Angiotensin II (AngII) is known to act in the anterior pituitary through phosphatidiloinositol breakdown, increasing the level of inositol-1,4,5-trisphosphate (IP3) and diacyloglycerol (DAG), a potential activator of protein kinase C (PKC). We examined the effect of estradiol and progesterone treatment in vivo on IP3 levels and activity of PKC under the influence of AngII. Three groups of intact female rats received in vivo injections of 17-Pestradiol, progesterone, and oil (control) for five days, and then the in vitro effect of AngII was examined using homogenate of the anterior pituitary. AngII increased either the IP3 concentration or the synapsin I phosphorylation catalyzed by PKC. Estradiol enhanced the basal (without AngII) IP3 level and PKC activity induced by AngII. Progesterone did not change the basal and AngII-induced IP3 concentrations. On the other hand, it decreased the basal PKC activity and blocked the effect of AngII. Our data suggest that ovarian steroids can modulate the effect of AngII on the anterior pituitary gland,