Plasma levels of LH and FSH in female rats with precocious puberty induced by hypothalamic lesions

To determine whether precocious puberty induced by anterior hypothalamic lesions was associated with alterations in plasma gonadotropin levels during the prepubertal period, lesions were made by radiofrequency in the anterior hypothalamus of 15 day old female rats and plasma levels of gonadotropins were determined by radioimmunoassay (RIA) at different time intervals following the lesion. Nonoperated and sham-operated littermates were used as a control. Lesioned animals showed precocious puberty as evidenced by early vaginal opening and first ovulation. They also became pregnant at an earlier age than controls and delivered their pups normally. Lesioned animals showed a more pronounced rate of increase in ovarian weight during the first 15 days following the lesion than that of control rats. Nevertheless, plasma FSH levels were not different in both groups. Plasma LH levels during the morning of the days preceding vaginal opening were somewhat higher in control rats than in lesioned animals. However, during the afternoons LH levels tended to be more elevated in lesioned rats than in controls, the difference being significant at Day 23. Estradiol injected subcutaneously inhibited compensatory ovarian hypertrophy in lesioned rats demonstrating the integrity of the estrogen negative feedback mechanism. The results were interpreted as not supporting the view that hypothalamic lesions induce precocious puberty by eliminating negative feedback to estrogen. The possibility arises that precocious puberty induced by hypothalamic lesions is determined by other mechanisms and an alternative explanation is suggested.