Insulin effects on the sympathetic contraction of rabbit ear arteries

Electrical field stimulation (4 Hz, 0.2 ms, 70 V supramaximal voltage, 10 s duration) produced contraction of perfused rabbit central ear arteries, and this contraction was reduced by incubation with insulin (0.6–200 mU/ml). This inhibitory effect of insulin was not significantly modified by removing the endothelium, or by treatment with N^W-nitro-l-arginine (l-NA, 10⁻⁴ M), meclofenamate (10⁻⁵ M), ouabain (10⁻⁶ M), or cocaine (10⁻⁵ M). Insulin (200 mU/ml) did not modify the vascular contraction due to exogenous norepinephrine (10⁻⁸–10⁻⁴ M) nor the relaxation due to acetylcholine (10⁻⁸–10⁻⁴ M). This suggests that insulin may reduce vascular contraction by sympathetic stimulation, and this effect is not dependent on endothelial nitric oxide, prostanoids, or Na⁺–K⁺ pump activation.