Effects of monoamine precursors on food intake in male rats

Effects of monoamine precursors on food intake in male rats were studied. Rats were subjected to an artificial circadian pattern of eating, i.e., a five-hour feeding program during daytime and food deprived during the rest of day. Feeding responses after treatment of drugs were examined. Intraperitoneal injection of L-beta-3, 4-dihydroxyphenylalanine (L-DOPA), DL-threo-dihydroxyphenylserine (DOPS), or 5-hydroxy-L-tryptophan (5-HTP) suppressed food intake. The suppression occurred within the first thirty minutes of the test period and their order of potency came out 5-HTP > L-DOPA = DOPS. The suppressive action of 5-HTP was very strong and lasted at least 3 days. The mechanism of this feeding suppressed action by either the central satiety center or the peripheral inhibiting system was discussed in this context.