Transformations of prostaglandin H 2 in the cat brain

Abstract

Transformations of prostaglandin H 2 were studied in the whole homogenate and subcellular fractions (microsomes, high-speed supernatant) of the cat brain. Prostaglandin H 2 was converted enzymatically to prostaglandin E 2, 6-ketoprostaglandin F 1α, and thromboxane B 2. While prostaglandin E 2and thromboxane B 2 predominated, respectively, in the whole homogenate and the microsomes, 6-ketoprostaglandin F 1α was formed in both tissue preparations. Pretreatment of the microsomes with reduced glutathione stimulated the formation of prostaglandin E 2 at the expense of 6-ketoprostaglandin F 1α and thromboxane B 2. Imidazole and 15-hydroperoxyarachidonic acid interfered with the microsome-induced transformations of prostaglandin H 2 to thromboxane B 2 and 6-ketoprostaglandin F 1α, respectively. No prostaglandin D 2 was detected even after treatment of the tissue with reduced glutathione. Prostaglandin H 2, on the other hand, was converted to prostaglandin F 2α, but the yield of this compound in native tissue was equal to, or lower than, that in boiled tissue. We conclude that the feline brain is endowed with several enzymes (prostaglandin E 2 isomerase, thromboxane A 2 and prostaglandin I 2 synthetases) competing for the added endoperoxide. All enzymes were located in the microsomes. No evidence was obtained indicating enzymic reduction of prostaglandin H 2 to prostaglandin F 2α.