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 ∆MAP and ∆HR were also compared with those in the control group (independent sample t test).

Results: ∆MAP with both doses of L-NAME (30: P=0.026 and 90: P=0.007) and ∆HR with the higher dose (P=0.034) were significantly higher than those in the control group. Maximal ∆MAP with both doses (P<0.01 and P<0.001, n=10) and maximal ∆HR 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). ∆MAP and ∆HR 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 (∆MAP: P<0.01 and ∆ HR: P<0.05, n=7).

Conclusion: Our results showed that the nitrergic system of the CnF had an inhibitory effect on central cardiovascular regulation.