Stress-induced suppression of testosterone secretion in male alligators (original) (raw)
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General and Comparative Endocrinology, 2004
All reptiles studied to date show an increase in circulating corticosterone following capture. This rise in corticosterone has also been shown in a number of instances to result in a decline in reproductive steroids within hours after capture. As a result of these observations it has been considered imperative to collect blood samples as soon as possible after capture to get reliable measures of reproductive hormones. It has been claimed, however, that there is no effect of capture stress on reproductive steroids in juvenile alligators held for 2 h following capture. As we generally reject blood samples that are not collected within 15 min of capture we decided to reinvestigate the effect of short-term capture (2 h) on corticosterone and testosterone in male alligators. Four groups of alligators, ranging in size from 74 to 212 cm total length were captured in a 2-week period in May, the time of year when testosterone levels are highest. Two groups were captured during the day (eight bled at capture and again at 2 h, eight bled at 2 h only) and two at night (10 bled at capture and again at 2 h, 10 bled at 2 h only). Testosterone and corticosterone in alligators bled immediately on capture and at 2 h were not significantly different in the AM and PM samples so the results were combined (Initial bleed: corticosterone, 0.95 AE 0.09 ng/ml, n ¼ 18; testosterone, 6.06 AE 2.09 ng/ml, n ¼ 18. Two-hour bleed: corticosterone 15.68 AE 1.91, n ¼ 18; testosterone, 2.75 AE 0.79, n ¼ 18). Both the increase in corticosterone and the decline in testosterone at 2 h were significant ðp < 0:05Þ. Corticosterone and testosterone in the alligators sampled only once at 2 h were not significantly different from the 2-h values in alligators sampled twice (corticosterone 15.04 AE 1.29, n ¼ 18; testosterone, 1.85 AE 0.62, n ¼ 18). These results clearly demonstrate that short-term capture stress results in a significant decline in testosterone in male alligators.
Effect of stress and ACTH1–24 on hormonal levels in male alligators, Alligator mississippiensis
Comparative Biochemistry and Physiology Part A: Physiology
The effect of stress and the synthetic adrenocorticotropic hormone (ACTHi_r,) on plasma cortisol (F), corticosterone (B), progesterone (P), and testosterone (T) were investigated in farm-reared subadult male alligators (30-50 kg body wt) during the breeding season (June). In experiment 1, blood was sampled immediately after capture of alligators. Alligators were then treated with a single dose of either ACTH1_r4 (0.25 mg/animal/ experimental) or a saline control. Additional blood samples were obtained at 0.5, 1, 1.5, 2 and 6 hr postinjection. After sampling, the alligators were released and recaptured just prior to each bleeding time. Alligators injected with ACTH1_r4 showed significant increase in plasma F and B levels over the saline injected group at 1 and 6 hr postinjection. Plasma P and T levels showed no significant difference between ACTH,_r+ and saline injected group throughout the sampling period. In experiment 2, alligators were treated with dexamethasone (10 mg/ animal), restrained for 3 hr and subsequently injected with AClX_r+ as in experiment 1. This group also demonstrated a significant increase in plasma F and B levels in ACTHi_r4 injected alligators over the saline-injected group only at 7.5 hr postinjection and as in experiment 1, P and T levels showed no significant difference. In experiment 1 and 2, capture stress alone induced significant rises in plasma F and B concentrations in both the saline and ACTH1_r4 groups. Progesterone levels in both experiments remained unaffected and Plasma T levels decreased significantly following stress. It appears that ACTH1_r4 stimulated further F and B secretion in the alligators but had no effect on P or T levels. There was no significant difference between alligators treated with ACTH or ACTH and dexamethasone which indicates that dexamethasone was not effective in inhibiting endogenous ACTH secretion. Like other reptiles, capture and serial bleedings induced a significant rise in corticosteroids during the period of stress.
