THE GOITROGENIC EFFECT OF NATURALLY OCCURRING L-5-VINYL- AND L-5-PHENYL-2-THIO-OXAZOLIDONE IN RATS

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Abstract
L-5-vinyl-2-thio-oxazolidone (VTO), found in the seeds of cruciferous weeds and in milk specimens from the endemic goiter districts of Finland, was fed to rats. A dose of 0.1 [mu]g/day had an almost significant and of 0.5 [mu]g/day a significant weight-increasing effect on the thyroid in 1-15 weeks. The quantities of VTOfound in milk specimens from endemic goiter districts of Finland are greater than the concentration of VTO in drinking fluid necessary for producing enlargement of the thyroid in rats. The minute daily oral doses of VTO that led to enlargement of the thyroid did not inhibit the radioiodine uptake of the gland. The smallest single oral dose of VTO which inhibited the 4-h radioiodine uptake in the ratthyroidwasO.lmg (almost significant) and 0.5 mg (significant), i.e. about 1000 times greater than the smallest daily amount which produced thyroid enlargement in long-term administration. The inhibition seemed to last for less than 8 hours. The goitrogenic activity of milk to which VTO had been added was still present after storage for one day, though VTO was no longer demonstrable by the chemical method of assay generally employed. L-5-phenyl-2-thio-oxazolidone (PTO), a compound also occurring naturally in weeds of the Cruciferae family, when administered to rats in doses as low as 2 [mu]g/day in long-term experiments, caused a distinct increase in relative thyroid weight, which appeared from 1 to 9 weeks after the start of the experiments. In the radioiodine tests, there were no clear-cut differences as compared with the control series. The results with both compounds show that the inhibition In the radioiodine uptake test after a single dose is too insensitive a method for the detection of minute amounts of goitrogens with a thiouracil-type of activity in foodstuffs.