Calcitonin gene-related peptide mediated neurogenic vasorelaxation in the isolated canine lingual artery.

The nature of neurogenic relaxation was investigated in ring preparations of canine lingual artery. In all experiments, the preparations were previously treated with guanethidine (5 x 10(-6) M) to block neurogenic constrictor responses. In the presence of norepinephrine (10(-5) M) to induce tone, electrical stimulation (10 V, 4 to 16 Hz, for 45 sec) produced relaxation of the rings in an endothelium-independent fashion. The relaxant response in endothelium-denuded rings was not changed by propranolol (10(-5) M), and atropine (10(-5) M) did not affect the relaxation elicited by electrical stimulation in endothelium-intact rings. NG-monomethyl-L-arginine (10(-4) M) or NG-nitro-L-arginine methyl ester (10(-4) M), a nitric oxide (NO) synthase inhibitor, had no effect on the electrical stimulation-induced relaxation of endothelium-denuded rings. Human calcitonin gene-related peptide (CGRP)-(8 - 37) (2 x 10(-8) M), a CGRP1-receptor antagonist, inhibited neurogenic relaxation of endothelium-denuded rings; substance P (10(-6) M) failed to mimic the observed effect of electrical stimulation. The demonstrated effect of electrical stimulation was inhibited by glibenclamide (10(-5) M), but not tetraethylammonium (2 x 10(-4) M); glibenclamide abolished the relaxation in response to exogenous CGRP or the ATP-sensitive K+ channel opener cromakalim (10(-6) M) in endothelium-denuded rings. Moreover, tetrodotoxin (3.13 x 10(-6) M) inhibited the relaxation of endothelium-denuded rings induced by electrical stimulation. The relaxation was selectively inhibited when endogenous CGRP had been depleted from perivascular nerves by capsaicin (10(-6) M). These results suggest that CGRP, but not NO, released from non-adrenergic non-cholinergic nerves by electrical stimulation produces relaxation of canine lingual artery that is mediated by activation of CGRP1 receptors.