Effect of stretching on the sensitivity of the guinea pig ileum to bradykinin and on its modification by bradykinin potentiating peptides.

The sensitivity of the guinea pig isolated ileum to bradykinin, but not to other agonists, was increased ca. 2-fold during the 3-4 h following mounting of the preparation under 1 g load. Concomitantly, a decrease was observed in the bradykinin potentiating effect of BPP9a, and of potentiator B but not potentiator C. This decrease was observed only with analogues of BPP9a or potentiator B which retained one or both of the basic amino acid residues in these peptides. Similar stretching of the rat isolated uterus did not affect bradykinin sensitivity or the potency of bradykinin potentiating peptides. Kininase activity of the ileum significantly increased during the 4 h period after mounting of the loaded preparation, but was not affected by treatment with BPP9a. It is proposed that bradykinin sensitivity is favoured by the changes in sodium and potassium transport in the cell membrane caused by stretching of the ileum, and that a similar mechanism may be partly responsible for the action of bradykinin potentiating peptides.