Free amino-nitrogen exchange across the hindquarters of fed and fasted sheep and pigs

Abstract

SUMMARYFree amino·N estimations were used to monitor the movement of free amino acids in blood passing through the hindquarters of sheep and growing pigs. The net uptakeor release of free amino·N was calculated from arterio-venous differences in the concentration of free amino·N measured in whole blood and plasma at short intervals of time.In both species the net change was an apparent release of free amino·N into venous blood. The release increased on fasting. Net uptake of free amino·N from blood was occasionally found at single sampling times due to loss from the cell compartment in sheep and from the plasma compartment in pigs. The uptake measured in whole blood was always less than in a single compartment of blood. The greatest fluctuation in free amino·N concentration occurred in the cells of aorta blood.It is concluded that both blood cells and plasma have independent roles in the net flux of free amino·N requiring determinations of amino acids in both whole blood and plasma to describe the exchange of blood free amino acids with tissue. A negative arteriovenous difference of free amino·N in blood across skeletal muscle is normal for healthy well-fed animals. Fasting increases the negativity.