VASCULAR-RESPONSES TO STIMULATION OF CAROTID, AORTIC AND CORONARY-ARTERY BARORECEPTORS WITH PULSATILE AND NON-PULSATILE PRESSURES IN ANESTHETIZED DOGS

This research was designed to compare coronary, carotid and aortic arc h baroreceptors in terms of the ranges of pressures required to elicit reflex vascular responses and the possible differences between the re sponses to pulsatile and non-pulsatile stimuli. Dogs were anaesthetize d with alpha-chloralose, artificially ventilated and the chests opened wide. A perfusion circuit allowed independent control of pressures di stending the three baroreceptor regions. A cardiopulmonary bypass and ventricular fibrillation prevented cardiac pulsations from influencing coronary baro-receptor pressure. The caudal region of the animal was perfused at constant flow and vascular resistance responses were asses sed from changes in perfusion pressure. Only tests in which the overal l response exceeded 3 kPa (22.5 mmHg) were analysed. Reflex responses were obtained to significantly lower coronary pressures than were requ ired to induce responses from other regions. The inflexion points of t he stimulus-response curves for pulsatile coronary, carotid and aortic pressures were 10.5 +/- 0.6, 15.5 +/- 1.8 and 16.4 +/- 1.7 kPa (79 +/ - 5, 116 +/- 14 and 123 +/- 13 mmHg, respectively; values are means +/ - S.E.M.). When the responses to pulsatile stimuli were compared with those to non-pulsatile stimuli, it was noted that for the carotid rece ptors, lower pressures were required to induce responses (inflexion pr essure less) and the slope of the stimulus-response curve was less. Pu lsatile aortic pressures induced a parallel (downward) displacement of the curve but no change in inflexion point or slope. The coronary bar oreceptor stimulus-response relationship was unaffected by pulsatility . These results show differences between the characteristics of the th ree baroreceptors with coronary receptors being unaffected by pressure pulsatility but likely to be of importance in hypotensive situations.