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

Oestradiol acting on a progesterone-primed uterus stimulates prostagla ndin (PG) F-2 alpha synthesis by the endometrium. In some species (not ably the sheep, cow and goat) oxytocin released from the ovary also fo rms 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 m echanisms by which these three hormones control endometrial PGF(2 alph a) synthesis and release are far from clear, Oxytocin stimulates the s ynthesis of inositol phosphates and diacylglycerol in the endometrium of some species, but whether this pathway is involved in endometrial P GF(2 alpha) synthesis is still open to question. There is evidence tha t increased endometrial PGF(2 alpha) synthesis is dependent upon incre ased endometrial protein synthesis but, apart from the recorded effect s of steroid hormones on the concentrations of phospholipase A(2), pro staglandin H synthase and oxytocin receptors, it is not known what oth er endometrial proteins are involved, Some disorders of menstruation a re 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, ex cept in the pig where the PGF(2 alpha) produced is directed from the v enous drainage to the uterine lumen, In those species in which endomet rial PGF(2 alpha) synthesis is dependent upon oxytocin secreted by the ovary, the conceptus secretes an interferon-tau (previously named tro phoblast 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 whi ch prevent endometrial PGF(2 alpha) synthesis during early pregnancy i n other species are not known, although it is clear that they are not interferons.