Metabolism of prostaglndin A. II. Isolation, characterization, and synthesis of PGA1 renal.

Since the renal cortex has recently been shown to be a major site of prostaglandin A₁ (PGA₁) metabolism, studies were undertaken to isolate and characterize the major metabolites. Homogenates of rabbit cortex (500g) were incubated with ³H-PGA₁ (50mg) in the presence of NAD⁺ (50mg). Acidic lipid extracts were subjected to linear gradient silicic acid chromatography. Six radioactive peaks were recovered, of which peak 4 was unconverted PGA₁. The major metabolites (1,3) were further subjected to reversed phase partition chromatography and TLC with and without silver nitrate. Three PGA₁ analogs were then synthesized via oxidation of the secondary alcohol group at C-15 by manganese dioxide (15-keto-PGA₁). The second compound was synthesized by hydrogenation of 15-keto-PGA₁ (15-keto 13, 14-dihydro PGA₁). The third compound (13, 14-dihydro PGA₁) was obtained by direct catalytic hydrogenation of PGA₁. Purification of these substances were achieved by a combination of silicic acid and thin layer chromatography. It was found that metabolite 1 cochromatographed on TLC (AgNO3) with synthesized 15-keto 13, 14-dihydro PGA₁. Both compounds were 100 times less potent than PGA₁ in lowering rat blood pressure. Metabolite 3 cochromatographed on TLC (AgNO3) with synthesized 13, 14-dihydro PGA₁. Both were as potent as PGA₁ in lowering rat blood pressure. Metabolites 1 and 3 absorbed UV at 221 nm but not at 280 nm following alkali treatment. These studies suggest that rabbit renal cortex metabolizes PGA₁ to what appears to be biologically active 13, 14-dihydro PGA₁ and biologically inactive 15-keto 13, 14-dihydro PGA₁. It remains possible that the hypotensive effect of PGA₁ is the result of its conversion to its biologically active 13, 14-dihydro derivative.