the decrease in serum DHEA may be related to an increased conversion to testosterone (12). We do not know why exercise increases (4,5,13,27,28), or has no effect (9,15) on serum DHEA and DHEAS levels in humans but decreases it in hamsters. One possibility is that exercise is more stressful in humans than hamsters. It is also possible that some of the differences between the human studies and the results reported here are related to the time when the blood samples were drawn in relation to the time of day the exercise occurred. Our study was concentrated on the effect of long-term exercise on basal DHEA and DHEAS levels where the blood samples were taken at 0800–1000 h, which is 4–6 h after the time when these animals stop wheel running activity (17,23). Giving exogenous DHEA to hamsters did not significantly increase running wheel activity, whereas testosterone did (Fig. 2). The effect of testosterone to increase running wheel activity in hamsters has been previously reported (1,7,22). However, the lack of effect of DHEA is further evidence that it is not involved in the inclination for hamsters to run on wheels. In summary, exercising hamsters tend to have lower basal serum DHEA and DHEAS levels than animals without access to running wheels, and exogenous treatment with DHEA had no effect on locomotor activity.
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