Effects of nitroglycerin on energy metabolism of rat reticulocytes

Nitric oxide (NO) in many cells inactivates aconitase and mitochondrial res piratory chain, and influenced glyceraldehyde 3-phosphate dehydrogenase act ivity. The aim of this study was to evaluate role of nitroglycerin (NTG), a widely used NO donor, on energy metabolism of rat reticulocytes. Rat retic ulocyte rich red blood cell suspensions containing 70-100% of reticulocytes , were aerobically incubated without (control) or in the presence of differ ent concentrations of (a) NTG (0.1, 0.25, 0.5, 1.0, 1.5 mmol/l), (b) 8-Br-c GMP (0.1, 0.5, 1.0 mmol/l) and (c) NaNO2 and NaNO3 (1 mmol/l). NTG in dose- and time-dependent manner decreased total (p > 0.05; EC50 = 0.78 +/- 0.05 mmol/l) and coupled (p < 0.05; EC50 = 0.50 +/- 0.04 mmol/l) and increased u ncoupled oxygen consumption (p < 0.05; EC50 = 0.36 +/- 0.01 mmol/l). They w ere accompanied by stimulation of glycolysis, as measured by increased gluc ose consumption and lactate accumulation (p<0.01; EC50 = 0.53 and 0.53 mmol /l, respectively). Levels of all glycolytic intermediates in the presence o f NTG indicate stimulation of HK-PFK, GA3PDH and PK activity. NTG significa ntly decreased ATP level, which accompanied by increased ADP and AMP levels . However, level of total adenine nucleotides (TAN) was significantly lower , which was consequence of increased catabolism of adenine nucleotides (inc reased hypoxanthine level; p<0.05). Stimulation of glycolysis accompanied w ith inhibition of the OxP, activation of HK-PFK, decrease of ATP and simult aneous rise of ADP and AMP levels, all together represent an example of Pas teur effect occurring in NTG-treated reticulocytes. In rat reticulocytes un der steady state conditions 93% of overall energy was produced by OxP, but only 7% by glycolysis. Due to decrease of coupled oxygen consumption in the presence of NTG, ATP production via OxP was significantly diminished. Simu ltaneous increase of glycolytic ATP production is not enough to provide con stant either ATP production or concentration. Calculated mean ATP-turnover time was prolonged even for 45% in the presence of 1.5 mmol/l NTG. Metaboli c effects of NTG were not mimic by exogenous 8-Br-cGMP, NaNO2 or NaNO3, whi ch indicate that NTG induced a) inhibition of coupled respiration and b) st imulation of glycolysis in rat reticulocytes are mediated by NO as an effec tor molecule.