Renal blood flow in acute cerebral ischemia in spontaneously hypertensive rats: effects of alpha- and beta-adrenergic blockade.

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Abstract
The influences of acute cerebral ischemia on renal hemodynamics were examined in spontaneously hypertensive rats in which cerebral ischemia was induced by bilateral carotid artery occlusion. Renal and cerebral blood flow were measured with a hydrogen clearance technique. Either phenoxybenzamine (0.5 mg/kg body wt) or propranolol (2 mg/kg) was given i.v. immediately after ischemia was induced to examine the drugs' effects on cerebral and renal hemodynamics. One hour after ischemia, cerebral blood flow was markedly reduced to 5, 3, and almost 0% of the preischemic value in the untreated, phenoxybenzamine-treated, and propranolol-treated rats, respectively. In contrast, renal blood flow at that time was decreased to 65, 88, and 67%, respectively. The calculated renal vascular resistance was similarly increased to 151% in the untreated and 136% in the propranolol-treated rats, but decreased to 82% in the phenoxybenzamine-treated rats. The present results indicate that in acute cerebral ischemia renal blood flow was considerably decreased with concomitant increased renal vascular resistance, and that such reduction in renal blood flow was minimized by alpha-adrenergic blockade but not by beta-blockade. It is concluded that activation of the alpha-adrenergic system in acute cerebral ischemia causes renal vasoconstriction.