Zanthoxylum piperitum, an Asian spice, inhibits food intake in rats

We investigated the effects of a total extract from Zanthoxylum piperitum fruit, of the volatile components of extract, and of a non-volatile fraction containing the major alkylamides of Zanthoxylum (NVA) on food intake in rats. In Experiment 1, three groups (A, B, C) of mildly food deprived rats were given one hour long feeding trials during which they were offered choices between an oat-bran wafer paired with vegetable oil and a wafer paired with a Zanthoxylum preparation in vegetable oil. Trials were divided into three blocks of two tests each. During Blocks 1 and 3, two wafers coated with vegetable oil were offered to establish baseline consumption. During Block 2, Group A was given choices between wafers coated with oil and wafers coated with total extract. Group B was offered oil coated wafers and wafers coated with the NVA fraction. Group C received two oil coated wafers. One was served on top of a screened dish containing a sample of total extract. In this manner, the rats were exposed to volatile compounds emanating from the extract but could not contact the extract. The second wafer was served on top of a screened sample of oil.

In Blocks 1 and 3 trials, the rats fed indiscriminately from both wafers. During Block 2, total extract, the NVA fraction and the volatile compounds from extract all significantly reduced food consumption. In Experiment 2, habituation to the NVA fraction and to the volatile constituents of extract was examined in two additional groups (D, E), using the methods described above. Baseline consumption was tested in Blocks 1 and 3 by offering two oil coated wafers. During Block 2, group D was given 10 trials with oil coated and NVA-fraction coated wafers. Group E was given 10 trials with oil coated wafers paired with the volatile constituents of total extract and with those of oil.

Both groups failed to habituate to the Zanthoxylum stimuli. Wafers treated with the NVA fraction and wafers paired with the volatile constituents of extract were avoided throughout the 10 test days.