The inhibitory effect of progesterone on lactogenesis during pregnancy is already evident by mid- to late gestation in rodents

LÓPEZ FONTANA CM; MASELLI ME; SALICIONI AM; CARÓN RW

REPRODUCTION FERTILITY AND DEVELOPMENT

CSIRO PUBLISHING

Año: 2011 vol. 24 p. 704 - 714

1031-3613

Lactogenesis is a very complex process highly dependent on hormonal regulation. In the present study, we investigated the time-course of the inhibitory actions of progesterone on prolactin secretion, mammary gland morphology, and lactogenesis from mid- to late gestation in rodents. Groups of pregnant rats were luteectomized or administered with mifepristone on days 10, 13,15 or 17 of gestation, and decapitated 28 or 48 h later. Whole blood samples and the inguinal mammary glands were taken for determinations of hormone levels and for measurement of mammary content of casein and lactose, and for tissue morphology analyses, respectively. Luteectomy or mifepristone evoked prolactin increases only after day 17 of gestation. Mammary content of casein was increased by both treatments regardless their  timing or duration. Mifepristone was less effective than luteectomy to induce lactose production and the effect was only observed after day 15 of gestation. Analysis of the mammary gland morphology confirmed the observed effect of progesterone on lactogenesis. Both treatments triggered a remarkable secretory activity in the mammary gland, even without a parallel epithelial proliferation, demonstrating that the mammary epithelium is able to synthesize milk compounds long before its full lobulo-alveolar development is achieved, provided that progesterone action is abolished. Thus, our study demonstrates that progesterone is a potent hormonal switch for the prolactin and prolactin-like effects on mammary gland development and its milk-synthesizing capacity during pregnancy, and that its inhibitory action is already evident by mid-pregnancy in rodents.