The diffusion coefficients of C60 in dichloromethane and benzonitrile solutions containing 0.1 M tetrabutylammonium perchlorate were determined by single potential-step chronoamperometry at small disk electrodes. The diffusion coefficients of C60 were obtained by curve fitting of the chronoamperograms to a theoretical equation by Shoup and Szabo. The values were (1.4 ± 0.3)× 10 -9 and (4.1 ± 0.3)× 10 -10 m 2 s -1 , respectively (the errors are 95% confidence limits). The diffusion coefficients of C60 -in these solutions were measured by double potential-step chronoamperometry. The ratios of the diffusion coefficients of C60 to those of C60 -were obtained from theoretical curves of the ratios of the current at the second potential step to the current at the first one. The values of the ratios were 1.2 ± 0.2 and 1.0 ± 0.3, respectively.
The synthesis and secretion of many hormones such as growth hormone (GH), melatonin, and corticosterone, exhibit temporal variations over each day and night. Oral administration of several nutritional factors, including L-ornithine, modulates these hormonal secretions and induces an acute increase in plasma GH levels. However, the impact of L-ornithine on the diurnal rhythms of hormone secretion remains unclear. In this study, we evaluated whether the diurnal rhythms of plasma GH, melatonin, and corticosterone secretion were altered by the daily administration of L-ornithine as well as the timing of the administration, in CBA/N mice. Our results showed that the plasma GH levels that peaked at light phase were amplified by L-ornithine (500 mg/kg) administered at Zeitgeber time (ZT) 22, but not at ZT10. Additionally, L-ornithine (1000 mg/kg) administered at ZT22 advanced the onset of the nocturnal rise of melatonin, which resulted in the elongation of the melatonin peak. On the other hand, L-ornithine (500 and 1000 mg/kg) administered at ZT10, but not at ZT22, suppressed the diurnal rhythm peaks of plasma corticosterone. The effects of L-ornithine on plasma GH rhythms lasted for at least 2 days after cessation of the daily administration. Running wheel activity during the active phase was slightly elevated by L-ornithine administration at ZT22, but the overall patterns were only slightly affected. L-Ornithine levels in the plasma and hypophysis after a single administration of L-ornithine at ZT22 were lower than those after administration at ZT10, suggesting that the metabolic rate of L-ornithine differs between day and night. In conclusion, our data suggest that a daily administration of L-ornithine regulates the diurnal rhythms of GH, melatonin, and corticosterone in a manner dependent on administration time, which might be related to the diurnal rhythms of L-ornithine metabolism.
SummaryBrain protein synthesis and the plasma concentration of growth hormone (GH) are sensitive to dietary ornithine. The purpose of this study was to determine whether dietary arginine, the metabolite of ornithine, affects the brain protein synthesis, and to that end, the effects of arginine on brain protein synthesis were compared with that of ornithine treatment in young rats. Two experiments were done on five or three groups of young rats (5-wk-old) given 0%, 0.25%, 0.5%, 0.7% arginine or 0.7% ornithine-HCl added to a 20% casein diet for 1 d (only one 3 h period) (Experiment 1), or given a diet containing 0% or 0.7% ornithine-HCl or 0.7% arginine added to a 20% casein diet (Experiment 2). The concentrations of plasma growth hormone (GH) and fractional rates of protein synthesis in the brains increased significantly with the 20% casein10.7% arginine diet and still more with the 20% casein10.7% ornithine diet compared with the 20% casein diet alone. In the cerebral cortex and cerebellum, the RNA activity [g protein synthesized/(g RNA·d)] significantly correlated with the fractional rate of protein synthesis. The RNA concentration (mg RNA/g protein) was also related to the fractional rate of protein synthesis in these organs. The results suggest that the treatment with arginine is likely to increase the concentrations of GH and the rate of brain protein synthesis in rats, and that the effects of arginine on brain protein synthesis and GH concentration were lower than that of ornithine. The RNA activity is at least partly related to the fractional rate of brain protein synthesis.
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