714 L. L. MILLER 
plasma amino acids at the end of the experiment. In such experiments we have 
previously alluded to the fact that the total free a-amino acid nitrogen of the per- 
fusion blood is maintained relatively constant for the first 2 or 3 h of the perfusion 
and then increases somewhat in the 5th and 6th h (see Fig. 12)% 18. 
In such experiments, although no amino acids are added to the perfusion mixture, 
there is a continuous, essentially linear production of urea®, 8 and maintenance or 
small increase in the total a-amino acid nitrogen level of circulating perfusing blood. 
Fig. 14 reveals that in such liver perfusions there has probably been a quantitative 
redistribution with an enhancement of the leucine-isoleucine and valine content. It 
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- 
— 
a — ~~ es 
339-0 
Fig. 13. Comparison of paper chromatograms prepared from free amino acid concentrates of 
plasma specimens taken at o and 5 h from isolated rat-liver perfusion. Liver donor, normal male 
Wistar rat (weight, 378 g); liver weight, ro.1 g; blood volume, 199 ml; standard complete amino 
acid mixture with glutamic acid replaced by an equal weight of glutamine!® and 500 mg glucose 
added at the outset of experiment. Duration of experiment, 5 h. For this and subsequent chro- 
matograms, equal volumes of plasma were precipitated with 10 vols. of 5% trichloroacetic acid. 
The clear filtrate was extracted with ether to remove excess trichloroacetic acid and the resulting 
aqueous solution concentrated in vacuo almost to dryness at 40°. The residues were taken up in 
a total volume of 1 or 2 ml of water and after thorough mixing, equal aliquots of the initial and 
final plasma free amino acids were placed at the origin of the chromatograms. 
References p. 721 
