Hormonal regulation of radioiodide uptake activity and Na+/I- symporter expression in mammary glands

The observation that radioiodide uptake (RAIU) activity, mediated by the Na +/I- symporter (NIS), is significantly increased in lactating breast sugges ts that RAIU and NIS expression in mammary gland are modulated by hormones involved in active lactation. We showed that both the NIS expression level and RAIU in rat mammary gland are maximal during active lactation compared to those in the mammary glands of virgin and pregnant rats as well as the i nvoluting mammary gland. In the lactating mammary gland, NIS is clustered o n the basolateral membrane of alveolar cells as a lesser glycosylated form than NIS in thyroid. The RAIU of lactating mammary gland was partially inhi bited by treatment with a selective oxytocin antagonist or bromocriptine, a n inhibitor of PRL release. These findings suggest that RAIU and NIS expres sion in mammary gland are at least in part modulated by oxytocin and PRL. I ndeed, we showed that NIS messenger ribonucleic acid level was increased in a dose-dependent manner by oxytocin and PRL in histocultured human breast tumors.