THE MECHANISM OF ACTION OF GONADOTROPHIC HORMONES IN AMPHIBIANS: THE STIMULATION OF Δ5-3β-HYDROXYSTEROID DEHYDROGENASE ACTIVITY IN TESTES OF XENOPUS LAEVIS DAUDIN

Abstract

SUMMARY: The effects of gonadotrophins on the Δ⁵-3β-hydroxysteroid dehydrogenase (3β-HSD) activity in testes of Xenopus laevis have been determined by histochemical and spectrophotometric methods. Methallibure was employed to inhibit the activity of endogenous pituitary gonadotrophins. Injections of pregnant mare serum gonadotrophin (PMS), human chorionic gonadotrophin (HCG), follicle stimulating hormone (FSH), or luteinizing hormone (LH) resulted in pronounced increases in 3β-HSD activity in the microsomal fraction. PMS was the most stimulatory; the injection of 250 i.u. resulted in an almost ten fold increase in activity. PMS and HCG were more effective than FSH and LH in stimulating 3β-HSD activity and PMS and FSH were more effective than HCG and LH respectively. The increases in activity were inhibited by concomitant injections of actinomycin. 3β-HSD activity was not stimulated directly by gonadotrophins in vitro, but another dehydrogenase or group of dehydrogenases appeared to be activated directly by HCG, FSH and LH but not by PMS. The results are discussed in relation to findings in mammals.