Changes of Hypothalamic LH-RF Content during the Rat Estrous Cycle

Anti-LH-RF serum was produced in rabbits by synthetic LH-RF-BSA conjugate prepard with bis-diazotized benzidine. Employing this antiserum, a radioimmunoassay for LH-RF was established with the assay range from 0.8 to 10 ng/ml. Acid extracts of hypothalami from 4 day cycling rats through various stages of the estrous cycle particularly in the afternoon of proestrus were measured for their LHRF contents. The hypothalamic LH-RF content was high at 10:00 on the day of proestrus and declined until 17:00 and thereafter, the content gradually increased to reach the basal level. Serum LH showed the highest level at 17:00 on the day of proestrus and fell at 21:00 on the same day. Accompaning this change of serum LH level, pituitary LH content began to decrease at 17:00 of proestrus. These results indicate that LH-RF released in the afternoon of proestrus may participate to stimulate the preovulatory discharge of LH in the rat.