Methaemoglobinaemia 



The rate of MHb removal by normal red cell enzymes is of the order 

 of 5 per cent of total pigment per hour, and the additional contribution 

 of 0-1 per cent per hour to be expected from ascorbic acid is negligible. 

 Thus in drug methaemoglobinaemias there is no reason to suppose 

 that ascorbic acid will be beneficial. In a case of enterogenous cyanosis, 

 however, Fishberg 18 has demonstrated a specific effect of ascorbic acid 

 in causing the disappearance of benzoquinoneacetic acid from the 

 urine of her patient and an immediate rise in the 2 combining power 

 of the blood. In this case the effect of ascorbic acid seems to be linked 

 with its activity as a component of the oxidizing enzyme system 

 responsible for the complete catabolism of tyrosine. 



From the point of view of oxygen transport, one would expect to 

 find some evidence of reduced exercise tolerance in the more severe 

 cases of methaemoglobinaemia, but except for the two cases of Lian 

 et at 2 described as dyspnoeic and the case of Sievers and Ryon 20 , such 

 evidence is notably lacking. K. Hitzenberger's 22 case with 40 per cent 

 MHb was a heavy labourer, while the second of the two cases of Deeny 

 et al l was a member of a hockey team. Gibson and Harrison 19 des- 

 cribed two further cases with 25-30 per cent MHb, neither aware of 

 any physical disability and both employed as farm labourers. This 

 finding is the more striking in that the presence of methaemoglobin 

 leads to a shift in the dissociation curve to the left, demon- 

 strated experimentally by R. C. Darling and F. J. W. Roughton 23 , 

 and observed in the naturally occurring condition by Hitzenberger 22 

 and Gibson and Harrison 19 . Associated with the shift to the left is a 

 change in form of the curve from sigmoid to hyperbolic which 

 theoretically should interfere still further with oxygen transport. There 

 appears to be room for a detailed physiological study of oxygen 

 transport in these cases and of the compensatory mechanisms which 

 are brought into play. 



Received September, 1948 



REFERENCES 



1 Deeny, J. Brit. med. J. 2 (1940) 864 



2 Lian, C, Frumusan, P. and Sassier, M. Bull. Soc. mid. H6p. Paris. 55 



(1939) 1194 



3 Cox, W. W. and Wendel, W. B. J. biol. Chem. 143 (1942) 331 



4 Deeny, J., Murdock, E. T. and Rogan, J. J. Brit. med. J. 1 (1943) 721 



6 Barcroft, H., Gibson, Q. H., Harrison, D. C. and McMurray, J. din. Set 

 5 (1945) 145 



229 



