322 E. ROBERTS AND D. G. SIMONSEN 
of these amino acids returned toward control levels as the glutamine content fell. 
The taurine level did not appear to be altered markedly during the experiment. 
The glutamic acid probably arose from the glutamine itself, since experiments with 
pL-(2-!@C]glutamine showed there to be a rapid cellular uptake of glutamine and a 
major conversion of the glutamine to glutamic acid*™* as well as rapid appearance of 
isotope in succinate, aspartate, glutathione, and pyrrolidone carboxylic acid. In the 
case of the other amino acids mentioned, the changes observed may possibly be 
attributed to the displacement of the amino acids from the cells and/or tissues into 
the fluid with a subsequent re-entry into the cells or removal from the fluid by the 
circulation when the content of glutamine fell. Rapid uptake and metabolism of 
glutamine has recently also been reported for Ehrlich ascites tumor cells*®. A more 
detailed exposition of the possible significance of glutamine in tumor metabolism is 
not germane to the present discussion and has been given elsewhere '. In contrast 
to the findings with glutamine, chromatograms of serial samples obtained after the 
injection of 50 mg of L-glutamic acid into a rat bearing the Yoshida tumor showed 
no evidence of uptake of glutamate by the tumor cells (Figs. 209-216). The glutamic 
acid level of the ascitic fluid fell rapidly after the injection, virtually none of this 
amino acid being detected in the fluid at the go-min period. Concentrations of the 
other amino acids detectable in the fluid were not altered perceptibly by the presence 
of large quantities of glutamic acid in the fluid, and no glutamine was detected. An 
experiment with pr-[2-“C]|glutamic acid was in agreement with the interpretation 
that glutamic acid does not enter the cells readily*4. Interestingly, the cytological 
observations suggested that the injection of glutamic acid had a slight but definite 
enhancing effect on the growth of the Yoshida sarcoma cells. The results with gluta- 
mine and glutamic acid are in keeping with the finding of a ready permeability to 
glutamine and a relative impermeability to glutamic acid of animal tissues in general**. 
Our interest was focused on a, y-diaminobutyric acid because of the intense 
accumulation of this substance by Ehrlich ascites tumor cells 1m vitro (see ref. 37 
for discussion). Under the latter experimental conditions almost all of the potas- 
sium is replaced by the amino acid and there is an entry of chloride and water 
causing the cells to swell. It was of interest to determine whether the extensive 
intracellular changes taking place during uptake of this substance would be associated 
with changes in content of any of the detectable ninhydrin-reactive constituents. 
Mice of the C57 black strain bearing the Ehrlich ascites tumor were injected intra- 
peritoneally with 20 mg of DL-a, y-diaminobutyric acid on the 5th day after trans- 
plantation of the tumor. Samples were taken at 5, ro and 20 min and 1, 2 and 24h 
after the injection (Figs. 217-230). Uptake of the amino acid into the cells occurred 
readily, maximal levels being attained at 1h (Fig. 225). At 24h (Fig. 229), traces, 
at most, of the diaminobutyrate were detected in the cells and none in the fluid 
(Fig. 230). Relatively large amounts of glutamic acid appeared in the ascitic fluid 
at 5 min (Fig. 220) after the injection, the levels decreasing progressively there- 
after. This amino acid was barely detectable in the control sample of ascitic fluid 
(Fig. 218). At rh (Fig. 225) an extraordinarily large amount of taurine appeared in 
the fluid and decreased in subsequent samples studied. Since neither the glutamic 
acid nor taurine levels of the tumor cells showed marked alteration during the course 
of the experiment, it is possible that release of these amino acids took place from 
tissues other than the tumor cells. With the exception of the presence of glutamine 
References p. 348/349 
