Incorporation of 18O2 into brain serotonin in vivo as a procedure for estimating turnover: a feasibility study in animals.

Serotonin (5HT) containing ¹⁸0 instead of ¹⁶0 was found in brain after exposing rats to an atmosphere of ¹⁸0₂. The ¹⁸0 incorporation appeared linear with time and 22% of the 5HT in striatum contained ¹⁸0 after one hour of exposure. ¹⁸0 entered 5HT by enzymatic reaction rather than by isotope exchange as treatment with p-chlorophenylalanine, to block tryptophan hydroxylase, prevented incorporation, while more ¹⁸0-5HT than normal was found in brain after treatment with pargyline, to block monoamine oxidase. Our studies suggest that the incorporation of ¹⁸0₂ into brain 5HT might be a feasible approach for evaluating 5HT turnover in animals and with some modification might be applied in man.