A PRELIMINARY INVESTIGATION OF THE PHARMACOLOGY OF THE HUMAN ISOLATED TAENIA COLI PREPARATION

Abstract

The effects of drugs on smooth muscle strips of human taenia coli, obtained from operation specimens, were studied in vitro. Both nicotinic and muscarinic sites of action of acetylcholine were demonstrated, the nicotinic effect being a relaxation. The sympathomimetic amines, adrenaline, noradrenaline, and isoprenaline produced a relaxation of the tissue by an action on adrenaline α- and β-receptors. The presence of both types of receptor was demonstrated by selective adrenergic blockade with pronethalol or Hydergine. Pronethalol in high concentrations gave a nonselective adrenergic blockade. The ganglion-stimulating agents nicotine and dimethylphenylpiperazinium produced a relaxation of the tissue in all concentrations. This relaxation was inhibited by pronethalol or physostigmine but no contractile component to ganglion stimulation was revealed when these two drugs were present together. These results indicate the presence of either sympathetic ganglia in the intrinsic nerve plexuses, or adrenergic stores in the bowel wall. There is no pharmacological evidence for parasympathetic ganglia in human sigmoid colon. Histamine produced relaxant, contractile or biphasic responses. The type of response was independent of the “tone” of the preparation. The responses were not modified by procaine, hyoscine or pronethalol, which result indicates that both the contractile and relaxant responses to histamine were due to a direct action of the drug on smooth muscle. 5-Hydroxytryptamine produced either a contraction or a relaxation of the tissue. The relaxation was due to a direct effect of the drug, since hexamethonium, procaine or pronethalol did not affect the response. No conclusions have been drawn regarding the mechanism of the contractile response to 5-hydroxytryptamine. The nature of the responses of the tissue to drugs was independent of the disease for which the specimen of colon was removed.