Cassava diet and cyanide metabolism in Wistar rats.

I . In the aetiopathogenesis, in Nigerians, of a degenerative neuropathy known as tropical ataxic neuropathy, chronic cyanide intoxication is believed to be the most important factor. The source of the cyanide is cassava (Manihot) and in Nigerian patients, plasma concentration of thiocyanate, a major detoxication product of cyanide, is high. 2. Since there is considerable doubt as to whether cyanide is readily released from cassava diet after ingestion, rats were fed on 80 and 100 yo purupuru (a cassava derivative) diets for periods varying between 6 and 18 months and their plasma thiocyanate levels were studied. Control rats were fed on a normal diet for the same periods. 3. Rats fed on the 100 yo purupuru diet were malnourished. Rats fed on the 80 % purupuru diet appeared normal, although their mean weight was less than the mean weight of rats fed on the normal diet. 4. Plasma thiocyanate was significantly higher in rats fed the purupuru diets than in the rats fed on the normal rat diet. 5. The concentration of thiosulphate sulphurtransferase, the enzyme that catalyses the conversion of cyanide into thiocyanate was the same in rats fed on the purupuru diets as in the control rats. 6. The results suggest that raised plasma thiocyanate levels found in Nigerian patients with ataxic neuropathy, as in rats fed cassava diet, is the result of detoxication of cyanide, as the concentration of thiocyanate in cassava and most food products eaten by Nigerians is low.