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Effect of Feeding a High Level of Rapeseed Meal on Weight Gains and Thyroid Function of Rats¹

Department of Nutrition, University of Guelph, Guelph, Onatrio, Canada

Weanling male rats were divided into four groups; three groups were fed ad libitum diets containing casein (C), rapeseed meal-variety (Bronowski) (BM) and commercial rapeseed-meal-B. napus (NM), respectively, and the fourth group was fed BM with consumption restricted to total intake of NM (BM-restricted). After 3 weeks, 5 µCi ¹²⁵I was injected into each rat for thyroid function studies. Weight gain of rats fed C or BM was superior to those fed NM or BM-restricted. The latter two treatments resulted in the enlargement of liver, kidney, thyroid and adrenal glands. Compared to rats fed C, thyroidal ¹²⁵I uptake of rats fed BM, BM-restricted or NM was significantly altered. With BM there was a more rapid initial uptake and slower release rate of ¹²⁵I, whereas for NM the pattern was similar to that for C but the total uptake was considerably less. The percentage of protein-bound ¹²⁵I, in serum of rats fed NM was lower than that of rats fed the other three diets over the experimental period. Paper chromatography of thyroid hydrolysates from rats fed NM showed a greater amount of ¹²⁵I^- and mono-¹²⁵I-tyrosine, and lesser amount of di-¹²⁵I-tyrosine, tri-¹²⁵I-thyronine and tetra-¹²⁵I-thyronine than hydrolysates from rats fed C, BM or BM-restricted. Results suggest that a high intake of glucosinolates affected thyroid function by blocking iodine trapping and iodine organification, whereas a low intake of glucosinolate had a stimulating effect on iodine uptake by the thyroid gland.

Manuscript received 2 February 1971.