Acute effects of 17beta-estradiol on myocardial pH, Na+, and Ca2+ and ischemia-reperfusion injury.

Evidence suggests that 1) ischemia-reperfusion injury is due largely to cytosolic Ca(2+) accumulation resulting from functional coupling of Na(+)/Ca(2+) exchange (NCE) with stimulated Na(+)/H(+) exchange (NHE1) and 2) 17beta-estradiol (E2) stimulates release of NO, which inhibits NHE1. Thus we tested the hypothesis that acute E2 limits myocardial Na(+) and therefore Ca(2+) accumulation, thereby limiting ischemia-reperfusion injury. NMR was used to measure cytosolic pH (pH(i)), Na(+) (Na(i)(+)), and calcium concentration ([Ca(2+)](i)) in Krebs-Henseleit (KH)-perfused hearts from ovariectomized rats (OVX). Left ventricular developed pressure (LVDP) and lactate dehydrogenase (LDH) release were also measured. Control ischemia-reperfusion was 20 min of baseline perfusion, 40 min of global ischemia, and 40 min of reperfusion. The E2 protocol was identical, except that 1 nM E2 was included in the perfusate before ischemia and during reperfusion. E2 significantly limited the changes in pH(i), Na(i)(+), and [Ca(2+)](i) during ischemia (P < 0.05). In control OVX vs. OVX+E2, pH(i) fell from 6.93 +/- 0.03 to 5.98 +/- 0.04 vs. 6.96 +/- 0.04 to 6.68 +/- 0.07; Na(i)(+) rose from 25 +/- 6 to 109 +/- 14 meq/kg dry wt vs. 25 +/- 1 to 76 +/- 3; [Ca(2+)](i) changed from 365 +/- 69 to 1,248 +/- 180 nM vs. 293 +/- 66 to 202 +/- 64 nM. E2 also improved recovery of LVDP and diminished release of LDH during reperfusion. Effects of E2 were diminished by 1 microM N(omega)-nitro-L-arginine methyl ester. Thus the data are consistent with the hypothesis. However, E2 limitation of increases in [Ca(2+)](i) is greater than can be accounted for by the thermodynamic effect of reduced Na(i)(+) accumulation on NCE.