The hormonal control of the amphibian ovary

Abstract

The ultimate control of amphibian gonadal function rests with environmen tal factors mediated through the hypothalamus. It appears that control of ovarian growth resides in the infundibular region and ovulation in the preoptic area. For normal temporal relationships between oocyte growth and ovulation to occur, an intact hypothalamo-pituitary complex is necessary. It is uncertain whether the several types of pituitary basophils considered, histologically as gonadotropin producing cells are in fact producing separate LH and FSH like hormones. Perhaps the concensus indicates a single hormone has both vitellogenic and ovulatory functions. This hormone stimulates estrogen synthesis and secretion by the ovarian follicle cells, and this steroid causes oviduct growth and the hepatic biosynthesis of vitellogenin, the major yolk platelet precursor. Uptake of this lipoprotein from the circulation and its conversion to the components of the platelet is mediated by the gonadotropin, the presence of which results in the establishment of a rapid micropinocytotic process at the level of the oocyte surface and of a mechanism for crystallization of the yolk. A sudden surge of pituitary hormone, when presented to fully grown oocytes leads to their maturation and ovulation, and to oviducal jelly release in some species. The active hormone is progestin in nature, again produced by the follicle cells.In this review the known factors involved in the hypothalamo hypophysio ovarian axis are discussed together with some consideration of outstanding problemsand the possible relevance ot ovipantv and ovovivipanty in amphibians to the ovarian control found in viviparous species. © 1972 by the American Society of Zoologists.