[17beta -estradiol inhibits carotid sinus baroreflex in male rats]

By perfusing isolated carotid sinus, the effect of 17beta-estradiol (E(2)) on carotid sinus baroreflex was observed in anesthetized male rats. The results obtained are as follows. (1) By perfusing with E(2) (10 micromol/L), the functional curve of baroreflex was shifted to the right and upward, with a peak slope (PS) decrease from 0.49+/-0.03 to 0.25+/-0.01 (P<0.01) and a reflex decrease in mean arterial pressure (reflex decrease, RD) from 7.37+/-0.42 kPa to 3.49+/-0.20 kPa (P<0.001), while the threshold pressure (TP) and saturation pressure (SP) were significantly increased from 9.52+/-0.68 kPa to 13.3+/-0.11 kPa (P<0.001) and 24.53+/-0.48 kPa to 27.52+/-0.20 kPa (P<0.01) respectively. Among the functional parameters of carotid baroreflex, the changes of RD, PS, TP and SP were dose-dependent. (2) Pretreatment with different doses of tamoxifen (1, 5, 10, 30 micromol/L), an inhibitor of estrogen receptor, did not block the effect of E(2) on carotid baroreflex. (3) Preperfusion with an inhibitor of NO synthase L-NAME (100 micromol/L) could completely abolish the effect of E(2) on carotid baroreflex. It is concluded that the inhibitory effect of E(2)on carotid sinus baroreflex may be mediated by NO release from endothelial cells, but not by a genomic mechanism.