Dual effect of glucose on cytoplasmic free Ca2+ concentration and insulin release reflects the beta-cell being deprived of fuel

Influence of basal glucose concentration on the response evoked by subsequent stimulation with the sugar, was evaluated by investigating changes in free cytoplasmic Ca2+ concentration, [Ca2+]i, and insulin release, using beta-cells isolated from obese hyperglycemic mice. When increasing the glucose concentration from 0 to either 11 or 20 mM, there was a transient decrease in both [Ca2+]i and insulin release. The decrease was followed by a pronounced increase in both of the parameters. When increasing the basal glucose concentration, the initial decrease gradually disappeared, being abolished already at 5 mM of the sugar and the subsequent increase appeared more rapidly. It is suggested that the observed decrease in [Ca2+]i and thereby insulin release reflects a phenomenon associated with fuel deprived beta-cells.     

Renewal of mitochondrial DNA in the liver of rats of different ages

The rate of mitochondrial DNA turnover was studied in the liver of adult and old rats. It was shown to decrease with aging in both the whole mitochondrial population and its heavy and light fractions. This decrease reflects the deceleration of the rate of liver mitochondrial biogenesis in old age and is considered to be a cause of energy deficiency of an old body.     

Cell density-dependent regulation of cell surface expression of two types of human tumor necrosis factor receptors and its effect on cellular response

Tumor necrosis factor (TNF) is a multipotential cytokine known to regulate the growth of a wide variety of normal and tumor cells. It has been shown that the density of cells in culture can modulate the growth regulatory activities of TNF, the mechanism of which, however, is not understood. In this report, we investigated the effect of cell density on the expression of TNF receptors. The receptors were examined on epithelial cells (e.g., HeLa), which primarily express the p60 form, and on myeloid cells (e.g., HL-60) known to express mainly the p80 form. We observed that binding of TNF to both cell lines decreased with increase in cell density. Scatchard analysis of binding on HeLa and HL-60 cells revealed a 4- to 5-fold reduction in the number of TNF receptors without any significant change in receptor affinity in both cell types at high density. The decrease in TNF receptor numbers at high cell density was also observed in several other epithelial and myeloid cell lines. The downmodulation at high cell density was unique to TNF receptors, since minimum change in other cell surface proteins was observed as revealed by fluorescent activated cell sorter analysis. Neutralization of binding with antibodies specific to each type of the receptors revealed that both the p60 and p80 forms of the TNF receptor were equally downmodulated. A decrease in leucine incorporation into proteins was observed with increase in cell density, suggesting a reduction in protein synthesis. Since inhibition of protein synthesis by cycloheximide also leads to a decrease in TNF receptors, it is possible that the density-dependent reduction in TNF receptor number is due to an overall decrease in protein synthesis. The density-dependent decrease in TNF receptors was accompanied by a decrease in intracellular reduced glutathione levels. A reduction in the number of receptors on TNF sensitive tumor cells induced by cell-density correlated with increase in resistance to the cytokine.     

Viability of beta-thalassemia hetero- and homozygotes in several populations of Central Asia]

Viability of hetero- and homozygotes for beta-thalassemia was studied in two isolated populations born after 1950 in conditions of malaria absence. Pregnancy outcomes and probability to get 16 years old were compared in marriages, in which one or both parents were heterozygous for beta-thalassemia, and in marriages, with both parents being normal. The ratio of children with normal genotype and children heterozygous for beta-thalassemia in families, where one parent was heterozygous for beta-thalassemia. Preliminary conclusions are made on the basis of the data obtained. Viability of children in families where one parent is heterozygous for beta-thalassemia is found to decrease in the absence of selective factors (malaria) as compared with normal children. The highest viability decrease was observed in the progeny of those families where both parents were heterozygous beta-thalassemia. Elimination mainly takes place within the first year of life.     

Dynamics of respiratory drive and pressure during NREM sleep in patients with occlusive apneas

To study the dynamics of respiratory drive and pressure in patients with occlusive apneas, diaphragmatic electromyogram (EMGdi), esophageal pressure (Pes), and genioglossal electromyogram (EMGge) were monitored during nocturnal sleep in five patients. Both EMGs were analyzed as peak moving time average, and Pes was quantitated as the peak inspiratory change from base line. During the ventilatory phase both EMGs decreased proportionally. The decrease in Pes was less than the decrease observed in EMGdi, and Pes generated for a given EMGdi increased during the preapneic phase in spite of the proportional decrease in EMGdi and EMGge during this period. We conclude that negative inspiratory pressures which lead to the passive collapse of oropharyngeal walls are dependent on both respiratory and upper airway muscle activity and that occlusive apneas of non-rapid-eye-movement (NREM) sleep do occur in spite of proportional changes observed in the activity of both muscle groups. The preapneic increase in negative inspiratory pressures generated for a given respiratory muscle activity is most likely due to the decrease in upper airway muscle activity that is associated with an increase in oropharyngeal resistance.     

