Pharmacological studies on 5-hydroxy-L-tryptophan (L-5HTP)

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Abstract
The effect of tryptophan hydroxylase inhibitor p-CPA [p-chlorophenylalanine] and 5-HT [5-hydroxytryptamine] precursor L-5HTP [L-5-hydroxytryptophan] was studied on conditional avoidance response and 5-HT content in rat brain. Continuous administration of p-CPA improved the acquisition of conditional avoidance response and retarded the loss of acquired response. Body weight gain was suppressed at the low level. When the conditional avoidance response of the rats reached a certain level, it was suppressed by giving L-5HTP at 25 and 50 mg/kg in the rats given p-CPA, but no effect was observed in the rats given CMC [carboxymethylcellulose]. The 5-HT content in the brain was reduced to 22% of the control value by a single administration of p-CPA 316 mg/kg, but it rapidly recovered to a normal level with L-5HTP administration. The presence or absence of p-CPA loading causes a significant difference in the appearance of behavior alteration in rats following administration of L-5HTP.