The hypogonadal (hpg) mouse has a congenital deficiency in gonadotrophin-releasing hormone and the gonads consequently lack exposure to endogenous gonadotrophins during development. To determine the effect of FSH on Leydig cell function in these animals adult hpg mice were injected twice daily with FSH (2 μg injections) or LH (40 ng injections, the presumed LH contamination of FSH used). Following FSH treatment there was a clear stimulation of the seminiferous epithelium and in animals injected with FSH plus [3H]thymidine, the incorporation of label was largely confined to the germ cells with no apparent uptake by the Sertoli cells. In FSH-treated testes the Leydig cells contained numerous large lipid droplets, similar to the unstimulated hpg testis. There was no evidence of the interstitial hyperplasia which is observed following injection of high doses of LH (2 pg twice daily).
There was no change in basal androgen content of the testis in vivo following FSH treatment but injection of a maximal dose of human chorionic gonadotrophin (hCG), 1 h before death, markedly increased testicular androgen content only in the FSH-treated group. Testicular androgen production in vitro was significantly increased following FSH treatment both under basal conditions (FSH-treated, 17·4 pmol/testis; control, 1·46 pmol/testis) and during stimulation by hCG (FSH-treated, 940 pmol/testis; control, 81 pmol/testis). Associated with the increased androgen production following FSH treatment there were significant increases in the activities of three steroidogenic enzymes; cholesterol side-chain cleavage (186-fold increase over control), 17α-hydroxylase (103-fold increase) and 17-ketosteroid reductase (177-fold increase). The fourth enzyme involved in androgen synthesis, 3β-hydroxysteroid dehydrogenase, shows relatively high activity in the control hpg testis and was only increased by sixfold following FSH treatment. There was no effect of FSH on 5α-reductase activity.
Results show that FSH causes a marked stimulation of the steroidogenic capacity of the hpg testis. Leydig cells do not contain FSH receptors and it is assumed that FSH acts through paracrine factors released by the Sertoli cells.
Journal of Endocrinology (1992) 135, 517–525
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