The blood-brain barrier in adrenaline-induced hypertension. Circadian variations and modification by beta-adrenoreceptor antagonists.

Rats were subjected to adrenaline-induced acute hypertension during either the day or night. Albumin leakage into the brain was studied with Evans blue and 125I labeled serum albumin. The leakage was significantly lower during the night than during the day (P less than 0.001). d,1-propranolol had a protective effect (P less than 0.001) during the day and a slight reduction of the radioactivity (P less than 0.05 in some parts of the brain) was obtained by metoprolol (10 mg/kg) but not by butoxamine (10 mg/kg). None of the drugs reduced the tracer leakage during the night. The results suggest that the degree of alertness is of importance for the function of the blood-brain barrier in acute hypertension. However, the present experimental situation does not allow a separation of the effect of alertness per se and dark/light cycles. The changed vulnerability during the night could be related to enhanced neuronal activity, altered beta-adrenoreceptor sensitivity or to hormonal factors.