Studies were carried out to determine the effects of the toxic principle linamarin, a cyanogenic glucoside, in a diet containing cassava (Manihot esculenta Crantz) in the form of gari fed to growing dogs for 14 weeks. There were three groups of dogs, each comprising six animals. One group was fed on a control diet with rice as the carbohydrate source, the second group was fed on cassava (gari) as the carbohydrate source and which was expected to release 10.8 mg HCN/kg cooked food, the third group was fed on the control diet to which enough NaCN was added at feeding time to release 10.8 mg HCN/kg cooked food in order to monitor the effects of the HCN released from gari. All diets contained 130 g erude protein (N × 6.25)/kg and were supplemented with vitamins and minerals. Each animal was given approximately 100 g diet/kg body weight for the duration of the experifnent. The biochemical variables investigated were plasma electrolytes, serum proteins, plasma-free amino acids, plasma enzymes and urine protein, and the histology of some metabolically active tissues, namely liver, kidney, myocardium, testis and adrenal gland, was studied. The gari diet caused an elevated plasma thiocyanate concentration (P < 0.01), elevated 24 h urinary thiocyanate excretion and elevated urinary protein excretion (P < 0.01), lowered serum albumin (P < 0.05), a plasma-free amino acid profile which resembled that found in kwashiorkor, lowered plasma K and Ca (P < 0.05). The rice + cyanide diet caused an elevated plasma thiocyanate (P < 0.01) and a 24 h urinary thiocyanate excretion that was significantly higher (P < 0.01) than that of the dogs fed on gari, but caused a urinary protein excretion that was significantly lower than that of the dogs fed on gari (P < 0.01), lowered serum albumin (P < 0.05), a plasma-free amino acid profile that indicated that the amino acids were not being utilized to the same extent as in the control (rice) group but were accumulating. Neither diet had an effect on plasma γ-glutamyltransferase (EC 2.3.2.2), alanine aminotransferase (EC2.6.1.2) or isocitrate dehydrogenase (EC 1.1.1.42) activities, plasma Na, Mg, and P concentrations. The gari diet caused generalized congestion and haemorrhage, periportal vacuolation of the liver, swelling, vacuolation and rupture of the epithelial cells of the proximal convoluted tubules of the kidney, myocardial degeneration and adrenal gland degeneration. In the testes there were occasional abnormal germ cells in the seminiferous tubules, and occasional seminiferous tubules denuded to basement membrane of germ cells but with remnants of Sertoli cells. Spermatogenesis, however, appeared to be normal since the percentage of round tubules in stage 8 of the spermatogenic cycle was not significantly different from that of the control dogs. The rice + cyanide diet caused nephrosis and a significantly reduced relative frequency of testicular tubules in stage 8 of the spermatogenic cycle (P < 0.01). There was also marked testicular germ cell sloughing and degeneration. There was adrenal gland hyperplasia and hypertrophy. It was concluded that the observed changes which occurred when the gari diet was consumed were not entirely due to cyanide.
