Daniel J C
J Reprod Fertil Suppl. 1981;29:35-50.
Delayed implantation is an obligate part of the reproductive cycle of many (possibly all) pinniped species, the duration of delay ranging from 2 to 4 months depending on the length of gestation. Blastocyst reactivation and implantation in the northern fur seal occur during decreasing photoperiods, and are preceded by increase in the circulating concentrations of oestradiol-17 beta and progesterone. However, neither experimental shortening of photoperiod, nor injections of oestradiol-17 beta or progesterone (or both) induced reactivation. Furthermore, these treatments had no effect on the composition or quantity of proteins in uterine flushings, examined by gel filtration (though changes are associated with spontaneous implantation). All treatments involving capture and caging of seals caused an increase in blastocyst mitotic activity (though not expansion), and it is suggested that this represents a response to stress. Experiments in which fur seal or rabbit blastocysts were cultured in vitro failed to identify a growth promoting substance whose absence from uterine fluid may account for the dormancy of blastocysts during diapause; however, these experiments did demonstrate the presence of an inhibitor or rabbit blastocyst growth in fur seal serum. It is suggested that an unidentified compound regulated by the ovary is involved in stimulating the increased uterine proliferation and secretion which are necessary for blastocyst reactivation.
延迟着床是许多（可能是所有）鳍足类动物繁殖周期中的一个必然阶段，延迟时间从2到4个月不等，具体取决于妊娠期的长短。北方海狗的胚泡重新激活和着床发生在光周期缩短期间，且在此之前，循环中的雌二醇-17β和孕酮浓度会升高。然而，无论是实验性地缩短光周期，还是注射雌二醇-17β或孕酮（或两者），都不会诱导重新激活。此外，通过凝胶过滤检测，这些处理对子宫冲洗液中的蛋白质组成或数量没有影响（尽管变化与自然着床有关）。所有涉及捕获和圈养海豹的处理都会导致胚泡有丝分裂活性增加（尽管没有扩张），有人认为这代表了对应激的一种反应。在体外培养海狗或兔子胚泡的实验未能鉴定出一种生长促进物质，子宫液中缺乏这种物质可能是胚泡在滞育期间休眠的原因；然而，这些实验确实证明了海狗血清中存在一种抑制兔子胚泡生长的物质。有人认为，一种由卵巢调节的未知化合物参与刺激子宫增殖和分泌增加，而这是胚泡重新激活所必需的。
