Sex differences in the mechano-energetic effects of genistein on stunned rat and guinea pig hearts

Although the phytoestrogen genistein (Gen) is considered protective in cardiovascular diseases, its direct effects on stunned hearts after transient ischemia-reperfusion (I/R) are unknown. This report studied the effects of 20 mu mol/L Gen on the mechano-calorimetric behaviour during I/R of rat and guinea pig hearts to evaluate the energetics of Ca2+ homeostasis. Isolated beating hearts were perfused with control Krebs solution inside a calorimeter with or without perfusion of Gen before a transient period of I/R. Left ventricular pressure development (P) and total heat rate (Ht) were continuously measured. At 37 degrees C, Gen did not change post-ischemic contractile recovery (PICR), but it increased the relaxation rate. However, PICR was reduced in hearts of male rats and guinea pigs at 30 degrees C. Total muscle economy (P/Ht) showed the same behaviour as P at each temperature. Inhibition of phosphatases with orthovanadate during Gen perfusion prevented a decrease in PICR in male rat hearts, suggesting that this effect is due to tyrosine kinase inhibition. Reperfusing ischemic hearts with 10 mmol/L caffeine-36 mmol/L Na+-Krebs induced contracture dependent on the sarcoreticular Ca2+ content. Contracture relaxation depends on mitochondrial Ca2+ uptake and Gen reduced the relaxation rate. Moreover, Gen prevented the increase in Rhod-2 fluorescence (free [Ca2+](m)) of rat cardiomyocytes. In guinea pig hearts, Gen maintained ischemic preconditioning, but was reduced by 5-hydroxydecanoate, suggesting the participation of mitochondrial adenosine triphosphate (ATP)-dependent K channels. Results suggest that Gen acts on several mechanisms that regulate myocardial calcium homeostasis and energetics during I/R, which differ in a temperature-and sex-dependent manner.