The toxic effect of different concentrations of "detoxified" rapeseed meal (DRSM) obtained by 2 h lixiviation was studied. This preparation contained 0.02 % oxazolidinethiones (VTO) and no detectable isothiocyanates (ITC). It was fed for 4 weeks to weanling rats in amounts that provided from 0 to 100 % of total dietary protein. The control diet provided 20% protein from casein. Another control group was fed crude rapeseed meal (RSM) to the same protein level. Growth rates and protein efficiency ratio (PER) were similar in rats fed DRSM and casein diets. The substitution of casein by increasing levels of DRSM did not modify PER. The weight of the liver, thyroid, heart, spleen, adrenals and kidneys was normal. In animals fed DRSM no histological changes were detected in the liver. The thyroid exhibited changes similar to, but of lesser severity than in animals fed crude RSM. It is suggested that other toxic compound(s) may be present in rapeseed meal that are not extractable by lixiviation. The need of further investigations of the effect of this "detoxified" product including functional studies before its extensive inclusion in animal or human diets is emphasised.
The toxic effect of two levels of semisynthetic D-5-vinyl-2-thiooxazolidone (VTO) (0.006 and 0.0012%) was compared in rats with that of 0.005% of the same substance present in ‘detoxified’ rapeseed meal (DRSM). Diets containing 10% protein as casein (control group) or DRSM were tested. Growth rates and protein efficiency ratio with DRSM were slightly less than in the controls. VTO did not affect the growth rate and seems to increase the protein efficiency ratio. Liver and thyroid weights were normal in rats fed DRSM. VTO increased liver weight independently of the concentration in the diet. The effect on thyroid weight was proportional to VTO concentration, and the glands reached weights twice or three times that of the normal. Both levels of semisynthetic VTO led to damage of the hepatic parenchyma. Liver weight was increased. Animals receiving DRSM did not show differences either in liver weight or histology compared to the controls. Thyroid histology of animals fed VTO or DRSM showed smaller follicles lined by tall cells and reduction of lumenal colloid. These changes were more severe in animals fed VTO. It is postulated that both VTO and isothiocyanate may decrease thyroid hormone production which in turn stimulates TRH and TSH release leading to glandular hyperplasia and hypertrophy.
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