The pineal and extra-pineal origins of 5-sulphatoxy N-acetyl-serotonin in humans

In humans 6-sulphatoxy melatonin (SaMT) is the principal metabolite of endo genous and exogenous melatonin. 5-sulphatoxy N-acetyl-serotonin (SNAS) is a minor metabolite of exogenous melatonin, but it has not been established w hether the levels of endogenous SNAS in plasma derives principally from end ogenous melatonin. We have developed the first radioimmunoassay (RIA) for S NAS and used it (together with RIAs for melatonin and SaMT) to determine wh ether endogenous SNAS derives from endogenous melatonin or from platelet se rotonin. Our results show a) the values of endogenous SNAS, unlike endogeno us SaMT, increased with blood collection procedures that increased the valu es of serotonin, b) the values of endogenous SNAS in urine or in platelet-p oor plasma were approximately the same as those of endogenous SaMT, but, un like SaMT, did not show a diurnal rhythm, and c) we confirmed that SNAS was a minor metabolite of orally ingested melatonin. Thus, our conclusion is t hat SNAS is a minor metabolite of exogenous melatonin, but is not a signifi cant metabolite of endogenous melatonin. In all probability, endogenous SNA S is principally the metabolite of platelet serotonin.