Pressor response mediated via histamine H1-receptors of the guinea-pig sympathetic ganglia.

In pithed guinea-pigs, the general characteristics and origin of the pressor response to intravenous injection of histamine were examined. Histamine (5-80 micrograms/kg) produced a rapid, short-lasting, constant, prominent and dose-dependent pressor response, followed by a secondary slight and prolonged depressor response. The vascular response to histamine was accompanied by a marked tachycardia. The pressor effect of histamine (30 micrograms/kg) was strongly reduced or abolished in animals pretreated with nicotine, reserpine, bretylium or 6-hydroxydopamine. Furthermore, pyrilamine, a histamine H1-receptor antagonist, antagonized in a dose-dependent manner the pressor response to histamine. On the contrary, metiamide, a histamine H2-receptor antagonist, as well as hexamethonium and atropine, cholinergic antagonists, did not suppress the pressor effect of histamine. The present experiments provide evidence that in guinea-pigs, the pressor component of the vascular response to histamine results predominantly from the activation of histamine H1-receptors in the sympathetic ganglia with consequent release of noradrenaline at postganglionic sympathetic nerve terminals.