EFFECT OF 1-METHYL-2-MERCAPTOMIDAZOLE (METHIMAZOLE-TAPAZOLE) ON FEED CONSUMPTION IN THE RAT.

Summary The mean daily feed consumption of a group of 18 female Sprague-Dawley Rolfsmeyer rats weighing a mean of 215 g during a 10-day period was 6.40 g/100 g bw. The rats were then injected subcutaneously daily with 400 μg/100 g bw of methimazole to block iodine uptake. After 10 days mean daily feed consumption was reduced to 5.97 g/100 g bw, a reduction of 6.72%, after 20 days to 5.72 g, a reduction of 10.63%, and after 30 days to 5.98 g, a reduction of 6.56%. The reductions in feed were statistically significant at P = 0.005 at each time interval. The I131 uptake was reduced from 28.08% to 1.36% after 24 days of treatment. Mean thyroid weight increased from 10.96 ± .81 mg to 21.78 ± .91 mg, an increase of 98.72% during the 30-day period, then decreased to 16.73 mg during a 7-day withdrawal period. Since reduction of feed intake to the extent observed has been shown to have no significant effect on TSR determination, it was concluded that methimazole could be used safely in estimation of TSR.