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

In the presence of ouabain (1 mM), acetylcholine and KCI (5 mM) evoked endo thelium-independent relaxations in rat hepatic arteries. Treatment with cap saicin (10 mu M), scopolamine (1 mu M) or CGRP(8-37) (3 mu M) prevented the se relaxations. Acetylcholine-induced relaxations in intact arterial segmen ts in the presence of indomethacin (10 mu M) and N-G-nitro-L-arginine (0.3 mM) were only partially inhibited by ouabain plus BaCl2 (30 mu M). However, ouabain plus BaCl2 almost abolished such relaxations in capsaicin-pre-trea ted preparations. In arteries without endothelium, the neurosecretagogue al pha-latrotoxin (1 nM) induced complete relaxations, which were abolished by CGRP(8-37) or pre-treatment with capsaicin. alpha-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 relaxa tion must be considered when this agent is used as a pharmacological tool. The results further suggest that CGRP is a nerve-derived hyperpolarizing fa ctor in the rat hepatic artery.