H2-HISTAMINERGIC ACTIVITY OF CLONIDINE IN GUINEA-PIG HEART

  • 1 January 1977
    • journal article
    • research article
    • Vol. 3  (2) , 95-106
Abstract
Clonidine perfusion (1 .mu.M) or injection (9.4-150.4 nmol) into the isolated perfused guinea pig heart caused an increase in contractile force, phosphorylase a and cyclic AMP levels. The effects of clonidine were blocked by burimamide (30 .mu.M). Propranolol (1 .mu.M), phentolamine (1 .mu.M) or reserpine treatment (5 mg/kg i.p., 24 h prior to the experiment) did not influence the cardiac effects of clonidine. Clonidine (0.1-100 .mu.M) also produced a dose dependent positive inotropic effect on right ventricle strips but had a negative chronotropic effect on the spontaneously beating right atria at higher concentrations (0.1-1.0 M). Burimamide did not block the clonidine-induced negative chronotropic effect. Clonidine did not increase contractile force in guinea pig left atria. It also did not influence the isoproterenol-and phenylephrine-induced increases in cardiac force of contraction but did antagonize the positive inotropic effect of 4-methylhistamine in the right ventricle. Clonidine may compete with 4-methylhistamine for the same receptor sites. The cardiac receptors for both biochemical and mechanical effects of clonidine are histamine receptors of the H2-type.

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