Sex differences to myocardial ischemia and beta-adrenergic receptor blockade in conscious rats

We recently documented sex differences in the susceptibility to reperfusion-induced sustained ventricular tachycardia and beta-adrenergic receptor blockade in conscious rats. However, the effect of sex on ischemia-induced ventricular arrhythmias and beta-adrenergic receptor blockade is under-investigated. Therefore, we tested the hypothesis that gonadal hormones influence the ventricular arrhythmia threshold (VAT) induced by coronary artery occlusion as well as the response to beta-adrenergic receptor blockade. The VAT was defined as the time from coronary occlusion to sustained ventricular tachycardia resulting in a reduction in arterial pressure. Male and female intact and gonadectomized (GnX) rats were instrumented with a radiotelemetry device for recording arterial pressure, temperature, and ECG, as well as a Doppler ultrasonic flow probe to measure cardiac output and a snare around the left main coronary artery. The VAT was determined in conscious rats by pulling on the snare. The VAT was significantly longer in intact females (5.56 +/- 0.19) vs. intact males (4.31 +/- 0.14 min). This sex difference was abolished by GnX. Specifically, GnX decreased the VAT in females (4.55 +/- 0.22) and increased the VAT in males (5.14 +/- 0.30 min). Thus male sex hormones increase and female sex hormones decrease the susceptibility to ischemia-induced sustained ventricular tachycardia. beta-Adrenergic receptor blockade increased the VAT in intact males and GnX females only. Thus gonadal hormones influence the response to beta-adrenergic receptor blockade. Uncovering major differences between males and females in the pathophysiology of the cardiovascular system may result in sex-specific optimization of patient treatments.