Manire Charles A, Rasmussen L E L, Gelsleichter James, Hess David L
Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236, USA.
Gen Comp Endocrinol. 2004 Apr;136(2):241-7. doi: 10.1016/j.ygcen.2003.12.018.
Among vertebrates, maternal transfer of hormones to offspring has been studied extensively in mammals (placental transfer) and more recently in oviparous birds and reptiles (yolk transfer). The placental viviparous bonnethead shark, Sphyrna tiburo, allows the investigation of both yolk and placental hormone transfers in a single organism. In this species, yolk provides nutrition for the first half of embryonic development and placental transfer provides the second half. As sex determination is complete prior to development of placental connections, it was postulated that yolk hormones would have a prominent role in embryonic regulation. The goal of the current study was to determine serum and yolk hormone concentrations during five reproductive stages, from pre-ovulatory through pre-implantation (pre-placental) stages. Radioimmunoassay was used to determine 17beta-estradiol, progesterone, and testosterone concentrations in both serum and yolk. When yolk and serum concentrations were compared, the yolk had significantly higher concentrations of both estradiol and progesterone during post-ovulation and early pregnancy. Yolk concentrations of testosterone were significantly less than serum at pre-ovulation, but there were no differences after that stage. When yolk concentrations were compared between stages, significantly higher concentrations of estradiol were present in ovulatory, post-ovulatory, and pre-implantation stages, while progesterone was significantly higher in post-ovulatory, early pregnancy, and pre-implantation stages and testosterone was higher in pre-ovulation. Most of these results are consistent with the published findings in birds and reptiles. Further, in the bonnethead shark, they suggest that yolk transfer of hormones is adequate for sexual differentiation in embryonic development and that estradiol probably has a significant developmental role.
在脊椎动物中，激素从母体向后代的转移在哺乳动物（胎盘转移）中已得到广泛研究，最近在卵生鸟类和爬行动物（卵黄转移）中也有研究。胎盘胎生的窄头双髻鲨（Sphyrna tiburo）使得在单一生物体中研究卵黄和胎盘激素转移成为可能。在这个物种中，卵黄为胚胎发育的前半期提供营养，胎盘转移则为后半期提供营养。由于性别决定在胎盘连接发育之前就已完成，因此推测卵黄激素在胚胎调节中会发挥重要作用。本研究的目的是确定从排卵前到着床前（胎盘形成前）这五个生殖阶段的血清和卵黄激素浓度。采用放射免疫分析法测定血清和卵黄中的17β-雌二醇、孕酮和睾酮浓度。比较卵黄和血清浓度时，排卵后和妊娠早期卵黄中的雌二醇和孕酮浓度均显著更高。排卵前卵黄中的睾酮浓度显著低于血清，但在此阶段之后则没有差异。比较各阶段的卵黄浓度时，排卵、排卵后和着床前阶段的雌二醇浓度显著更高，而排卵后、妊娠早期和着床前阶段的孕酮浓度显著更高，排卵前睾酮浓度更高。这些结果大多与已发表的鸟类和爬行动物的研究结果一致。此外，在窄头双髻鲨中，这些结果表明激素的卵黄转移足以支持胚胎发育中的性别分化，并且雌二醇可能具有重要的发育作用。
