Platelet-activating factor in human decidua: Its role in parturition

Abstract

Platelet-activating factor (PAF) has been shown to play an important role in both fetal lung maturation and in parturition and it has been demonstrated that part of the PAF present in the amniotic fluid is associated with surfactant and, therefore, of lung origin. PAF receptors are present in type II pneumonocytes and the addition of the autacoid promotes both glycogenolysis and increased surfactant secretion from these cells. Moreover, type II pneumonocytes and a human amnion-derived cell line (WISH) have the capability of metabolizing PAF to ethanolamine phospholipids. It has also been established that PAF will cause intracellular Ca2+ mobilization and promote myosin phosphorylation and increased contractility in myometrial strips. Increased PAF biosynthesis in fetal tissues takes place during the latter stages of pregnancy, simultaneously with a decrease in the activity of PAF-acetylhydrolase (PAF-AH) in maternal plasma. The activity of PAF-AH is decreased by the administration of estrogens in vivo and is increased by glucocorticoids and progestins. A number of agents lower the secretion of PAF-AH by decidual macrophages, including 1,25-(OH)2D3, bacterial lipopolysaccharides, and some cytokines (IL1, TNF-α). This inhibitory action may result in higher levels of PAF and increased myometrial contractility as a consequence of infectious processes. PAF causes a profound intestinal necrosis when administered to rats by intravenous injection. Pretreatment with dexamethasone protects against this disease. The presence of PAF-AH in human milk may explain the protective effect of mother's milk against necrotizing enterocolitis.