Hemoglobin-methemoglobin system

The automated method differs from the ICSH method chiefly in that oxidation and ligation of heme iron occur after the hemes have been released from globin. Therefore, ferricyanide and cyanide need not diffuse into the hemoglobin and methemoglobin, respectively. Because diffusion is rate-limiting in this reaction sequence, the overall reaction time is reduced from approximately three minutes for the manual method to 3 —15 seconds for the automated method. Reaction sequences in the Coulter S + II and the Technicon H 1 and H 2 are similar. Moreover, similar reactions are used in the other Coulter systems and in the TOA and Unipath instmments. 

Several in vitro studies proved that treatment of intact erythrocytes with nitrites causes the oxidation of hemoglobin to methemoglobin by radical generation along with a decrease in reduced glutathione (GSH) level associated with erythrocyte membrane dysfunctions and namely altered cell ionic flux, lipid peroxidation, and perturbation of membrane transport (Batina et al 1990 May et al 2000). Nitrate/ nitrite-induced oxidation of biological molecules potentiates reactions, which interfere in the oxidative chain and which can affect some antioxidant systems. 

Methemoglobinemia as an adverse effect of prilocaine (8) has been reported more often than with any other local anesthetic. It is caused by a metabolite and is a particular problem in neonates, who have an immature methemoglobin reductase system and residual fetal hemoglobin, increasing the risk of sjmptomatic methemoglobinemia. 

CHRONIC HEALTH RISKS central nervous system effects blood disorders (increased methemoglobin decreased hemoglobin concentration) enlargement of spleen hemosiderosis of liver, kidneys and testes suspected carcinogen. 

Nitrates and nitrites are spread within environmental, food, industrial, and physiological systems. Nitrate may be reduced by bacteria to nitrite, and nitrite produces carcinogenic nitrosamines. Nitrite is also commonly employed in cured meat products to provide antimicrobial action, color fixation, and preservation. Nitrite can oxidize hemoglobin iron(II) to iron(III) resulting in methemoglobin, leading to a condition known as methemoglobinemia in children mainly. In excess, nitrates and nitrites may be toxic. 

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