Effects of prostaglandins on baroreflex during reperfusion of the ischaemic myocardium.

Abstract

1. The present study was planned to: (i) determine whether the baroreflex control of heart rate (HR) and renal sympathetic nerve activity (RSNA) was attenuated during reperfusion of short-term ischaemic myocardium; and (ii) study whether blockade of prostaglandin synthesis with indomethacin reversed the inhibitory baroreflex. 2. Arterial pressure was lowered with intravenous sodium nitroprusside before coronary occlusion and 3 min after release of a 5 min occlusion of the left circumflex coronary artery in anaesthetized rabbits. The protocol was repeated 20 min after indomethacin (5 mg/kg, i.v.) or indomethacin vehicle (50 mmol/L tris(hydroxymethyl)aminomethane buffer, pH 8.4) treatment. In addition, this study was performed in a group of vagotomized rabbits. 3. Before indomethacin treatment, the slope of the mean arterial pressure (MAP)-RSNA relationship decreased from -3.3+/-0.77 to -2.01+/-0.69% change in RSNA/mmHg (P < 0.05) during reperfusion of ischaemic myocardium in intact rabbits. The decrease in the slope was reversed by administration of indomethacin. However, the decrease in the slope was not reversed by indomethacin vehicle. Furthermore, the reduction in the slope of the MAP-RSNA relationship during reperfusion of ischaemic myocardium was abolished in vagotomized rabbits. However, there was no inhibition of the slope of the MAP-HR relationship during reperfusion of ischaemic myocardium in either intact or vagotomized rabbits. 4. In conclusion, our data suggest that prostaglandins released by ischaemic myocardium can attenuate the baroreflex-mediated response of RSNA to lowered arterial pressure via vagal afferents during reperfusion of short-term ischaemic myocardium.