The present study was carried out to investigate the effects of vitamin E-deficiency and supplementation of alpha-tocopheryl acetate (TOCA) on renin release from renin granules. Male Wistar rats were fed either a control or a vitamin E-deficient diet for 4 weeks. Subsequently, the vitamin E-deficient rats received dietary supplementation of TOCA (40 mg/100 g diet) for 5 d. The renin granule fraction was prepared from the kidney cortex homogenate by a discontinuous sucrose density gradient centrifugation. The intake of vitamin E-deficient diet for 4 weeks resulted in an increased level of endogenous lipid peroxides in the renin granule fraction, accompanied by a marked decrease in alpha-tocopherol content, and led to a significant increase in the rate of renin release from the granules during incubation at 37 degrees C. These changes in alpha-tocopherol content, lipid peroxide level and renin release in the renin granule fraction were restored to the control values by dietary TOCA supplementation. Similarly, dietary supplementation of N,N'-diphenyl-p-phenylenediamine (80 mg/100 g diet), which has an antioxidative ability, suppressed the increases in lipid peroxidation and renin release due to vitamin E-deficiency, although this compound was ineffective in restoring alpha-tocopherol levels. These results suggest that vitamin E functions in maintenance of membrane integrity of renin granules by inhibiting the lipid peroxidation.