HISTAMINE-INDUCED CONTRACTIONS AND INHIBITORY ACTIONS OF D-600, PAPAVERINE AND BENACTYZINE ON THEIR CONTRACTIONS IN THE GUINEA-PIG TAENIA COLI

Abstract

The histamine-induced contractions and effects of some smooth muscle relaxants on their contractions were examined in the guinea-pig taenia coli. Application of Ca to the Ca-free physiological solution caused a contraction of the taenia coli (Ca contration), and histamine accelerated and increased the Ca contraction (H · Ca contraction). Histamine also contracted the taenia coli in the Ca-free solution (Ca (-) · H contraction). D-600 which preferentially reduces the Ca influx into muscle cells, more effectively depressed the H · Ca contraction and more feebly the Ca (-) · H contraction than histamine-induced contraction in the normal physiological solution. Papaverine inhibited the H · Ca contraction and the Ca (-) · H contraction more than the histamine-induced contration. Benactyzine was a specific agent against the Ca (-) · H contraction.When the Ca contraction reached the peak, application of histamine induced a further contraction. D-600 effectively inhibited the Ca contraction and the further contraction induced by histamine. Although papaverine blocked the Ca contraction similamly to D-600, the application of histamine produced a large contraction. Benactyzine induced only a feeble inhibition on the Ca contraction, but it was effective against the following contraction caused by histamine.Histamine probably mobilizes the extracellular and cellular Ca and contracts the smooth muscle. Papaverine seemn to ishibit smooth muscle contractions by diverse actions. Benactyzine may exert the main inhibtion on the mobilization of the cellular Ca through the competition with Ca. In the intestinal smooth muscle, nitroprusside which is known to act on intracellular binding sites for Ca in some vascular smooth muscle is entirely different from benactyzine.