Transformations of prostaglandin H2 in the cat brain

Transformations of prostaglandin H2 were studied in the whole homogenate and subcellular fractions (microsomes, high-speed supernatant) of the cat brain. Prostaglandin H2 was converted enzymatically to prostaglandin E2, 6-ketoprostaglandin F 1 alpha, and thromboxane B2. While prostaglandin E2 and thromboxane B2 predominated, respectively, in the whole homogenate and the microsomes, 6-ketoprostaglandin F1 alpha was formed in both tissue preparations. Pretreatment of the microsomes with reduced glutathione stimulated the formation of prostaglandin E2 at the expense of 6-ketoprostaglandin F1 alpha and thromboxane B2. Imidazole and 15-hydroperoxyarachidonic acid interfered with the microsome-induced transformations of prostaglandin H2 to thromboxane B2 and 6-ketoprostaglandin F1 alpha, respectively. No prostaglandin D2 was detected even after treatment of the tissue with reduced glutathione. Prostaglandin H2, on the other hand, was converted to prostaglandin F2 alpha, 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 E2 isomerase, thromboxane A2 and prostaglandin I2 synthetases) competing for the added endoperoxide. All enzymes were located in the microsomes. No evidence was obtained indicating enzymic reduction of prostaglandin H2 to prostaglandin F2 alpha.