HIGH GLUCOSE ENHANCES GROWTH FACTOR-STIMULATED NITRIC-OXIDE PRODUCTION BY CULTURED RAT MESANGIAL CELLS

Nitric oxide (NO) contributes to the alterations in glomerular hemodyn amics and extracellular matrix accumulation observed in diabetic nephr opathy. High glucose concentrations directly inhibit NO production by rat mesangial cells (RMC). However, the role of peptide growth factors and chemokines in regulating NO synthesis by RMC under normal and hig h glucose conditions has not been studied. Therefore, we examined the effect of IGF-I, EGF, TGF-beta, and RANTES on NO production by RMC mai ntained in normal (5.6 mM) or high glucose (33.3 mM) for 48 h. NO synt hesis was determined by measuring nitrite accumulation in conditioned media with the Greiss reaction. In normal glucose media, IGF-I, EGF, a nd RANTES had no effect on nitrite accumulation while TGF-beta inhibit ed NO synthesis. In high glucose conditions, IGF-I and EGF significant ly enhanced NO production. The effects of RANTES and TGF-beta were unc hanged by an elevated glucose concentration. EGF-induced stimulation o f NO production in high glucose media was associated with parallel alt erations in iNOS gene and protein expression. The modest enhancement i n nitrite accumulation provoked by IGF-I in high glucose conditions wa s not accompanied by demonstrable increases in iNOS mRNA abundance or protein content. In conclusion, peptide growth factors modulate the di rect inhibitory effect of high glucose on NO production by cultured me sangial cells. These actions in vivo may limit the adverse consequence s of reduced NO production in promoting diabetic nephropathy.