Methaemoglobin reductase

Nilsson, A., Engberg, G., Henneberg, S., Danielson, K., and De Verdier, C.-H. (1990). Inverse relationship between age-dependent erythrocyte activity of methaemoglobin reductase and prilocaine-induced methaemoglobinaemia during infancy. Br. J. Anaesth. 64,72-76. 

No untoward effect is observed until the capacity of methaemoglobin reductase (or other enzymes supplying reducing equivalents) is exceeded. Above these saturation levels, the typical dose-response characteristics usually take the form of increasing incidence or severity of lesions with increasing dose. 

The development of methaemoglobinae-mia was demonstrated in one case (154 ). In view of the metabolism of nitroprusside the possibility of formation of methaemoglobin is not surprising, and secondarily cyanmet-haemoglobinaemia can be formed. In the correspondence subsequent to the publication of the case report concerned, however, it was pointed out that some factor other than nitroprusside administration may have played a role in this case, e.g. a congenital deficiency in red cell methaemoglobin reductase activity (1 55, 156 ),... 

The enzymes GSH peroxidase, GSH reductase and SOD collaborate to ensure that the red cell is protected from the effects of methaemoglobin and superoxide. Disposal of hydrogen peroxide may occur by catalase, in a reaction which is also dependent on NADPH. This vital coenzyme is provided via the PPP. Although the PPP operates in all cell types for the provision of pentose sugars and nucleotides, its role in the RBC is more directed to cell survival than cell division. 

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