EFFECT OF HYPERINSULINEMIA AND HYPERAMINOACIDEMIA ON MUSCLE AND LIVERPROTEIN-SYNTHESIS IN LACTATING GOATS

The experiment was carried out to clarify the roles of insulin and ami no acids on protein synthesis in fed lactating goats (30 days postpart um). Protein synthesis in the liver and various skeletal muscles was a ssessed after an intravenous injection of a large dose of unlabeled va line containing a tracer dose of L-[2,3,4-H-3]valine. The animals were divided into three groups. Group I was infused with insulin (1.7 mu m ol/min) for 2.5 h under glucose, potassium, and amino acid replacement . Group A was infused with an amino acid mixture to create stable hype raminoacidemia for 2.5 h. Group C animals were controls. The fractiona l synthesis rates (FSR) were 31.5 +/- 2.2, 6.5 +/- 0.4, 4.3 +/- 0.8, 4 .0 +/- 1.2, 3.9 +/- 1.2, and 3.6 +/- 0.4%/day (SD) in liver, masseter, diaphragm, anconeus, semitendinosus, and longissimus dorsi, respectiv ely, for group C. Neither hyperinsulinemia in group I nor hyperaminoac idemia in group A had an effect on FSR in the skeletal muscles. FSR in the liver was not affected by hyperinsulinemia but was stimulated by hyperaminoacidemia (+30%, P < 0.05). In contrast to previous experimen ts in which a labeled amino acid was constantly infused, this study re vealed a stimulating effect of amino acids on protein synthesis in the liver but not in skeletal muscles. As previously observed in studies with the constant-infusion method, insulin had no effect on protein sy nthesis.