Prostaglandin metabolism. I. Cytoplasmic reduced nicotinamide adenine dinucleotide phosphate-dependent and microsomal reduced nicotinamide adenine dinucleotide-dependent prostaglandin E 9-ketoreductase activities in monkey and pigeon tissues.

Homogenates of pigeon heart, brain, lung, liver, and the formed elements of blood and of monkey brain, liver, spleen, kidney, lung, uterus, heart, and the formed elements of blood contain an enzyme which catalyzes the reduction of the 9-keto group of prostaglandin E to form prostaglandin F. The prostaglandin E 9-ketoreductase in all of these tissues uses NADPH much more effectively than NADH and is found in the cytoplasmic fraction. In monkey liver, there is a second prostaglandin 9-ketoreductase, which is present in the microsomal fraction and uses NADH much more efficiently than NADPH. The activities of the prostaglandin 9-ketoreductases are extremely sensitive to the oxidized cofactors, and in vivo may be regulated by the relative concentrations of reduced and oxidized coenzymes. Such enzyme activities may, in turn, regulate the diverse physiological processes involving these two classes of prostaglandins.