Insulin resistance is a common feature in first-degree relatives of NIDDM patients. To explore the mechanism(s) behind this condition in more detail, a percutaneous muscle biopsy (vastus lateralis) was performed in 25 first-degree relatives of NIDDM patients and 21 control subjects to examine muscle fiber composition and capillary density. Insulin-stimulated glucose disposal (Rd) was determined employing a hyperinsulinemic-(insulin infusion rate 0.6 mU · kg−1 · min−1) euglycemic clamp. Rd (5.76 ± 0.35 vs. 8.06 ± 0.36 mg · kg lean body weight [LBW]−1 · min−1 P < 0.001) and estimated Vo2max (49.3 ± 2.8 vs. 57.2 ± 3.5 mg · kg LBW−1 · min−1, 0.05 < P < 0.10) were decreased in the relatives. The number of type lib fibers (29.5 ± 2.5 vs. 21.0 ± 2.8%, P < 0.05) was increased in the relatives, whereas no significant differences were found in other fiber types or capillary density between the groups. Correlations were observed between number of type I fibers (positive), number of type lib fibers (negative), and capillary density (positive) versus Rd as well as estimated Vo3max (P < 0.05). In a multiple linear regression analysis with Rd as a dependent variable, estimated Vo2max, family history of NIDDM, and number of type lib fibers (P < 0.001, r2 = 0.64) significantly determined the level of Rd, whereas capillary density did not. In conclusion, insulin-resistant first-degree relatives of NIDDM patients are characterized by an increased number of type lib muscle fibers. Whether this finding reflects a reduced physical activity level and fitness in the relatives or is of primary genetic origin remains to be determined.
Evidence of an Increased Number of Type IIb Muscle Fibers in Insulin-Resistant First-Degree Relatives of Patients with NIDDM
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Birgit Nyholm, Zhuqing Qu, Andreas Kaal, Steen Bønnelykke Pedersen, Claus Højbjerg Gravholt, Jesper Løvind Andersen, Bengt Saltin, Ole Schmitz; Evidence of an Increased Number of Type IIb Muscle Fibers in Insulin-Resistant First-Degree Relatives of Patients with NIDDM. Diabetes 1 November 1997; 46 (11): 1822–1828. https://doi.org/10.2337/diab.46.11.1822
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