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Department of Medicine, Divisions of 1 Geriatrics, 2 Endocrinology, and the Diabetes Research and Training Center, Albert Einstein College of Medicine, New York, New York 10461
Increased total fat mass (FM) and visceral fat (VF) may
account in part for age-associated decrease in hepatic insulin action. This study determined whether preventing the changes in body fat distribution abolished this defect throughout aging. We studied the
F1 hybrid of Brown Norway-Fischer 344 rats (n = 29), which we assigned to caloric restriction (CR) or fed ad libitum
(AL). CR (55% of the calories consumed by AL) was initiated and used at 2 mo to prevent age-dependent increases in FM and VF. AL rats were
studied at 2, 8, and 20 mo; CR rats were studied at 8 and 20 mo. VF and
FM remained unchanged throughout aging in CR rats. AL-fed rats at 8 and
20 mo had over fourfold higher FM and VF compared with both CR groups.
Insulin clamp studies (3 mU · kg
1 · min
1
with somatostatin) were performed to assess hepatic insulin
sensitivity. Prevention of fat accretion resulted in a marked
improvement in insulin action in the suppression of hepatic glucose
production (HGP) (6.3 ± 0.3 and 7.2 ± 1.2 mg · kg
1 · min
1
in 8- and 20-mo CR rats vs. 8.3 ± 0.5 and 10.8 ± 0.9 mg · kg
1 · min
1
in 8- and 20-mo AL rats, respectively). The rate of gluconeogenesis (by
enrichment of hepatic uridine diphosphate glucose and
phosphoenolpyruvate pools by
[14C]lactate) was unchanged in all groups. The
improvement in hepatic insulin action in the CR group was mostly due to
effective suppression of glycogenolysis (4.4 ± 0.3 and 4.9 ± 0.3 mg · kg
1 · min
1
in 8- and 20-mo CR rats vs. 5.8 ± 0.6 and 8.2 ± 1.0 mg · kg
1 · min
1
in 8- and 20-mo AL rats, respectively). The results demonstrated the
preservation of hepatic insulin action in aging CR rats. Therefore, body fat and its distribution are major determinants of age-associated hepatic insulin resistance.
obesity; caloric restriction
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