Changes in the LHRH-immunoreactivity of hypothalamic structures during late pregnancy and after parturition in the guinea pig.

LHRH-immunohistochemistry and radioimmunoassay of the gonadotropins were used to demonstrate changes in the LHRH content of the hypothalamus during late pregnancy and after parturition in the guinea pig. Immediately after parturition a decrease in the amount of LHRH-associated fluorescence was observed in the medial preoptic area. Only 12 h later similar changes were found in the median eminence. In the precommissural region no obvious changes were noted in the quantity of LHRH-immunoreactive "terminals" and "synapses". The radioimmunoassay of the gonadotropins shows an increase of LH shortly after parturition which reaches the level of a preovulatory rise, whereas the amount of FSH does not vary significantly. The role of the medial preoptic area and the OVLT in the regulation of the estrous cycle through LHRH is discussed.