Estudo farmacológico dos receptores purinérgicos de átrios de ratos normotensos e espontaneamente hipertensos

• Autor(a) principal: Rodrigues, Juliano Quintella Dantas [UNIFESP]
• Data de Publicação: 2016
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UNIFESP
• dARK ID: ark:/48912/001300000gxpd
• Texto Completo: https://sucupira.capes.gov.br/sucupira/public/consultas/coleta/trabalhoConclusao/viewTrabalhoConclusao.jsf?popup=true&id_trabalho=4542305; http://repositorio.unifesp.br/handle/11600/48564
• topic: Hipertensão; Receptor purinérgico; Noradrenalina

Hypertension is a disease that presents a high prevalence and mortality. In its genesis have been described a dysfunction of sympathetic neurotransmission. The sympathetic nervous terminal, in addition to noradrenaline, releases the neurotransmitter ATP, which activates the purinergic receptors and modulates cardiac function, per se or through its metabolite adenosine. Therefore, the hypothesis of this study was that functional alterations in the P1 (A1, A2A, A2B, and A3) and P2 (P2X and P2Y) purinergic system may be related to the cardiac dysfunction observed in hypertension. Thus, this work aimed to study the chronotropic action of adenosine on the right atrium and identify which purinergic receptors are responsible for the biphasic inotropic effect of ATP on the left atrium of hypertensive animals. We use the right atrium to investigate the cardiac chronotropism because contains the sinoatrial node, primary pacemaker of the heart, of male normotensive Wistar rats (NWR) and spontaneously hypertensive rats (SHR). Our results show that adenosine, an endogenous non-selective agonist of P1 receptors and the CPA, a selective agonist of A1 receptors, decreased the atrial chronotropism of NWR and SHR in a concentration dependent manner, culminating in cardiac arrest (0 bpm). The negative chronotropic effects of both adenosine and CPA are potentiated on the right atrium of the SHR. Our results also showed that the simultaneous incubation of the selective antagonists of A2 (ZM241385) and A3 (MRS1523) receptors did not alter the chronotropic response of adenosine, suggesting an exclusive role of the A1 receptor. These results are corroborated by the fact that DPCPX, a selective A1 antagonist, inhibits the action of CPA in the right atria of both strains. Pre-incubation of the right atrium with pertussis toxin, which inactivates Gi protein subunit ?, reduced by 80% the negative chronotropic effects of adenosine only on the right atrium of NWR. This inhibitory effect of PTX was not observed in SHR atrium, suggesting there is a dysfunction in the Gi protein pathway. Furthermore, our results showed the involvement of phospholipase C ? (P C ?) and AC enzymes in A1 receptor signaling on the right atrium of NWR and SHR, because the negative chronotropic effect of CPA was potentiated by the PLC ? inhibitor, U73122, and blocked by the AC inhibitor, NKY80 To investigate the ATP inotropic effect, we used left atria preparations of adults NWR and SHR, submitted to transmural electrical stimulation (2 Hz, 5 ms). Our results shown that ATP promoted biphasic inotropic effect on atria of both strains: an initial negative inotropic effect followed by a subsequent positive inotropic effect. On the left atrium of both NWR and SHR, the negative inotropic effect of ATP was related mainly to the direct activation of A1 receptors excluding the participation of its metabolite adenosine. Compared with NWRs, the negative inotropic responses of ATP on the atria were lower and the positive inotropic responses of ATP were higher in SHRs. Furthermore, suramin, a non-selective antagonist of P2 receptors, abolished the positive inotropic effect of ATP on the left atria of NWR and SHR. Also, in both strains, the selective agonist of P2X2 and P2X3 receptors ?-?-Me-ATP (100 µM) only increased the inotropism of left atrium, mimicking the positive inotropic effect of ATP. Our data also show that the positive inotropic effect of ATP does not depend on the release of noradrenaline by the sympathetic nerve terminal because the pre-incubation of propranolol, beta blocker, on left atria in both strains did not change the positive inotropic effects of ?-?-Me-ATP or the ATP. However, pretreatment of left atrium with 6- hydroxydopamine, that promotes the chemical denervation of the sympathetic nerve terminal, completely abolished the positive inotropic effects of ATP and ?-?-Me-ATP, in both NWR and SHR left atria. This result indicates that the positive inotropic response of ATP dependent of presynaptic components. Finally, the positive inotropic effect of ATP was potentiated in the presence of MRS 2179 (300 nM), P2Y1 receptor antagonist. This result suggests that the P2Y1 receptor is presynaptic and it has an inhibitory action. In summary, our results show that the negative chronotropic response of adenosine is enhanced on the right atrium of SHR, probably due to an increase in signal pathway of Gi protein. Furthermore the positive inotropic effect of ATP presents increased on the left atrium of the SHR, process are due to presynaptic effects on 6- hydroxydopamine-sensitive neurons in left atrium of NWR and SHR. These effects involve activation of facilitatory presynaptic P2X2R and P2X3R and inhibitory P2Y1R.