A comparison of two progestins on myocardial ischemia–reperfusion injury in ovariectomized monkeys receiving estrogen therapy

OBJECTIVEIt has been reported that the progestin medroxyprogesterone acetate (MPA), but not norethindrone acetate (NETA), inhibits the beneficial vascular effects of post-menopausal estrogen therapy, but their effects on the myocardium are unclear. The goal of this study is to compare the effects of these two progestins on post-ischemic myocardial damage. METHODSOvariectomized monkeys were fed an atherogenic diet for 18 months while receiving, or not receiving (control, n=15), the monkey equivalent to a womanʼs dose of 5 μg ethinyl estradiol with either 1 mg NETA daily (n=15) or 2.5 mg MPA daily (n=15). The left anterior descending coronary artery was occluded for 1 h and then released to allow myocardial reperfusion for 4 h. Infarct size was quantified using the histochemical stain triphenyl-tetrazolium chloride. Regional myocardial blood flow was measured by 15 μm neutron-activated microspheres, blood pressure and heart rates with a pneumatic cuff, stroke volume by echocardiography, coronary output by thermodilution and neutrophil accumulation in the myocardium using myeloperoxidase (MPO) activity. RESULTSThe infarct size (area of necrosis/area at risk) was similar between the control group (21±3%) and the MPA group (29±3%) (P0.05). CONCLUSIONSNETA, but not MPA, diminished ischemia–reperfusion injury in estrogen-treated post-menopausal females. The mechanism(s) of this difference remains unclear.