Secretion of I131 into milk by lactating rat mammary glands

Abstract

The amount of I131 secreted in 8 hours into milk of lactating rats was determined on the 14th day of lactation using a technique which effected almost complete removal of milk from all 12 mammary glands. The mammary glands and kidneys each trapped 35–40% of the injected I131 dose when the isotope was injected after the mammary glands of the rats had been emptied of milk. The amounts of I131 eliminated via milk and urine were not affected by the dietary level of iodide. Milk from these animals contained twice as much as I131 and four to five times more per gram of milk as milk from glands which were partially full at the time of I131 administration. A significant reduction in thyroidal I131 uptake accompanied the increased loss of I131 via the milk from the previously empty mammary glands. These data indicate that lactating rat mammary glands are powerful iodide traps which, in cooperation with the kidneys, reduce the amount of iodide available for thyroxine synthesis.