Population-based study of the relationship among muscle morphology, insulin action, and hypertension

To examine whether changes in muscle morphology are linked to the metabolic abnormalities associated with the insulin resistance syndrome, muscle morp hology and the metabolic profile were examined in 52 individuals with untre ated hypertension (mean arterial pressure [MAP] = 117 +/- 7 mm Hg) and 38 c arefully matched controls (MAP = 89 +/- 5 mm Hg). Oral glucose tolerance te sts and hyperglycemic clamps were performed for measurements of insulin act ion on glucose disposal and suppression of nonesterified fatty acids (NEFA) . Fully automated, computer-aided techniques were used for morphometric mea surements of muscle biopsies from m. vastus lateralis. The hypertensive and normotensive groups did not differ in insulin sensitivity to glucose dispo sal (0.18 +/- 0.16 v 0.19 +/- 0.13 mu mol/kg/min/pmol/L; P = .20) and NEFA suppression (87.5 +/- 7.3 v 87.2 +/- 9.4%, P > 0.30) during a hyperglycemic clamp. The groups were similar in the proportion of types 1, 2a, and 2b mu scle fibers, fiber size, and capillary density. Fiber roundness (ratio of f iber perimeter squared to fiber area) differed in the hypertensive (1.51 +/ - 0.07) and normotensive (1.58 +/- 0.12, P = .004) groups, showing that the muscle fibers in the hypertensive group were more rounded in shape, a nons pecific change often seen after minimal ischemic lesions. The quotient expr essing fiber roundness was associated with systolic (r = -0.29, P = .01) an d diastolic (r = -0.32, P = .005) blood pressure. We conclude that persons with mild and moderate hypertension do not have ab normalities in muscle morphology that could explain the impairment of insul in action often observed in this condition. However, hypertensive individua ls have increased muscle fiber roundness. Ii: is wondered whether hypertens ion may be a condition with defects in the regulation of the transmembranou s ion transport, leading to raised intracellular sodium concentration, swel ling of the cytoplasma, and roundening of the fibers. Am J Hypertens 1999;1 2:1209-1216 (C) 1999 American Journal of Hypertension, Ltd.