THE FLUOROMETRIC DETERMINATION OF 5‐METHOXYTRYPTAMINE IN MAMMALIAN TISSUES AND FLUIDS

— Using a sensitive and specific fluorometric procedure involving selective extraction, reaction of the extracts with o ‐phthalaldehyde (OP), separation of the OP derivatives by TLC, and determination of fluorescent characteristics and intensities, we have detected and measured 5‐methoxytryptamine, (5‐MT) in various central and peripheral tissues and fluids of the rat, dog, baboon, and man. Distribution of 5‐MT in peripheral tissues of the rat seemed to parallel that of 5‐HT, with highest levels being found in the gastrointestinal (GI) tract and Harderian gland, regions that are rich in 5‐HT and have been reported to contain systems capable of methylating 5‐HT. 5‐MT was detected in the lung, plasma, kidney, spleen, and heart of the rat. 5‐MT was present in the CNS of all species examined. No marked interspecies differences were observed. In the rat CNS, the regional distribution of 5‐MT did not parallel that of 5‐HT indicating that the systems for the synthesis, uptake, or transport of 5‐MT might be different than for 5‐HT. Pretreatment of rats with iproniazid resulted in a 50% increase in whole brain 5‐MT. Reserpine pretreatment had no effect, indicating that the storage or release mechanisms for 5‐MT are different than for the conventional amine transmitters. 5‐MT was detected in human CSF and urine but not in plasma. These data indicate that 5‐MT, a compound with potent pharmacological properties, is more widely distributed in the mammalian body than had previously been supposed.