708 DYNAMIC ASPECTS — AMINO ACID POOL TURNOVER 
THE ROLE OF THE LIVER AND JHE NON-HEPATIC TISSUES 
IN THE REGULATION OF FREE AMINO ACID LEVELS 
IN THE BLOOD 
LEON L. MILLER 
Departments of Radiation Biology and Biochemistry, School of Medicine and Dentistry, 
University of Rochester, Rochester, N.Y. (U.S.A.) 
It is the purpose of this report to describe observations made with the isolated rat- 
liver perfusion technique and with the eviscerated surviving rat in connection with 
the metabolism of the amino acids. 
In the first part of this paper, studies are described in which “C-labeled amino 
acids were used from which it will become apparent that the liver plays an important, 
but not exclusive, role in the oxidation of all of the amino acids, and that the essential 
amino acids histidine, lysine, arginine, methionine, threonine, phenylalanine and 
tryptophane are almost exclusively oxidized by the liver. Further, it will be seen 
that the non-hepatic tissues are fully as capable as the liver of oxidizing a large 
group of amino acids, including leucine, isoleucine and valine. 
The second portion of this report will deal with the changes produced in the plasma 
amino acids in the course of isolated rat-liver perfusion, and these changes will be 
compared briefly with the amino acid picture seen in the plasma of the eviscerated 
surviving rat. Here it will be emphasized that not only is the liver concerned with 
the oxidative destruction of excessive quantities of a variety of amino acids but it is 
also concerned with the active production or release of amino acids serving to main- 
tain blood levels above minimum values. These latter observations, based originally 
upon paper-chromatographic procedures, have been extended and refined more 
recently by the application of the automatic amino acid analyzer technique of 
MOORE, SPACKMAN AND STEIN}. 
METHODS 
Before discussing these experiments, some reference should be made to the isolated 
rat-liver perfusion technique as it has been developed in our laboratories. The 
operative procedure and the properties of the isolated rat liver in the perfusion have 
been described in some detail? 3.The apparatus used is diagrammed in Fig. 1. The 
glass components readily made from commonly available standard laboratory glass- 
ware are now commercially available* as is also the stripping action pump originally 
described by Crisp AND DE BroskeE‘. The system developed in our laboratories 
allows sampling of blood, expired COg, and the liver without interrupting the course 
of an experiment. 
The criteria of the functional vitality of the isolated perfused liver have been 
discussed elsewhere?. 
* Blaessig Glass Specialties, 645 Atlantic Avenue, Rochester 9, N.Y. (U.S.A.). 
References p. 721 
