Generation of hypophysiotropic activity in hypothalamic extracts in vitro

The luteinizing hormone (LH) and follicle stimulating hormone (FSH) releasing activity, as well as the prolactin (PRL) release-inhibiting activity were measured in both neutral aqueous, and acid ethanolic extracts of rat hypothalami. LH and FSH-releasing activities were detectable only in the latter type of extract, whereas PRL release-inhibiting activity appeared in both. Neutral ultrafiltrates of the neutral extracts contained no gonadotropin releasing activity, however, acidification of the filtration medium induced its appearance. PRL release was inhibited by both neutral and acid filtrates. These results suggest that LH and FSH releasing factor(s) may be stored in the hypothalamus in an inactive form from which the active peptide is generated in vitro under acid conditions; however, this does not appear to be true for the component(s) responsible for the inhibition of PRL release.