Endotoxemia can be caused by obesity, environmental chemical exposure, abiotic stressors and bacterial infection. Circumstances that deleteriously impact intestinal barrier integrity can induce endotoxemia, and controlled experiments have identified negative impacts of lipopolysaccharide (LPS; an endotoxin mimetic) on folliculogenesis, puberty onset, estrus behavior, ovulation, meiotic competence, luteal function and ovarian steroidogenesis. In addition, neonatal LPS exposures have transgenerational female reproductive impacts, raising concern about early life contacts to this endogenous reproductive toxicant. Aims of this review are to identify physiological stressors causing endotoxemia, to highlight potential mechanism(s) by which LPS compromises female reproduction and identify knowledge gaps regarding how acute and/or metabolic endotoxemia influence(s) female reproduction.
Immunocytochemistry was used to detect the presence of oestrogen and progesterone receptors in the cervices of prepubertal lambs, seasonally anoestrous ewes, cyclic ewes, and pregnant ewes of known gestational stages, to define the roles of gonadal steroids in cervical function. The presence of the immediate early gene product, c-Fos, a marker for cellular activation, was also investigated using immunocytochemistry and in situ hybridization. Oestrogen receptor immunoreactivity was restricted to the endometrium on days 0–3 of the oestrous cycle (day 0 = oestrus). In immature animals, very few scattered nuclei in the endometrium were immunoreactive. Oestrogen receptor immunoreactivity was not apparent in the endometrium during the remainder of the oestrous cycle or in this region in anoestrous animals. In pregnant ewes, oestrogen receptor immunostaining appeared as relatively few isolated nuclei in the connective tissue stroma. Progesterone receptor immunoreactivity was found in the endometrium at days 0–3 of the oestrous cycle and also in the luminal epithelium, the myometrium and the blood vessels. Progesterone receptor immunoreactivity was also found in these regions, with the exception of the endometrium, at all other stages examined. Immunostaining for c-Fos was present in the endometrium at days 0–3 of the oestrous cycle, and some scattered immunopositive nuclei were present in prepubertal animals. c-Fos immunoreactivity was also found in the myometrium and in blood vessels at all other stages examined. Visualization of c-fos gene expression by in situ hybridization showed that it occurred in the luminal epithelium and blood vessels at oestrus, but was restricted to the blood vessels in all other samples examined.
Early exposure of pregnant gilts to oestrogen, prior to the normal period of porcine conceptus oestrogen secretion, disrupts the uterine environment resulting in complete embryonic mortality during the period of placental attachment to the uterine surface. The current study evaluates the uterine insulin-like growth factor (IGF) system following endocrine disruption of early pregnancy in gilts through exposure to exogenous oestrogen on Days 9 and 10 of gestation. Endometrial IGF gene and protein expression, IGF-I receptor (IGF-IR) gene expression, and uterine lumenal content of IGF binding proteins (IGFBPs) were evaluated in control and oestrogen-treated gilts on Days 10, 12, 13, 15 and 17 of gestation. Oestrogen treatment altered endometrial IGF-I and IGF-IR gene expression on Days 12 and 13 of gestation. Uterine content of IGF-I and IGF-II in control gilts was greatest on Days 10, 12, and 13 followed by a four- to sixfold decrease on Day 15 of gestation. Oestrogen treatment caused a premature proteolysis of IGFBPs within the pregnant pig uterus on Day 10 of gestation, and an earlier decline in uterine lumenal IGF-I content. Results demonstrate that early exposure of pregnant gilts to oestrogen causes premature loss of uterine IGFs during the period of conceptus elongation. Timing for the release of uterine IGFs during early porcine conceptus development may play an important function in the ability of the conceptus to attach and survive during the establishment of pregnancy.
Previous studies have suggested that the porcine endometrium may express several tissue kallikreins during the estrous cycle and early pregnancy. The present study investigated porcine endometrial and conceptus tissue kallikrein 1, 4, 11, and 14 mRNA expression during the estrous cycle and early pregnancy. Tissue kallikrein (KLK) gene expression was evaluated using quantitative RT-PCR and in situ hybridization. KLK1 expression was similar across the estrous cycle and early pregnancy, and localized to the endometrial luminal (L) and glandular (G) epithelium. KLK4 endometrial mRNA expression was greatest on days 0, 5, and 10 when compared with days 12, 15, and 17 of the estrous cycle and greater in cyclic compared with pregnant gilts. Expression of KLK4 was more intense in the stroma and uterine epithelium from days 0 to 10 of the estrous cycle. Endometrial KLK11 mRNA was not different between cyclic and pregnant gilts but the expression was greatest on days 10 and 12 compared with all other days evaluated. There was an increased intensity of KLK11 gene expression in the stratum compactum on day 10 of the estrous cycle and early pregnancy. Endometrial KLK14 mRNA expression was not detectable on days 5 and 10 but was expressed on days 0, 12, 15, and 17 of the estrous cycle and pregnancy. KLK14 expression was localized in the uterine L and G epithelium, and stroma throughout the endometrium after day 10. Conceptus KLK1 mRNA did not change from days 10 to 17 of gestation. However, conceptus KLK4, and 14 mRNA expression was greatest on day 10 with expression declining after day 14 of gestation. Expression of the various tissue kallikreins in the endometrium and conceptus during the estrous cycle and early pregnancy in the pig can serve in the activation of growth factors and tissue remodeling during the establishment of pregnancy.