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

The positive-feedback action of oestradiol-17 beta on LH 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 subcutaneous injection of 35 micrograms oestradiol benzoate. The sustained elevation in oestradiol-17 beta levels achieved by the injections resulted in a marked suppression of circulating testosterone concentrations. Subcutaneous injections (0.5 mg/injection) of testosterone or dihydrotestosterone to gonadectomized males and females immediately following and 8 h after oestradiol benzoate 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. In contrast, progesterone implants (achieving progesterone concentrations similar to those obtained with the injections), maintained during and for 8 days before the oestradiol benzoate treatment, effectively inhibited positive feedback. LH responses to the various treatments were similar in gonadectomized males and females. These data suggest a relative unimportance of testicular secretions in suppressing oestrogen-induced LH release in the adult marmoset and indicate similarities between the control of positive feedback in male and female primates.