SKELETAL-MUSCLE BLOOD-FLOW - A POSSIBLE LINK BETWEEN INSULIN RESISTANCE AND BLOOD-PRESSURE

Insulin resistance has recently been found to be a common feature of essential hypertension. We have tested the hypothesis that reduced skeletal muscle blood flow in response to insulin may at least partially account for the wide range of insulin sensitivity observed in normotensive subjects. To this end, we studied 19 lean (body mass index less-than-or-equal-to 27) subjects exhibiting basal mean arterial pressures ranging from 58 to 110 mm Hg. All subjects were normotensive with the exception of one. Each subject was studied at baseline and during a hyperinsulinemic (600 milliunitS/M2 per minute) euglycemic clamp to quantitate insulin sensitivity. Mean arterial pressure was monitored invasively, and both leg (muscle) blood flow and cardiac output were measured by indicator dilution techniques, allowing the determination of both systemic and leg (or muscle) vascular resistance. In response to hyperinsulinemia, both cardiac output and leg blood flow increased approximately 37% and 80% (p<0.01), respectively. Rates of insulin-mediated glucose uptake were inversely correlated with the baseline mean arterial pressure (r=-0.62, p<0.01). The individual increment in leg blood flow above baseline in response to insulin was inversely proportional to the height of the baseline mean arterial pressure (r=-0.59, p<0.01). Mean arterial pressure and insulin-mediated glucose uptake were not correlated with either age or body fat content. The femoral arteriovenous glucose difference during hyperinsulinemia was not correlated with either basal mean arterial pressure or the rate of insulin-mediated glucose uptake. In summary, among normotensive subjects, 1) the rate of insulin-mediated glucose uptake is inversely proportional to the basal mean arterial pressure, 2) the increase in insulin-mediated muscle blood flow is inversely related to the basal mean arterial pressure, and 3) muscle glucose extraction is not related to the basal mean arterial pressure or the rate of insulin-mediated glucose uptake. In conclusion, attenuated insulin-mediated skeletal muscle blood flow appears to be a major cause of insulin resistance in subjects with elevated mean arterial pressure. Our data in normotensive subjects do not exclude the coexistence of other defects in glucose uptake and metabolism; nevertheless, they strongly support a hemodynamic basis for the insulin resistance observed in patients with hypertension.