The sequential effects of estrogen administration and hypertension on cardiac function in ewes

Our objective was to study the effect of estrogen administration and moderate hypertension on left ventricular size, pump function, and contractility in chronically instrumented ewes.

Ewes were either given 0.06 mg/kg 17beta-estradiol intramuscularly (n = 8) or were made hypertensive (n = 6) by inflation of an occluder around the aorta and were studied weekly. After 3 weeks each ewe received the opposite treatment.

Estrogen administration caused an increase in left ventricular chamber size at a given pressure, fractional 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 fractional shortening (20.0% +/- 4.4%) and stroke volume (1.3 +/- 0.3 mL/kg). With hypertension first, there was no left ventricular enlargement, even with subsequent estrogen administration, and there were no changes in left ventricular pump function. End-systolic pressure and stress-dimension relationships did not change with either treatment. The end-systolic wall stress-fractional shortening relationship was likewise unchanged, suggesting that neither treatment changed contractility.

The left ventricle previously exposed to hypertension does not remodel when exposed to estrogen, and cardiac pump function decreases when the estrogen enlarged heart is faced with moderate, subacute hypertension.