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881.
John G. Rueter 《Journal of phycology》1983,19(1):101-104
The toxicity of Cu to Thalassiosira weissflogii (Grunow) was investigated, focusing on the internal soluble pool of silicic acid. Silicic acid uptake and growth rates were found to be functions of both the cupric ion activity and the concentration of silicic acid in the growth medium. The soluble pool of Si per cell depended on the balance between the uptake rate and the division rate. The soluble pool in non-dividing cultures reflected simply the uptake rate (and inhibition by copper of the uptake rate), but in dividing cultures the soluble pools had complex patterns with time depending on uptake rates and timing of division. Intracellular soluble pools of silicic acid are a good indicator for the relative inhibition of uptake and growth processes. 相似文献
882.
Buspirone produces a dose-dependent but short-lived elevation in striatal dopamine (DA) metabolites in the rat. , buspirone possesses an affinity similar to sulpiride for DA receptors (3H-spiperone). A moderate affinity for α1 receptors was also observed while buspirone was inactive at α2, β, muscarinic and serotonin2 receptors. This pharmacological profile as well as previous behavioral data indicate that buspirone may be a potential “atypical” neuroleptic. 相似文献
883.
Abstract: The pool size and synthesis of phosphatidic acid derived from [2-3 H]glycerol were studied in bovine whole retinas and subcellular fractions. Microsomal preparations from retinas incubated with [2-3 H]glycerol displayed the highest percentage labeling of phosphatidic acid at 5 min of incubation; labeling decreased rapidly thereafter. In drug-treated retinas,0.5 m M propranolol increased the endogenous content of phosphatidic acid and stimulated [2-3 H]glycerol labeling in whole retina and microsomal and postmicrosomal supernatant fractions. This effect was observed during short-term incubations and was reversible. In pulse-chase experiments, 60 min of reincubation greatly reduced the labeling effect, although propranolol still enhanced phosphatidic acid labeling. At the same time, endogenous phosphatidic acid accumulated and reincubation without propranolol reversed the effect. During accumulation, the amount of palmitate increased and that of oleate decreased, whereas the relatively high level of docosahexaenoate in phosphatidic acid remained unchanged. It was concluded that this propranolol-induced effect is due to cationic amphiphilic drug activity in the endoplasmic reticulum that results in a partial inhibition of phosphatidic acid degradation and a stimulation of its de novo synthesis. Hence, net synthesis of phosphatidic acid can be assessed in the retina during short-term incubation with propranolol. 相似文献
884.
Abstract: The higher-molecular-weight elongation factor-1 (EF-1H) of the chick brain was observed to contain three subunits (denominated α, β, and γ), contrary to a previous report that the brain EF-1H consisted of aggregates of low-molecular-weight elongation factor- 1 (EF-1L). Crude EF-1H, obtained from 20-day embryonic brain, was treated with 0.4 M ammonium chloride and 0.1 mM GTP, and EF-1βγ, was obtained using a DEAE-Sephadex column equilibrated in 0.025 mM GTP. Both EF-1β, and EF-1γ, were isolated by means of a DE-52 column equilibrated in 6 M urea and were found to have molecular weights of 2.8 and 4.8 × 104, respectively. EF-1β and EF-1γ were also obtained from young rat and calf brains by the same procedures. The molecular weight of the isolated EF-1α was 5 × 104. It was found that EF-1β stimulated the two EF-1α-dependent reactions, i.e., phenylalanyl-tRNA binding (reaction 1) and polyphenylalanine synthesis (reaction 2), and also stimulated the nucleotide exchange reaction in the EF- 1α-guanine nucleotide binary complex (reaction 3). The degrees of stimulation of reactions 1, 2, and 3 by the addition of EF-1β were 2 to 3 times, about 18 times, and 2 to 3 times as much as with EF-1α alone, respectively. The amino acid compositions of EF-1α -1β, and -1γ and EF-2 were very similar to those of other eukaryotic tissues. Thus the constituents and properties of EFs of the brain were found to be basically similar to those of other tissues of eukaryotes, although EF-1β, and EF-1, had not been reported in the brain. A possible physiological significance of EF-1β during brain development is also discussed. 相似文献
885.
