Relationship of Serum Immunoreactive Somatomedin-C to Dietary Protein and Energy in Growing Rats

Abstract

Protein-energy undernutrition has its most devastating consequences during growth. Postal somatic growth now appears to be regulated in large part by the somatomedins, a family of growth hormone-dependent peptide mitogens. This study, using growing rats as the model, was designed to determine the relationship between protein and energy intake and serum immunoreactive somatomedin-C. Four-week-old male Sprague-Dawley rats were fed ad libitum three levels of isoenergetic protein diets (5%, 10%, and 15% lactalbumin) at each of three levels of energy (ad libitum, 75% or 50% of ad libitum quantities). Dietary fat was held constant at 11.9% as cottonseed oil. At 5 weeks of age, serum somatomedin-C concentration was predominately influenced by the dietary protein and increased linearly as protein intake increased from 5% to 15%. at 6, 9, and 12 weeks of age, serum somatomedin-C concentration was influenced by both protein and energy intake, although protein intake appeared to be the more important variable. Serum somatomedin-C was highly correlated with both body weight (r = 0.84, P less than 0.001) and tail length (r = 0.74, P less than 0.01). These results indicate that measurement of immunoreactive somatomedin-C provides a valuable biochemical index of protein-energy nutriture.

Reduction of Serum Insulin-like Growth Factor-I by Dietary Protein Restriction Is Age Dependent

“…The changes in IGF-I observed are attributable primarily to the dietary protein deprivation, because the energy intakes of protein-restricted rats were equivalent to controls. Our observations agree with the results of Prewitt et al (6), which show that serum IGF-I in postweanling rats is influenced by dietary protein and that reduction of IGF-I has a linear relationship to the degree of protein restriction. The results obtained are not due to nonspecific interference by IGF binding proteins in the RIA on unextracted serum, because similar changes were also observed when IGF-I was determined after separation from the binding proteins.…”

“…The GH-dependent peptide IGF-I is widely believed to be one of the principal stimulators of the cell proliferation that results in somatic growth (1). Regulated by food intake and nutritional status (2,3), serum concentrations of IGF-I are reduced by restriction of energy or protein (4)(5)(6). These reductions in IGF-I, which occur despite adequate serum GH concentrations, may be due to decreased liver GH receptors or postreceptor defects in GH action (4,7).…”

Glucose absorption, hormonal release and hepatic metabolism after guar gum ingestion

“…Nevertheless, the possible different protein binding capacities of IGF-1 as regards hepatic, arterial and portal blood should also be considered even if every precaution as indicated by Daughaday and Rotwein (1989), has been taken in the sample preparation for IGF-1 radioimmunoassay. The lower IGF-1 plasma concentrations and splanchnic production after ingestion of guar gum was in agreement with the sensitivity of IGF-1 secretion level to the nutritional status observed in man, calf, rat and pig (Prewett et al, 1982;Isley et al, 1983;Coxam et al, 1989;Buonomo and Baile, 1991 Moreover, it was the result of the previous adaptation to guar gum diet and not an acute effect.…”

The effect of growth hormone treatment on growth in zinc deficient rats

“…Nutritional variables may be equally as important as GR in regulating IGF-I levels (Furlanetto, 1990). protein and/or energy restriction has been shown to depress IGF-I levels in rats (Phillips and Young, 1976;Priee et AL., , 1979;Prewitt et al, 1982) and in humans (Isley et al, 1983;Clemmons et al, 1985). In these nutritional insults, the mechanism(s) for the depression of IGF-I have not been a simple decline in circulating GH levels.…”