Comparison of responses to T-kinin and bradykinin in the mesenteric vascular bed of the cat

Angiotensin-(1-7) potentiates responses to bradykinin but does not change responses to angiotensin I

Angiotensin-(1-7) (Ang-(1-7)), a bioactive peptide in the renin-angiotensin system, has counterregulatory actions to angiotensin II (Ang II). However, the mechanism by which Ang-(1-7) enhances vasodepressor responses to bradykinin (BK) is not well understood. In the present study, the effects of Ang-(1-7) on responses to BK, BK analogs, angiotensin I (Ang I), and Ang II were investigated in the anesthetized rat. The infusion of Ang-(1-7) (55 pmol/min i.v.) enhanced decreases in systemic arterial pressure in response to i.v. injections of BK and the BK analogs [Hyp3, Tyr(Me)8]-bradykinin (HT-BK) and [Phe8psi (CH2-NH) Arg9]-bradykinin (PA-BK) without altering pressor responses to Ang I or II, or depressor responses to acetylcholine and sodium nitroprusside. The angiotensin-converting enzyme (ACE) inhibitor enalaprilat enhanced responses to BK and the BK analog HT-BK without altering responses to PA-BK and inhibited responses to Ang I. The potentiating effects of Ang-(1-7) and enalaprilat on responses to BK were not attenuated by the Ang-(1-7) receptor antagonist A-779. Ang-(1-7)- and ACE inhibitor-potentiated responses to BK were attenuated by the BK B2 receptor antagonist Hoe 140. The cyclooxygenase inhibitor sodium meclofenamate had no significant effect on responses to BK or Ang-(1-7)-potentiated BK responses. These results suggest that Ang-(1-7) potentiates responses to BK by a selective B2 receptor mechanism that is independent of an effect on Ang-(1-7) receptors, ACE, or cyclooxygenase product formation. These data suggest that ACE inhibitor-potentiated responses to BK are not mediated by an A-779-sensitive mechanism and are consistent with the hypothesis that enalaprilat-induced BK potentiation is due to decreased BK inactivation.

The pharmacology of T-kinin and des-Arg(11)-T-kinin in primary cultures of rat bladder smooth muscle cells

T-kinin and its putative carboxypeptidase product des-Arg(11)-T-kinin are members of the kinin family that are unique to the rat. Primary cultures of rat bladder smooth muscle cells were used to investigate the pharmacology of these peptides. Calcium imaging experiments showed that rat bladder smooth muscle cells responded to both bradykinin and des-Arg(9)-bradykinin with an increase in [Ca(2+)](i) and responses to both agonists could be observed in the same cell. A more detailed pharmacological characterisation with a range of bradykinin receptor agonists and antagonists using 45Ca(2+) efflux confirmed the presence of both B(1) and B(2) bradykinin receptors. Using this cellular model, we confirm that T-kinin is a bradykinin B(2) receptor agonist and show for the first time that des-Arg(11)-T-kinin is a potent and selective bradykinin B(1) receptor agonist. In addition, using cells expressing the cloned rat and human bradykinin B(2) receptors plus the Ca(2+)-sensitive protein aequorin, T-kinin was shown to be selective for the rat over the human bradykinin B(2) receptor.