Abstract
Effects of smooth muscle relaxants on histamine-, Ba2+-and Ca2+-induced contractions, or on electrical activities were examined in the longitudinal smooth muscle of guineapig ileum or taenia coli, respectively. Papaverine, D-600 and diltiazem effectively inhibited the Ca2+ responses and the tonic components of the histamine and Ba2+ responses. Especially, D-600 and diltiazem depressed the Ca2+ responses in much lower concentrations than papaverine and theophylline. In contrast, benactyzine and etomidoline were not specific antagonists against the Ca2+ responses, and they were effective inhibitory agents on the phasic responses to histamine and Ba2+. Nitroprusside failed to reduce the three types of contractions effectively. These results suggest that these seven relaxants can be divided into four types. Influence of those relaxants on spontaneously-and Ba2+-evoked electrical activities are compatible with the above differentiation. The four types of relaxants used in this study seem to exert their actions on smooth muscle in different way. Nitroprusside, however, is not a potent relaxant against contractions of the intestinal smooth muscles.
