Blood oxygen-carrying function during the oxidative stress induced by lipopolysaccharide with a modification of the L-arginine-NO pathway

PURPOSE

Our aim was to study the blood oxygen-carrying function during the oxidative stress with a modification of the L-arginine-NO pathway.

MATERIAL AND METHODS

Oxidative stress was induced by intravenous administration of Escherichia coli lipopolysaccharide (LPS) to rabbits. To modify the L-arginine-NO pathway, animals were administered with NG-nitro-L-arginine methyl ester intravenously 60 min after the LPS. Mixed venous blood was sampled for evaluation of blood oxygen transport before and at 120 and 240 min after the LPS administration; tissue samples (heart, lung, liver, kidney and muscle) were also prepared. The following parameters were measured hemoglobin-oxygen affinity, concentrations of conjugated dienes, Schiff bases, alpha-tocopherol and activity of catalase.

RESULTS

During the NO synthase inhibition the oxidative stress was characterized by a shift of hemoglobin oxygen dissociation curve rightwards, more prominent activation of lipid peroxidation and decreased tissue levels of antioxidant defense factors.

CONCLUSIONS

The inhibition of NO generation induces a shift of prooxidant-antioxidant balance--obviously, not only due its potentially high levels and reactivity with the various target molecules (with a development of oxidative stress), but also because of the lower contribution of other factors including the hemoglobin-oxygen affinity change into the body antioxidant potential.

Prooxidant-antioxidant balance in animals with enhanced hemoglobin-oxygen affinity under acute normobaric hypoxia

The content of main lipid peroxidation (LPO) products and antioxidant defense (AD) factors were investigated in rats without a treatment and with preliminary rise of hemoglobin-oxygen affinity (HOA) by cyanate under acute normobaric environmental hypoxia. Under acute hypoxia the cyanate-treated rats expressed the lower contents of conjugated dienes (CD), thiobarbituric acid-reactive substances (TBARS), Schiff bases (SB) and higher alpha-tocopherol (alpha-T) concentration, and catalase (CAT) activity than in control animals (mainly in tissues). The regression analysis of HOA, LPO and AD parameters in investigated material indicated the close positive correlations of oxygen pressure for hemoglobin half-saturation (p50) with CD, TBARS, and SB, and negative correlation of p50 with alpha-T and CAT. The results of experiments with intended HOA increase during the hypoxia and observed weakened activities of the free radical processes suggest that blood oxygen-binding properties can have an important role in the mechanisms of prooxidant-antioxidant balance.

High hemoglobin affinity to oxygen and its relationships with lipid peroxidation during fever

The effects of high hemoglobin-oxygen affinity (HOA) on rectal temperature and lipid free radical oxidation were investigated in red blood cells, heart, liver and kidneys of male rats during fever. Fever was induced by intraperitoneal injection of Salmonella typhi lipopolysaccharide (LPS; 5.0 mg kg(-1)). HOA was increased by addition of 0.5% sodium cyanate to drinking water for eight weeks. HOA modification (actual half-saturation oxygen pressure, P50act, decreased to 23.3+/-0.7 vs. 31.6+/-0.7 Torr in control; p < 0.001) weakened a febrile response: rise of temperature after 4 hours was 0.79+/-0.2 degrees C vs. 1.38+/-0.1 degrees C in rats with normal HOA (p < 0.05). In red cells and tissues of rats with normal HOA, concentrations of conjugated dienes and Schiff bases increased during fever, and alpha-tocopherol level and catalase activity decreased. Rats with increased HOA had an inverse pattern of such changes. Changes in rectal temperature and markers of free radical oxidation correlated with a shift of oxyhemoglobin dissociation curve leftwards. The present results indicate that the intentional increment of HOA may substantially diminish lipid peroxidation activity, increase the body antioxidant content during fever and decrease the febrile response on LPS.

