Occurrence and determination of a natriuretic hormone, 2,7,8-trimethyl- 2-(β-carboxyethyl)-6-hydroxy chroman, in rat plasma, urine, and bile

The occurrence of a new natriuretic hormone, 2,7,8-trimethyl-2-(β- carboxyethyl)-6-hydroxy chroman (LLU-α, γ-CEHC) in rat plasma was demonstrated and its concentration was determined using a coupled-column HPLC with a fluorometric derivatization with 4-N,N-dimethylaminosulfonyl-7- piperazino-2,1,3-benzoxadiazole (DBD-PZ) followed by O-acetylation. The concentration of LLU-α was 328 ± 113 nM in rat plasma (N = 5). LLU-α was found in not only urine, but also bile, suggesting an enterohepatic circulation in body. We also assigned the configuration at C-2 of LLU-α in these biological fluids as (S)-form by an HPLC with a chiral column. The LLU- α concentration decreased significantly by fasting for 3 days (P < 0.01). These results support the possibility that LLU-α is produced from γ- tocopherol in diet via oxidative metabolism without racemization. (C) 2000 Academic Press.