IGF-I receptors in embryonic skeletal muscle of three strains of chickens selected for differences in growth capacity.

IGF-I receptors in embryonic skeletal muscle from three strains of chickens have been characterized. Specific receptors for IGF-I were present in breast and thigh skeletal muscle of 13 d chicken embryos. Dissociation rate constants (Kd) for breast muscle of a slow growing layer strain (Leghorn), an intermediate growth strain (Synthetic Whiterock), and a fast growing broiler strain (Cornish) were 3.24, 3.04, and 2.68 nM, respectively. Kd for the thigh muscle of the slow, intermediate and fast growing strains were 3.30, 2.90 and 3.29 nM, respectively. Kd values were not significantly different between strains or between tissues (p greater than .05). Receptor concentration (Bmax) in breast muscle of slow, intermediate and fast growing strains were 1.22, 1.08 and 0.92 pM/mg protein, respectively. Receptor concentration in thigh muscle of the slow, intermediate and fast growing strains were 0.95, 0.76, and 0.79 pM/mg protein, respectively. Bmax values were significantly different (p less than .05) between breast muscle (1.08 +/- .05 pM/mg protein) and thigh muscle (.84 +/- .05 pM/mg protein). IGF-I receptor number for breast muscle although not statistically significant (p greater than .05), indicated a trend towards differences between the slow growing Leghorn strain and the faster growing Cornish strain. The results suggest that strains of birds with different growth capacity may have different densities of IGF-I receptors in breast skeletal muscle plasma membranes.