Prolactin stimulation of iodide uptake into mouse mammary gland explants

These studies show that prolactin (PRL) stimulates iodide accumulation in cultured mouse mammary tissues. This effect of PRL likely causes the elevated concentration of iodide that occurs in the milk of a number of species. In time course studies, an initial effect of PRL occurred after 4 h, whereas a maximum two- to threefold increase was observed after 24 h. In dose-response studies, 1 ng/ml PRL elicited a significant response, whereas PRL concentrations >5 ng/ml stimulated maximum responses. Other lactogenic hormones, including human growth hormone (GH) and human placental lactogens, also stimulated iodide uptake, whereas nonlactogenic substances, including bovine GH, bovine serum albumin, and thyroid-stimulating hormone, were without effect. PRL had no effect on iodide uptake into fat cells. In further studies it was shown that PRL stimulates iodide incorporation into macromolecules in a 10% trichloroacetic acid precipitable tissue fraction as well as in a pH 4.6 isoelectric precipitate. The findings from these studies suggest that PRL may stimulate both the accumulation of free iodide in milk and iodide incorporation into milk proteins.