Estrogen-dependent hypotensive effects of ethanol in conscious female rats

This study investigated the role of estrogen in the acute hemodynamic responses to intragastric (i.g.) ethanol in conscious female rats. Changes evoked by ethanol or equal volume of water in mean arterial pressure, heart rate, cardiac index, stroke volume (SV), and total peripheral resistance were followed in sham-operated, ovariectomy (OVX) vehicle-treated (OVX-veh), and OVX 17beta-estradiol (E2)-treated (OVX-E2) Sprague-Dawley rats. Plasma norepinephrine (NE) was measured as an index of sympathetic activity. In sham-operated rats, ethanol caused significant decreases in mean arterial pressure that were associated with significant reductions in cardiac index and SV, whereas total peripheral resistance was not changed. Measured plasma NE levels were not affected by ethanol except for a significant reduction observed one time. OVX abolished the hypotensive effect of ethanol and the associated decreases in cardiac output, SV, and plasma NE. Treatment of OVX rats with E2 restored the hypotensive and sympathoinhibitory (decreases in plasma NE) responses to ethanol. Blood ethanol concentrations were not affected by OVX or subsequent E2 administration. These findings suggest that intragastric ethanol elicits estrogen-dependent decreases in blood pressure in female rats, which results mainly from a reduction in cardiac output. The mechanism by which ethanol elicits E2-dependent hypotension remains to be determined.