Role of estrogen receptors and aromatase on brain protein synthesis rates in ovariectomized female rats fed genistein.

We have reported that the dietary addition of genistein, a phytoestrogen found abundantly in soy products, stimulates brain protein synthesis rates of ovariectomized female rats. In the present study, we determine whether stimulation of brain protein synthesis rates in ovariectomized female rats by the dietary addition of genistein was conducted via estrogen receptors and aromatase-mediating actions. After ovariectomy, Wistar female rats were treated with genistein, the estrogen receptor antagonist ICI 182,780, and/or fadrozole a systemic aromatase inhibitor. In the cerebral cortex, the cerebellum and the hypothalamus, the fractional (Ks) rates of protein synthesis were increased by the dietary addition of genistein. These effects of genistein were inhibited by the administration of ICI 182,780 and fadrozole. However, the degrees to which ICI 182,780 and fadrozole inhibited the effects of genistein differed depending on the brain region. This result suggests that dietary genistein elevates the rate of protein synthesis in the brain of ovariectomized female rats. In addition, the estrogen receptors of the brain and the aromatase of the peripheral tissue and brain are, at least partly, related to the rate of brain protein synthesis caused by genistein.

Effect of dietary protein quantity and quality on the brain protein synthesis rate in ovariectomized female rats.

The purpose of this study was to determine whether the quantity and quality of dietary protein affected the rate of brain protein synthesis in ovariectomized female rats. Two experiments were conducted on the ovariectomized female rats (12 weeks old) given diets containing 20%, 5%, or 0% casein (experiment 1) and 20% casein, 20% soy protein, 20% gluten, or 20% gelatin (experiment 2) for 10 d, respectively. The fractional rates of protein synthesis in the brain declined with a decrease of the quantity and quality of dietary protein. In the brain, the RNA activity [g of protein synthesized/((g of RNA) d)] was significantly correlated with the fractional rate of protein synthesis. The RNA concentration (mg of RNA/g of protein) was not related to the fractional rate of protein synthesis in any organ. The results suggest that the rate of protein synthesis in the brain declines with the decrease of the quantity and quality of dietary protein in ovariectomized female rats, and that RNA activity is at least partly related to the fractional rate of brain protein synthesis.

Role of N-acetylglutamate concentration and ornithine transport into mitochondria in urea synthesis of rats given proteins of different quality.

The purpose of this study was to find whether the concentration of N-acetylglutamate and ornithine transport into mitochondria would regulate urea synthesis when the dietary protein quality was manipulated. Experiments were done on three groups of rats given diets containing 10 g of gluten, 10 g of casein, or 10 g of whole egg protein/100 g for 10 days. The plasma concentration and urinary excretion of urea, the liver concentration and synthesis of N-acetylglutamate, the liver concentrations of glutamate and lysine, and the liver ornithine transport into mitochondria increased with the decrease in quality of dietary protein. A reverse correlation was observed between the activities of urea cycle enzymes, the plasma concentration of arginine, and urinary excretion of urea under these conditions. N-Acetylglutamate concentration and ornithine transport into mitochondria in the liver were closely correlated with the excretion of urea. These results suggest that greater N-acetylglutamate concentration and ornithine transport into isolated mitochondria in the liver of rats, given the lower quality of protein, stimulate urea synthesis and that the concentrations of glutamate and lysine in the liver are at least partly related to the hepatic N-acetylglutamate synthesis and ornithine transport, respectively.

Changes in tissue protein synthesis are involved in regulating urea synthesis in rats given proteins of different quality.

The purpose of present study was to determine whether the regulation of urea synthesis is mediated through changes in supply of amino acids by protein synthesis and whether the concentration of ammonia, or activities of amino acid catabolizing enzymes, regulate urea synthesis when the dietary protein quality is manipulated. Experiments were done on three groups of rats given diets containing 10 g gluten, 10 g casein or 10 g whole egg protein/100 g for 10 d. The urinary excretion of urea, and the liver concentrations of glutamate, serine and alanine increased with a decrease in quality of dietary protein. The fractional and absolute rates of protein synthesis in tissues declined with the decrease in quality of dietary protein quality. The ammonia concentration in plasma and liver, and activities of hepatic amino acid catabolizing enzymes was not related to urea excretion under these conditions. These results suggest that the lower protein synthesis seen in tissues of rats given the lower quality of protein is likely to be one of the factors to increasing the supply of amino acids and stimulating urea synthesis.

Dietary genistein affects brain protein synthesis rates in ovariectomized female rats.

The purpose of this study was to determine whether genistein affects the rate of brain protein synthesis in ovariectomized female rats. Experiments were conducted on three groups of 12-wk-old female rats: those in group 1 were ovariectomized to reduce the level of plasma sex hormone; those in group 2 were ovariectomized and fed diets containing 0.01% genistein; and those in group 3 were sham-operated controls. The fractional rates of protein synthesis in the brain of ovariectomized rats fed genistein were significantly greater than those in ovariectomized rats without genistein treatment. In the cerebral cortex and cerebellum, the RNA activity [g protein synthesized/(g RNA.d)] significantly correlated (r > 0.86, P < 0.001) with the fractional rate of protein synthesis. The RNA concentration (mg RNA/g protein) was not related to the fractional rate of protein synthesis in any organ. The results suggest that the addition of genistein to the diet of ovariectomized female rats is likely to increase the rate of protein synthesis in the brain, and that RNA activity is at least partly related to the fractional rate of brain protein synthesis.

Effect of adding dietary methionine to a low soy protein diet on the brain protein synthesis rate in ovariectomized female rats.

A deficiency of sex hormones affects brain function in mammals, including the decrease of protein synthesis. Recently, we have shown that the protein synthesis in the brain depended on the quality of dietary protein in ovariectomized female rats. The methionine is the first limiting amino acid for the recommended dietary allowance of amino acids in soy protein. The purpose of this study was to determine whether the addition of dietary methionine affected the rate of brain protein synthesis in ovariectomized female rats fed on the soy protein diet. Experiments were conducted on two groups of ovariectomized female rats (24 week) given the diets containing 5% soy protein or 5% soy protein + 0.2% methionine for 10 d. The fractional rates of protein synthesis in cerebral cortex and cerebellum significantly increased with an addition of dietary methionine. In the brain, the RNA activity [g protein synthesized/((g RNA) x d)] was significantly correlated with the fractional rate of protein synthesis. The RNA concentration (mg of RNA/g of protein) was not related to the fractional rate of protein synthesis in any organ. The results suggest that the addition of limiting amino acid for the low soy protein elevates the rate of protein synthesis in the brain of ovariectomized female rats, and that RNA activity is at least partly related to the fractional rate of brain protein synthesis.

Effects of quantity and quality of dietary protein on the brain polysome profile in aged rats.

The purpose of this study was to determine whether the quantity and quality of dietary protein affected the polysome profile of the brain in aged rats. Two experiments were done on three groups of aged rats (30 wk) given the diets containing 20% casein, 5% casein, or 0% casein (experiment 1), and 20% casein, 20% gluten, or 20% gelatin (experiment 2) for 10 d. The aggregation in brain ribosomes declined with a decrease of quantity and quality of dietary protein except in the hippocampus. The RNA concentration (mg RNA/g protein) did not differ among the three groups varying the dietary protein in any brain regions. The results suggest that the higher quantity and quality of dietary protein improves the polysome profile in the brain of aged rats, and that the polysome profile is at least partly related to the mechanism by which the dietary protein affects brain protein synthesis in aged rats.