Resumo

Introduction: Adenosine, in the nucleus tractus solitarii (NTS), acts as a potent modulator of sympathetic activity, with a powerful modulatory action on cardiovascular control. Nitric oxide (NO) also plays an important role in cardiovascular control in the NTS by acting as a hypotensive agent. The relationship between NO and adenosine in the peripheral system is well established in the literature. However, this relation in the NTS is not explored. The goal of this study was to analyze the modulatory effect of A2a adenosine receptors on the mRNA of the enzyme nitric oxide synthase (nNOS) in cultured brainstem cells of spontaneously hypertensive (SHR) and normotensive rats (WKY). Methods: All the procedures and protocols were performed in accordance with the Institutional Guidelines for Animal Experimentation (CEA/IB-USP). Cell cultures were made using the medulla oblongata of one-day old WKY and SHR. After 7 days in culture, cells were treated with the selective agonist for the A2a adenosine receptors (CGS 21 680 Sigma, St. Louis, USA) at three different concentrations (1µM, 10µM and 100µM) during the period of 6, 12 and 24 hours to assess the levels of nNOS mRNA. The mRNA was extracted after these periods, and stored at -80 º C for subsequent analysis by RT-PCR in real time. The data were analyzed by statistical test of multiple comparisons (ANOVA), followed by Dunnet post-test, where differences were found between treatments with the agonist and the respective controls (n = 3, P <0.05). Results: Results were expressed as fold-change ± standard deviation and compared to control WKY (1.00±0). The data for the period of 6h showed a significant increase in levels of mRNA for nNOS at concentrations of 1µM (1.33±0.06), 10µM (2.70±0.12) and 100µM (3.04±0.15) agonist selective for the WKY strain, while the results for the SHR showed a significant increases in levels of NOS mRNA only at concentrations of 10µM (0.68±0.11) and 100µM (0.98±0.03). Regarding the experiments related to the period of 12 hours, the treatment for the WKY strain resulted in a decrease in mRNA levels of nNOS enzyme in concentrations of 10µM (0.87±0.02) and 100µM (0.75±0.04), whereas in SHR there was only a significant decrease in concentration of 100µM (0.33±0.03). Finally, the analysis relating to treatment for 24h showed, for WKY, a significant increase in the levels of nNOS mRNA at all concentrations, 1µM (1.78±0.12), 10µM (1.86±0.12) and 100µM (2.67±0.11), whereas for SHR there was no significant difference between treated groups and control (1µM 0.15±0.11; 10µM 0.34±0.18; 100µM 0.46±0.17). Conclusion: This study suggests that stimulation of adenosine A2a receptor modulates mRNA levels of the enzyme nNOS, and this modulatory effect on different strains SHR compared to WKY animals. The interaction between these systems may be important for the development of hypertension in SHR. This study was supported by grants from FAPESP and CNPq.