Core temperature is a greater influence than endogenous 17β-estradiol on the exercise-induced accumulation of myocardial heat shock protein mRNA

Female rats typically do not show significant increases in myocardial Hsp70 after exercise unless trained (exercise over days or weeks). 17β-Estradiol (E2) has been linked to this inhibition, but it varies considerably over the rodent estrus cycle. Consequently, we examined whether the inhibitory effects of endogenously produced E2 (measured immediately pre-exercise) were acute in exercised female Sprague-Dawley rats (60 min treadmill running at 30 m·min^-1). Myocardial hsp70-1 and hsp70-2 mRNA were measured 30 min post-exercise, and their expression was inversely correlated with pre-exercise plasma E2 (hsp70-1 mRNA, r² = 0.308, p = 0.011; hsp70-2 mRNA, r² = 0.238, p = 0.029). However, hsp70-1 and hsp70-2 mRNA exhibited much stronger correlations with core temperature achieved during exercise (r² = 0.812, p = 0.000; and r² = 0.738, p = 0.000, respectively). Consequently, although endogenous E2 in gonadally intact female rats may attenuate myocardial hsp70 mRNA accumulation, suggesting a reason why training maximizes this response in females, core temperature during exercise is still a greater stimulus to this response.