Cartledge Victoria A, Jones Susan M
School of Zoology, University of Tasmania, Private Bag 5, Hobart TAS 7001, Australia.
Gen Comp Endocrinol. 2007 Jan 1;150(1):132-9. doi: 10.1016/j.ygcen.2006.07.021. Epub 2006 Sep 18.
In mammals, oestrogens generally stimulate adrenal function whilst androgens are inhibitory, and gestating females down-regulate their acute response to stressors in order to protect current reproductive investment. This study aimed to determine if adrenocortical function is similarly modulated by sex and reproductive status in the viviparous lizard, Egernia whitii. We compared the adrenocortical response to acute capture stress in female E. whitii during active (post-ovulatory and gestating) and quiescent (post-partum) phases of their reproductive cycle. We also compared the responses of reproductively quiescent males and females to acute stress and ACTH challenge to determine if there are sex-related differences in HPA axis activity when the influence of reproductive hormones is minimal. The females' responses to acute capture stress varied significantly with reproductive stage, and quiescent females displayed the strongest immediate response, with a rapid and sustained increase in plasma corticosterone (CORT) concentrations. Post-ovulatory females showed the most conservative adrenocortical response and while gestating females showed a large immediate response, this was not as prolonged as in quiescent females. Reproductively quiescent males and females exhibited similar responses to acute stress, and also responded similarly to ACTH injection, with plasma CORT reaching maximal concentrations of 52.1 and 59.4 ng/mL, respectively. Reproductively quiescent females treated with oestrogen exhibited greater responsiveness to ACTH than control females, although basal plasma CORT concentrations were unaltered: these results suggest that the attenuation of the acute stress response observed in reproductively active females of E. whitii may be regulated upstream of ACTH secretion. Our results demonstrate that the activity of the HPA axis is modulated by reproductive status in this viviparous reptile, and that gestating females are able to buffer their embryos from the potentially adverse effects of elevated plasma corticosteroids.
在哺乳动物中，雌激素通常会刺激肾上腺功能，而雄激素则起抑制作用，怀孕的雌性会下调其对应激源的急性反应，以保护当前的生殖投资。本研究旨在确定胎生蜥蜴惠氏石龙子（Egernia whitii）的肾上腺皮质功能是否同样受到性别和生殖状态的调节。我们比较了惠氏石龙子雌性在生殖周期的活跃期（排卵后和妊娠期）和静止期（产后）对急性捕捉应激的肾上腺皮质反应。我们还比较了生殖静止期的雄性和雌性对急性应激和促肾上腺皮质激素（ACTH）刺激的反应，以确定在生殖激素影响最小的情况下，下丘脑-垂体-肾上腺（HPA）轴活动是否存在性别相关差异。雌性对急性捕捉应激的反应随生殖阶段有显著变化，静止期雌性表现出最强的即时反应，血浆皮质酮（CORT）浓度迅速且持续升高。排卵后的雌性表现出最保守的肾上腺皮质反应，妊娠期雌性虽有较大的即时反应，但不如静止期雌性持续时间长。生殖静止期的雄性和雌性对急性应激的反应相似，对ACTH注射的反应也相似，血浆CORT分别达到最大浓度52.1和59.4 ng/mL。用雌激素处理的生殖静止期雌性对ACTH的反应比对照雌性更强，尽管基础血浆CORT浓度未改变：这些结果表明，惠氏石龙子生殖活跃雌性中观察到的急性应激反应减弱可能在ACTH分泌的上游受到调节。我们的结果表明，在这种胎生爬行动物中，HPA轴的活动受到生殖状态的调节，并且妊娠期雌性能够保护其胚胎免受血浆皮质类固醇升高的潜在不利影响。
