An aldose reductase with 20 alpha-hydroxysteroid dehydrogenase activity is most likely the enzyme responsible for the production of prostaglandin f2 alpha in the bovine endometrium.

Prostaglandins are important regulators of reproductive function. In particular, prostaglandin F2 alpha (PGF(2 alpha)) is involved in labor and is the functional mediator of luteolysis to initiate a new estrous cycle in many species. These actions have been extensively studied in ruminants, but the enzymes involved are not clearly identified. Our objective was to identify which prostaglandin F synthase is involved and to study its regulation in the endometrium and in endometrial primary cell cultures. The expression of all previously known prostaglandin F synthases (PGFSs), two newly discovered PGFS-like genes, and a 20 alpha-hydroxysteroid dehydrogenase was studied by Northern blot and reverse transcription PCR. These analyses revealed that none of the known PGFS or the PGFS-like genes were significantly expressed in the endometrium. On the other hand, the 20 alpha-hydroxysteroid dehydrogenase gene was strongly expressed in the endometrium at the time of luteolysis. The corresponding recombinant enzyme has a K(m) of 7 microM for PGH(2) and a PGFS activity higher than the lung PGFS. This enzyme has two different activities with the ability to terminate the estrous cycle; it metabolizes progesterone and synthesizes PGF(2 alpha). Taken together, these data point to this newly identified enzyme as the functional endometrial PGFS.