Many mammals have more than one mammary gland. Milk production is decreased in the gland with low milk consumption, while other glands continue milk synthesis. This study was undertaken to clarify the intragland feedback mechanism of milk production. First, tryptophan hydroxylase (TPH) and its downstream product serotonin (5-HT) were induced in the mammary epithelium of pituitary-grafted prolactin-deficient mice. Second, in the primary mammary epithelial cell culture, inhibitors of 5-HT signaling evoked morphological and molecular signs of activated lactation. Third, TPH mRNA was increased and milk protein mRNAs were decreased in unsuckled glands of lactating dams. Fourth, injection of a peripherally-acting inhibitor of 5-HT synthesis to the dam increased the milk intake of pups. These results support the idea that filling of the gland raised by lactogens increases the level of local TPH/5-HT, which in turn suppresses milk production.Gordon Research Conferences Mammary Gland Biolog
