Prostaglandins and reproduction. 1. Physiological aspects

Eicosanoids are a family of polyunsaturated 20-carbon fatty acids and their metabolites. The metabolites are produced by 3 enzymatic pathways--the cyclooxygenase pathway providing prostaglandins (PGs) the lipoxygenase pathway and the epoxygenase pathway. Arachidonic acid (C20:4) is the most common fatty acid precursor in mammalian cells where it is incorporated as an ester into the membrane lipid complex. The eicosanoids have a variety of effects on cell activities including secretion muscle contraction cell growth and differentiation. The type of effect stimulation or inhibition depends on the metabolite its concentration the metabolic activity of the cell and the involvement of other humoral factors. The message may be transmitted via a specific membrane receptor to a specific transduction system--the adenyl or guanyl cyclase system and mobilization of free cytosolic Ca2+ or via the participation of membrane ion channels. Depending on which is involved the eicosanoid message applies to the cell in which it was synthesized or to neighboring cells (autocrine or paracrine action). Eicosanoids especially the PGs are involved in many reproductive processes--in the hypothalamic-pituitary axis in the ovary (follicle maturation and luteolysis) in the oviducts gamete migration and in the uterus (ovum implantation and parturition). PGs seem to have a variety of species-dependent effects on the normal onset of labor. In sheep there is an increase in fetal cortisol a drop in the progesterone/estrogen ratio and increased PG synthesis. In women there is an increase in phospholipase A2 activity in amnios and uterus with an increase in PGE2 in the 1st tissue and in PGF2alpha in the 2nd. The PGs from seminal fluid have several actions. They effect fertility by acting on the female genital tract or on spermatozoa. PGE1 and PGE2 influence the fertilization capacity. PGS also effect the process of ejaculation (inhibition of stimulatory effect of noradrenaline. Finally they effect the immune responses--PGEs and 19 hydroxy PGEs immunosuppressive characteristics. (authors modified) (summary of ENG FRE)