Modifications in the bradykinin main chain are not necessary for antagonistic activity in rat blood pressure assay

Previous studies demonstrated that the presence of a bulky acyl substituent at the N-terminus of B(2) antagonists significantly influenced the interaction of the peptide with B(2) receptors, thus increasing potency in the blood pressure test. Reported results also suggested that even minor changes in the structure of analogues might be of importance in designing more potent B(2) antagonists. On the other hand, it was learned that the effects of acylation might vary substantially with the chemical character of the acyl group. It seemed that either the positive or the negative charge on the N-terminal acyl group influenced the activity of the analogues because a suppressed antagonistic potency due to these modifications was observed. Bearing all these findings in mind, it was decided to check how N-terminal acylation would affect the pharmacological activity of bradykinin. Of the many acylating agents tested previously on B(2) antagonists, it was decided to use acridin-9-ylacetic acid (Ana) and anthracen-9-ylacetic acid (Ata). The potencies of the analogues were assessed by their ability to inhibit vasodepressor response of exogenous BK in conscious rats and by their ability to inhibit the contractions of isolated rat uterus evoked by BK.