Central opiate system regulation of baroreflex control of coronary conductance

Abstract

The central μ opiate agonist, fentanyl, causes a neurogenically mediated systemic vascoconstriction in both rabbit and man. The human coronary circulation may participate in this response, since myocardial ischaemia (ST segment depression on ECG) has been reported during fentanyl anaesthesia by Thomson et al. in a group of patients undergoing coronary artery bypass surgery. In dogs, fentanyl causes haemodynamic changes which are blocked by i.v. naloxone; there is also concommitant coronary vascoconstriction, which is prevented by prior infusion of alpha-adrenoceptor agents. In this study, central nervous opiate receptor stimulation effects on the gain of baroreflex control of coronary conductance, were examined in conscious dogs in experimental complete heart block and with ventricles paced; atrial rate was free to vary naturally. Circumflex flow was measured by Doppler flowmeter. Aortic pressure was raised by inflating a balloon in the descending thoracic aorta