ANALYSIS OF 5-METHOXYTRYPTAMINE AT THE FEMTOMOLE LEVEL IN THE RAT ANDQUAIL BRAIN BY GAS-CHROMATOGRAPHY ELECTRON-CAPTURE NEGATIVE-ION CHEMICAL-IONIZATION MASS-SPECTROMETRY

A sensitive method for the measurement of endogenous 5-methoxytryptami ne in brain tissue has been developed using capillary column gas chrom atography-electron-capture negative-ion chemical ionization mass spect rometry. 5-Methoxytryptamine was first converted to N-[H-2(3)]acetyl-5 -methoxytryptamine by reaction with hexa-deuterated acetic anhydride, followed by reaction with pentafluoropropionic anhydride to yield the highly electron-capturing 3,3'-spirocyclic pentafluoropropionyl indole nine derivative. Quantitative analysis was carried out by selected-ion monitoring of the [M-HF](.-) and [M-HF-DF](.-) ion intensity of the 3 ,3'-spirocyclic pentafluoropropionyl indolenine derivative, using 5-me thoxy-[alpha,alpha,beta,beta-H-3(4)]tryptamine as the internal standar d. The presence of 5-methoxytryptamine in the brain tissue was demonst rated. In the absence of a monoamine oxidase inhibitor, the mean+/-S.D . levels of 5-methoxytryptamine in the rat and quail whole brain were found to be 30+/-6 and 347+/-52 pg/g, respectively. The possible physi ological functions of 5-methoxytryptamine as a neuromodulator and/or n eurotransmitter have to be considered.