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 108 mg HCN/kg cooked food, the third group was fed on the control diet to which enough NaCN was added a t 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 crude protein (N x 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 experiment. 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 < OOl), 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 y-glutamyltransferase (EC 2.3.2,2), alanine aminotransferase (EC 2.6.1.2) 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 ricefcyanide 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...

Cassava (Manihot esculenta Crantz) is an important dietary staple for more than 500 million people in developing countries. People eat 60% of the cassava produced and one third of the harvest feeds animals. All cultivars of cassava contain the cyanogenic glucoside, linamarin, but in different concentrations. The roots of those cultivars with high cyanogenic content are processed to reduce the level of linamarin, because linamarin is hydrolysed in the intestinal tract of both men and animals by microbial flora and HCN is released. Researchers have implicated the sublethal levels of HCN produced on ingestion in the development of a number of metabolic diseases in both man and animals when cassava-based diets are consumed over a long period of time but the release of HCN cannot fully explain the metabolic effects of ingested linamarin. A significant amount of linamarin remains intact and is excreted in the urine. It appears that the intact linamarin inhibits Na+K+ATPase causing electrolyte imbalance within the cell. This phenomenon is exacerbated by free radicals generated by the hypoxia/normoxia cycles created by cyanide released from linamarin, which cause lipid peroxidation and cell membrane damage. When the supply of endogenous thiosulphate is adequate, cyanide plays a very minor role in the development of lesions. The amount of damage is related to the quantity of linamarin routinely ingested at sublethal levels. There appears to be species differences in the rate of the development of diseases and the intensity.

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Growing dogs were divided into three groups and were fed on a control (rice) diet, a diet in which cassava (Manihot esculenta Cvantz; gari) was used as the carbohydrate source, and the rice diet to which cyanide (equivalent to that present in gari) was added. Each group consumed its diet for 14 weeks, during which plasma thiocyanate concentration and plasma lipase (EC 3.1 . l . 3) activity were monitored. Plasma free amino acids were determined from pooled samples taken at the end of the experimental period, and the insulin status of the dogs was evaluated using the gluconeogenic index. The dogs were killed and the pancreas examined for histopathology. Dogs fed on both gari diet and the rice + cyanide diet generated significant amounts of thiocyanate when compared with the controls, with the rice + cyanide group having higher plasma thiocyanate than the gari group (P < 0.01). Plasma lipase activity rose significantly at the end of the experimental period in the dogs fed on gari (P < 0.05).Gluconeogenesis from protein was greatest in the dogs fed on gari, five times greater than that in the control dogs, while gluconeogenesis from protein in the dogs fed on rice + cyanide was approximately twice as high as that of the control dogs. Histopathological examination of the pancreas showed haemorrhage, necrosis, fibrosis and atrophy of the acinar tissue and fibrosis of the islets of Langerhans in the dogs fed on gari. The pancreas of the dogs fed on rice+cyanide showed similar lesions but haemorrhage was not prominent and fibrosis was more marked. The present study indicated that a hypoinsulinaemia developed which was more severe in the animals fed on gari than in the dogs fed on the rice+cyanide diet and that the condition was not related to the level of plasma thiocyanate or the histopathology observed.Pancreatopathy : Cassava diet: Dog

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _Growing dogs were divided into three groups and were fed on nutritionally-balanced diets. Control dogs were fed on a rice diet, the cassava (gari) group ate a diet in which gari provided the carbohydrate source, while the rice +cyanide group consumed the rice diet to which hydrocyanic acid (equivalent to that present in gari) was added. Each group consumed its diet for 14 weeks, during which plasma thiocyanate concentration and total serum triiodothyronine (T3) were monitored. At the end of the experiment the concentrations of the plasma free amino acids phenylalanine and tyrosine, the thyroid weights and histology were determined. While plasma thiocyanate remained undetectable in control dogs, animals consuming both gari and rice +cyanide generated significant amounts. In the control dogs and the gari group, total serum T, increased 40 and 38.8 % respectively from the basal level by the end of the period (P < 0.02). In contrast there was a decrease in T, by 36 % in the dogs fed on rice + cyanide (P < 0.05).This group also showed significant thyroid enlargement and a histological picture consistent with parenchymatous goitre, whereas the gari group was essentially normal. The relatively low mean thyroid weight, the rise in total serum T, level and the normal histological appearance of the gland indicate that dogs that consumed the gari diet were essentially normal with respect to their thyroid function, in spite of their high blood thiocyanate content. In contrast, dogs that consumed rice with cyanide suffered from hypothyroidism and goitre. It is suggested that the gari diet, despite generating thiocyanate endogenously, when taken in a nutritionally-balanced diet with high-quality animal protein, has no deleterious effects on thyroid function.Thyroid: Cassava diet: Dog