Gonadotropic effects of cholera enterotoxin in the rat testis slices: Stimulation of adenylate cyclase activity and testosterone synthesis from cholesterol.

Abstract

SynopsisThe effects of cholera enterotoxin (CET) on the male gonad was investigated using testis slices of the rat.CET stimulated adenylate cyclase activity of the interstitial tissue of the rat testis, increased cyclic AMP (cAMP) production and testosterone release from the interstitial tissue in vitro, thus mimicking effects of LH and human chorionic gonadotropin (hCG). CET also stimulated adenylate cyclase activity of the seminiferous tubules and increased cAMP production, whereas hCG did not exhibit such an effect.The stimulatory effect of CET on adenylate cyclase activity of the rat testis occurred with a lag time of about 30 min, reached the maximum level after 2-hr incubation and continued over 6 hr. Testosterone release by CET was observed within 1-to 2-hr incubation, when the increase in cAMP was already demonstrated.The steroidogenic effect of CET was enhanced at low concentration (1 mM) of theophylline and inhibited at high concentration (20mM) of theophylline. Protein synthesis inhibitors (puromycin and cycloheximide) abolished these steroidogenic effect completely, but not cAMP production.Tracer studies of active site(s) of CET in testicular steroidogenesis revealed that the stimulation of testosterone synthesis by CET was, like hCG, due to the stimulation of the conversion of cholesterol to testosterone.These results suggest that CET stimulates the adenylate cyclase/cAMP system of the interstitial tissue (probably of Leydig cells) and stimulates testosterone synthesis from cholesterol, and that once the adenylate cyclase of Leydig cells has been stimulated, the biosynthetic pathway leading to testosterone is quite similar to that caused by gonadotropins (LH and hCG), although the activation mechanism of adenylate cyclase seems to be different each other.

Prolonged stimulation of adenylate cyclase activity and testosterone production by cholera enterotoxin with suppression of gonadotropin release in rats.

“…The present data of in vivo studies are quite consistent with our previous in vitro findings that CET stimulates adenylate cyclase/cyclic AMP system of testicular cells (probably of Leydig cells) and increases testosterone production (Sato et al, 1975(Sato et al, , 1977. Furthermore, we have demonstrated that a single intratesticular CET-injection persistently but not permanently stimulated the enzyme activity and caused the sustained elevation of serum testosterone concentration for at least3days, probably resulting in the stimulation of negative feedback mechanism of hypophyseal-testicular axis to suppress the LH release during these periods.…”

“…Previously we reported that CET stimu lated adenylate cyclase activity of rat testis slices with a lag time of about30 min, caused an increase in cyclic AMP accumulation and stimulated testosterone synthesis from cholesterol in vitro, and suggested that these gonadotropic effects were exerted directly on Leydig cells (Sato et al, 1975;Sato and Ohsawa, 1977). This assumption was recently confirmed by Cooke et al,(1977) using purified Leydig cells of rat testes.…”