Metabolism of Prostaglandin Endoperoxide in Various Tissues of the Rat
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The conversion of a prostaglandin endoperoxide biosynthesis intermediate into many important end products by several tissues of the rat was studied. Two specific areas of the rat were dealt with: the brain and the gastrointestinal system. The rat heart was also investigated. The rat brain was found to produce PGD2 from the endoperoxide in almost complete exclusion of all other prostaglandins. Mass spectral analysis confirmed the PGD2 identity. The PGD2 synthetase enzyme was found to be located in the high speed supernatant, indicating a soluble enzyme. Enzyme concentration studies were done, and a linear relation was observed for the enzyme concentration and PGD2 production. Furthermore, after a time study was done, it was found that the maximum production of PGD2 (50-60% of total radioactivity) was reached within 1 min. Inhibition studies done with plasma albumin, and PHMB and glutathione as inhibitors revealed that the enzyme was real and quite specific. Partial purification of the enzyme was attempted, but failed. In vivo experiments were performed with direct injection of PGD2 into the brain and injection subcutaneously. A sedation effect in the rat was observed. A lowering of body temperature was also noted. Furthermore, the effects of the two types of injection were identical, indicating that PGD2 is well able to pass the blood-brain barrier. Incubations with tissues from the gastrointestinal system revealed a production of 6-keto-PGF 1a (PGX metabolite) as evidenced by a mass spectral analysis. Physiological conditions for this production (25% of keto formation) (high enzyme to substrate ratio) were favored over non-physiological conditions (:6% 6-keto formation). The PGX synthetase enzyme was finally located in the micro somal (membrane) fraction, however, it was possible to remove the enzyme from the membrane by the use of a Polytron homogenizer. Inhibition studies indicated that U-51,605 (9,11,diaza prosta-5,lJ-dienoic acid) and glutathione were able to inhibit the PGX synthetase enzyme, approximately halfing the production of FGX in favor of the production of other classical prostaglandins. Incubation done with the heart tissue revealed a large production of 6-keto-PGF1a (:35% 6-keto-PGF1a ). No other studies were done with heart tissue.