Time course of allergen induced nitric oxide synthase mRNA expression in mice model of anaphylaxis

Abstract

Rationale The inducible isoform of nitric oxide synthase (iNOS) was implicated in the pathogenesis of anaphylaxis. iNOS activation depends on de novo synthesis of both RNA and protein. Therefore it is assumed that several hours are required for its full activation. Yet the hemodynamic response in anaphylaxis has been documented as early as minutes after allergen exposure. Experiments were designed to determine the time course of allergen induced iNOS mRNA expression and activity in mice model of anaphylaxis. Methods BALB/c mice were actively sensitized and challenged by ovalbumin to induce anaphylaxis. Tissues were removed and blood was drawn in different time points during 16 hours after the induction of anaphylaxis. Nitric oxide generation was measured with a Griess assay, and lung and heart iNOS mRNA was studied by reverse transcriptase-polymerase chain reaction. Results A significant increase in lung and heart iNOS mRNA expression was evident as early as 10 minutes after allergen challenge. The quantity of iNOS mRNA reached its peak (p<0.05 vs baseline) between 30 to 60 minutes after challenge and declined to baseline levels after 4 hours. Plasma nitric oxide concentration after the allergen challenge increased from a baseline level of 26.2 ± 1.8 micromol/L to a peak level of 78.6 ± 3.8 micromol/L (p<0.05 vs baseline) at 30 minutes and then decreased to 22.7 ± 1.9 micromol/L at 16 hours. Discussion These results provide evidence of the rapid activation of iNOS after induction of anaphylaxis by allergen challenge and thus support the role of nitric oxide in the early hemodynamic response in anaphylaxis.