Inhibition of in vitro human chorionic gonadotropin - simulated testosterone production in testis and of the ovulation in the rat by charcoal - treated rat testicular extract

Abstract

Inhibition of in vitro human chorionic gonadotropin - simulated testosterone production in testis and of the ovulation in the rat by charcoal - treated rat testicular extract Arata de Bellabarba, Gabriela; Bishop, Walter y Rojas, Francisco J.

Abstract

Previously, we describe the presence of a factor obtained from a 105,000 x g supernatant of rat testis that was found to inhibit human chorionic gonadotropin (hCG) binding to gonadal receptors. In the present study, similarly prepared testicular extract was tested for its effects on in vitro hCG - stimulated testosterone production by isolated testis interstitial cells and for its effect on spontaneous ovulation in the rat. Incubation of interstitial cells with charcoal - treated extract significantly inhibited the steroidogenic response to hCG in a dose related - manner. This inhibition was also apparent after heating the extract for 10 min at 100º C. Preincubation of the cells with charcoal - treated extract resulted in an inhibitory effect that was not readily reversed by subsequent addition of hCG, revealing an element of irreversibility in the mechanism of inhibition. A single i. p. injection of testicular extract given between 1430 - 1630 h of proestrus inhibited spontaneous ovulation in the rat. This effect was also observed after heating the extract for 10 min at 100º C; in contrast, no significant effect was obtained with the injection of a similar dose of liver extract. Administration of 5 IU hCG after pretreatment whit the testicular extract did not reserve the inhibitory effect on ovulation, indicating that this effect was probably exerted at the hypothalamus - pituitary level. It is concluded that the aqueous testicular extract contains a factor able to antagonize the physiological events mediated by luteinizing hormone (LH)/hCG, and that this factor is consistent with the presence of an LH / hCG - binding inhibitory activity in rat testis.