Decrease in IL‐10 and increase in TNF‐ α levels in renal tissues during systemic inhibition of nitric oxide in anesthetized mice

Earlier, we demonstrated that the inhibition of nitric oxide synthase ( NOS ) by nitro‐ l ‐arginine methyl ester ( l ‐ NAME ) infusion increases the endogenous production of proinflammatory cytokine, tumor necrosis factor ( TNF ‐ α ). In the present study, we examined the hypothesis that inhibition of nitric oxide ( NO ) production leads to the suppression of interleukin ( IL )‐10 (anti‐inflammatory cytokine) generation which facilitates the enhancement of TNF ‐ α production endogenously. Using appropriate enzyme‐linked immunosorbent assay kits and immunohistochemical staining, the levels of IL ‐10 and TNF ‐ α in plasma (P) and in renal tissues (R) were measured in anesthetized mice (C57BL/6; ~10 weeks age; n  = 6/group) infused with or without l ‐ NAME (200  μ g/min/kg; i.v. for 2 h). Compared to vehicle‐treated control mice, l ‐ NAME ‐treated mice had a lower level of IL ‐10 (P, 0.3 ± 0.1 vs. 2.6 ± 0.6 ng/mL; R, 0.5 ± 0.1 vs. 3 ± 0.1 ng/mg protein) and a higher level of TNF ‐ α (P, 432 ± 82 vs. undetected pg/mL; R, 58 ± 7 vs. 6 ± 5 pg/mg protein). IL ‐10 protein expression, present mostly in the distal nephron segments in control mice, was markedly downregulated in l ‐ NAME ‐treated mice. Compared to control mice, TNF ‐ α expression increased 2.5‐fold in renal cortical sections (mostly in the distal nephron segments) in l ‐ NAME ‐treated mice. Coinfusion of a NO donor, S ‐nitroso‐ N ‐acetyl‐penicillamine ( SNAP ; 25  μ g/min/kg) with l ‐ NAME in a separate group of mice prevented these changes in IL ‐10 and TNF ‐ α induced by l ‐ NAME . IL ‐10 infusion (0.075 ng/min/g) in l ‐ NAME ‐treated mice markedly attenuated l ‐ NAME ‐induced increments in TNF ‐ α . Thus, these results demonstrate that NOS inhibition decreases endogenous IL ‐10 generation and thus, minimizes its immune downregulating action on the TNF ‐ α production in the kidney.