Action of some natural peptides on the stomach of the anaesthetized rat.

Different peptides of natural origin were studied for their stimulant activity on the stomach of the anaesthetized rat. The group of the tachykinins (substance P and its analogues) showed a noticeable spasmogenic activity on the whole stomach from the fundus to the pylorus. Threshold doses ranged between 0.1 and 5 microgram/kg by i.v. route and the order of potency was: eledoisin greater than phyllomedusin greater than physalaemin greater than uperolein greater than substance P. A good correlation between the dose and the duration of the spasmogenic effect was always observed and tachyphylaxis never occurred. Experiments carried out with different kinds of inhibitors suggested that tachykinins act directly on the smooth muscle of the stomach. Taking into account also results obtained in other experimental conditions it was possible to state that the N-terminal part of the molecule of these peptides has a certain importance in determining the degree of their potency in the different tests. The peptide motilin, which does not belong to the family from a chemical point of view, was scarcely active, if at all, in modifying the motility of the rat stomach.