Role of the Sympathetic Control of Vascular Resistance in Ethanol-Clonidine Hemodynamic Interaction in SHRs

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Abstract
Our previous studies showed that ethanol selectively counteracts centrally mediated hypotensive responses. In this study, we investigated the role of sympathetic nerve activity, cardiac output (CO), and total peripheral resistance (TPR) in this antagonistic hemodynamic interaction between ethanol and clonidine. Changes in blood pressure (BP), heart rate (HR), CO, stroke volume (SV), and TPR elicited by intracisternal (i.c.) clonidine and subsequent ethanol or saline were evaluated in conscious freely moving spontaneously hypertensive rats (SHRs). Clonidine (0.5 μg, i.c.) evoked hypotension was due to a significant reduction in TPR (from 3.6 ± 0.21 to 2.8 ± 0.17 mm Hg/ml/min/100 g), which was associated with a significant (p