In this study using Sprague-Dawley rats, to investigate the mechanism of changes in baroreceptor reflex control in ethanol-fed rats (3∼5g/㎏ of 20％ ethanol two times daily for 3 weeks), (1) alterations in blood pressure and heart rate in response to phenylephrine and clonidine were observed in the pithed rats, (2) the changes in baroreceptor reflex sensitivity and the response to clonidine administered into nucleus tractus solitarius (NTS) were compared between two groups.
１. The clearance of ethanol was 25.1㎎/hr and biological half-life was 3.23hr in ethanol-fed rats.
２. Ethanol-fed rats showed a decrease in body weight change rate in association with decrease in fool intake.
３. Following ethanol administration for 3 weeks, little difference in arterial blood pressure and heart rte between two groups was observed not only in intact rats but also in pithed rats.
４. In pithed rats, the pressor response to phenylephrine and clonidine (alpha-1 and alpha-2 adrenoceptor postsynaptic effect) was not differed between two groups. However, both electrical power voltage required to increase heart rate and the cardi-inhibition by clonidine (alpha 2-adrenoceptor presynaptic effect) were increased in ethanol group.
５. In the ethanol-fed rats, reflex change in heart rate in response to increased blood pressure by phenylephrine was markedly attenuated, and likewise reflex change in heart rate in response to decreased blood pressure by nitroprusside was also reduced.
６. Decreases in blood pressure and heart rate by clonidine administration via NTS were significantly attenuated in ethanol-fed rats.
Based on these results, it is suggested that in chronic ethanol-fed rats a decrease in baroreflex sensitivity is closely related with the functional alterations in baroreflex control mechanism of NTS and this may precede the development of hypertension.
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