Central hypertensive action of histamine in conscious normotensive cats

In conscious normotensive cats intraventricular (i.c.v.) administration of histamine (2.0-50.0 mug) induced dose-related rises in blood pressure, with no increase in heart rate. The hypertensive response elicited by a sub-maximal dose of histamine (10.0 mu i.c.v.) was significantly antagonised by central pretreatment with the H1-receptor antagonist mepyramine maleate (200 mug i.c.v.) but not by the H2-receptor antagonist metiamide hydrochloride (1.0 mg i.c.v.). Behavioural responses were obtained in response to to histamine (10.0 and 50.0 mug i.c.v.), which were not antagonised by these antihistamine pretreatments.