[Antispasmodic mechanisms of actions of isoproterenol and papaverine with special reference to their relation to Ca (experiments using the isolated rat rectum)].

Antispasmodic mechanisms of isoproterenol and papaverine were investigated in relation to the mobilization of Ca in the rat's isolated rectal muscle. The findings on the relaxing effects of isoproterenol and papaverine on the contractions induced by increasing concentrations of K and on the modifications in the shape of K- and ACh-induced contractions by these two agents suggest that the antispasmodic mechanism of isoproterenol may be related to inhibition of the transmembrane influx of Ca as well as release of Ca, whereas that of papaverine may be related to not only inhibition of the transmembrane influx of Ca and release of Ca but also to inhibition of the ability of contractile elements responding to Ca. Furthermore, analysis of the concentration-action curves of K and acetylcholine concerning the phasic and the tonic contractions affected by isoproterenol and papaverine (Table 1) provide additional evidence for such a hypothesis.