Reflex responses to stimulation of mechanoreceptors in the left ventricle and coronary arteries in anaesthetized dogs.

Abstract

SUMMARY1. Previous work has shown that physiological increases in mean aortic root pressure, which change the pressure in both the coronary circulation and the left ventricle, result in reflex vasodilatation. This study was undertaken to attempt to localize the reflexogenic area mainly responsible for the reflex.2. In anaesthetized, artificially ventilated dogs, cannulae connected to perfusion systems were inserted in the ascending aorta, left ventricular apex and left atrium. This allowed us to change the pressures in: (a) the aortic root including both the coronary arteries and the left ventricle; (b) aortic root and coronary arteries, at constant ventricular pressure; and (c) in the ventricle, with mean (although not pulse) aortic pressure constant. Aortic and carotid baroreceptors were perfused at constant pressure and reflex responses were determined from changes in perfusion pressures (flows constant) to a vascularly isolated hindlimb and to the remainder of the systemic circulation.3. Combined changes in mean aortic root (coronary arterial) and ventricular systolic pressures consistently resulted in decreases in perfusion pressures. A change in only mean aortic root (coronary arterial) pressure, with ventricular pressure constant, also resulted in decreases in perfusion pressures and these were only a little smaller than those to the combined stimulus. Changes in ventricular systolic pressure resulted in responses averaging only about 30 % of those to the combined stimulus.4. Setting mean aortic root or ventricular systolic pressures at different levels did not affect the responses to changes in pressures in the other region.5. These results show that physiological increases in pressure in the aortic root and coronary arteries, in the absence of changes in pressure in the left ventricle, cause reflex vasodilatation. The relatively small response occurring when ventricular pressure was changed could be due either to a contribution from ventricular receptors or to a change in the stimulus to coronary receptors resulting from changes in the ventricular or aortic pulse.6. We conclude that the reflex effects of increases in mean aortic root pressure are due mainly to stimulation of coronary arterial baroreceptors. MS 1970 J. K. A. AL-TIMMAN AND OTHERS

Afferent discharges from coronary arterial and ventricular receptors in anaesthetized dogs.

“…This response occurs in preparations in which the pressures distending aortic and carotid baroreceptors and the left atria are held constant (Challenger, McGregor & Hainsworth, 1987;Tutt, McGregor & Hainsworth, 1988;Vukasovic, Tutt, Crisp & Hainsworth, 1989;Al-Timman & Hainsworth, 1992). In the accompanying paper (Al-Timman, Drinkhill & Hainsworth, 1993), we showed that the responses were due mainly to changes in coronary pressure but responses did also occur to changes in ventricular pressure. Because of the likely influence of mechanical changes in the ventricle on coronary receptors as well as changes in the pulsatile stimulus to the receptors, we were unable to determine whether both stimuli were affecting the same, or different populations of receptors.…”

“…Using this technique we concluded that the vascular responses to the combined test (aortic root, coronary arterial and left ventricular systolic pressures) were due more to the increase in aortic and coronary pressures than to the change in ventricular systolic pressure. On average, the response to the coronary pressure test was over twice that to the ventricular pressure test (Al-Timman et al 1993). These findings raised several questions.…”

Convergence properties of solitary tract neurones driven synaptically by cardiac vagal afferents in the mouse

“…Al-Timman et al 1993;McMahon, Drinkhill & Hainsworth, 1996), and simultaneous central neurophysiological recordings have never been attempted. Finally, although probing the heart has been a method used in peripheral fibre recording studies to identify the receptive fields of cardiac afferents (see Introduction) it was not technically possible to do this while maintaining a central neuronal recording in the present study.…”

“…Finally, although probing the heart has been a method used in peripheral fibre recording studies to identify the receptive fields of cardiac afferents (see Introduction) it was not technically possible to do this while maintaining a central neuronal recording in the present study. It should be emphasized that intraventricularly injected chemical stimulants will have access to receptors within the myocardial tissues as well as coronary baroreceptors (Brown, 1965;Al-Timman et al 1993;McMahon et al 1996). Further, raising LVEDP will also elevate pressure in the left atrium and activate left atrial mechanoreceptors.…”

Cardiovascular control from cardiac and pulmonary vascular receptors

“…Increases in coronary pressure from 8 kPa (60 mmHg) induced vasodilatation. Reproduced with permission from Al‐Timman et al ().…”