ESTRADIOL ELEVATES PROTEIN-KINASE-C CATALYTIC ACTIVITY IN THE PREOPTIC AREA OF FEMALE RATS

Estrogen acts in the brain to regulate female reproductive physiology and behavior, and protein kinase C (PKC) is estrogen-regulated in many estrogen-responsive tissues. We examined whether estrogen regulates P KC in the hypothalamus (HYP) and preoptic area (POA), brain regions wh ich mediate estrogenic control of female reproductive function. PKC ac tivity in tissue from hormone-treated and control female rats was meas ured, in the presence of phorbol ester and calcium, by quantifying P-3 2 incorporation into a substrate peptide. PKC catalytic activity incre ased significantly in POA tissue extracts from estradiol-treated, ovar iectomized (OVX) female rats but not in HYP or cortical extracts. Phor bol ester potentiation of cAMP accumulation also was examined to deter mine whether the ability of PKC to potentiate adenylyl cyclase activit y was affected by estrogen. PKC stimulation potentiated forskolin-indu ced cAMP accumulation to a greater degree in POA, but not HYP, slices from estrogen-treated OVX female rats. PKC enzyme levels were examined using phorbol-12,13-dibutyrate binding assays and immunoblots. Estrog en treatment did not change phorbol ester binding affinity or the dens ity of binding sites in the POA. or HYP. Immunoblots for the alpha, be ta, and gamma PKC isoforms combined, or the gamma PKC isoform alone, d id not detect differences between hormone-treated and control OVX fema le rats. Therefore, estrogen treatment increased PKC catalytic activit y in the POA of OVX female rats but not in the HYP. However, the incre ased PKC catalytic activity was not correlated with detectable changes in the level of the alpha, beta, or gamma PKC isoforms or in the dens ity of phorbol ester binding sites.