Subcellular hypothalamic fractions active on ovulation and luteinizing hormone release in the rat

Nuclear, microsomal and cytosol fractions were obtained from hypothalamic cells by differential centrifugation in sucrose solutions of different molarities. The nuclear fraction (NF) from immature female rats had an inhibitory effect on ovulation induced with pregnant mare's serum (PMS) in immature rats and with luteinizing hormone (LH) in chlorpromazine (CPZ)-treated proestrous rats. The microsomal fraction from the same rats increased both types of ovulation. Nuclear and microsomal fractions obtained from immature male rats were inactive on ovulation. Cytosol fractions were inactive. NFs active to inhibit ovulation significantly reduced the release of LH induced with synthetic LH-RH in immature male rats and in chronically castrated male rats primed with testosterone (T).