Susceptibility of the isolated female rat heart to ischemia‐induced ventricular fibrillation varies with estrous cycle stage

Abstract

The vast majority of studies employing the isolated perfused rat heart model to study ischemic arrhythmias have used male rats only. The objective of this study was to determine the variation in susceptibility to ischemia‐induced ventricular fibrillation (VF) in isolated female rat hearts with the changing endogenous reproductive hormonal environment associated with the estrous cycle.Hearts were isolated from female rats under anesthesia and perfused with 3 mM K+ Krebs solution. Experiments were grouped according to estrous cycle stage that was determined by prior vaginal lavage (n=9–13 per group). A group of male rats was used as the control. Regional ischemia was induced by coronary ligation and maintained for 30 min. The incidence of VF was determined from the ECG.The incidence of VF in male hearts was 100%, while the incidence of VF in female hearts was also high but varied with stage of the estrous cycle (proestrus 89%, diestrus 78%, metestrus 100%, estrus 69%; p>0.05). There was no difference between groups in time to onset of VF or ischemic zone size (range 40–44% of total ventricular weight).In conclusion, the susceptibility of isolated female rat hearts to ischemic VF is comparable to that of male rat hearts. However, the variation in VF susceptibility in female rat hearts associated with the different stages of the estrous cycle may affect the statistical power of a study.Supported by a WVSOM intramural grant.