THE SEQUENTIAL EFFECTS OF ESTROGEN ADMINISTRATION AND HYPERTENSION ONCARDIAC-FUNCTION IN EWES

OBJECTIVE: Our objective was to study the effect of estrogen administr ation and moderate hypertension on left ventricular size, pump functio n, and contractility in chronically instrumented ewes. STUDY DESIGN: E wes were either given 0.06 mg/kg 17 beta-estradiol intramuscularly (n = 8) or were made hypertensive (n = 6) by inflation of an occluder aro und the aorta and were studied weekly. After 3 weeks each ewe received the opposite treatment. RESULTS: Estrogen administration caused an in crease in left ventricular chamber size at a given pressure, fractiona l shortening (21.9% +/- 2.9% to 28.5% +/- 3.7%), and stroke volume (1. 4 +/- 0.3 mL/kg to 1.6 +/- 0.3 mL/kg). Subsequent hypertension further increased left ventricular size at a given pressure but decreased fra ctional shortening (20.0% +/- 4.4%) and stroke volume (1.3 +/- 0.3 mL/ kg). With hypertension first, there was no left ventricular enlargemen t, even with subsequent estrogen administration, and there were no cha nges in left ventricular pump function. End-systolic pressure and stre ss-dimension relationships did not change with either treatment. The e nd-systolic wall stress-fractional shortening relationship was likewis e unchanged, suggesting that neither treatment changed contractility. CONCLUSIONS: The left ventricle previously exposed to hypertension doe s not remodel when exposed to estrogen, and cardiac pump function decr eases when the estrogen enlarged heart is faced with moderate, subacut e hypertension.