Phenylalanine Metabolism in Sheep Infused With Glucose Plus Insulin. I. Effects on Plasma Phenylalanine Concentration, Entry Rate and Utilization by the Hindlimb

Experiments were conducted with chronically catheterized sheep to study the relationships between plasma phenylalanine concentration, entry rate (determined with 3 H-phenylalanine), and utilization by the hindlimb during infusions of either saline (S) or glucose plus insulin (G+I). Infusions of G+I approximately doubled (P < 0.10) plasma insulin concentrations but maintained glucose concentrations similar to S-infused animals. Phenylalanine concentrations and entry rates decreased (P < 0.10) with G+I infusions. Phenylalanine arteriovenous differences and net plasma exchange across the hindlimb (arteriovenous differences multiplied by plasma flow) were not affected by treatments. However, the rates of plasma 3 H-phenylalanine removed by the hindlimb were greater (P < 0.10) in G+I (17 μmol h −1 kg 0.75 ) than S (9 μmol h −1 kg 0.75 ) treated animals. These rates of hindlimb removal accounted for 26 and 10% of the phenylalanine entry rate, respectively. These data indicate that although G+I infusions decreased plasma phenylalanine concentrations and entry rates, a greater proportion of the entry rate was utilized by the hindlimb in G+I than in S sheep.