The metabolism of prostaglandin D2 after inhalation or intravenous infusion in normal men.

Tritium-labelled prostaglandin D2 (PGD2) was administered to normal volunteers by either intravenous infusion or inhalation in order to establish which metabolites of PGD2 are initially found in human plasma. Inhaled PGD2 was rapidly absorbed from the airways, as indicated by the rapid appearance of tritium in the plasma. Metabolites chromatographically similar to 9 alpha,11 beta-PGF2 and 13,14-dihydro-15-keto-9 alpha,11 beta-PGF2 were found after both routes of administration. At later time points, other unidentified compounds were present. Only after intravenous infusion was there evidence of metabolites with 9 alpha,11 alpha stereochemistry of the ring hydroxyl functions. In human lung, 9 alpha,11 beta-PGF2 was metabolized in the presence of NAD+ to compounds tentatively identified by gas chromatography/mass spectrometry (GC/MS) as 15-keto-9 alpha,11 beta-PGF2 and 13,14-dihydro-15-keto-9 alpha,11 beta-PGF2. Thus, after 11-ketoreductase-dependent metabolism of PGD2 to the biologically active compound 9 alpha,11 beta-PGF2, further metabolism probably proceeds by the combined action of 15-hydroxyprostaglandin dehydrogenase/15-ketoprostaglandin-delta 13-reductase (15-PGDH/delta 13R). Both 9 alpha,11 beta-PGF2 and its 13,14-dihydro-15-keto metabolite may be useful analytes for the measurement of PGD2 turnover, and may therefore prove to be important in understanding the pathophysiological significance of this putative mediator.