H2-receptors mediate histamine-induced variations in the permeability of the blood-brain barrier of rats.

Earlier investigations suggested that histamine H2-receptors mediate alterations in cerebrovascular permeability in mammals. The objective of this study was to observe the effects of the H2-receptor antagonist ranitidine on histamine-stimulated alterations in the permeability of the blood-brain barrier (BBB) of rats. Normotensive Wistar-Kyoto (WKY) (control) and spontaneously hypertensive (SHR) rats were premedicated with ranitidine (1 mg/kg), followed by histamine (1.25, 2.5 or 5.0 micrograms/kg) or saline. Animals were anesthetized and permeability of the BBB was evaluated with 99mTc-labeled sodium pertechnetate (TcO4-) or with 131I-labeled human serum albumin (RISA). In both control and hypertensive rats, ranitidine blocked histamine-induced changes in cerebrovascular permeability, but did not inhibit histamine-stimulated systemic hypotension. The alterations in the permeability of the BBB did not correlate with variations in blood pressure produced by histamine.