Hormonal regulation of testicular functions in reptiles

Testicular functions are controlled by important multifactors: environmental, hypothalamic-pituitary, and paracrine factors secreted by testicular cells. The existence of different gonadotropins and their role in testicular functions are have been described. In chelonians and crocodilians, two distinct pituitary gonadotropins similar to mammalian follicle-stimulating hormone (FSH) and luteinizing hormone (LH) regulate two functions, respectively: spermatogenesis and steroidogenesis. In contrast, in squamates, has been purified and characterized a single gonadotropin that controls both testicular functions. Regarding steroids, androgens differentially regulate spermatogenesis, depending on reproductive stages, while estrogens are implicated at low concentrations in the control of spermiogenesis and at high levels in testicular regression. In addition, several paracrine factors such as neuropeptides from testicular cells, and other molecules secreted by macrophages and mast cells of Leydig and Sertoli cells, play critical roles in the regulation of spermatogenesis, steroidogenesis, and testicular immune responses.