Serotonergic mechanisms involved in the suppression of feeding by 5-HTP in rats

The effect of 5-hydroxytryptophan (5-HTP), the serotonin precursor, on food intake in rats was investigated in this study. 5-HTP (100 mg/kg, i.p.) reduced food intake by 68.9% of control level. The anorectic effect of 5-HTP was antagonized by cyproheptadine (CYP, 4 mg/kg, i.p.), a serotonin receptor blockade. However, the anorectic effect of 5-HTP was also antagonized by propranolol (PROP 1mg/kg, i.p.) and sulpiride (SULP, 20 mg/kg, i.p.), while Pinodol (PIN 2mg/kg, i.p.) and Haloperidol (HAL 0.5 mg/kg, i.p) did not affect the suppressive effect of 5-HTP on food intake by 5-HTP. These results indicates that the anorectic action of 5-HTP was mediated by the serotonergic mechanism through 5-HT1 and 5-HT2 receptors.