Resumo

Introduction: Adenosine receptor subtype 2a (A2aR) plays a modulatory role in the central nervous system participating in several physiological processes. One brain area where A2aR can be found is the nucleus tractus solitarii (NTS), which is located at the dorsal portion of medulla oblongata. The NTS is an important center for cardiovascular control and other autonomic functions. Hypertension is a multifactor disease that can be triggered by central mechanisms, such as inappropriate modifications of neurotransmitter systems. The goal of this study was first to determine the A2aR profile by means of binding, protein and mRNA expression analysis from the medulla oblongata of newborn spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY), and subsequently, to establish a comparison with A2aR profile in cultured cells to evaluate possible differences between those two experimental models. Methods: All the procedures and protocols were performed in accordance with the Institutional Guidelines for Animal Experimentation (CEA/IB-USP protocol number 065/2008). Tissue samples were dissected from medulla oblongata of one-day old WKY and SHR, and submitted to protein (n=3) and RNA extraction (n=3) to evaluate A2aR protein and mRNA, and also sectioned in a cryostat (n=4) to evaluate A2aR binding. Cell culture was performed using the same area from the experiment mentioned above and submitted to binding, western blotting and real time -PCR, to evaluate A2aR binding, protein and mRNA levels. All data were evaluated by Student`s t-test. Results: Data are expressed as value ± standard error. We observed that SHR (9.62±1.31) medulla oblongata sections presented a decrease in selective A2aR agonist [3H] CGS 21680 binding when compared to the WKY (14.95±1.1). Furthermore, A2aR protein level (SHR3.53±0.15; WKY2.25±0.13) and mRNA expression (SHR1.57±0.09; WKY1.0±0.01) in tissue samples from dorsal medulla oblongata were increased in SHR as compared to WKY rats. SHR and WKY cell cultures demonstrated similar A2aR profile when compared to the tissue sample. SHR cells (SHR7.1±0.6; WKY32.3±0.3) presented a decreased A2aR binding and an increased protein (SHR3.3±0.5; WKY2.5±0.3) and mRNA expression (SHR1.7±0.4; WKY1.0±0.01) compared to the WKY cells. Adenosine A2a receptor binding, protein level and mRNA expression have different profiles in hypertensive and normotensive strains, observed in tissue and cell culture of the medulla oblongata (p<0.05). Discussion: The present study demonstrated physiological differences in A2aR binding, protein and mRNA levels in the medulla oblongata between newborn SHR and WKY rats. In addition, we demonstrated that at least for the A2a receptor both methodologies presented the same profile, which validated the cell culture experimental model for in vivo studies of A2aR. This study was supported by grants from FAPESP, CAPES and CNPq.