We fed adult mink diets containing supplemental iodine,from o 50 320ppm,for one or seven months prior to breeding.Bllod samples collected from the adults and their offspring(kits)at 4wk post-partum were assayed for total thyroxine(T4),triiodothyronine(T3),reverse T3(rT3),and T4-binding indices.As expected T4 concentrations of the adult and kit mink varied inversely with the level of supplemental iodine.In addition,T3 and r T3 concentrations decreased gradually in kits from the long-term experiment in response to the increased dietary iodine of the dams.T3 concentrations of kits from dams fed iodine short-term decreased markedly while r T3 concentrations were elevated greatly in response to increased dietary iodine of the dam.These decreases in hormone levels are due to serum odine blocking the thyroid uptake of iodine and subsequent decrease of hormone synthesis,Excess iodine may also block the effect of thyroid stimulating hormone.The T4-binding indices of the adults,in general,were depressed,while the T4-binding indices of the kits were more variable.These effects are probably due to fluctuations in thyroglobulin.
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