Studies on the responses of the isolated rectum of domestic chick (Gallus domesticus) to drugs.

The responses of the isolated rectum of the domestic chick (Gallus domesticus) to some drugs have been investigated. The tissue was found to be qualitatively and quantitatively similar to conventional mammalian gastrointestinal smooth muscles in its responses to pharmacological agents, and serves as a useful isolated smooth muscle preparation for investigating drug actions and interactions. Acetylcholine and its natural or synthetic analogues induced atropine-sensitive contractions of the tissue, while noradrenaline and other sympathomimetic drugs examined caused phentolamine-sensitive relaxations. 5-hydroxytryptamine contracted the tissue preparation, while histamine evoked a biphasic action (either a contraction or a relaxation, or even both occurring together one after the other). Potassium or barium ions contracted the muscle while magnesium ions relaxed it. Nicotine and dimethylphenylpiperazinium showed no effects on the muscle. The pharmacological implications of these findings are discussed. The receptor types present on the muscle have been classified as muscarinic cholinoceptors; histamine H1-and H2receptors; 5-hydroxytryptamine receptors, and alpha-adrenoceptors respectively.