Estrogen modulation of angiotensin-stimulated phosphoinositide hydrolysis in slices of rat anterior pituitary

In this study, slices of rat anterior pituitary were prelabeled with ³H]myo-inositol and the ability of angiotensins II and III to stimulate ³H]phosphoinositide hydrolysis was characterized. When using tissue derived from ovariectomized rats, dose-response experiments revealed that angiotensin II significantly increases ³H]inositol monophosphate formation (in the presence of 10 mM LiCI) at concentrations of 10 nM and above. Maximal stimulation by angiotensin II was observed at 1 μM (228% of basal) and 50% maximal stimulation was at 10.8 ± 2.7 nM. Angiotensin III was less potent when compared to angiotensin II (maximal stimulation at 10 μM; 220% of basal: 50% maximal stimulation, 475 ± 159 nM). When using normal female rats, significant stimulation by angiotensin II was not observed until 1 μM angiotensin II. When ovariectomized rats were treated for 7 days with 17β-estradiol, increases in ³H]inositol monophosphate induced by 1 μM angiotensin II were significantly reduced when compared to sesame oil vehicle controls.This study shows that estrogen down-regulates angiotensin receptor coupling in the anterior pituitary. Moreover, it illustrates the influence of the hormonal state of the animal on the regulation of the effects of angiotensins in this tissue.