Analysis of a five-compartment system with continuous infusion and its application to the study of amino acid turnover

✍ Scribed by M.R. Aub; J.C. Waterlow

• Publisher: Elsevier Science
• Year: 1970
• Tongue: English
• Weight: 351 KB
• Volume: 26
• Category: Article
• ISSN: 0022-5193
• DOI: 10.1016/s0022-5193(70)80015-7

✦ Synopsis

An analysis has been made by matrix methods of the behaviour of a five-compartment system in which tracer is infused at a constant rate into the central compartment. This model has been used to interpret results obtained on serum, liver and muscle in rats receiving a constant intravenous infusion of [U-l*C]lysine. The five compartments correspond to the free lysine pools of serum, liver and muscle and the protein pools of liver and muscle. When rate constants determined experimentally are inserted in the equations, it is shown that for the first few hours of infusion the specific activities in the five-pool model are virtually identical with those given by a three-pool model in which there are irreversible "leaks" of labelled lysine from the free lysine pools into the protein pools. It follows that in short experiments (less than ten hours) re-entry of labelled amino acid from the breakdown of labelled protein can be neglected without significant error. The specific activities of free lysine in serum, liver and muscle rapidly reach a quasi-plateau. The plateau specific activity is not the'same in all three compartments, and is highest in serum. From the relative specific activities at plateau it is possible to calculate the extent to which intracellular lysine is derived from the breakdown of protein. The results showed that in liver 37~ and in muscle 12Yo of lysine entering the intracellular pool was derived from protein catabolism. In the steady state these values also represent the extent to which, within each tissue, amino acids are reutilized for protein synthesis. If a steady state is assumed, and if the pool sizes, the plateau specific activities, and any one pair of rate constants are determined experimentally, all the rate constants of the system can be calculated.