New bradykinin analogues acylated on the N-terminus: effect on rat uterus and blood pressure.

Our previous studies suggested that acylation of the N-terminus of several known B2 antagonists with various kinds of bulky acyl groups consistently improved their antagonistic potency in rat blood pressure assay. On the other hand, our earlier observations also seemed to suggest that the effects of acylation on the contractility of isolated rat uterus depended substantially on the chemical character of the acyl group, as we observed that this modification might either change the range of antagonism or even transform it into agonism. Bearing all this in mind, we decided to synthesize seven new analogues of bradykinin by N-terminal acylation with various acyl groups of a moderately potent B2 antagonist, previously synthesized by Stewart's group, D-Arg-Arg-Pro-Hyp-Gly-Thr-Ser-D-Phe-Thi-Arg. The analogues were tested in vitro for their blood pressure-lowering and uterotonic activities. The modifications either preserved or increased the antagonistic potency in the rat blood pressure test. On the other hand, all seven substituents negatively influenced the interaction with the rat uterine receptors. Our results may be helpful for designing new B2 agonists and antagonists.