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

Abstract

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.