Polyvalent inhibitory action of fusidic acid in isolated rat liver cells

The steroidic antibiotic fusidic acid showed a polyvalent action on isolated rat liver cells. It displayed a strong inhibitory capability on protein synthesis in intact cells even stronger than that previously reported in cell-free extracts. Also, it inhibited basal gluconeogenesis and promoted an increase of the membrane permeability to trypan blue. However, the effects on both protein synthesis and basal gluconeogenesis were observed at doses smaller than those required to reduce the cell viability.     

Cell growth of skeletal muscle as an indicator of protein requirements of the adult rat

Skeletal muscle growth, muscle nucleic acids and muscle protein synthesis capacity, were measured to evaluate the protein requirement of adult rats. Wistar rats were fed on diets containing 4%, 10% or 20% casein + D,L-methionine. All diets were provided for 21 days beginning at 90 days of age. Body weight, food efficiency and net weight change increased as the casein content of the diet increased. Muscle DNA, RNA and RNA/protein were lost, but protein and protein/DNA increased on the 4% and 20% protein diet. This fact involves an aplasia phenomenon although the hypertrophic growth is maintained. Alterations of the insulin and GH plasma levels were observed. These findings indicate that for adult rats the 4% and 20% protein diets are not adequate for the period of adult maintenance.     

Effect of ACTH, dexamethasone, and adrenalectomy on the secretion of testosterone in the rat

The effect of ACTH (100 micrograms/animal/day, i.p.), dexamethasone (75 micrograms/animal/day, s.c.), both for three consecutive days, and adrenalectomy, with or without dexamethasone, maintained according to the group, one, two or three days, on the plasmatic testosterone and corticosterone levels, has been studied in adult male Wistar rats. ACTH and adrenalectomy produced a high decrease in testosterone levels (p less than 0.001 for the three days studied). Dexamethasone produced lower testosterone levels in the first day followed by partial recuperation between the second and the third days of its administration. Dexamethasone produced the effects mentioned for intact animals. The changes in corticosterone levels were according to an adequate response of the hypothalamus-pituitary-adrenal system under these experimental circumstances. ACTH exerts an inhibitory effect on testosterone secretion in the rat, so that such an effect from the data obtained after adrenalectomy and simultaneous dexamethasone injections, does not seems to be mediated either by the presence of adrenals or high corticosterone levels.     

苦绳的一个新甾体成分

从苦绳(Dregea sinensis Hemsl.),和分出一新的甾体成分,Dresigenin A(I),经化学反应及光谱分析证明其结构为12-O-乙酰基-20-O-(2-甲基丁酰基)二氢肉珊瑚甙元[12-O-acetyl-20-O-(2-methylbutyryl)dihydrosarcostin]。     

Autolysis of the cell wall. Its possible role in endogenous and IAA-induced growth in epicotyls of Cicer arietinum

Indoleacetic acid (IAA), a factor that induces growth in epicotyls of cicer arietinum L. cv. Castellana, increases the autolytic capacity of the cell walls by 50%, suggesting that autolysis is related to the processes of cell wall loosening that accompany growth. IAA promotes an increase in the specific activities of the enzymes involved in autolysis, mainly α-galactosidase (EC 3.2.1.22). This relationship autolysis-growth. was also observed in a study of the autolytic capacity of cell walls from regions of the epicotyl with different growth capacity. The sugars released and the level of enzymatic protein were higher in the subapical region that towards the base.     

Inorganic-carbon uptake by a small-celled strain of Stichococcus bacillaris

Air-grown cells of a marine, small-celled (2 m diameter) strain of Stichococcus bacillaris contained appreciable carbonic-anhydrase activity but this was repressed when cells were grown on air enriched with 5% (v/v) CO₂. Assay of carbonic-anhydrase activity using intact cells and cell extracts showed all activity was intracellular in this Stichococcus strain. Measurement of inorganic-carbon-dependent photosynthetic O₂ evolution at pH 5.0, where CO₂ is the predominant form of inorganic carbon, showed that the concentration of inorganic carbon required for half-maximal rate of photosynthetic O₂ evolution [K_0.5(CO₂)] was 4.0 M for both air- and CO₂-grown cells. At pH 8.3 the K_0.5(CO₂) was 0.3 mM for air-grown and 0.6 mM for CO₂-grown cells. Sodium ions did not enhance bicarbonate utilization. Measurement of the internal inorganic-carbon pool (HCO ₃ ^– +CO₂) by the silicone-oil-layer centrifugal filtering technique showed that air- and CO₂-grown cells were able to concentrate inorganic carbon up to 20-fold in relation to the external medium at pH 5.0 but not at pH 8.3. In this alga the high affinity for CO₂ and inorganic-carbon accumulation in CO₂- and air-grown cells results from active CO₂ transport that is not dependent on carbonic-anhydrase activity.Abbreviation Hepes 4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid