Effects of porcine conceptus secreted products on uterine production of prostaglandins

During early pregnancy in pigs, uterine secretion and production of prostaglandins (PGs) are altered. This is due to a switch in secretion of endometrial PGs from an endocrine to an exocrine direction which is initiated by conceptus-derived estradiol. In addition, results reported within this dissertation indicate that porcine conceptus secretory products (pCSP) stimulate endometrial production of PGs. Exposure of the luminal surface of endometrium to pCSP, in vitro, or incubation of uterine explants with pCSP, stimulated secretion of prostaglandin F{dollar}sb{lcub}2alpha{rcub}{dollar} (PGF{dollar}sb{lcub}2alpha{rcub}{dollar}) and prostaglandin-E{dollar}sb2{dollar} (PGE) and activity of the substance was not dependent on estrogen priming of the endometrium in vivo. The stimulatory factor appears to be a low molecular weight, heat labile and trypsin-sensitive substance which is active at low concentrations (0.5 to 1 {dollar}mu{dollar}g/ml). Additionally, the stimulatory factor may associate with higher molecular weight substances and may be dependent on these carriers for its biological activity.; Results of another study indicate that altered secretion of PGs during early pregnancy in pigs is not related to changes in presence of the PG synthetase enzyme within specific cell types. Further, it is not related to differential activation of a calcium-independent endometrial phospholipase A2 (PLA{dollar}sb2),{dollar} which is thought to be the primary rate limiting enzyme in the synthesis of PGs. However, in vitro, the ability of pCSP to stimulate secretion of PGF{dollar}sb{lcub}2alpha{rcub}{dollar} may depend on PLA{dollar}sb2.{dollar} Characterization of a porcine endometrial PLA{dollar}sb2{dollar} enzyme revealed it to be one of a relatively small number of intracellular calcium-independent PLA{dollar}sb2{dollar} enzymes which may be beneficial to reproduction by regulating uterine production of PGs in pigs.; The results of studies reported in this dissertation also indicate that an initial response of the uterine endometrium to the presence of elongating conceptuses during maternal recognition of pregnancy is increased expression of a transcription regulatory factor, c-fos, which may be involved with altered endometrial secretory activity during this period and extension of the interestrous interval. It is hypothesized that estradiol, secreted by elongating conceptuses, is the primary stimulus for increased transcription of the c-fos gene. In addition, expression of c-fos during the initial maternal recognition of pregnancy period (Days 11 to 12) may alter endometrial responsiveness to estradiol during a second critical window of estrogen secretion (Days 15-16), which is also necessary for maternal recognition of pregnancy.