Estradiol and progesterone modulation of angiotensin II receptors in the arcuate nucleus of ovariectomized and lactating rats.

The expression of angiotensin II (Ang II) receptors in the brain is modulated by estradiol and progesterone. Considering that Ang II plays a critical role in controlling prolactin secretion and that neurons in the arcuate nucleus (ARC) are the main regulator of this function, the present study aimed to evaluate ARC Ang II receptor binding in 2 experimental models with different estradiol and progesterone plasma levels. Animals were divided into 4 groups: ovariectomy (OVX) plus oil vehicle, OVX plus estradiol and progesterone replacement, lactating rats on day 7 postpartum, and lactating rats on day 20. Animals were killed by decapitation, and the brains were removed. Ang II receptors were quantified by autoradiography in ARC. Trunk blood samples were collected, and plasma estradiol and progesterone were measured by radioimmunoassay. Treatment of OVX rats with estradiol and progesterone increased Ang II receptor binding when compared to OVX vehicle-treated animals. Plasma estradiol (r = +0.77) and progesterone (r = +0.87) were highly correlated with Ang II receptors in ovariectomized animals. Lactating rats (day 20) showed a significant decrease in Ang II receptor binding and plasma progesterone when compared to lactating rats (day 7), however, no difference was seen in plasma estradiol. Plasma levels of progesterone (r = +0.81), but not estradiol (r = +0.32), were highly correlated with Ang II receptors in lactating rats. In conclusion, present results show that ARC Ang II receptors decreases on day 20 of lactation compared to day 7 and are highly correlated with plasma progesterone, indicating a pivotal role for progesterone in this regulation.