Involvement of sensory nerves in vasodilator responses to acetylcholine and potassium ions in rat hepatic artery

In the presence of ouabain (1 m M ), acetylcholine and KCl (5 m M ) evoked endothelium‐independent relaxations in rat hepatic arteries. Treatment with capsaicin (10 μ M ), scopolamine (1 μ M ) or CGRP 8–37 (3 μ M ) prevented these relaxations. Acetylcholine‐induced relaxations in intact arterial segments in the presence of indomethacin (10 μ M ) and N G ‐nitro‐ L ‐arginine (0.3 m M ) were only partially inhibited by ouabain plus BaCl 2 (30 μ M ). However, ouabain plus BaCl 2 almost abolished such relaxations in capsaicin‐pre‐treated preparations. In arteries without endothelium, the neurosecretagogue α‐latrotoxin (1 n M ) induced complete relaxations, which were abolished by CGRP 8–37 or pre‐treatment with capsaicin. α‐Latrotoxin also induced a smooth muscle hyperpolarization (12±2 mV), which was abolished by CGRP 8–37 . The ability of ouabain to disclose a CGRP‐mediated neurogenic relaxation must be considered when this agent is used as a pharmacological tool. The results further suggest that CGRP is a nerve‐derived hyperpolarizing factor in the rat hepatic artery. British Journal of Pharmacology (2000) 130 , 27–32; doi: 10.1038/sj.bjp.0703258