Plasma concentrations of 5-methoxytryptamine, 5-methoxytryptophol and melatonin after 5-methoxytryptamine administration of golden hamsters: physiological implications

5-Methoxytryptamine (5-MT), 5-methoxytryptophol (5-ML) and melatonin (Mel) were measured in the plasma after 2, 5, and 8 weeks administration of 25 micrograms 5-MT to golden hamsters kept under long photoperiod. 5-MT showed a one compartment kinetic profile in the plasma with half lives of 14.8 min after 2 weeks, 15 min after 5 weeks and 19.1 min after 8 weeks. A rapid metabolism of 5-MT was shown, Mel and 5-ML being detected in the plasma following 5-MT administration. However it was also shown that the gonadal atrophy observed after 5-MT administration cannot be due to its metabolism into these 2 compounds. Indeed when exogenously administered at a dose generating the same plasma concentration as that observed after 5-MT, the gonadal regression observed after the association of 5-ML and Mel is much less than that observed after 5-MT. 5-MT is thus a compound of great physiological interest.