Effects of Light on Dopamine Metabolism in the Chick Retina 总被引:5,自引:4,他引:1
The effect of prolonged exposure to light on the activity of dopaminergic neurons and dopamine (DA) metabolism of chick retinae was investigated. alpha-Fluoromethyldopa, a potent and specific irreversible inactivator of aromatic amino acid decarboxylase, was used to assess DA turnover after inhibition of synthesis, and also to assess in vivo tyrosine hydroxylase activity by dihydroxyphenylalanine accumulation. After 48 h of light exposure, retinal DNA in 12-day-old chicks was about 30% higher (p less than 0.005) whereas dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were elevated two to three times (p less than 0.005) the level of controls kept in the dark for the same period. DA turnover was about twofold faster in the light (t 1/2 = 31 min) than in the dark (t 1/2 = 65 min). Tyrosine hydroxylase, assayed in vitro with saturating levels of cofactor and substrate, increased by about 50% after light exposure. The apparent tyrosine hydroxylase activity in vivo was approximately sixfold higher in the light than the dark. These results are interpreted and discussed in terms of the regulation of DA synthesis, and the use of DOPAC and HVA as indices of DA function in the retina. 相似文献
886.
Abstract: The possibility that γ-hydroxybutyrate (GHB), a metabolite of γ-aminobutyric acid (GABA), may play a role in the CNS has recently come to attention. We describe here a sensitive and specific mass fragmento-graphic technique that allows the measurement of picomole amounts of GHB in single rat brain areas. Moreover, we show that GHB can accumulate postmortem, an effect that is blocked by the use of microwave irradiation to kill the animals. To understand further the relationship between GABA and GHB formation, we treated rats with drugs known to inferfere with GABA metabolism at different levels and concomitantly measured GABA and GHB in cerebral cortex and cerebellum. Isoniazide, which blocks the formation of GABA, also decreases GHB. Blockers of the catabolism of GABA, such as aminooxyacetic acid and γ-acetylenic GABA, increase GABA levels and decrease those of GHB. Sodium dipropylacetate increases both GABA and GHB, supporting the hypothesis that this effective antiepileptic drug also blocks in vivo the enzyme that converts succinic semialdehyde to succinic acid. 相似文献
887.
G. Clementi F. Nicoletti F. Patacchioli A. Prato F. Patti C.E. Fiore † M. Matera U. Scapagnini 《Journal of neurochemistry》1983,40(3):885-886
Abstract: The effects of calcitonin on neurochemical parameters related to the tuberoinfundibular dopaminergic system have been investigated in an attempt to elucidate how calcitonin decreases serum prolactin levels. Intracerebroventricular human or salmon calcitonin injection decreases serum prolactin, medial basal hypothalamic dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) and hypophysial DA and increases hypophysial DOPAC. Results suggest that calcitonin may decrease prolactin secretion via the tuberoinfundibular dopaminergic system. 相似文献
888.
Abstract: D, L(±)-4-Hydroxy-3-methoxyphenylglycol (HMPG) labelled with three deuterium atoms was used to study turnover of plasma free HMPG following an intravenous injection. Ten healthy men were given a pulse dose of either 4.3 μmol or 2.2 μmol of labelled HMPG ([2H3]HMPG piperazine salt). Plasma and urine levels of both endogenous and labelled HMPG were subsequently followed by gas chromatography-mass spectrometry with selected ion detection. Kinetic calculations based upon a single-compartment model were consistent with a monoexponential elimination of plasma free HMPG. The half-life of HMPG was 0.46 and 0.78 h (mean values in the two dose groups). The HMPG production rate was 2.01 and 2.35 μmol/hour, and the urinary excretion rate of HMPG (free and conjugated) was 0.48 and 0.47 μmol/h. The endogenous plasma level of free HMPG was 25 and 33 nmol/L. The results show that HMPG turns over rapidly and that HMPG is further metabolized extensively. About one-fourth of the HMPG produced is excreted in urine as free and conjugated HMPG. 相似文献
889.
Two new compounds isolated from the fruits of Pedalium murex are characterized as heptatriacontan-4-one and tetratriacontanyl octacosanoate by spectral studies. Pentatriacontane, sitosterol, hexatriacontanoic acid, hentriacontanoic acid, ursolic acid and vanillin have also been isolated and identified. 相似文献
890.
Analyses of the sulphatides in the pollen and style of Oenothera missouriensis show that these membranous lipids are comparatively less important in the styles than in the pollen. Incompatible pollination is followed by a large increase in sulphatides, whereas cross-pollination also causes an increase in sulphatide but to a much lesser extent. This mobilization of sulphatides in the membrane is discussed in term of permeability. 相似文献