L-arginine, L-ornithine and L-glutamine levels. Tissue culture supernatants from CL-2, CL-19, and Renca cells were collected at 24, 48, and 72 hours. They were analyzed by HPLC after deproteinization with methanol and derivatization with OPA for (A) L-arginine and (B) L-ornithine and (C) L-glutamine. Standards of L-arginine, L-ornithine and L-glutamine in methanol were run with each experiment. Results are expressed as means ± SE of duplicate determinations from four independent experiments. (* P = 0.005. ** P < 0.0001 significant differences for CL-19 compared to the other cell lines).