Regulation of oestrogen-induced LH release in male and female marmoset monkeys (Callithrix jacchus)

Abstract

The positive-feedback action of estradiol-17.beta. [E2] on LH [luteinizing hormone, lutropin] release was studied in gonadectomized male and female and intact male marmoset monkeys. Positive feedback was observed in normal intact males in response to a single s.c. injection of 35 .mu.g estradiol benzoate. The sustained E2 level elevation achieved by the injections resulted in a marked suppression of circulating testosterone concentrations. Injections (s.c.) (0.5 mg/injection) of testosterone or dihydrotestosterone to gonadectomized males and females immediately following and 8 h after failed to inhibit positive feedback. Similar treatment with progesterone (1.0 mg/injection) tended to standardize both positive and negative components of the feedback response. Progesterone implants (achieving progesterone concentrations similar to those obtained with the injections), maintained during and for 8 days before the E2 treatment, effectively inhibited positive feedback. LH responses to the various treatments were similar in gonadectomized males and females. A relative unimportance of testicular secretions in suppressing estrogen-induced LH release in the adult marmoset is suggested. Similarities between the control of positive feedback in male and female primates are indicated.