Time course of lipopolysaccharide-induced nitric oxide synthase mRNA expression in rat glomeruli

The decrease in glomerular filtration rate that is characteristic of sepsis has been shown to result from the local glomerular inhibition of endotheli al nitric oxide synthase (NOS) by nitric oxide (NO) generated from the indu cible isoform of NOS (iNOS), iNOS activation depends on de novo synthesis o f both RNA and protein. Therefore it is assumed that several hours are requ ired for ifs full activation. Yet the renal hemodynamic response in sepsis has been documented as early as 60 minutes after lipopolysaccharide (LPS) a dministration. Experiments were designed to determine the time course of LP S-induced glomerular iNOS mRNA expression and activity in rats. Rats were t reated with LPS (2 mg/kg body weight rp), Kidneys were removed after 1, 2, 4, 6, and 16 hours. Glomeruli were isolated and incubated. Nitric oxide gen eration was measured with a Griess assay, and iNOS mRNA was studied by reve rse transcriptase-polymerase chain reaction. Similar time course experiment s were repeated in glomeruli isolated from normal rats and exposed to LPS i n vitro. A significant increase in iNOS mRNA expression was evident as earl y as 60 minutes after both in vivo and in vitro administration of LPS. The quantity of iNOS mRNA reached its peak between 2 to 4 hours after administr ation and declined to baseline levels after 16 hours. Immunohistochemical s tudies were remarkable for a significant increase in the staining for iNOS in glomeruli 2 hours after the in vivo administration of LPS, Plasma nitric oxide concentration after the in vivo administration of LPS increased from a baseline level of 11.25 +/- 0.8 mu mol/L to a peak level of 62.9 +/- 3.8 mu mol/L (P < .05 vs baseline) at 4 hours and then decreased to 17.5 +/- 1 .9 mu mol/L at 16 hours. Similar results were obtained when the glomerular generation of nitric oxide after in vivo administration of LPS was measured (2.6 +/- 0.8 pmol/h/mu g tissue, 17.2 +/- 2.1 pmol/h/mu g tissue (P < .05 vs baseline), and 0.4 +/- 0.65 pmol/h/mu g tissue, respectively). These res ults provide evidence of the rapid activation of glomerular iNOS after in v ivo and ex vivo administration of LPS and thus support the role of nitric o xide in the early renal hemodynamic response to LPS.