Chapter 3 - Hormonal Regulation of Testicular Functions in Reptiles

Abstract

Publisher Summary Reptiles are the first phylogenetic group in which spermatogenesis occurs in seminiferous tubules lined by peritubular cells. Testicular functions are regulated by multifactor, environmentally important, hypothalamo–hypophysial, and testicular cells-secreted paracrine factors. The existence of different gonadotropins and their role in testicular functions are interesting in reptiles. In chelonians and crocodilians, two distinct pituitary gonadotropins similar to mammalian follicle-stimulating hormone (FSH) and luteinizing hormone (LH) regulate two different functions: spermatogenesis and steroidogenesis, respectively. Conversely, the purification and characterization of pituitary gonadotropin from different families of snake reveal the existence of a single gonadotropin that controls both testicular functions in squamates. To date, cDNA has been cloned for either FSH or LH but not for both FSH and LH from a single squamate. With respect to sex steroids, androgens differentially regulate spermatogenesis, depending on reproductive phases, while estrogens are implicated in post-spermatogenic testicular regression. In addition, several uncharacterized paracrine factors secreted by Leydig and Sertoli cells, macrophages, and mast cells play critical roles in the regulation of spermatogenesis, steroidogenesis, and testicular immune responses.