Coronary reactive hyperaemia after two periods of coronary occlusion in the anaesthetized goat

In the coronary circulation an ischaemic preconditioning obtained with two periods of 2.5 min each of occlusion of the left circumflex coronary artery alters the pattern of a coronary reactive hyperaemia which follows 15 s only of occlusion of the studied artery. The most remarkable change consists of a reduction of 40-45% of the time required by the flow to reach the maximum hyperaemic peak (time to peak) after the brief occlusion. The present investigation was planned to study whether the time to peak of the hyperaemia following the second 2.5 min preconditioning occlusion was shorter than the hyperaemia following the first occlusion. Experiments performed in the anaesthetized goat, in which coronary flow was measured with an electromagnetic flow-probe placed around the left circumflex coronary artery showed that in the hyperaemia occurring after the second preconditioning occlusion the time to peak was reduced by 18% only. The moderate effect of the second preconditioning occlusion in reducing the time to peak is attributed to the fact that the heart was already partially preconditioned after the first occlusion and that after relatively long periods (2.5 min) of occlusion the metabolic component of the hyperaemic response was so predominant to partially mask the role of the vascular mechanisms presumably responsible for the reduction of the time to peak.