Determining the cardiovascular effects of nitric oxide in the dorsolateral Periaqueductal Gray (dlPAG) in anaesthetised rats.

OBJECTIVE

The dorsolateral periaqueductal gray (dlPAG) is an area located in the brain stem that performs a host of functions including cardiovascular regulation. Owing to the presence of nitric oxide (NO) in this area, we investigated its effect on the cardiovascular system.

METHODS

We divided rats into four groups: 1) control; 2) l-arginine (L-Arg, a precursor for nitric oxide, 60 nmol); 3) l-NAME (N omega-nitro-l-arginine methyl ester, a nitric oxide synthase inhibitor, 90 nmol); and 4) sodium nitroprusside (SNP, a nitric oxide donor, 27 nmol). After anaesthesia, the rats were mounted on a stereotaxic apparatus and the drugs were microinjected into the dlPAG. Cardiovascular parameters were continuously recorded by a PowerLab system connected to the cannulated femoral artery via a pressure transducer. The changes (Δ) of systolic blood pressure (SBP), mean arterial pressure (MAP), and heart rate (HR) were calculated at different times as compared to the control group.

RESULTS

In the l-NAME group, the ΔSBP, ΔMAP, and ΔHR were not significantly affected compared to the control group. In the L-Arg group, ΔSBP and ΔMAP increased; however, only SBP showed a significant increase compared to the control group. In the SNP group, SBP and MAP were significantly affected in comparison to the controls. Additionally, ΔHR decreased in both L-Arg and SNP, but was only significant in L-Arg.

CONCLUSION

Our study showed that NO of dlPAG has a pressor effect and attenuates baroreflex bradycardia. However, its pressor effect is more significant.