Effects of ovokinin on isolated aortas of guinea pigs, normotensive and spontaneously hypertensive rats

Ovokinin, a peptide recently isolated from an enzymatic digest of ovalbumin, has been shown to mediate vasorelaxation of the canine mesenteric artery through bradykinin B1 receptors. Bradykinin can mediate both vasorelaxation and vasocontraction depending upon the tissue or species investigated. The aim of this study was to characterize ovokinin further by determining whether the effects of this peptide, like bradykinin, vary when using different species and tissue preparations as well as different contracting agents. Isolated aortic rings from guinea pigs, normotensive rats, and spontaneously hypertensive rats were exposed to phenylephrine, prostaglandin F2a, potassium chloride, or bradykinin. Bradykinin contracted guinea pig and spontaneously hypertensive rat aortas, however, it had no effect on normotensive rat aortas. In this study, ovokinin did not exhibit activity in any of the preparations except in guinea pigs, where it potentiated the contraction elicited by bradykinin only. This potentiation was blocked when rings were pretreated with captopril, a kininase II inhibitor. Ovokinin may also exhibit slight vasorelaxing activity in spontaneously hypertensive rat aortas precontracted with prostaglandin F2a. These findings suggest that, like bradykinin, the effects of ovokinin are species- and tissue-dependent. The action of ovokinin on the guinea pig aorta may involve kininase II, which is partly responsible for the degradation of bradykinin and other kinins.