On the Stimulation of Testicular Steroidogenesis in the Rabbit by Interstitial Cell-Stimulating Hormone

Interstitial cell-stimulating hormone (ICSH or LH) increases the conversion of cholesterol-7α-,³H to testosterone-³H in slices of rabbit testis in vitro, whether the hormone is administered as a single intravenous injection or added to the incubation medium in vitro. ICSH added in vitro or administered in vivo was without demonstrable effect upon the conversion of pregnenolone-7α-³H to testosterone-³H by slices of testis. In the light of these findings and of previous observations of the action of ICSH upon the testis in vitro, it is concluded that, under the experimental conditions used, the hormone stimulates steroidogenesis at some step(s) beyond cholesterol and before pregnenolone. (Endocrinology78: 690, 1966)