ESTROGEN-INDUCED LEFT-VENTRICULAR CHAMBER ENLARGEMENT IN EWES

We studied the chronic effect of administration of a single large intr amuscular dose of 17beta-estradiol on left ventricular chamber size an d output in the ewe. Fourteen oophorectomized ewes were successfully i nstrumented and studied, with measurements made of left ventricular, a ortic, right and left atrial pressures, left ventricular stroke volume , and left ventricular minor axis dimension. Unanesthetized ewes were studied before and 1, 2, and 3 wk after intramuscular administration o f 0.6 mg/kg 17beta-estradiol (7 ewes) or 1.5 ml sesame oil placebo (7 ewes). Left ventricular end-diastolic pressure-end-diastolic dimension (LVEDP-EDD) and left ventricular end-diastolic pressure-stroke volume (LVEDP-SV) relationships were quantified during graded inferior vena caval occlusion and volume infusion. Left ventricular end-diastolic di ameter was larger after estrogen but not after placebo administration. The LVEDP-EDD relationship shifted progressively rightward, indicatin g left ventricular chamber enlargement in the estrogen group but was u nchanged in the placebo group. The plateau limb of the LVEDP-SV relati onship in the estrogen group shifted up from a mean stroke volume of 7 7.1-89.5 ml/beat and did not change in the placebo group. We conclude that administration of a single large intramuscular dose of 17beta-est radiol resulted in left ventricular chamber enlargement and increased stroke volume in the ewe.