Exogenous nitric oxide reduces glucose transporters translocation and lactate production in ischemic myocardium in vivo

Abstract

Nitric oxide (NO) inhibits myocardial glucose transport and metabolism, although the underlying mechanism(s) and functional consequences of this effect are not clearly understood. We tested the hypothesis that NO inhibits the activation of AMP-activated protein kinase (AMPK) and translocation of cardiac glucose transporters (GLUTs; GLUT-4) and reduces lactate production. Ischemia was induced in open-chest dogs by a 66% flow reduction in the left anterior descending coronary artery (LAD). During ischemia, dogs were untreated (control) or treated by direct LAD infusion of (i) nitroglycerin (NTG) (0.5 microg.kg(-1).min(-1)); (ii) 8-Br-cGMP (50 microg.kg(-1).min(-1)); or (iii) NO synthase inhibitor L-nitro-argininemethylester (40 microg.kg(-1).min(-1); n = 9 per group). Cardiac substrate oxidation was measured with isotopic tracers. There were no differences in myocardial blood flow or oxygen delivery among groups; however, at 45 min of ischemia, the activation of AMPK was significantly less in NTG (77 +/- 12% vs. nonischemic myocardium) and 8-Br-cGMP (104 +/- 13%), compared with control (167 +/- 17%). Similarly, GLUT-4 translocation was significantly reduced in NTG (74 +/- 7%) and 8-Br-cGMP (120 +/- 11%), compared with control (165 +/- 17%). Glucose uptake and lactate output were 30% and 60% lower in NTG compared with control. Inhibition of NO synthesis stimulated glucose oxidation (67% increase compared with control) but did not affect AMPK phosphorylation, GLUT-4 translocation and glucose uptake. Contractile function in the ischemic region was significantly improved by NTG and L-nitro-argininemethylester. In conclusion, in ischemic myocardium an NO donor inhibits glucose uptake and lactate production via a reduction in AMPK stimulation of GLUT-4 translocation, revealing a mechanism of metabolic modulation and myocardial protection activated by NO donors.

Fig. 1.

LV function. (A) Changes in percentage of shortening of the LV wall in the LAD territory at 15, 30, and 45 min of ischemia. Negative values indicate paradoxical elongation during systole and postsystolic shortening. (B) Changes in MVO₂ during ischemia. (C–E) Changes in myocardial FFA (C), glucose (D), and net lactate uptake (E) at 15, 30, and 45 min of ischemia. Negative values in E indicate a switch from net lactate uptake to net output during ischemia. (F–H) Changes in myocardial FFA (F), glucose (G), and lactate (H) oxidation at 15, 30, and 45 min of ischemia. For lactate oxidation, measurements were made only at baseline and 15 and 45 min of ischemia (n = 9 for all groups). *, P < 0.05 vs. baseline; #, P < 0.05 vs. control group.

Fig. 2.

Myocardial anaerobic metabolism. Changes in myocardial lactate release (A) and hydrogen ion production (B) at 15, 30, and 45 min of ischemia. For lactate output, measurements were made only at baseline and 15 and 45 min of ischemia (n = 9 for all groups). *, P < 0.05 vs. baseline; #, P < 0.05 vs. control group.

Fig. 3.

Glucose transport activation. Percentage increases in GLUT-4 translocation to the sarcolemma (A) and in AMPK phosphorylation (B) in the ischemic compared with nonischemic region of the heart (n = 9 for all groups). *, P < 0.05 vs. nonischemic region; #, P < 0.05 vs. control group. Representative bands from Western blot analyses to assess changes in GLUT-4 translocation (C) and AMPK phosphorylation (D) are also shown.