Effects of urea ((a) and (b)), creatinine ((c) and (d)), and iron ions Fe³⁺ ((e) and (f)) on respiratory burst of peritoneal phagocytes. Dose-response curves showing the intensities of respiratory burst calculated from AUC values for nonprimed ((a), (c), and (e)) and LPS-primed (100 ng/mL, 20 min; (b), (d), and (f)) cells. Cells were exposed to tested agents for 30 min prior to CL measurements. Results are given as mean ± SEM relative to controls on the basis of five independent experiments.