Preserved Relative Dispersion but Blunted Stimulation of Mean Flow, Absolute Dispersion, and Blood Volume by Insulin in Skeletal Muscle of Patients With Essential Hypertension

Abstract

Background —We examined the integrity of the effects of insulin on mean muscle blood flow, flow heterogeneity, and blood volume in essential hypertension. Methods and Results —Positron emission tomography, combined with [ 15 O]H 2 O and [ 15 O]CO as tracers for direct measurement of blood flow and volume in skeletal muscle, and a new bayesian iterative reconstruction algorithm allowing pixel-by-pixel quantitation of blood flow and flow dispersion, were used. Measurements were performed basally after an overnight fast and under normoglycemic hyperinsulinemic conditions in 11 newly diagnosed, untreated mildly hypertensive men (age, 35±1 years; body mass index, 25.2±0.4 kg/m 2 , blood pressure 141±4/96±2 mm Hg, mean±SE) and 11 matched normotensive men. Insulin-stimulated whole body glucose uptake was significantly decreased in the hypertensive men (41±4 μmol/kg per minute) compared with the normotensive (59±4 μmol/kg per minute, P <0.005) men. Mean blood flow in skeletal muscle was significantly lower in the hypertensive than the normal subjects basally (1.7±0.2 versus 2.7±0.4 mL/0.1 kg per minute, P <0.05) and during hyperinsulinemia (2.3±0.2 versus 4.2±0.8, P <0.05). The flow response to insulin (0.6±0.2 versus 1.9±0.5 mL/0.1 kg per minute, hypertensive versus normal subjects, P <0.05) was also significantly blunted. Muscle blood volume was significantly lower in the hypertensive than in the normal subjects, both basally (3.0±0.2 versus 3.5±0.2 mL/0.1 kg, P <0.05) and during hyperinsulinemia (3.1±0.2 versus 4.0±0.2 mL/0.1 kg muscle, P <0.02). The increase in muscle blood volume by insulin was significant in the normal ( P <0.05) but not the hypertensive subjects. Regional pixel-by-pixel analysis within femoral muscles revealed significant spatial heterogeneity of blood flow. Insulin increased absolute dispersion of blood flow significantly more in the normal subjects than in the hypertensive subjects ( P <0.05). Conclusions —True flow heterogeneity, as judged from the coefficients of variation (relative dispersion), was comparable between the groups basally and during hyperinsulinemia. We conclude that mean flow, its absolute dispersion, and blood volume exhibit insulin resistance in patients with essential hypertension.