THE CONTROL OF PROSTAGLANDIN PRODUCTION BY THE ENDOMETRIUM IN RELATION TO LUTEOLYSIS AND MENSTRUATION

Oestradiol acting on a progesterone-primed uterus stimulates prostaglandin (PG) F-2 alpha synthesis by the endometrium. In some species (notably the sheep, cow and goat) oxytocin released from the ovary also forms part of the physiological stimulus for increased endometrial PGF(2 alpha) production, The corpus luteum contains high concentrations (> 1 mu g/g tissue) of this peptide in these species, The intracellular mechanisms by which these three hormones control endometrial PGF(2 alpha) synthesis and release are far from clear, Oxytocin stimulates the synthesis of inositol phosphates and diacylglycerol in the endometrium of some species, but whether this pathway is involved in endometrial PGF(2 alpha) synthesis is still open to question. There is evidence that increased endometrial PGF(2 alpha) synthesis is dependent upon increased endometrial protein synthesis but, apart from the recorded effects of steroid hormones on the concentrations of phospholipase A(2), prostaglandin H synthase and oxytocin receptors, it is not known what other endometrial proteins are involved, Some disorders of menstruation are associated with abnormal PG production by the endometrium, but the reasons for this abnormality are not clear, During early pregnancy an increase in PGF(2 alpha) synthesis by the endometrium is prevented, except in the pig where the PGF(2 alpha) produced is directed from the venous drainage to the uterine lumen, In those species in which endometrial PGF(2 alpha) synthesis is dependent upon oxytocin secreted by the ovary, the conceptus secretes an interferon-tau (previously named trophoblast protein-1) which prevents oestradiol and oxytocin acting on a progesterone-primed uterus from stimulating endometrial PGF(2 alpha) synthesis, The identities of the factors produced by the conceptus which prevent endometrial PGF(2 alpha) synthesis during early pregnancy in other species are not known, although it is clear that they are not interferons.