Nursing for 48 Hours from Birth Supports Porcine Uterine Gland Development and Endometrial Cell Compartment-Specific Gene Expression

The first 2 wk of neonatal life constitute a critical period for estrogen receptor alpha (ESR1)-dependent uterine adenogenesis in the pig. A relaxin receptor (RXFP1)-mediated, lactocrine-driven mechanism was proposed to explain how nursing could regulate endometrial ESR1 and related gene expression events associated with adenogenesis in the porcine neonate during this period. To determine effects of nursing on endometrial morphogenesis and cell compartment-specific gene expression, gilts (n = 6-8/group) were assigned at birth to be either 1) nursed ad libitum for 48 h, 2) gavage fed milk replacer for 48 h, 3) nursed ad libitum to Postnatal Day (PND) 14, or 4) gavage fed milk replacer for 48 h followed by ad libitum nursing to PND 14. Uteri were collected on PND 2 or PND 14. Endometrial histoarchitecture and both ESR1 and proliferating cell nuclear antigen (PCNA) labeling indexes (LIs) were evaluated. Laser microdissection was used to capture epithelium and stroma to evaluate treatment effects on cell compartment-specific ESR1, VEGFA, and RXFP1 expression. Imposition of a lactocrine-null state by milk replacer feeding for 48 h from birth retarded endometrial development and adenogenesis. Effects of replacer feeding, evident by PND 2, were marked by PND 14 when endometrial thickness, glandularity, and gland depth were reduced. Consistently, in lactocrine-null gilts, PCNA LI was reduced in glandular epithelium (GE) and stroma on PND 14, when epithelial ESR1 expression and ESR1 LI in GE were reduced and stromal VEGFA and RXFP1 expression increased. Results establish that lactocrine signaling effects morphogenetic changes in developing uterine tissues that may determine reproductive capacity later in life.