Beneficial effects of estrogen on cardiac stunning in female rabbits

To determine the effect of estrogen treatment on the contractile, relaxation, and chronotropic responses of hearts of female rabbits to cessation of perfusion.

Adult female rabbits were treated either with estradiol or with the vehicle (control). The hearts were then isolated and perfused at constant pressure by the Langendorff technique. A saline-filled balloon connected to a pressure transducer was inserted in the left ventricle in order to assess the mechanical function of the isolated heart. Cardiac stunning was induced by halting the perfusion of the coronary vasculature for four successive periods of 1, 3, 5, and 5 minutes, followed by reperfusion between nonperfusion periods. Changes in cardiac function induced by the cessation of perfusion were assessed by monitoring the changes in heart rate and in left ventricular pressure ([dP/dt]max as an index of ventricular contractility and [dP/dt]min as an index of ventricular relaxation). Changes in coronary flow were determined at baseline and following reperfusion.

Halting coronary perfusion decreased (dP/dt)max, and (dP/dt)min and slowed left ventricular contractions both in control and in estrogen-treated hearts. The depressant effects of flow cessation on left ventricular (dP/dt)max and (dP/dt)min were smaller in estrogen-treated hearts than in control hearts. Treatment with estrogen had no effect on the changes on the heart rate in responses to cessation of flow and to reperfusion. Treatment with estrogen increased coronary flow by 40%. Coronary reperfusion increased coronary flow transiently, but the effects did not differ significantly between control and estrogen-treated hearts.

Short-term treatment of adult female rabbits with doses of estrogen that are physiologic for the rabbit exerts a protective effect on cardiac contractility from repetitive periods without perfusion.