Heat stress‐induced B 1 receptor synthesis in the rat: an ex vivo study

1 This ex vivo study was performed to characterize B 1 receptor induction in rats submitted to heat stress. Changes in aortic isometric tension were recorded after a 90 min in vitro incubation with [des‐Arg 9 ]‐bradykinin. B 1 receptor mRNA were detected in aorta and heart using RT–PCR technique. 2 Aortic rings from sham rats did not respond to [des‐Arg 9 ]‐bradykinin. In contrast, this agonist induced a concentration‐dependent relaxation of aortic rings from rats submitted to lipopolysaccharide (LPS) treatment or to heat stress 24 h earlier. 3 The concentration‐dependent relaxation induced by [des‐Arg 9 ]‐bradykinin on aortic rings from heat‐stressed rats was abolished by [des‐Arg 10 ]‐HOE 140, a selective B 1 receptor antagonist. 4 In endothelium denuded aortic rings from heat‐stress rats, [des‐Arg 9 ]‐bradykinin induced a concentration‐dependent constriction. 5 Pretreatment of intact aortic rings from heat‐stress rats with the cyclo‐oxygenase inhibitor, diclofenac (1 μ M ) did not prevent the concentration‐dependent relaxation in response to [des‐Arg 9 ]‐bradykinin. In contrast, NO synthase inhibition with N ω ‐nitro‐ L ‐arginine methyl ester (30 μ M ) totally prevented the vasorelaxant response. 6 B 1 receptor mRNA were not detected in aorta and heart from sham animals but were present in tissue from heat‐stressed and LPS‐treated rats. 7 In conclusion, our results suggest that heat stress induces a transcriptional activation of the B 1 receptor gene. The induction of B 1 receptors leads to an endothelium‐ and NO‐dependent vasorelaxant response to [des‐Arg 9 ]‐bradykinin.British Journal of Pharmacology (1998) 125 , 812–816; doi: 10.1038/sj.bjp.0702146