Effect of insulin on the venoconstrictive response to norepinephrine in normal human subjects: the influence of sodium status.

Hyperinsulinemia and insulin resistance have been implicated in the pathogenesis of essential hypertension, with alterations in insulin-induced vasodilatation as one possible mechanism. The aims of this study were to assess the local vasodilatory action of insulin on a dorsal hand vein and the influence of sodium status on the insulin effect in healthy human subjects. Distensibility of a superficial hand vein and response to norepinephrine, insulin, and nitroglycerine were measured by the linear variable differential technique. Fourteen healthy subjects were studied after a low (20 mmol) and high (200 mmol) sodium diet for 7 days. All subjects gained weight (P < .005) and had higher central venous pressure (P = .003) on a high sodium intake. Baseline mean arterial pressure, heart rate, and fasting plasma glucose levels were not significantly different between the two diets. High sodium diet, however, resulted in a higher calculated insulin/glucose ratio (P = .029) implying reduced tissue sensitivity to insulin. Baseline plasma norepinephrine was significantly higher on the low (1.29 +/- 0.13 nmol/L) compared with the high sodium diet (0.79 +/- 0.11 nmol/L) (P < .005). The dorsal hand vein was significantly more dilated at the baseline level on a low sodium (2.60 +/- 0.12 mm) than on a high sodium diet (2.20 +/- 0.12 mm) (P = .034). However, the maximal constriction achieved with norepinephrine was not significantly different between the two diets. Only an insulin dose of 0.8 mU/min on a low sodium diet was able to significantly dilate the norepinephrine preconstricted vein (77 +/- 9% of baseline diameter versus ED50) (P = .002).(ABSTRACT TRUNCATED AT 250 WORDS)