Effects of low cobalamin diet and chronic cyanide toxicity in baboons

The effects of a low cobalamin (Cbl) diet, together with chronic cyanide or thiocyanate administration in some animals have been investigated in baboons over a period of 42 months. All animals remained healthy throughout the study and gained weight at a similar rate. None became anaemic or showed major haematological changes and there were no major neurological changes. Plasma total Cbl in the animals on the low Cbl diet fell within 9 months to values below the lower limit in man and were lowest at 24 months in baboons not receiving cyanide or thiocyanate. A striking feature in all animals, however, was an apparently seasonal increase in the plasma total Cbl each autumn with a corresponding decrease the following spring. This fluctuation was detected by radioisotopic assay but not by Euglena. Methylmalonic (MMA) excretion after oral valine ranged from 0.1--8.4 mg/24 h and was greatest in animals on the low Cbl diet and not receiving cyanide or thiocyanate. The results suggested an inverse relationship between MMA excretion and plasma total Cbl. Plasma thiocyanate was consistently higher in animals receiving cyanide or thiocyanate and at the end of the study plasma cyanide was highest in animals on the low Cbl diet receiving cyanide. The results support the suggestions that cyanide affects bodily handling of Cbl and that hydroxo-cobalamin plays a part in detoxication of cyanide.