Effects of exogenous donor of nitric oxide-sodium nitroprusside on energy production of rat reticulocytes.

The effects of the sodium nitroprusside (SNP), a nitric oxide (NO) donor clinically used in the treatment of hypertensive emergencies on the energy production of rat reticulocytes were investigated. Rat reticulocyte-rich red blood cell suspensions were aerobically incubated without (control) or in the presence of different concentrations of SNP (0.1, 0.25, 0.5, 1.0 mM). SNP decreased total and coupled, but increased uncoupled oxygen consumption. This was accompanied by the stimulation of glycolysis, as measured by increased glucose consumption and lactate accumulation. Levels of all glycolytic intermediates indicate stimulation of hexokinase-phosphofructo kinase (HK-PFK), glyceraldehyde 3-phosphate dehydrogenase (GAPD) and pyruvate kinase (PK) activities in the presence of SNP. Due to the decrease of coupled oxygen consumption in the presence of SNP, ATP production via oxidative phosphorylation was significantly diminished. Simultaneous increase of glycolytic ATP production was not enough to provide constant ATP production. In addition, SNP significantly decreased ATP level, which was accompanied with increased ADP and AMP levels. However, the level of total adenine nucleotides was significantly lower, which was the consequence of increased catabolism of adenine nucleotides (increased hypoxanthine level). ATP/ADP ratio and adenylate energy charge level were significantly decreased. In conclusion, SNP induced inhibition of oxidative phosphorylation, stimulation of glycolysis, but depletion of total energy production in rat reticulocytes. These alterations were accompanied with instability of energy status.

Effects of nitric oxide donors on energy metabolism of rat erythrocytes.

It is known that nitric oxide (NO) influences the activities of glycolytic enzymes, resulting in alteration of glycolysis rate. We investigated the effect of NO donors on the energy metabolism of rat erythrocytes. Rat erythrocyterich blood suspensions were aerobically incubated for 2 hours (1) as controls or (2) with different concentrations of NO donors: nitroglycerin (NTG), isosorbide dinitrate (ISDN), molsidomine (MO), and sodium nitroprusside (SNP). NTG, ISDN, MO, and SNP significantly (p < 0.05) increased glucose consumption and lactate accumulation in rat erythrocytes in a dose-dependent manner, indicating stimulation of glycolysis. The increased rate of glycolysis was accompanied by elevation of energy production (p < 0.05), but no changes in ATP levels were observed. The dose-dependent increase of glycolytic ATP production and the unaltered levels of ATP resulted in considerably shortened ATP-turnover time with the maximal experimental doses of NO donors used, indicating the stimulation of the ATP-consuming process in rat erythrocytes. The metabolic effects of NTG, ISDN, MO, and SNP were not mimicked by exogenous 8-Br-cGMP, NaNO2, or NaNO3, suggesting that the NO donor-induced stimulation of glycolysis and abbreviation of ATP-turnover time in rat erythrocytes was mediated by NO as an effector molecule, irrespective of the irreversible scavenger effect of hemoglobin. The implications of the NO effect on energy metabolism of erythrocytes is discussed.