Role of the Nitrergic System of the Cuneiform Nucleus in Cardiovascular Responses in Urethane-Anesthetized Male Rats

Background: The presence of nitric oxide (NO) in the cuneiform nucleus (CnF) has been previously shown. In this study, NG-nitro-L-arginine methyl ester (L-NAME) (an inhibitor of NO synthase), L-arginine (L-Arg) (a precursor of NO), and sodium nitroprusside (SNP) (a donor of NO) were microinjected into the CnF and cardiovascular responses were investigated. Methods: Seventy male rats were divided into 7 groups (n=10 each): 1) saline, 2 and 3) L-NAME (30 and 90 nmol), 4 and 5) L-Arg (20 and 60 nmol), and 6 and 7) SNP (9 and 27 nmol). After anesthesia, the femoral artery was cannulated and cardiovascular parameters were recorded using a PowerLab system. Time course changes in mean arterial pressure (ΔMAP) and heart rate (ΔHR) were calculated and compared with those in the control group (repeated measures ANOVA). Maximum ΔMAP and ΔHR were also compared with those in the control group (independent sample t test). Results: ΔMAP with both doses of L-NAME (30: P=0.026 and 90: P=0.007) and ΔHR with the higher dose (P=0.034) were significantly higher than those in the control group. Maximal ΔMAP with both doses (P<0.01 and P<0.001, n=10) and maximal ΔHR with the higher dose (P<0.01) were significantly higher than those in the control group. Changes in L-Arg with both doses were not significantly higher than those in the control group (P=0.26, n=8). ΔMAP and ΔHR of SNP only with the higher dose were significantly lower than those in the control group (P=0.006 and P=0.035), and maximal responses with the higher dose were lower than those in the control group (ΔMAP: P<0.01 and ΔHR: P<0.05, n=7). Conclusion: Our results showed that the nitrergic system of the CnF had an inhibitory effect on central cardiovascular regulation.