Effect of oestradiol 17 β on prostaglandin biosynthesis by the uterus of ovariectomized rat and guinea pig

In vitro prostaglandin biosynthesis by uteri of ovariectomized rats and guinea pigs treated or untreated with oestradiol 17 β, administered subsutaneously, was measured by R.I.A. of PGF2α and PGE2. Incubations with [1-14C] arachidonic acid were also performed and labelled metabolites were analyzed by TLC. The main metabolite in rats was 6 keto PGF1α and in decreasing order of magniture, PGF2α and PGE2. In guinea pig PGF2ga was the main product. Ovariectomy in rats completely changed the pattern of synthesized prostanoids: PGI2 production was doubled when compared to cycling rats and PGE2 increased 10 fold. PGF2α walues were similar to the mean value measured during the cycle. OE2 treatment almost completely inhibited PGI2 synthesis and reduced PGE2 by half. Total PG synthesis in OE2 treated animals was decreased by 5 fold when compared to spayed rats. Endogenous PGFsα synthesis was slightly stimulated. In the guinea pig OE2 treatment of ovariectomized animals increased the total synthesis from 50 per cent. PGF2α was always the main metabolite. In conclusion OE2 regulation of uterine PG synthesis is depending on the animal species and cannot be explained by a unique effect on the cyclooxyhenase, but rather by an interplay on the various enzymes of the arachidonic acid cascade.