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Impairment of Noninsulin-Mediated Glucose Disposal in the Elderly^*

GRAYDON S. MENEILLY, DARIUSH ELAHI, KENNETH L. MINAKER, ANNE L. SCLATER and JOHN W. ROWE^||

Division on Aging, Harvard Medical School; Charles A. Dana Research Institute and the Harvard Thorndike Laboratory, Joint Department of Medicine, Beth Israel and Brigham and Women’s Hospitals, Harvard Medical School; and the Geriatric Research Education Clinical Center, Brockton/West Roxbury Veterans Administration Medical Center Boston, Massachusetts 02215

Address all correspondence and requests for reprints to: K. L. Minaker, M.D., Beth Israel Hospital, 330 Brookline Avenue, Boston, Massachusetts 02215.

While normal aging is characterized by resistance to insulin-mediated glucose disposal (IMGU), the effect of age on noninsulin-mediated glucose disposal (NIMGU), which is responsible for the majority of basal glucose uptake, has not been completely evaluated. These studies were conducted on healthy nonobese young (n = 10; age, 20–30 yr) and old (n = 10; age, 62-80 yr) men. Each subject underwent two paired studies in random order. In all studies a [³H]glucose infusion was used to measure glucose uptake and production rates, and somatostatin (500 µg/h) was infused to suppress endogenous insulin release.

In study A, plasma glucose was kept close to fasting levels (5.6 mmol/L) using an euglycemic clamp protocol for 4 h. Plasma insulin decreased to less than 20 pmol/L within 15 min and remained suppressed thereafter in all studies. Steady state (15–240 min) plasma glucagon levels were slightly greater in the elderly [young, 86 ± 5 (±SE); old, 98 ± 2 ng/L; P < .05]. Basal glucose uptake was similar in both groups (young, 877 ± 21; old, 901 ± 24 µmol/min). Glucose uptake during the last hour of the study (180–240 min) was used to represent NIMGU, because insulin action was assumed to be absent by this time. NIMGU was less in the elderly (young, 744 ± 18; old, 632 ± 32 µmol/min; P < 0.01). In study B, plasma glucose was kept at about 11 mmol/L for 4 h using a hyperglycemic clamp protocol. Plasma insulin decreased to less than 20 pmol/L within 15 min and remained suppressed thereafter in all studies. Steady state plasma glucagon levels were slightly but not significantly higher in the elderly (young, 88 ± 6; old, 100 ± 4 ng/L). Basal glucose uptake (young, 910 ± 27; old, 883 ± 25 µmol/min) and NIMGU (young, 933 ± 36; old, 890 ± 16 µmol/min; P = NS) were similar in both young and old subjects.

We conclude that aging is associated with impairment in NIMGU only in the basal state, which may explain in part the increase in fasting glucose with age.

^* This work was supported in part by USPHS Grant AG-600599 and General Clinical Research Grant RR-01032.

Fellow of the Medical Research Council of Canada.

Recipient of the Greenwall Foundation Award from the American Federation of Aging Research.

Supported by a grant from the Ontario Ministry of Health.

^|| Supported in part by the MacArthur Foundation Research Program on Successful Aging.

Received May 24, 1988.

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