RESUMO
Platelets of reserpinized rabbits, incubated in buffer containing tritiated 5-hydroxytryptamine (3H-5HT), have the ability to convert 3H-5HT into labeled compound(s) extractable with alkaline-chloroform. The bulk of the chloroform-extractable radioactivity showed a Rf value similar to authentic melatonin on silicagel thin-layer chromatography. The labelled product eluted with ethanol from the silicagel area where melatonin was suspected to reside was identified as melatonin by mass spectrometry and radioimmunoassay. Our in vitro experiments demonstrate that rabbit platelets are capable of converting 5-HT into melatonin apparently because they possess the enzymatic equipment necessary for this biosynthesis i.e. serotonin N-acetyltransferase and hydroxyindole-O-methyltransferase.