Effect of vasopressin on myocardial reactive hyperaemia in the isolated fibrillating dog heart.

The effect of 0.15 IU/min vasopressin (VA) administered intracoronarily on postocclusion reactions following 15 sec, 30 sec, 60 sec, and 120 sec occlusions of the left coronaries of the isolated fibrillating dog heart were studied at constant pressure or constant volume perfusion with arterial blood of another dog. Basal perfusion pressure was kept at the level of 150 mmHg. Preocclusion state and postocclusion reactions were characterized by changes in coronary conductance. Peak conductance, maximum conductance, reactivity, time to peak conductance, mean transit time and repayment were computed for characterizing reactive hyperaemia. In the control state the post-occlusive conductance--time curve was higher, but shorter in duration with constant pressure perfusion than with constant volume perfusion. Upon the administration of VA, basal conductance decreased considerably while with constant pressure perfusion the hyperaemic reactions underwent hardly any change. In contrast, using constant volume perfusion, the duration of reactive hyperaemia was shortened by VA. Consequently, the differences in mean transit time observed in the controls resulted from the unequal perfusion techniques disappeared on the application of VA. On both constant pressure and constant volume perfusion, maximum conductance decreased as a result of the decrease in basal conductance, therefore the reactivity of the coronary vessels increased markedly. It is concluded that myogenic vasorelaxation may contribute to reactive hyperaemic responses not only on brief, but also on prolonged occlusion. The basal vascular tone is of importance in the coronary adaptation to ischaemia.