17β-Estradiol inhibits angiotensin II activation of area postrema neurons

It is well established that the area postrema, as a circum-ventricular organ, is susceptible to modulation by circulating hormones and peptides. Furthermore, activation of the area postrema has been shown to modulate central neurons involved in the regulation of cardiovascular function and blood pressure. In particular, the vasoactive peptide angiotensin II (ANG II) has been shown to inhibit baroreflex regulation of heart rate and increase sympathetic outflow and blood pressure via activation of area postrema neurons. Estrogen is thought to protect against hypertension in both humans and animal models and has been shown in a number of systems to alter the effects of ANG II. The purpose of the present study was to determine the effects of estrogen on ANG II activation of area postrema neurons. In this study, the effects of ANG II and KCl on fura 2-measured cytosolic Ca2+ concentration ([Ca2+](i)) responses in cultured area postrema neurons in the presence and absence of 12-h exposure to 100 nM 17beta-estradiol (E-2) were evaluated. In neurons incubated in control vehicle media, 50 nM ANG II increased [Ca2+](i) by 92 +/- 12%. In neurons preincubated with 100 nM E-2 ANG II increased [Ca2+](i) by only 68 +/- 11%, for a total inhibition of the ANG II-evoked response of 24%. Coapplication of the estrogen receptor antagonist ICI-182,780 did not inhibit the effects of E-2. In the same cells in which the effects of E-2 on ANG II-evoked responses were tested, the effects of incubation in E-2 on the depolarization-induced increased [Ca2+](i) due to 60 mM KCl were also tested. Incubation of the cells with 100 nM E-2 increased the KCl-evoked [Ca2+](i) response, and this response was blocked by ICI-182,780. These results suggest that in the area postrema, estrogen may utilize multiple pathways to modulate neural activity and responses to ANG II.