Efeitos do ATP e dos receptores purinérgicos da área A5 na neurotransmissão do quimiorreflexo em ratos não-anestesiados

Abstract

The aim of this study was to evaluate the possible involvement of purinergic P2 receptors in the A5 area on arterial blood pressure and heart rate control and on cardiovascular responses to peripheral chemoreflex activation in non-anesthetized rats. We observed that the microinjection of α,β-methylene ATP [0.625 and 1.25 nmol/100nl - P2X receptor agonist) induced an increase in mean arterial pressure (+0.0±0.5 vs. +25±5 and +25±3 mmHg) and heart rate (+0.9±2 vs. +39±9 and +56±10 bpm) when compared to the effects induced by the vehicle (n=8, p<0.05). The pressor and tachycardia responses induced by α,β-methylene ATP (1.25nmol/100nl) were reduced (+33±6 vs. +14±5 mmHg and +70±11 vs. +27±13 bpm) by the previous microinjection of the P2 receptors antagonist, PPADS (Pyridoxal-phosphate-6-azophenyl-2’,4’-disulfonate - 0.5nmol/100nl). However, bilateral microinjection of PPADS (0.5nmol/100nl) in the A5 area produced no changes in pressor (+38±6 vs. +39±6; +43±4; +41±3; +40±2; +37±5 mmHg) and bradycardic responses (-253±8 vs. -237±25; -248±12; -250±17; -251±13 and 253±17 bpm) of the chemoreflex when compared with the control response (n=5, p>0.05). Similarly to the isolated blockade, the simultaneous blockade of purinergic P2 and ionotropic glutamate receptors by sequential microinjection of the antagonists PPADS (0.25nmol/50nl) and kinurenic acid (2nmol/50nl) in the A5 area of non anesthetized rats promoted no significant changes in pressor (+49±3 vs +41±4; +46±5; +47±4; +44±3, +47±4 mmHg) and bradycardic (-252±23 vs -259±28; 250±11; -268±11; -260±10; -259±14 bpm) responses of chemoreflex (n=6, p>0.05). Our results show for the first time that purinergic P2 receptors in the A5 area participate of blood pressure and heart rate control. However, the purinergicreceptors, alone or combined with ionotropic glutamate receptors, do not participate in the integration of cardiovascular responses of the chemoreflex in non-anesthetized rats.