[Changes of hypothalamic LH-RH content induced by estradiol injection into female rats (author's transl)].

The 4 day cycling Wistar strain rats were sacrificed by decapitation on the several conditions. By radioimmunoassay, hypothalamic luteinizing hormone-releasing hormone (LH-RH) and serum luteinizing hormone (LH) were measured. From the present experiments, the following results were obtained. 1. At 17:00 on proestrus, a peak in serum LH level was observed. At the same time, hypothalamic LH-RH content was decreased. 2. After the administration of estradiol (E2) on diestrus I, hypothalamic LH-RH content increased gradually and reached the peak about one day later. Moreover, serum LH peak appeared on diestrus II. But the change of E2 administration time didn't take part in the time of LH peak. 3. When the group of the rats were administered progesterone at appropriated time in addition to the E2 administration at 12:00 on diestrus I, serum LH peak on diestrus II was repressed through the changes of LH-RH.