I¹³¹ accumulation by the lactating rat mammary gland

¹ Department of Physiology, University of Tennessee, Memphis, Tennessee

The mammary glands of lactating rats fed a low-iodine diet accumulated 50% of an injected I¹³¹ dose or five times as much as the thyroid gland and twice as much as excreted by the kidneys in 17–24 hr. Rats which accumulated greater amounts of I¹³¹ in their mammary glands had significantly lesser thyroidal I¹³¹ uptakes. KClO₄ and methimazole significantly reduced accumulation of I¹³¹ in milk, KClO₄ being the more potent. Methimazole acted primarily in reducing the binding of I¹³¹ to milk protein. The concentration of I¹³¹ in milk, trichloroacetic acid-precipitable I¹³¹ in milk and in plasma, and ratio of milk I¹³¹ to plasma I¹³¹ were significantly reduced by the addition of iodide to the diet. The amount of I¹³¹ in the milk was not correlated with the amount of milk secreted. Exogenous thyroxin inhibited thyroidal I¹³¹ uptake but did not influence accumulation of I¹³¹ by the mammary gland. Injection of thyrotrophin restored thyroidal uptake of I¹³¹ but did not affect accumulation of I¹³¹ by the mammary gland.

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