Preliminary evidence for a CNS site of action for ovarian inhibin

The ovariectomized rat bearing estrogen-containing silastic capsules underwent a primary FSH rise at 1700 hrs on all days studied. A more prolonged secondary FSH rise also occurs beginning at 2100 hrs. The primary FSH rise was attenuated or blocked by injection of charcoal-extracted porcine follicular fluid (pFF) or an extract of pFF (pFFX) limited to substances having molecular weights between 10,000 and 30,000 d. Application of pFFX directly to the dorsal anterior hypothalamic area (dAHA) by means of chronically implanted cannulas resulted in attenuation of the primary FSH rise. Similar application to medial preoptic area (mPOA) was without effect. These findings suggest that an active FSH suppressing agent, presumably ovarian inhibin, may be acting at least in part at the level of the central nervous system.