The estrogen receptor-α agonist PPT decreases cardiac myofilament activation.

<p>Myocardium was treated with the estrogen receptor-α agonist PPT (100 nM) for 1 (A) (N = 9), 2.5 (B) (N = 9), or 5 min (C) (N = 22). Untreated controls showed no differences at any time, and are combined as a single group in each graph (N = 23). Maximum actomyosin MgATPase activity tended to decrease following PPT treatment, but did not reach statistical significance. Actomyosin MgATPase activity at submaximal calcium levels (<10 µM free calcium) was decreased with estrogen receptor-α activation. EC₅₀ values were increased, demonstrating a decrease in myofilament calcium sensitivity. The estrogen receptor-α antagonist MPP (1 µM) blocked the effects of 1 (D) (N = 3), 2.5 (E) (N = 3), and 5 min (N = 5) (F) PPT.