Ovarian control of gonadotropin secretion during induced precocious sexual maturation in the rat

In sexually immature female rats 'primed' with a unilateral basal hypothalamic lesion on day 23 of life, a gonadotropin surge was triggered by progesterone (P) on day 26. The influence of sequential ovariectomy (OVX) on this response was studied in an attempt to elucidate the mode of action of brain lesions inducing precocious sexual maturation in this species. OVX, carried out on days 23-26, abolished or greatly reduced the LH surge, but had little effect on basal LH concentrations. In contrast, basal FSH concentrations rose rapidly after OVX. In lesioned rats, the post-castration rise of FSH could be prevented by leaving the ovaries in place during the 1st 24 or 48 h. It is concluded that the lesion-induced maturation of the positive feedback mechanism underlying the pubertal preovulatory gonadotropin surge is mediated by the ovaries. In prepubertal rats at this age, tonic FSH release, but not tonic LH release, is under tight negative feedback control.