To determine whether insulin has a vasodilator action on the artery and vein, the effects of insulin at varying concentrations (120 μU/ml, 1.2 mU/ml, 12 mU/ml, and 120 mU/ml) on vasoconstriction by norepinephrine (NE) and angiotensin II (ANG II) were studied in the isolated rabbit femoral artery and vein. Helical strips were suspended in an organ bath filled with modified Krebs solution (pH 7.4), were gassed with 95% O2/5% CO2 at 36°C, and isotonic contractions were measured. Insulin significantly and dose dependently inhibited the vasoconstriction induced by NE (10−8 M for the artery and 10−7 M for the vein) at ≥1.2 mU/ml for both the artery and vein and the vasoconstriction induced by ANG II (3 × 10−10 M for the artery and 3 × 10−9 M for the vein) at ≥1.2 mU/ml for the artery and ≥12 mU/ml for the vein. The results indicate that insulin has an inhibitory effect on NE- and ANG II–induced contraction in both the artery and vein, and this appeared to be a contributory factor in the hypotensive effect observed in diabetic patients treated with insulin.

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