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Am J Physiol Endocrinol Metab 276: E143-E150, 1999;
0193-1849/99 $5.00
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Vol. 276, Issue 1, E143-E150, January 1999

Insulin-like growth factor I stimulates cardiac myosin heavy chain and actin synthesis in the awake rat

Lawrence H. Young, Yin Renfu, Xiaoyue Hu, Sang Chong, Syed Hasan, Ralph Jacob, and Robert S. Sherwin

Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510

To determine the effect of insulin-like growth factor I (IGF-I) on cardiac contractile protein synthesis in vivo, we measured L-[ring-2,6-3H]phenylalanine incorporation into myosin heavy chain and actin during intravenous infusions (4 h) of either saline or IGF-I (1 µg · kg-1 · min-1) in awake rats. After an overnight fast, IGF-I increased myosin synthesis by 29% compared with saline (11.5 ± 0.8 vs. 8.9 ± 0.6%/day, P < 0.01) and actin synthesis by 26% (7.2 ± 0.3 vs. 5.7 ± 0.3%/day, P < 0.01), with similar effects in left and right ventricles and a comparable effect on mixed cardiac protein. When amino acids were infused with IGF-I, a further increase in myosin synthesis was observed (P < 0.01). In fed rats, despite higher baseline synthesis rates than in fasted rats (P < 0.01), IGF-I also increased the synthesis of myosin (12.3 ± 0.5 vs. 9.9 ± 0.5%/day, P < 0.01) and actin (8.8 ± 0.3 vs. 7.5 ± 0.2%/day, P < 0.01) compared with saline. IGF-I infusion had no hypoglycemic effect and did not change heart rate or blood pressure. Thus relatively low-dose IGF-I has a direct action in vivo to acutely increase heart contractile protein synthesis in both fasted and fed awake rats.

heart; contractile proteins


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