Involvement of phosphatidylinositol 3-kinase (PI3K), mitogen-activated protein kinase kinase (MEK)-1 and p38-kinase in leptin/IL-1-induced nitric oxide synthase (NOS). Dose-dependent effect of (a,a1) LY294002, (b,b1) PD098059 and (c,c1) SB203580 on nitrite (NO2-) production and NOS type II protein expression in stimulated and unstimulated ATDC5 cells. Stimulations were conducted in serum-free conditions. Each inhibitor was added 1 hour before cytokine co-stimulation. Values are expressed as mean ± standard error of the mean. OB, leptin; WB, western blot.