[Gonadotropin releasing activity of different regions of rat brain and the probability of presence of a factor which inhibits it in the suprachiasmatic region].

The amount of gonadotropin-releasing hormone (Gn--RH) was measured in the preoptic area and in some parts of hypothalamus by radioimmunoassay. Maximal level was found in the median eminence next followed by that in the portions containing n. arquatus or retrochiasmatic area. The preoptic area contained less Gn--RH. The quantity of Gn--RH was negligible in the suprachiasmatic area. If tested in both supra- and retrochiasmatic areas simultaneously the amount of Gn--RH was much lower than in the retrochiasmatic area alone. Existence of inhibiting or inactivating factor in the suprachiasmatic fragment is suggested. The amount of Gn--RH was small in hypothalamic areas including n. paraventricularis, n. supraopticus, mamillary bodies. From among all the fragments tested the pineal body showed the lowest Gn--RH. There was no correlation between the serum LH concentration and the amount of Gn--RH in any investigated area except the preoptic one.