In vitro inhibitory effect of estradiol on testosterone production

Abstract

The ability of estradiol (E 2) to inhibit testosterone production by rat testes in vitro was investigated. E 2 concentrations from 5 × 10 −10 M to beyond the limit of E 2 solubility failed to affect testosterone production in the absence of luteinizing hormone (LH) during 3 h incubations. LH (2 ng/ml) stimulated testosterone production was inhibited by approximately 50% with a supersaturating concentration of E 2 but not by lower concentrations. The inhibitory potency of E 2 was not significantly increased when the testicular tissue was incubated with E 2 for 3 h prior to a 3 h incubation with both LH and E 2. The requirement for very high in vitro concentrations of E 2 to inhibit LH stimulated testosterone production may be related to the observed instability of the cytoplasmic E 2 receptor during the incubations. The E 2 receptor concentration declined from 7.4 ± 0.7 fmol/mg cytosol protein in non-incubated testes to 1.2 ± 0.1 fmol/mg after 6.5 h of incubation.