Effect of NAC and SCF on nitric oxide generation and hematopoietic colony formation. (A) Nitric oxide generation (measured in the form of nitrite) in J774 cells. J774 cells were incubated with H81.9 (10 or 100 μg/mL) with or without the addition of NAC (15 mmol/L) for 1 to 3 days. In J774 cells NO production triggered by H81.9 was significant at 48 and 72 hours (P < .01); results in the presence of NAC were not different from controls. (B) Effect of sin-1, alone or in combination with NAC or SCF on colony formation from canine LTMCs. Sin-1 (100 μg/mL), NAC (0.5 mmol/L), and SCF (100 ng/mL) were added to LTMCs weekly beginning at the time of recharging. CFU-GM in sin-1–treated cultures were lower than in controls at all timepoints (see Fig 3). NAC significantly protected colony formation at 2, 3, and 4 weeks (P < .01). SCF had a protective effect in weeks 1 and 2 (P < .01) but not at later points. Shown are the means ± SEM of three experiments expressed as percent of controls.