[Effect of histamine on motor and vascular effects on the small intestine induced by acetylcholine].

In acute experiments on cats, an isolated portion of the small intestine was perfused with a constant blood flow pump. Contractile activity of the intestine was estimated by means of isometric tension. Arterial vessel reactions were reflected in perfusion pressure shifts. Responses of the venous section of the perfused vascular bed were recorded by means of accumulography technique. The subthreshold dose of histamine (10(-9) or 10(-7) g/ml, 0.8 ml/min) potentiated the contractile responses of the jejunum induced with i. a. administration of acetylcholine (0.1 X 10(-4) g). Blockade of nicotinic receptors with benzohexonium and H1-histamine receptors with suprastin did not affect the potentiating effect of histamine. Dilatatory responses of arterial vessels induced by acetylcholine could be either increased or decreased against the background of histamine. The drug did not modulate responses of the intestinal venous vessels however. The modulating effect of histamine on the acetylcholine-induced contractile responses of the jejunum seems to be actualized through the participation of H2-histamine receptors.