Mediation by B1 and B2 receptors of vasodepressor responses to intravenously administered kinins in anaesthetized dogs

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Abstract
1 Vasodepressor responses to intravenous (i.v.) injection of bradykinin (BK) and des-Arg9-BK, a selective B1 kinin receptor agonist, were characterized following i.v. pretreatment with selective B1 ([Leu8]-des-Arg9-BK) and B2 (Hoe 140) kinin receptor antagonists in anaesthetized dogs. 2 Des-Arg9-BK (0.05–3.3 nmol kg−1) produced dose-dependent decreases in mean arterial blood pressure with a ED50 0.4 nmol kg−1. The vasodepressor effects evoked by des-Arg9-BK (0.6 nmol kg−1) and BK (0.2 nmol kg−1) were greater after i.v. and i.a. injections, respectively. 3 The vasodepressor response to BK (0.6 nmol kg−1) but not to des-Arg9-BK (0.6 nmol kg−1) was significantly (P < 0.001) blocked by pretreatment with the B2 receptor antagonist, Hoe 140. 4 The vasodepressor response to des-Arg9-BK (0.6 nmol kg−1) but not to BK (0.6 nmol kg−1) was significantly (P < 0.001) reduced by pretreatment with the selective B1 receptor antagonist, [Leu8]-des-Arg9-BK. Although both B1 and B2 receptor antagonists caused a transient fall in blood pressure, their inhibitory action was unlikely to be related to a desensitization mechanism. 5 Inhibition of prostaglandin synthesis with indomethacin prevented the vasodepressor response induced by arachidonic acid (1 mg kg−1, i.v.) but not that to BK or des-Arg9-BK (0.6 nmol kg−1). 6 These results suggest, firstly, that the vasodepressor responses to i.v. BK and des-Arg9-BK are mediated by the activation of B2 and B1 receptors, respectively; secondly, that prostaglandins are not involved in the vasodepressor responses to kinins. These findings provide pharmacological evidence for the existence of functionally active B1 receptors in canine cardiovascular homeostasis.