Chapter 4 - Hormonal Regulation of Ovarian Function in Reptiles

Abstract

Publisher Summary This chapter discusses in detail regarding hormonal regulation of ovarian function in reptiles. In reptiles, the ovaries are paired, hollow, oval (or, in snakes, elongate) structures attached to the dorsal body wall by a mesovarium. The reptilian ovary has two primary functions: the production of gametes and the secretion of hormones with regulatory effects on the female reproductive system. Ovarian differentiation begins during embryonic development. In many species, primordial follicles are present in the ovary by the time of hatching. The ovary produces steroid hormones (estrogens, androgens, and progestins) that circulate in association with plasma-binding proteins and bind to three complementary classes of specific tissue receptors. Metabolism of the primary steroids by peripheral tissues may involve either derivatization or conjugation. Ovarian activity is regulated via the hypothalamo–pituitary–gonadal (HPG) axis. Follicular maturation typically involves the deposition of large amounts of yolk during vitellogenesis, which is stimulated by estrogens secreted by the granulose cells. In both oviparous and viviparous reptiles, the postovulatory follicles are transformed into secretory corpora lutea, which produce progesterone for species-specific periods. Luteolysis is stimulated by prostaglandins. Further research is particularly required into non-steroidal hormones produced by, or influencing, the reptilian ovary.