Effect of arginase inhibitor nor-NOHA on cell proliferation. (A) Proliferation of CL-2, CL-19 and Renca cells was assessed by [3H]-thymidine incorporation at 24, 48, and 72 hours in culture. At 72 hours, the growth rates for CL-19 and Renca cells were significantly greater than CL-2 (* P = 0.009 and ** P = 0.003 respectively). (B) nor-NOHA (2 mM) and [3H]-thymidine were added at the same time and cell proliferation was determined at 24, 48, and 72 hrs. Cultured cells without the inhibitor were used as controls. Only CL-19 proliferation was significantly inhibited (* P = 0.010) compared to the untreated control cells. Results are expressed as CPM means ± SE of triplicate determinations from five independent experiments.