H1- and H2-receptors for histamine in the ileum of the guinea pig.

Clark's equation used in its inverted form (double reciprocal plots) was shown to be valid regarding the interaction of histamine with its receptors in the guinea-pig ileum. Burimamide, a typical H2-receptor antagonist potentiated the stimulating effect of small concentrations of histamine (10(-6) M) on the intestinal smooth muscle, probably, by blocking H2-receptors which may show the opposite effect. The calculated parameters of affinity (pKn) remained constant under different conditions. A linear correlation between length of the preparation and maximal contractions has been found.