Gonadotropin-induced testosterone response in peripubertal male alligators
General and Comparative Endocrinology, 2004
Based on the response to three different gonadotropin challenges, we evaluated seasonal production of testosterone in a group of captive-raised four-year-old male alligators that varied in size. To stimulate gonadal steroidogenesis, we injected each alligator with ovine FSH (150 ng/ml plasma). Plasma testosterone concentrations were measured in repeated blood samples taken between 0 and 72 h after FSH injection. To determine if there was seasonal variation in response, we repeated the experiment on the same alligators three times during the breeding season (March, May, and July, 2000). All alligators responded to exogenous FSH by exhibiting increased plasma concentrations of testosterone (p < 0:0001 for all months). However, the degree of the response depended on body size. Thus, larger alligators produced more testosterone and were more affected by changes in season compared to smaller alligators. We have previously observed that juvenile male alligators display seasonal changes in plasma testosterone concentrations that mimic the cycle observed in adult males. Our present data suggest that seasonal changes in plasma testosterone appear to be associated not only with changes in gonadotropin release but in gonadal responsiveness as well. We propose, given these observations, that alligators experience an extended period of puberty, during which the gonads synthesize gradually increasing steroid hormone concentrations. These peripubertal animals are not juveniles but sub-adults capable of responding to the seasonal signals associated with reproductive timing in adults.
Biology of Reproduction, 2011
The seasonal patterns of two primary plasma androgens, testosterone (T) and dehydroepiandrosterone (DHEA), were assessed in adult male alligators from the Merritt Island National Wildlife Refuge, a unique barrier island environment and home to the Kennedy Space Center in Florida. Samples were collected monthly from 2008 to 2009, with additional samples collected at more random intervals in 2007 and 2010. Plasma T concentrations peaked in April, coincident with breeding and courtship, and declined rapidly throughout the summer. Seasonal plasma T patterns in smaller though reproductively active adult males differed from those in their larger counterparts during the breeding season. Both size classes showed significant increases in plasma T concentration from February to March, at the beginning of the breeding season. However, smaller adults did not experience the peak in plasma T concentrations in April that were observed in larger adults, and their concentrations were significantly lower than those of larger males for the remainder of the breeding season. Plasma DHEA concentrations peaked in May and were significantly reduced by June. This is the first study to demonstrate the presence of DHEA in a crocodilian, and the high plasma DHEA concentrations that paralleled the animals' reproductive activity suggest a reproductive and/or behavioral role in adult male alligators. Similar to androgen variations in some birds, plasma DHEA concentrations in the alligators were considerably higher than T concentrations during the nonbreeding season, suggesting a potential role in maintaining nonbreeding seasonal aggression.
Effect of mammalian gonadotropins on testosterone secretion in male alligators
Journal of Experimental Zoology, 1987
Male farm-reared alligators were injected with mammalian FSH, LH, hCG, prolactin, or saline. A blood sample was taken immediately prior to injection of hormone and at 24 h postinjection. Testosterone concentrations in the plasma were then determined by radioimmunoassay. Only the alligators injected with FSH showed a significant increase in plasma testosterone. In a second series of experiments male alligators were injected with ovine LH, ovine FSH, or saline and bled at 0 , 2 , 4 , 16, and 24 h postinjection. Again, only the alligators injected with FSH showed significant increases in plasma testosterone at 16 and 24 h postinjection. Mammalian LH does not appear to stimulate testosterone secretion in male alligators.
Stress, reproduction, and adrenocortical modulation in amphibians and reptiles
2003
While the hypothalamo–pituitary–adrenocortical (HPA) response to stress appears to be conserved in vertebrates, the manner in which it is activated and its actions vary. We examine two trends in the stress biology literature that have been addressed in amphibian and reptilian species:(1) variable interactions among stress, corticosterone, and reproduction and (2) adrenocortical modulation. In the first topic we examine context-dependent interactions among stress, corticosterone, and reproduction.