Kormanik G A
Department of Biology, University of North Carolina, Asheville 28814.
J Exp Biol. 1988 Jul;137:443-56. doi: 10.1242/jeb.137.1.443.
The gestation period for embryos of the spiny dogfish, Squalus acanthias (L.) lasts for nearly 2 years. During the latter part of this period the pups remain in the uterus and the fluid surrounding the embryos resembles sea water with respect to the major ions, but is low in pH (approx. 6), high in partial pressure of carbon dioxide (approx. 3 mmHg; 1 mmHg = 133.3 Pa), low in total carbon dioxide content (approx. 0.2 mmol l-1), and may have a total ammonia concentration of up to 22 mmol l-1. Thus the conditions under which the pups complete their development in utero is quite remarkable. The derivation of these conditions was examined in late-term pregnant females, from whose uterine horns the pups had been removed, by monitoring changes that occurred in instilled uterine sea water. The mother is responsible for reducing the pH, reducing the total carbon dioxide content and elevating the partial pressure of carbon dioxide to the levels observed in fresh-caught females, in less than 24 h. The ammonia concentration is also elevated, but this takes rather longer. The decreased pH is responsible for the accumulation of ammonia in the uterine sea water, and it also serves to protect the pups from the toxic effects of NH3, by converting it to the relatively non-toxic ionic form, NH4+. The reasons for the establishment of these uterine seawater conditions are still not evident.
棘鲨（Squalus acanthias (L.)）胚胎的妊娠期持续近2年。在此期间的后期，幼鲨留在子宫内，胚胎周围的液体在主要离子方面类似于海水，但pH值较低（约为6），二氧化碳分压较高（约为3 mmHg；1 mmHg = 133.3 Pa），总二氧化碳含量较低（约为0.2 mmol l-1），总氨浓度可能高达22 mmol l-1。因此，幼鲨在子宫内完成发育的条件相当特殊。通过监测注入子宫的海水中发生的变化，对怀孕后期的雌性棘鲨进行了研究，这些雌性棘鲨的子宫角中的幼鲨已被取出。母亲负责在不到24小时的时间内将pH值降低、总二氧化碳含量降低，并将二氧化碳分压提高到在刚捕获的雌性棘鲨中观察到的水平。氨浓度也会升高，但这需要更长的时间。pH值的降低导致子宫海水中氨的积累，并且它还通过将氨转化为相对无毒的离子形式NH4+来保护幼鲨免受NH3的毒性影响。建立这些子宫海水条件的原因仍然不明确。
