Preference for dietary fat induced by release of beta-endorphin in rats.
OBJECTIVE
To determine whether beta-endorphin contributes to the ingestion of and preference for dietary oil, we examined the relationship between the dynamics of beta-endorphin, before and after the ingestion of corn oil, and the intake volume of corn oil.


METHODS
Rats were offered 5% corn oil for 20 min for 5 consecutive days so they could acquire a preference for corn oil. On day 6, seven groups of rats were presented with the oil for defined time periods, and we measured the beta-endorphin levels in the serum and cerebrospinal fluid (CSF) before and after the presentation of corn oil as well as the consumed volume of corn oil at defined time points.


RESULTS
Beta-endorphin levels in serum and CSF were significantly increased 15 min after the ingestion of corn oil, followed by a rapid decrease and maintenance at the basal level throughout the rest of the experimental period. The intake of corn oil was the lowest in the time period of 15-30 min, when the beta-endorphin level reached a peak value. The intake volume of corn oil might be inversely correlated with beta-endorphin levels in serum and CSF. The pretreatment of naloxone, an antagonist of the opioid receptor, decreased the initial licking rate for corn oil and increased the latency for corn oil in the licking test.


CONCLUSIONS
The beta-endorphin was rapidly released after oil ingestion, which contributed to the hedonic preference and ingestive behavior for fat.
Mizushige
Takafumi
T
Laboratory of Nutrition Chemistry, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan. tmizushige@kumc.edu
Saitoh
Katsuyoshi
K
Manabe
Yasuko
Y
Nishizuka
Taichi
T
Taka
Yuichi
Y
Eguchi
Ai
A
Yoneda
Takeshi
T
Matsumura
Shigenobu
S
Tsuzuki
Satoshi
S
Inoue
Kazuo
K
Fushiki
Tohru
T
D000818:Animals; D003314:Corn Oil / Q000494:pharmacology; D004041:Dietary Fats; D004326:Drinking; D005518:Food Preferences / Q000187:drug effects*; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D001615:beta-Endorphin / Q000097:blood / Q000134:cerebrospinal fluid / Q000502:physiology*
D004041:Dietary Fats; D009292:Narcotic Antagonists; D009270:Naloxone; D001615:beta-Endorphin; D003314:Corn Oil