P763Ovariectomy increases epinephrine-induced mortality in a rat takotsubo cardiomyopathy model: the effects of estrogen supplementation

Abstract

Background: Takotsubo cardiomyopathy (TCM) is an acute heart failure syndrome that can occur after a period of intense emotional stress, characterised by a hypokinetic apex and a hyperkinetic base. We have previously shown that a single IV injection of epinephrine can recapitulate the syndrome in male rats. As TCM usually occurs in post-menopausal females we gave the same epinephrine dose to normal female and ovariectomised (OVX) rats with or without short or long-term (2 weeks) estrogen replacement. Methods: OVX rats were anaesthetised with 2% isoflurane in 100% O2 and a parasternal long-axis echocardiograph was acquired. For short-term estrogen treatment, 600ng 17$β$-estradiol was infused IV 5 minutes before epinephrine injection (4.3x10-8mol.100g-1). For 2-week replacement, osmotic minipumps were implanted containing 17$β$-estradiol (238$μ$g.day-1) in 50:50 glycerol:DMSO. Fractional shortening was measured before and at 5 minute intervals after epinephrine using M-mode images from the apex and base of the left ventricle. QTc was calculated using the LabChart 7 ECG Analysis Module from a Lead II ECG. Results: Compared to males, female non-OVX rats had reduced mortality and did not exhibit TCM-like contraction patterns when given the same epinephrine bolus (6.25% vs. 46% mortality; P<0.01). OVX rats showed increased mortality compared to non-OVX females (75% vs. 6.25%; P<0.001, n=12-16); death was typically due to VF. Two-week E2 supplementation (n=10) reduced mortality compared to OVX (no minipump) (10% vs. 75% mortality; P=0.007). Vehicle minipump (n=10) had a similar but non-significant trend to reduce mortality (40% vs. 75%; P=0.38) with the result that E2 vs. vehicle was not significantly different (P=0.30, n=10). Acute estrogen supplementation did not significantly reduce mortality (75% vs. 50%; P=0.4, n=12 per group). Vehicle and E2 minipump groups had significantly (P<0.0001 and P<0.01, respectively) shorter QTc intervals compared to OVX (no minipump) (OVX=200{\textpm}2.36ms, n=12; E2=158{\textpm}8.86ms, n=11; Vehicle=173{\textpm}4.61 ms, n=11). The difference in QTc interval between E2 and vehicle groups was not significant. Conclusion: Female rats are protected from epinephrine-induced sudden death. Loss of ovarian function predisposes rats to epinephrine-mediated death; acute estrogen infusion did not reverse this but 2 week E2 treatment did. There appeared to be an interacting effect of the DMSO vehicle on this reduction, as well as the decrease in QTc interval: we suggest this may be a result of its effect to reduce ROS.