Pigs experience significant conceptus loss near mid-gestation, correlating with increasing glandular epithelial (GE) development and secretory activity. Secreted phosphoprotein 1 (SPP1, osteopontin) increases in GE between days 30 and 40 of pregnancy and is expressed in the GE of day 90 pseudopregnant pigs, suggesting that progesterone (P4) from corpora lutea is responsible for induction of SPP1 in GE. In this study, pigs were ovariectomized and treated daily with P4 to assess effects of 40 days of P4 exposure on SPP1, P4 receptor (PGR), uteroferrin (ACP5), and fibroblast growth factor 7 (FGF7) expression in porcine endometria. PGR mRNA decreased in pigs injected with P4 compared with pigs injected with corn oil (CO), and PGRs were downregulated in the luminal epithelium (LE) and GE. ACP5 mRNA increased in pigs injected with P4 compared with pigs injected with CO, and ACP5 was induced in the GE of P4-treated pigs. FGF7 mRNA increased in pigs injected with P4 compared with pigs injected with CO, and FGF7 was induced in the LE and GE of P4-treated pigs. SPP1 mRNA was not different between pigs injected with P4 compared with pigs injected with CO, and SPP1 was not present in the GE of P4-treated pigs. Therefore, long-term P4, in the absence of ovarian and/or conceptus factors, does not induce SPP1 expression in GE. We hypothesize that a servomechanism involving sequential effects of multiple hormones and cytokines, similar to those for sheep and humans, is required for GE differentiation and function, including the synthesis and secretion of SPP1.
Daniel W Bailey, Kathrin A Dunlap, David W Erikson, Atish K Patel, Fuller W Bazer, Robert C Burghardt and Greg A Johnson
Daniel W Bailey, Kathrin A Dunlap, James W Frank, David W Erikson, Bryan G White, Fuller W Bazer, Robert C Burghardt and Greg A Johnson
In pigs, endometrial functions are regulated primarily by progesterone and placental factors including estrogen. Progesterone levels are high throughout pregnancy to stimulate and maintain secretion of histotroph from uterine epithelia necessary for growth, implantation, placentation, and development of the conceptus (embryo and its extra-embryonic membranes). This study determined effects of long-term progesterone on development and histoarchitecture of endometrial luminal epithelium (LE), glandular epithelium (GE), and vasculature in pigs. Pigs were ovariectomized during diestrus (day 12), and then received daily injections of either corn oil or progesterone for 28 days. Prolonged progesterone treatment resulted in increased weight and length of the uterine horns, and thickness of the endometrium and myometrium. Hyperplasia and hypertrophy of GE were not evident, but LE cell height increased, suggesting elevated secretory activity. Although GE development was deficient, progesterone supported increased endometrial angiogenesis comparable to that of pregnancy. Progesterone also supported alterations to the apical and basolateral domains of LE and GE. Dolichos biflorus agglutinin lectin binding and αv integrin were downregulated at the apical surfaces of LE and GE. Claudin-4, α2β1 integrin, and vimentin were increased at basolateral surfaces, whereas occludins-1 and -2, claudin-3, and E-cadherin were unaffected by progesterone treatment indicating structurally competent trans-epithelial adhesion and tight junctional complexes. Collectively, the results suggest that progesterone affects LE, GE, and vascular development and histoarchitecture, but in the absence of ovarian or placental factors, it does not support development of GE comparable to pregnancy. Furthermore, LE and vascular development are highly responsive to the effects of progesterone.