γ-tocotrienol, a vitamin E homolog, is a natriuretic hormone precursor

Abstract

2,7,8-Trimethyl-2-(β-carboxyethyl)-6-hydroxychroman (γ-CEHC), a metabolite of γ-tocopherol and γ-tocotrienol, was identified as a new endogenous natriuretic factor. However, γ-tocopherol and γ-tocotrienol, both precursors of γ-CEHC, have never directly been observed to have natriuretic potency. Thus, we investigated whether γ-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 γ-tocotrienol subgroups given only corn oil-removed vitamin E and oil supplemented with γ-tocotrienol, respectively. After oral administration of three experimental doses, rat urine was collected and γ-CEHC, urine volume, sodium, and potassium content were determined. Only in rats given a high-NaCl diet did γ-tocotrienol accelerate and increase sodium excretion, showing no effect on potassium excretion. Sodium excretion in the high-NaCl group given γ-tocotrienol was 5.06 ± 2.70 g/day, and in the control group given γ-tocotrienol, 0.11 ± 0.06 g/day. Furthermore, γ-tocotrienol affected urine volume in the specific condition of high-NaCl body stores and γ-tocotrienol supplementation. In this study, we found that γ-tocotrienol, one of the natural vitamin E homologs, stimulates sodium excretion in vivo, suggesting that γ-tocotrienol possesses a hormone-like natriuretic function.