(Hypertension. 1997;29:700-705.)
© 1997 American Heart Association, Inc.
Articles |
Contrasting Autonomic and Hemodynamic Effects of Insulin in Healthy Elderly Versus Young Subjects
the Departments of Internal Medicine (M.H., V.K.S., A.L.M.), Anesthesia (C.A.S., E.A.A.), and Pediatrics (R.P.H.), Cardiovascular and Clinical Research Centers, University of Iowa College of Medicine, Veterans Affairs Medical Center, Iowa City.
Correspondence to Erling A. Anderson, PhD, Department of Anesthesia, University of Iowa Hospitals and Clinics, Iowa City, Iowa, 52242-1081. E-mail erling-anderson@uiowa.edu
Acute increases in plasma insulin produce both sympathoexcitation and vasodilation in normal young adults. Aging is associated with insulin resistance and may alter the sympathetic or the vascular responses to insulin. Therefore, we assessed sympathetic and vascular responses to acute physiological increases in plasma insulin levels in 10 healthy, normotensive elderly (65±2 years) and 12 normal young (27±1 years) subjects matched for body mass index (25±1 kg/m2 in both groups). We measured muscle sympathetic nerve activity (microneurography), FBF (plethysmography), heart rate, and blood pressure and calculated forearm vascular resistance and insulin sensitivity (M value) during a 90-minute hyperinsulinemic/euglycemic clamp. M values were 4.3±0.4 mg·kg-1·min-1 in the elderly and 8.4±1.4 mg·kg-1·min-1 in the young subjects (P<.05). Baseline muscle sympathetic nerve activity was higher in the elderly subjects (33±3 versus 15±2 bursts per minute, P<.05); however, the absolute and percent increases in muscle sympathetic nerve activity were smaller in the elderly than in the young subjects (+10±1 versus +15±1 bursts per minute, or +37±11% versus +110±16%, P<.05). Forearm vascular resistance decreased with insulin from 46±2 to 31±3 units in the young but increased with insulin in the elderly subjects from 37±3 to 47±7 units (P<.05). Heart rate increased in young but not in elderly subjects. Insulin did not change blood pressure in either group. In conclusion, as opposed to vasodilation in young adults, insulin caused vasoconstriction in healthy elderly individuals. The failure of the vasodilator action of insulin in the elderly may permit even modest insulin-induced sympathoexcitation to elicit vasoconstriction. We speculate that the vasoconstrictor response to insulin may further potentiate insulin resistance in the elderly.
Key Words: insulin • sympathetic nerve activity • vascular resistance • blood pressure • elderly
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