Administration of dihydrotestosterone to rhesus monkeys inhibits gonadotropin-stimulated ovarian steroidogenesis.

Androgens, in addition to serving as a substrate for estrogen biosynthesis, exert autocrine/paracrine actions on ovarian function. However, much of the information regarding the actions of androgens on the ovary has been obtained using rodents, and the extent to which these results can be extrapolated to higher primates is uncertain. The current study was initiated to determine the effects of dihydrotestosterone (DHT) and testosterone (T) on the responsiveness of the rhesus monkey ovary to exogenous FSH and LH in vivo. Rhesus monkeys whose spontaneous gonadotropin secretion was interrupted with a GnRH antagonist received s. . implants of either DHT or T for 5 d before and continuing throughout a 15-d i.v. infusion of human FSH and LH. Neither T nor DHT treatment synergized with FSH/LH to stimulate estrogen production or increases in ovarian weight. Rather, administration of DHT significantly reduced estrogen secretion and the augmentation of ovarian weight in response to exogenously administered FSH and LH. These results indicate that high concentrations of DHT are antagonistic to gonadotropin-stimulated ovarian function in primates.

Administration of insulin-like growth factor I to rhesus monkeys does not augment gonadotropin-stimulated ovarian steroidogenesis.

Although it is well established that IGF-I is able to amplify the actions of FSH and LH on ovarian cells in vitro, little information is available regarding the effects of IGF-I on ovarian function in vivo. To address this question, rhesus monkeys whose spontaneous gonadotropin secretion was interrupted with a GnRH antagonist received continuous iv infusions of saline, IGF-I (240 microg/kg.d), or IGF-I (240 microg/kg.d) plus human GH (hGH) (200 microg/kg.d) 7 d before and continuing throughout a 15-d iv infusion of hFSH and hLH during which serum LH concentrations were maintained at 7-10 mIU/ml and FSH concentrations were incrementally increased every 3 d from 7.5 to 17.5 mIU/ml. Serum estradiol concentrations in saline-treated control animals did not differ (P > 0.05) from animals treated with IGF-I + hGH. In contrast, serum estradiol levels in IGF-I-treated animals were significantly less (P < 0.05) than those of control or IGF-I + hGH-treated animals. Serum androstenedione levels did not differ among the three treatment groups. Analysis of follicular fluids on the final day of gonadotropin infusion indicated that intrafollicular IGF-I concentrations paralleled serum IGF-I concentrations in all treatment groups. Measurement of the ratio of IGF-I to IGF-binding protein-3 in follicular fluids indicated that there was not a disproportionate increase in I-binding protein-3 in animals infused with either IGF-I alone or IGF-I + hGH. Concentrations of GH in follicular fluids of IGF-I treated animals were less than control animals suggesting that the diminished responsiveness of ovaries to FSH in the IGF-I treatment group may have been due to reduced GH.