MODE OF ACTION OF PARTIAL AGONISTS ON TAENIA CAECUM OF GUINEA PIG AND DRUG-RECEPTOR THEORY

Actions of cholinergic drugs, adrenergic drugs and 5-hydroxytryptamine (5-HT) were examined with the ganglion free taenia caecum (or taenia coli) from the guinea pig mounted in Magnus apparatus or the sucrose gap apparatus. The cholinergic partial agonists in enough concentrations of produce their maximal contractions had a non-specific inhibitory action. The adrenergic partial agonist or ephedrine in enough concentrations to produce its maximal relaxation contracts the smooth muscle. These results suggest that as all the partial agonists have two effects or contraction and relaxation, the maximal responses to the partial agonists are smaller than that to the full agonist. The fact that inhibitions of the action of the full agonists by dibenamine are identical with each other suggests that the stimuli produced by all the full agonist-receptor complexes are same. Though the maximal response to 5-HT was smaller than that to the cholinergic full agonist or butyltrimethylammonium (BuTMA), 5-HT in enough concentrations to produce their maximal response had not the non-specific inhibitory action. Stimulus produced by the 5-HT-receptor complexes is smaller than that by the BuTMA-receptor complexes. Furthermore, relation between inward movements of Ca++ and stimuli produced by the drug-receptor complexes was discussed in this paper. © 1969, The Japanese Pharmacological Society. All rights reserved.