9deoxydelta 9 delta 121314dihydroprostaglandin d2 a metabolite of prostaglandin d2 formed in human plasma incubation of prostaglandin d2 pgd2 with human plasma yielded a product that has been identified as 9deoxy910didehydro1213didehydro1314dihydropgd2 9deoxydelta 9 delta 121314dihydropgd2 the identification was based on mass spectrometry uv spectrometry mobilities and retention time on tlc and hplc and nmr the conversion of pgd2 to this product was dependent on the incubation time and the amount of plasma added to a reaction mixture and was abolished by prior boiling the conversion rate of pgd2 to this metabolite was 003 nmolmin per mg of protein of whole plasma at ph 80 at 37 degrees c similar conversion was also found by incubating pgd2 with human serum albumin added at the concentration found in plasma these results suggest that the conversion of pgd2 to this product is catalyzed by the enzymatic action of a plasma protein probably serum albumin the biological activities of this compound were examined in several systems it showed negligible activity in inhibition of human platelet aggregation and relaxation of rabbit stomach strip on the other hand it exhibited a three times stronger inhibitory activity ic50 18 microm than pgd2 ic50 5 microm on the growth of l1210 cultured cells