School of Biological Sciences, Illinois State University, Normal, IL 61790, USA.
School of Biological Sciences, Illinois State University, Normal, IL 61790, USA.
Gen Comp Endocrinol. 2019 Oct 1;282:113221. doi: 10.1016/j.ygcen.2019.113221. Epub 2019 Jul 10.
Progesterone has received substantial attention for the essential role it plays in establishing and maintaining pregnancy in placental vertebrates. Despite the prevalence of progesterone during development, relatively little is known about how embryos respond to progesterone. This is true of placental vertebrates as well as egg-laying vertebrates where levels of progesterone in the yolk tend to be higher than most other steroids in the yolk. Bird eggs provide an opportunity to investigate the effects of progesterone on embryonic development because progesterone can be easily manipulated without any confounding effects on maternal physiology. To understand how progesterone might influence embryonic development, it is important to characterize the metabolic fate of progesterone given its potential to be converted to a wide range of steroids. We investigated the metabolic fate of tritiated progesterone over the first four days of development using chicken eggs (Gallus gallus) and identified 5β-pregnanedione as the primary metabolite during this period. After only one day of development, 5β-pregnanedione could be detected within the yolk. Levels of 5β-pregnanedione in both the yolk and albumen tended to rise early in development but conjugated metabolites began to accumulate towards the end of our sampling period. Additionally, in vitro assays using embryo homogenates collected after 72 h of development demonstrated that embryos were capable of carrying out the conversion of progesterone to 5β-pregnanedione. Overall these results have important implications for deciphering the mechanisms through which yolk progesterone might influence embryonic development. Effects could arise via progesterone receptors or receptors capable of binding 5β-pregnanedione but we found no evidence that progesterone is serving as a precursor for androgen or estrogen production.
孕激素在胎盘脊椎动物中建立和维持妊娠方面发挥着重要作用，因此受到了广泛关注。尽管在胚胎发育过程中孕激素普遍存在，但人们对胚胎如何对孕激素做出反应知之甚少。这既适用于胎盘脊椎动物，也适用于产卵脊椎动物，因为蛋黄中的孕激素水平往往高于蛋黄中大多数其他类固醇。鸟类的蛋为研究孕激素对胚胎发育的影响提供了机会，因为可以很容易地操纵孕激素，而不会对母体生理学产生任何混杂影响。为了了解孕激素如何影响胚胎发育，重要的是要描述孕激素的代谢命运，因为它有可能转化为广泛的类固醇。我们使用鸡卵（Gallus gallus）研究了 tritiated 孕激素在发育的头四天的代谢命运，并在此期间确定 5β-孕烷二酮为主要代谢产物。仅在发育的第一天，蛋黄内就可以检测到 5β-孕烷二酮。在蛋黄和蛋清中的 5β-孕烷二酮水平在发育早期往往会升高，但共轭代谢物在我们的采样期结束时开始积累。此外，使用发育后 72 小时收集的胚胎匀浆进行的体外测定表明，胚胎能够将孕激素转化为 5β-孕烷二酮。总的来说，这些结果对揭示蛋黄孕激素影响胚胎发育的机制具有重要意义。这种影响可能是通过孕激素受体或能够结合 5β-孕烷二酮的受体产生的，但我们没有发现孕激素作为雄激素或雌激素产生的前体的证据。
