Stimulation of angiotensinogen mRNA levels in rat pituitary by estradiol

Angiotensin II (ANG II) is a putative paracrine hormone in the anterior pituitary. Angiotensinogen mRNA, however, is not detectable by Northern blot hybridization, suggesting that ANG II may not be synthesized within the pituitary. An alternative explanation may be that angiotensinogen gene activity is low under normal conditions, with angiotensinogen mRNA being below the level of detection. Utilizing a sensitive solution hybridization method, we sought to determine whether angiotensinogen mRNA could be detected in pituitaries from normal male rats or ovariectomized (OVX) rats treated with estradiol (E2) for 4 days. Very low levels of angiotensinogen mRNA were detected from male or OVX rat pituitaries, but E2 treatment resulted in a marked dose-dependent increase in pituitary angiotensinogen mRNA levels. Levels of angiotensinogen within the pituitary were not significantly different after the E2 treatment. Angiotensinogen mRNA levels in liver and brain were much higher than in the pituitary but were not altered significantly by the chronic E2 treatment. These results are consistent with the local synthesis of angiotensinogen in the pituitary and further suggest that pituitary angiotensinogen gene transcription is regulated by estrogen.