HYPOTHALAMIC CONTROL OF PITUITARY GONADOTROPHINS

Abstract

SUMMARY Impairments in gestation, parturition, and milk ejection were produced when electrolytic lesions were placed in the median eminence of the tuber cinereum of pregnant rats at various stages of gestation. Thus, uterine implantation of ova was blocked in 65% of rats following placement of lesions on day 1 of gestation, and implantation of ova was induced in these animals by administration of oestrogen. When lesions localized to the caudal median eminence were placed on days 4–9, implantation was not blocked but abortion-resorption resulted in 90% of cases. Replacement studies during pregnancy in rats with lesions in the caudal median eminence suggest that (1) all aborting rats were deficient in gonadotrophins necessary for secretion of oestrogen, and (2) half of them were deficient in luteotrophin as well. (That is, luteotrophin had no replacement value, while oestrogen therapy permitted maintenance of gestation in 54% of cases, and oestrogen plus progesterone allowed 100% to remain pregnant.) In rats receiving lesions on days 7–9 and maintaining gestation to term, 32% of those with severe diabetes insipidus experienced difficulty during delivery. Placement of lesions after day 13 impaired neither gestation nor parturition. The observation that most rats with lesions were able to deliver their litters normally but were unable to eject milk following suckling stimuli suggests that oxytocin is not essential for parturition in this species. Most of the rats with lesions failed to resume oestrous cycles; of the few showing return of normal or irregular cycles, the majority failed to mate.