Browne Patience, Conley Alan J, Spraker Terry, Ream Rolf R, Lasley Bill L
Population, Health and Reproduction, University of California, Davis, 1114 Tupper Hall, 95616, USA.
Gen Comp Endocrinol. 2006 Jun;147(2):175-83. doi: 10.1016/j.ygcen.2005.12.019. Epub 2006 Feb 13.
Recent precipitous population declines in northern fur seal (Callorhinus ursinus) and other Alaskan pinniped populations are due in part to reduced fecundity and have emphasized deficits in basic reproductive knowledge of these species. Following estrus and mating, fertilized female pinnipeds experience an obligatory delayed implantation lasting several months and non-pregnant (pseudopregnant) females are indistinguishable by sex steroid levels during this time. The current study examined circulating steroid concentrations and ovarian expression of key steroid-synthesizing enzymes in northern fur seals to identify changes associated with embryonic implantation, data necessary for estimating early pregnancy rates of the population. Blood samples were collected from 84 female fur seals captured on an Alaskan rookery from October 15 to November 30, a period spanning the end of the delay and subsequent uterine implantation of the fertilized blastocyst in this species. Concentrations of progesterone, estradiol, and estrone measured in blood collected during boreal fall were contrasted with samples collected during late summer from post-ovulatory females and males. Serum sex steroids were also related to ovarian expression of key enzymes responsible for androgen (17alpha-hydroxylase/17,20-lyase, cytochrome b5, and 3beta-hydroxysteroid dehydrogenase) and estrogen (aromatase cytochrome P450) synthesis. Enzymes necessary for androgen synthesis were highly expressed in ovaries, and accordingly, endocrine profiles were expanded to include DHEA, androstenediol, androstenedione, and testosterone. Estradiol concentrations were universally low and free and conjugated estrone were the primary circulating estrogens in fur seal sera. No implantation-associated peak was identified for estrogens or progesterone and mean values of progesterone and estrone were actually greater in female serum samples collected during summer than fall. However, there was a significant positive relationship between fall sampling date and testosterone concentration. Additionally, DHEA concentrations in females were lower in samples collected during the implantation period than during the summer embryonic delay. These data suggest androgens may play a substantial regulatory role in the embryonic delay of northern fur seals.
近期，北海狗（Callorhinus ursinus）以及阿拉斯加其他鳍足类动物种群数量急剧下降，部分原因是繁殖力降低，这凸显了我们对这些物种基本生殖知识的欠缺。发情和交配后，受精的雌性鳍足类动物会经历数月的强制性着床延迟，在此期间，未怀孕（假孕）的雌性动物无法通过性类固醇水平来区分。本研究检测了北海狗体内循环类固醇浓度以及关键类固醇合成酶的卵巢表达情况，以确定与胚胎着床相关的变化，这些数据对于估算该种群的早期妊娠率至关重要。在10月15日至11月30日期间，从阿拉斯加一个繁殖地捕获了84只雌性海狗并采集血样，这段时间涵盖了该物种延迟期结束以及受精囊胚随后在子宫着床的阶段。将北方秋季采集的血液中孕酮、雌二醇和雌酮的浓度与夏末从排卵后雌性和雄性采集的样本进行对比。血清性类固醇还与负责雄激素（17α-羟化酶/17,20-裂解酶、细胞色素b5和3β-羟基类固醇脱氢酶）和雌激素（芳香化酶细胞色素P45）合成的关键酶的卵巢表达有关。雄激素合成所需的酶在卵巢中高度表达，因此，内分泌谱扩展到包括脱氢表雄酮、雄烯二醇、雄烯二酮和睾酮。雌二醇浓度普遍较低，游离和结合雌酮是海狗血清中主要的循环雌激素。未发现雌激素或孕酮与着床相关的峰值，实际上，夏季采集的雌性血清样本中孕酮和雌酮的平均值高于秋季。然而，秋季采样日期与睾酮浓度之间存在显著正相关。此外，雌性动物在着床期采集的样本中脱氢表雄酮浓度低于夏季胚胎延迟期。这些数据表明，雄激素可能在北海狗的胚胎延迟中发挥重要的调节作用。
