Effects of long-term progesterone on developmental and functional aspects of porcine uterine epithelia and vasculature: Progesterone alone does not support development of uterine glands comparable to that of pregnancy

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 longterm 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 α_v 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.