Assay of substance P on goldfish intestine in a microbath

A technique is described for testing the effects of drugs on the intestine of goldfish in a microbath (0.05 ml.). This preparation may be used for the assay of substance P, which causes contractions of the muscle in doses as small as 1 m-u. Other substances in tissue extracts also act on this muscle, but the effects of most of these can be abolished by antagonists. Some tissues, however, contain an unknown substance which causes powerful contractions of the muscle and interferes with the assay of substance P. An attempt to demonstrate the release of substance P in the central nervous system was unsuccessful.