Development of a chronic sheep model for the study of regional coronary control mechanisms

We have previously shown in the dog that resting and baroreflex control of coronary blood flow conductance varies among coronary territories and is dependent on ventricular rate (VR) (Quail et al Clin Exp Pharmacol Physiol : 23 :866–73, 1996). It is unknown if such mechanisms exist in other species. The aim was to develop a sheep model for the analysis of control systems in coronary circulation and thus allow comparison with the dog. Merino ewes were prepared under isoflurane anesthesia. Pulsed Doppler flow probes were implanted on the right (RF), circumflex (CF) and anterior descending (AF) coronary arteries. Pacemaker leads were attached to the left atrial appendage and right ventricle. Aortic (AP) and central venous (CVP) catheters were placed via the superficial cervical artery and vein to measure pressure (Bishop et al Arch Physiol Biochem : 111: 313–4, 2003). All wires and catheters were exteriorized and protected by a backpack. The sheep recovered for 7 days. Coronary data were collected under conditions of sinus rhythm followed by pacing. The range of VR studied was 75–180 min −1 . Increasing VR by pacing produced minimal change in AP or CVP, while CF, RF and AF increased to 150% 136% and 119% of control at 180min −1 . The pattern of coronary conductance in each territory followed flow. These early data show that the awake triple coronary sheep model is feasible and suggest that regional differences exist in the flow response to increasing VR in the ovine coronary circulation. Further studies are required to analyze the control mechanisms involved. Funding: Hunter Medical Research Institute