The antiarrhythmic effects of ischaemic preconditioning in anaesthetized dogs are prevented by atropine; role of changes in baroreceptor reflex sensitivity

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Abstract
Dogs, anaesthetized with chloralose and urethane, were subjected to a 25 min occlusion of the left anterior descending coronary artery. This resulted in ventricular ectopic activity, a reduction in baroreflex sensitivity (BRS, measured following the intravenous administration of phenylephrine), elevations in the epicardial ST‐segment and increases in the degree of inhomogeneity of electrical activation, both measured from the ischaemic region of the left ventricular wall. These changes were markedly reduced when the 25 min occlusion was preceded, 20 min earlier, by a 5 min (preconditioning) occlusion of the same coronary artery (e.g. VF during ischaemia reduced from 40% in the controls to 0%; P−1 post‐occlusion in preconditioned dogs; cf. 1.28±0.29 to 0.45±0.12 mmHg ms−1 respectively in the controls, P−1 i.v. followed by a continuous infusion of 0.04 mg kg−1 h−1). For example, VF during occlusion was increased from 0% in the preconditioned dogs to 40% (P−1; PBritish Journal of Pharmacology (2002) 135, 55–64; doi:10.1038/sj.bjp.0704445