Metabolic hormones and tissue concentrations of mRNA for IGF-I in lines of sheep that differ in their protein synthesis response to feed intake

Abstract

The rate of protein synthesis in the skin and muscle of sheep that have been genetically selected for high wool staple strength (SS) is less dependent on the level of dietary intake than that of low SS sheep. This study examined potential hormonal mediators of this difference in responsiveness. Sheep from SS+ and SS-genotypes were fed at 0·4, 1·1 or 1·8 times maintenance. Circulating concentrations of metabolic hormones and tissue concentrations of the mRNA for IGF-I were measured and compared with rates of protein synthesis measured previously. Plasma concentrations of GH, insulin, cortisol, thyroxine and IGF-I responded similarly to dietary intake in both genotypes, but SS+ sheep had higher plasma concentrations of IGF-I at all levels of nutrition (P<0·05). There were no interactions between diet and genotype. The concentration of mRNA for IGF-I was higher in the liver of SS+ sheep (P<0·05), and tended to increase (P=0·06) with nutrient intake, but there were no significant effects of genotype or nutrition in skin, muscle or gut. Concentrations of mRNA for IGF-I were not related to the rate of protein synthesis in any tissue examined. It was concluded that IGF-I did not drive the rate of protein synthesis directly, but it may mediate the responsiveness of protein synthesis rate, or protein degradation rate, to nutrient supply.

Effects of field bean (Vicia faba L. var. minor) dietary supplementation on plasma thyroid hormones, insulin, insulin‐like growth factor‐1 concentrations and mohair characteristics in growing Angora goat kids

“…Circulating levels of total IGF-1 were not different between the two groups, while a positive correlation with the level of nutrition was previously reported in sheep (Bass et al, 1991;Adams et al, 2000;Pittroff et al, 2006) and goats (Magistrelli et al, 2005). It is noteworthy that dietary supplementations, with soybean, failed to induce a rise in plasma INS and IGF-1 in Merino rams, an effect which was observed with cowpea and lupin (Blache et al, 1996).…”

“…The main physiological role of insulin‐like growth factor‐1 (IGF‐1) produced by liver and other tissues is the stimulation of tissue growth and differentiation, including cell proliferation, migration and morphogenesis during the onthogenic development of hair follicles (Stenn et al., 1996; McElwee and Hoffmann, 2000). In sheep, systemic IGF‐1 levels are correlated with the nutritional level (Bass et al., 1991; Adams et al., 2000).…”