The blood-brain barrier in young spontaneously hypertensive rats

It has been shown that the blood-brain barrier (BBB) of chronically hypertensive adult spontaneously hypertensive rats (SHR) is less susceptible to disruption during acute superimposed hypertension than normotensive controls. The purpose of this study was to determine if the BBB of young SHR, not yet markedly hypertensive, was similarly protected during super-imposed acute hypertension. Spontaneously hypertensive rats (n = 22) and normotensive Wistar-Kyoto rats (WKY) (n = 23) 4-5 weeks of age were anesthetized with secobarbital sodium (50 mg/kg) intraperitoneally and acute hypertension was produced by an intravenous injection of norepinephrine (75 micrograms). Permeability of the BBB was studied with radioactive iodine serum albumin (RISA) injected intravenously. The ratio of brain-to-blood RISA X 100 was used as an index of permeability of the BBB expressed as % protein transfer. In WKY exposed to acute hypertension mean arterial pressure increased by 52 +/- 2 mmHg and in SHR the increase was 49 +/- 3 mmHg. The protein transfer of the cerebral hemispheres was 1.17 +/- 0.30% in WKY and 0.90 +/- 0.20% in SHR (P less than 0.40). These data indicate that BBB protein transfer during acute superimposed hypertension does not differ between young SHR and WKY. Thus, the reduced susceptibility to BBB disruption in chronically hypertensive adult SHR is not present in young SHR, making them as susceptible as WKY to cerebral complications related to protein transfer during acute hypertension.