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Journal of Lipid Research, Vol. 44, 1530-1535, August 2003
Copyright © 2003 by American Society for Biochemistry and Molecular Biology

-Tocotrienol, a vitamin E homolog, is a natriuretic hormone precursor

Hisako Saito^*, Chikako Kiyose^*, Hiroyuki Yoshimura, Tadahiko Ueda, Kazuo Kondo^1,* and Osamu Igarashi^**

^* Institute of Environmental Science for Human Life, Ochanomizu University, Bunkyo-ku, Tokyo, 112-8610, Japan
Eisai Co. Ltd., Bunkyo-ku, Tokyo, 112-8088, Japan
Tokyo Metropolitan Research Laboratory of Public Health, Shinjuku-ku, Tokyo, 169-0073, Japan
^** Ibaraki Christian University, Hitachi-city, Ibaraki, 319-1295, Japan

¹ To whom correspondence should be addressed. e-mail: kkondo{at}cc.ocha.ac.jp

2,7,8-Trimethyl-2-(ß-carboxyethyl)-6-hydroxychroman (-CEHC), a metabolite of -tocopherol and -tocotrienol, was identified as a new endogenous natriuretic factor. However, -tocopherol and -tocotrienol, both precursors of -CEHC, have never directly been observed to have natriuretic potency. Thus, we investigated whether -tocotrienol could cause natriuresis and diuresis in rats. The rats were divided into two groups that were given a control or a high-sodium diet for 4 weeks, and then subdivided into placebo and -tocotrienol subgroups given only corn oil-removed vitamin E and oil supplemented with -tocotrienol, respectively. After oral administration of three experimental doses, rat urine was collected and -CEHC, urine volume, sodium, and potassium content were determined. Only in rats given a high-NaCl diet did -tocotrienol accelerate and increase sodium excretion, showing no effect on potassium excretion. Sodium excretion in the high-NaCl group given -tocotrienol was 5.06 ± 2.70 g/day, and in the control group given -tocotrienol, 0.11 ± 0.06 g/day. Furthermore, -tocotrienol affected urine volume in the specific condition of high-NaCl body stores and -tocotrienol supplementation.

In this study, we found that -tocotrienol, one of the natural vitamin E homologs, stimulates sodium excretion in vivo, suggesting that -tocotrienol possesses a hormone-like natriuretic function.

Abbreviations: -CEHC, 2,7,8-trimethyl-2-(ß-carboxyethyl)-6-hydroxychroman; -CEHC-Me, methyl ester of -CEHC

Supplementary key words -CEHC • vitamin E metabolism • natriuresis • urine volume

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