Tissue-specific differences in insulin binding affinity and insulin receptor concentrations in skeletal muscles, adipose tissue depots and liver of cattle and sheep

Abstract

AbstractDifferences in insulin binding affinity and in concentrations of insulin receptor, were found in a variety of tissues taken, at slaughter, from mature steers (701 (s.d. 23) kg) and growing lambs (47 (s.d. 2·1) kg). In both species, liver had lower insulin binding affinity than skeletal musclesm. pectineus m. longissimus dorsiandm. rectus capitis(allP< 0·001) and subcutaneous, omental and perirenal adipose depots (allP< 0·001). Site-specific differences in affinity for insulin existed between adipose depots (subcutaneous < omental,P< 0·05; subcutaneous < perirenal,P< 0·001) and between tissue-types (subcutaneous fat <m. pectineusskeletal muscle,P< 0·05;m. rectus capitis< perirenal fat,P< 0·05) in steers. In lambs also, receptor affinity for insulin differed between tissue-type (m. longissimus dorsi< perirenal fat,P< 0·05;m. rectus capitis< subcutaneous fat,P< 0·05 andm. rectus capitis< perirenal fat,P< 0·001) but lambs did not show the adipose depot-specific differences in insulin affinity observed in steers. Insulin receptor concentration differed between adipose depots (subcutaneous < omental,P< 0·05; subcutaneous < perirenal,P< 0·01) and between tissue-type (m. pectineus< perirenal fatP< 0·05) in steers and perirenal and subcutaneous adipose depots of lambs had higher receptor concentrations thanm. longissimus dorsiandm. pectineusP< 0·001). This is the first study to demonstrate, in any species, differences in insulin receptor binding affinity and receptor concentration in a wide range of tissues (liver, skeletal muscles and adipose depots) from the same individual. Such differences in meat-producing animals could, through effects on tissue sensitivity and/or responsiveness to insulin, influence nutrient partitioning to tissues and affect overall rates of lipid storage and net protein synthesis.