Induction of nitric oxide synthase and interleukin-1β, but not heme oxygenase, messenger RNA in rat brain following peripheral administration of endotoxin

Previous studies have suggested that both nitric oxide (NO) and carbon monoxide (CO) are important modulators of the inflammatory response, while more recent data have implicated both gases as regulators of hypothalamic neuroendocrine function, particularly the hypothalamo-pituitary-adrenal axis. We have, therefore, investigated the modulation of the transcripts for the synthetic enzymes for both NO and CO following the intraperitoneal administration of lipopolysaccharide, serotype B5 055, over the course of 24 h. The mRNA for type I or neuronal nitric oxide synthase (nNOS), and type II or inducible (iNOS), and heme oxygenase, ('inducible') and heme oxygenase, ('constitutive'), were reverse transcribed to cDNA, amplified by the polymerase chain reaction, and then quantified using a co-amplified internal standard, β-actin. This allowed for assessment of relative changes in transcript concentration. In addition, these were compared to changes in expression of the cytokine, IL-1β. Finally, absolute levels of the synthetic enzyme transcripts were assessed by means of co-amplification in the presence of varying amounts of mutant templates in a competitive PCR reaction. Our data revealed rapid induction of IL-1β, iNOS and HO₁ in the liver, returning to baseline at 24 h. In the hypothalamus, all transcripts were present under basal conditions, but only IL-1β and iNOS were induced by the LPS. We conclude that hypothalamic IL-1β and iNOS can be induced by a non-lethal dose of endotoxin, and are, thus, in a position to mediate certain of the neuroendocrine consequences to inflammatory stress.