The blood-brain barrier in renovascular hypertension.

Cerebral vessels of the spontaneously hypertensive rat (SHR) are less susceptible to disruption of the blood-brain barrier to proteins during acute hypertension than normotensive controls. This protective adaptation in SHR during acute hypertension is thought to be due to cerebral vascular hypertrophy which leads to increased vascular resistance and attenuation of the increase in cerebral blood flow and blood-brain disruption during acute hypertension. To determine if a similar relationship is present in the renovascular form of chronic hypertension, we studied blood-brain barrier protein transfer in Sprague-Dawley normotensive and two-kidney, one clip hypertensive rats during control conditions and during superimposed acute hypertension. The renovascular clip was applied at one month of age and all rats were studied 2-3 months later. During control conditions, the mean arterial pressure of the normotensive (NT) and renovascular hypertensive (RV) animals was significantly different (NT 131 ± 6, RV 189 ± 11* mm Hg, *p < 0.05) but the cerebral hemisphere protein transfer was low and did not differ [NT O.OS ± 0.00, RV 0.08 ± 0.04% (NS)]. During acute hypertension, the rise in arterial pressure in the normotensive group (A49 ± 4 mm Hg) did not differ from the renovascular hypertensive group (A36 ± 7 mm Hg), but protein transfer across the cerebral vasculature was increased significantly in the renovascular hypertensive group (NT 0.08 ± 0.01%, RV 0.40 ± 0.14*, *p < 0.0S). These results suggest that cerebral vessels of renovascular hypertensive rats are more susceptible to blood-brain barrier disruption during acute hypertension than normotensive controls. Thus, susceptibility of the blood-brain barrier to disruption during acute hypertension differs between the two forms of animal hypertension, renovascular and the previously studied SHR. This observation may relate to the clinical impression that hypertensive encephalopathy (associated with enhanced blood-brain barrier permeability) is more frequent in patients with hypertension of renal origin than in those patients with hypertension from other causes.