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Ingestive Behavior and Neurosciences

Orally Administered Zinc Stimulates Food Intake via Vagal Stimulation in Rats^1,2,3

⁴ Department of Science of Food Function and Health, Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555 Japan ⁵ Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho Uji, Kyoto 611-0011, Japan ⁶ Department of Behavioral Medicine, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1Sakuragaoka Kagoshima 890-8520, Japan

We investigated the role of zinc in food intake regulation using rats during early-stage zinc deficiency without decreasing zinc concentrations in plasma and tissues. Plasma, liver, and hypothalamic zinc concentrations were not affected in male Sprague-Dawley rats fed a zinc-deficient (Zn-Def) diet for 3 d compared with the pair-fed control group, which was pair-fed a zinc-sufficient diet to the intake of the Zn-Def diet. Zinc sulfate at a dose of 19 µmol/kg body weight was orally or intraperitoneally (i.p.) administered in rats fed a Zn-Def diet for 3d and food intake was measured. We found that zinc stimulated food intake after oral but not i.p. administration. The mRNA expression of neuropeptide Y (NPY) and orexin in the hypothalamus significantly increased 3 h after oral but not i.p. administration of zinc. Pretreatment with an antagonist for NPY Y₁ receptor or orexin OX₁ receptor blocked orexigenic activity after oral administration of zinc. The stimulation of food intake by oral administration of zinc was abolished by vagotomy. Taken together, orally administered zinc may stimulate food intake via orexigenic peptides coupled to the afferent vagal stimulation in rats after short-term treatment with a Zn-Def diet.

^* To whom correspondence should be addressed. E-mail: ohinata{at}kais.kyoto-u.ac.jp.

Manuscript received 24 July 2008. Initial review completed 4 September 2008. Revision accepted 21 December 2008.