Cyclic analogue of bradykinin possessing selective and prolonged biological activity.

Cyclo-[(N epsilon 1-Lys1, Gly6)-bradykinin] and its deprotected non-cyclic precursor, PheGlyProPheArg LysProProGly, were synthesized using the conventional methods of peptide chemistry. Similar to bradykinin, the cyclopeptide elicits a depressor reaction in rats, as revealed by the experiments in vivo. Its duration of action, however, is greater by several orders of magnitude. At the same time, it appears to exhibit no myotropic activity when applied in vitro to extravasal smooth muscle preparations (uterus and ileum of the rat). The non-cyclic precursor lacks the depressor activity, but produces a slight myotropic effect (alpha = 0.6 +/- 0.09; pD2 = 5.9 +/- 0.17).