Rabbit aortic rings pre-contracted with 1 microm phenylephrine were exposed to organ fluid of isolated guinea pig cochleas which had been subjected to electrical field stimulation (FS, 50 Hz, 50 V, 0.2 ms over 2 min). This resulted in an endothelium-dependent relaxation of the vessel rings sensitive to glibenclamide, an ATP-sensitive K+channel blocker. Tetrodotoxin (1 microm) added to the cochlear fluid blocked the vasorelaxant effect of cochlear FS and it attenuated vasorelaxation when added to aortic rings. The relaxation response paralleled an increase in the level of calcitonin gene-related peptide (CGRP) in both cochlear and vascular organ fluids from undetectable pre-stimulation values to 0.12+/-0.029 and 0.44+/-0.051 n m, respectively. We conclude that CGRP possibly contributes to cochlear nerve stimulation-induced endothelium-dependent vasorelaxation.
Copyright 1999 The Italian Pharmacological Society.