Effect of nitric oxide synthase inhibition on hemoglobin-oxygen affinity and lipid peroxidation in rabbits during fever

BACKGROUND

Nitric oxide (NO) is one of the most important biologic messengers and takes part in the development of fever. It can influence on the body prooxidant-antioxidant balance by different ways including interaction with hemoglobin (Hb).

METHODS

The effects of nitric oxide synthesis inhibition on the febrile response, hemoglobin-oxygen affinity and parameters of lipid peroxidation were studied in rabbits with fever. The fever was induced by intravenous administration of lipopolysaccharide from Salmonella typhi (0.6 microg/kg). Mixed venous blood was taken before the administration and 60, 120 and 180 min after it. The following parameters were measured: half-saturation oxygen pressure (P(50)), concentrations of conjugated dienes, Schiff bases and alpha-tocopherol in plasma and red blood cells, and activity of catalase in red blood cells.

RESULTS

The intravenous administration of the nitric oxide synthase inhibitor (N(omega)-nitro-L-arginine; 5x10(-3) M) reduced the lipopolysaccharide-induced rise in body temperature. After 180 min the actual P(50) had decreased from 35.0+/-1.7 to 29.4+/-1.3 mm Hg. An increase in the lipid peroxidation parameters and a decrease of the antioxidant system indices were observed. The administration of L-arginine to prevent nitric oxide synthase inhibition was accompanied by a shift of the oxyhemoglobin dissociation curve rightwards, more marked activation of the free radical processes and a greater elevation of body temperature. The multiple regression analysis showed a close linear correlation between P(50) and conjugated dienes, Schiff bases, alpha-tocopherol and catalase.

CONCLUSION

These results suggest that the increased hemoglobin-oxygen affinity found after the inhibition of nitric oxide synthesis lowers the oxygen flow to tissues and its fraction utilized in free radical oxidations, which finally causes a reduction of the fever response to the lipopolysaccharide.

The effect of NO synthase inhibition on blood oxygen-carrying function during hyperthermia in rats

Hyperthermia is known to be accompanied by considerable worsening of body oxygen delivery. Nitric oxide (NO) is a messenger that contributes to the regulation of oxygen transport (vasodilation, formation of nitrosohemoglobin, erythrocyte deformability), but also has cytotoxic effects (when abundantly generated by inducible NO synthase and through a formation of peroxynitrite). The effects of NO synthesis inhibition on the blood oxygen transport (hemoglobin-oxygen affinity and erythrocyte deformability) were investigated in rats with hyperthermia. The most considerable changes in blood oxygen transport indices and the most pronounced hypoxia were observed in rats that received the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) i.p. Its administration before heating significantly impaired body oxygen delivery, with a shift of the oxyhemoglobin dissociation curves rightwards and lowering of erythrocyte deformability. The changes in the blood oxygen transport in animals receiving L-arginine and L-NAME to prevent NO synthase inhibition were similar to those in rats treated with isotonic NaCl before heating.

Fe(2+)-initiated chemiluminescence in rats with high hemoglobin-oxygen affinity during fever

The effect of high hemoglobin-oxygen affinity (HOA) on chemiluminescence initiated by Fe2+ was studied in rat plasma and red cell ghosts during fever. The high HOA was induced by daily ingestion of sodium cyanate with drinking water for 8 weeks. Rats with high or normal HOA received i.p. lipopolysaccharide Salmonella typhi (LPS). The half-saturation oxygen pressure (p50) after 240 min of fever was 23.3 +/- 0.7 in cyanate-treated rats comparing with 30.4 +/- 0.4 Torr in the group received placebo. The maximal value of initiated chemiluminescence rose in plasma and red cell ghosts of rats with normal HOA by 26.5 and 27.5%, respectively, and in rats with modified HOA by 17.1 and 23.8%, respectively. The antioxidant activity of plasma and red cell ghosts decreased under high HOA to a less extent. These investigations show that the lowering of oxygen flux to tissues due to hemoglobin carbamylation may decrease the production of free radicals in rats during fever.