Methallibure studies on Tilapia: II. Effect of tilapia pituitary homogenate (TPH), human chorionic gonadotropin (HCG) and testosterone propionate (TP) on the testes of Methallibure-treated Tilapia nigra

Abstract

In Methallibure-suppressed T. nigra testes high and low doses of TPH and HCG stimulate a qualitatively similar reactivation of spermatogenesis resulting in a significant elevation of testicular weight and G.S.I.; interstitial tissue hypertrophy and hyperplasia with a significant increase in the cell and nuclear sizes and spermiation. These effects are dose-dependent and independent of Methallibure. It is argued that Methallibure is a central rather than a peripheral gonadotropin blocking agent.

TP produced no spermatokinesis at any of the doses administered. When Methallibure is withdrawn TP significantly suppressed interstitial cell and nuclear sizes suggesting a central blockage of an ICSH-like gonadotropin. TP at the highest doses produced a variable degree of spermiation.

It is concluded that while the spermiation effect of gonadotropin might be mediated by androgens, there is little evidence to suggest that testosterone mediates the spermatokinetic effects of gonadotropins.