Chronic alcohol consumption lowers blood pressure but enhances vascular contractility in Wistar rats

To determine the effect of chronic alcohol consumption upon blood pressure, blood pressure reactivity and vascular contractility in Wistar rats.

Wistar rats were fed a liquid diet containing 36% ethanol; control rats were pair fed.

Rats were maintained on diets for 18 weeks. Indirect systolic blood pressure was measured weekly. Catheters were implanted for assessment of direct arterial pressure and blood pressure reactivity to norepinephrine, angiotensin II and ethanol injections. In a subgroup of rats, contractility of isolated mesenteric resistance vessels was measured.

In comparison with simultaneously pair-fed controls, ethanol-treated rats developed significantly lower blood pressure within 3 weeks of exposure to alcohol; this continued throughout the study. Despite the reduction in blood pressure, in vitro assessment of vascular contractility in mesenteric resistance vessels indicated that ethanol consumption significantly enhanced vascular contractility to norepinephrine and attenuated the vasodepressive effects of ethanol. Measurement of blood pressure reactivity to infused pressor agents showed no difference between controls and ethanol-treated rats in response to norepinephrine but a significantly attenuated pressor response to angiotensin II was observed in ethanol-treated rats.

The blood pressure results contrast with reports of elevated blood pressure in Wistar rats given ethanol in drinking water. This disparity may be due to nutritional factors. Increased vascular contractility combined with hypotension suggests that cardiovascular regulatory systems offset the direct effects of ethanol upon the vasculature. This view is reinforced by the lack of difference between groups in blood pressure reactivity to norepinephrine. The attenuated angiotensin II responses in the ethanol-treated rats suggests altered levels of circulating angiotensin II in this group.