The Metabolism of I¹³¹by Surviving Slices of Rat Mammary Tissue1

TWO juxtaposed, dissociable processes participate in the thyroidal manufacture of hormone. First, the thyroid transports inorganic iodide against a concentration gradient (VanderLaan and VanderLaan, 1947; Taurog, Chaikoff and Feller, 1947). Secondly, the accumulated anion is employed in organic iodinations within the thyroid gland (Morton and Chaikoff; 1943; Schachner, Franklin, and Chaikoff, 1944). Isolated similar functions have been reported in extrathyroidal sites. For example, concentration differentials for ionic iodide are regularly established in saliva and in gastric secretions (Lipschitz 1929; Schiff, Stevens, Molle, Steinberg, Kumpe and Stewart, 1947). As yet, an extrathyroidal model displaying both properties has not been described. In 1944, the classical experiments of Keston demonstrated the presence of soluble iodinating enzymes in unpasteurized milk. Van Middlesworth, Tuttle, and Haney (1954) have shown that such iodinations of milk proteins may also occur in vivo. Recently, Honour, Myant, and Rowlands (1952) have reported that inorganic iodide is concentrated by the lactating human breast.