A technique to estimate the rate of whole body nitric oxide formation in conscious mice

Abstract

Objective. We have established a technique to estimate the total rate of nitric oxide (NO) formation in mice, based on inhalation of a stable oxygen isotope ( 18O 2). Changes of NO production with age were also studied. Methods. The experiments were performed in eight-week- ( n=6) and eight-month-old ( n=6–7), respectively, female (C57/Bl6 × CBAca) mice. Pairs of conscious mice were kept in an air-tight closed system allowing breathing of a mixture containing 18O 2. The 18O 2-technique was validated by l-NAME (10 mg/kg) and lipopolysaccharide (LPS, 8 mg/kg) administration. The concentrations of O 2 and CO 2 in the system were controlled and plasma nitrate analyzed by GC/MS technique. Results. NO formation was similar in young and old mice (young=7.68 ± 1.47 vs. old = 6.25 ± 1.49 μmol/kg/h, n.s.). Total NO production was reduced after l-NAME treatment in young animals by 91% and in old animals by 71% ( p<0.05 for both), whereas LPS administration increased NO production (114 ± 17%, p<0.05). Conclusion. NO formation is unaltered with age in mice. The 18O 2-technique is a valid and specific technique to estimate whole body NO production in conscious mice.