Measurement of Tryptophan Hydroxylase Activity in Rat Pineal Glands and Pinealocytes Using an HPLC Assay With Electrochemical Detection


  • Ivan N. Mefford is presently at the National Institutes of Mental Health, Bethesda, MD 20892.

  • Richard Grady Jr. is presently at the Upjohn Co., Kalamazoo, MI 49009.

Address reprint requests to Dr. David Sugden at his present address, Department of Physiology, King's College, London W8 7AH, England.


A method for measuring tryptophan hydroxylase activity by assaying the product 5-HTP using high-performance liquid chromatography (HPLC) with electrochemical detection is described. A nocturnal elevation (80%) in rat pineal gland tryptophan hydroxylase activity was detected. Experiments on isolated rat pinealocytes with the protein synthesis inhibitor cycloheximide indicate that tryptophan hydroxylase turns over rapidly in these cells. This method will be valuable in studies of the adrenergic mechanisms regulating pineal tryptophan hydroxylase activity.