Prostaglandin biosynthesis by the rat uterus during the oestrus cycle, temporal correlation with plasma oestradiol and progesterone concentrations, identification of 6 keto PGF1 alpha as the major metabolite.

Prostaglandin biosynthesis was studied in the rat uterus during the oestrous cycle. Uterine homogenates were incubated for 20 minutes inthe presence of exogenous substrate (2.10(-5)M). PGF2 alpha and PGE2 were measured by R.I.A.. A sharp peak of PGF2 alpha and a smaller peak of PGE2 were observed at prooestrus, 20 h. Another small PGE2 peak occurred at dioestrus II, 15 h. The lowest values of both PGs were found on dioestrus, 15 h. Plasma oestradiol concentrations were highest at proestrus, 15 h and 20 h. A sharp progesterone peak occurred at prooestrus, 20 h. The PGF2 alpha peak is next to the oestradiol peak and is superimposable or lags slightly beyond the progesterone peak. Incubation with 14C arachidonic acid and subsequent analysis of extracts by TLC and scanning showed that the major metabolite is PGI2, identified as 6 keto PGF1 alpha. The conversion rate of arachidonic acid into 6 keto PGF1 alpha is 5 times higher than into PGF2 alpha. 6 Keto PGF1 alpha was further identified by GC/MS. No significant difference was observed between 6 keto PGF1 alpha production during oestrus and dioestrus.