LOCAL-CONTROL OF PARATHYROID HORMONE-RELATED PROTEIN SECRETION BY THEMAMMARY-GLAND OF THE GOAT

In late-pregnant goats, daily removal of secretion from one mammary gl and stimulated an early secretion of fluid by that gland in five of th e six animals studied. This early secretion of fluid was accompanied b y an early increase of parathyroid hormone-related protein (PTHrP) 1-8 6 concentration in the secretion of that gland alone. When lactation w as established, glands emptied thrice daily secreted PTHrP (1-86) in g reater quantities and concentrations than glands emptied once daily co ncurrently in the same animals. Toward the end of lactation, abrupt ce ssation of emptying one gland caused levels of PTHrP (1-86) to decline in the fluid in that gland but not the contralateral, emptied gland. We conclude that, in the goat, PTHrP (1-86) secretion into milk is lin ked to autocrine factor(s) that stimulate milk secretion when fluid is removed from the gland.