Age-related changes in ADMA–DDAH–NO pathway in rat liver subjected to partial ischemia followed by global reperfusion

Abstract Background Liver function is affected during ischemia/reperfusion (IR). We evaluated the effect of the aging process on selected parameters determining the NO level in rat liver subjected to IR. Methods The animals were divided into the C-2 and the IR-2 group of young rats (2–4 months old) and the C-12 and the IR-12 group of older rats (12–14 months old). Livers belonging to the IR-2 and the IR-12 group were subjected to partial ischemia (60 min) and reperfusion (4 h). Blood samples were obtained after surgeries to estimate the activity of aminotransferases, as well as just before ischemia and during reperfusion (15, 120, and 240 min) to estimate concentration of arginine (Arg) and its derivatives: asymmetric and symmetric dimethylarginine (ADMA, SDMA). After IR, dimethylarginine dimethylaminohydrolase (DDAH) activity and protein concentration of inducible nitric oxide synthase (iNOS) were measured in liver homogenates. Results In the IR-2 group ADMA level increased the most between 15 and 120 min of reperfusion and was the highest of all the groups (0.72 ± 0.2 μmol/l). In the IR-12 group ADMA level decreased significantly and was lower compared to all the other groups at 15 min (0.42 ± 0.2 μmol/l) and to IR-2 at 120 (0.52 ± 0.1 μmol/l) and 240 min (0.38 ± 0.1 μmol/l) of reperfusion. Only the IR-2 group SDMA level increased significantly between 15 (0.75 ± 0.9 μmol/l) and 240 min (1.0 ± 1.2 μmol/l) of reperfusion. At the beginning of the surgery the Arg level was significantly higher in young rats (C-2: 102.1 ± 35.7 μmol/l; IR-2: 114.63 ± 28.9 μmol/l) than in older ones (C-12: 41.88 ± 44.7 μmol/l; IR-12: 28.64 ± 30.6 μmol/l). In the C-2 group the Arg level (77.41 ± 37.5 μmol/l) and Arg/ADMA (A/A) ratio (138.03 ± 62.8 μmol/l) were significantly higher compared to the ischemic groups at 15 min and to all the other groups at 120 (Arg: 47.17 ± 31.7 μmol/l; A/A: 88.28 ± 66.2 μmol/l) and 240 min (Arg: 43.87 ± 21.9 μmol/l; A/A: 118.02 ± 106.3 μmol/l). In the IR-2 group Arg level (11.4 ± 12.0 μmol/l) and A/A ratio (16.11 ± 16.2 μmol/l) decreased significantly at 15 min and during the next phase of reperfusion the levels of those parameters were low, comparably to those in IR-12. As a result of IR, a decrease in DDAH activity and an increase in iNOS protein concentration were observed only in the young rats. Conclusions We found that in the non-ischemic groups the Arg level may be affected by the aging process. Under IR conditions, important changes in DDAH–ADMA–NO pathway were observed only in young livers.