Central cardiovascular actions of histamine in rats: involvement of histamine H2-receptors.

Centrally induced pressor effects, associated with tachycardia have previously been demonstrated after intraventricular (i.c.v.) injections of histamine. The selective histamine H2-receptor agonists dimaprit (1--500 microgram) and 4-methyl histamine (1--10 microgram), and the histamine H1-receptor agonist 2-methyl histamin (1--10 microgram) elicited rises in blood pressure and heart rate after i.c.v. administration in urethane-anaesthetised rats. Metiamide (400--800 microgram, i.c.v.) antagonised the cardiovascular responses induced by dimaprit and 4-methyl histamine, but not the responses induced by 2-methyl histamine. In contrast mepyramine (100 microgram, i.c.v.) failed to antagonise the dimaprit-induced effects. It is concluded that histamine H1 and H2-receptors are present in the central nervous system of rats. Selective stimulation of either H1- or H2-receptors can lead to pressor effects associated with tachycardia after i.c.v. administration of specific agonists in urethane-anaesthetised rats. These responses are selectively antagonised by the respective receptor antagonists.