The effects of L-glutamate and its analogues upon the membrane conductance of central murine neurones in culture

Neurones from brain and spinal cord of foetal mice were grown dissociated in monolayer cultures for 4--6 weeks prior to electropharmacological analysis. Neurones were immersed in a Hanks balanced salt solution while drugs and ions were applied by pressure microperfusion during intracellular recordings obtained by conventional techniques. L-Glutamate and its analogues, L-aspartate, DL-homocysteate, N-methyl-D-aspartate, and DL-ibotenate activated two distinct mechanisms of excitation. The primary effect was depolarization accomplished by an apparent decrease of neurone input conductance (Gm). However, in most instances an expected increase in Gm was also observed, especially if membrane potential was reduced by tonic depolarization. Another glutamate analogue, DL-kainate, never decreased Gm and invariably increased Gm at all membrane potentials tested. The decrease of Gm evoked by glutamate and related compounds was strongly dependent upon membrane potential. It was most pronounced at potentials near resting values (-40 to -60 mV) and diminished both with depolarization or hyperpolarization from this range. This apparent decrease favoured the electrogenesis of regenerative potentials that were insensitive to tetrodotoxin. A voltage-dependent increase in sodium and (or) calcium conductance (GNa, GCa) or a decrease in potassium conductance (GK) is suggested to account for this decrease in Gm. Divalent cations (Mg and Co) reduced the depolarizing actions of all amino acids except for those to kainate. The decrease in Gm was more sensitive to Mg than was the increase of Gm. However, the receptor antagonist DL-alpha-aminoadipate blocked both changes in conductance and responses to all amino acids with the exception of those to kainate. The possible existence of multiple receptors for glutamate is also discussed.     

Phase dependence in winter physiological condition of cyclic voles

Lack of food resources has been suggested as a factor which limits the growth of cyclic vole populations. During peak phases of the cycle, vole population growth typically ceases during late autumn or early winter, and is followed by a decrease in density over the winter. To investigate whether this decrease is due to increased mortality induced by a depletion of food resources, we studied overwinter food consumption and physiological condition of field voles ( Microtus agrestis ) in western Finland in both an increase and a decrease phase of a three-year population cycle. The growth rate of vole populations was negatively related both to prevailing vole densities and to densities six months earlier. The condition index of voles, as well as their blood levels of haematocrit, proteins, free fatty acids and immunoglobulin G, were positively related to population growth rate when populations were declining. When populations were increasing, these parameters tended to be negatively related to population growth rate. The overall physiological condition of voles was lower in the winter of the decrease phase as compared to the increase phase. The return rate of voles, a proxy of survival, was also lower in the decrease than in the increase phase of the cycle and positively related to haematocrit levels. Almost 90% of all green vegetation shoots were consumed by voles during the winter of the decrease phase while only two thirds were eaten in the increase phase. Our results suggest that the winter decrease phase of cyclic vole populations is associated with both a deterioration in the physiological condition of voles and a significant depletion of winter food resources. This implies that malnutrition induces poor physiological condition in voles, which in turn may increase mortality either directly through starvation or indirectly through increased susceptibility to predators and pathogens.     

Adaptation of Pseudomonas putida S12 to ethanol and toluene at the level of fatty acid composition of membranes.

Pseudomonas putida S12 was more tolerant to ethanol when preadapted to supersaturating concentrations of toluene. Cellular reactions at the membrane level to the toxicities of both compounds were different. In growing cells of P. putida S12, sublethal concentrations of toluene resulted in an increase in the degree of saturation of the membrane fatty acids, whereas toxically equivalent concentrations of ethanol led to a decrease in this value. Contrary to this, cells also reacted to both substances with a strong increase of the trans unsaturated fatty acids and a corresponding decrease of the cis unsaturated fatty acids under conditions where growth and other cellular membrane reactions were totally inhibited. While the isomerization of cis to trans unsaturated fatty acids compensates for the fluidizing effect caused by ethanol, a decrease in the degree of saturation is antagonistic with respect to the chemo-physical properties of the membrane. Consequently, the results support the hypothesis that the decrease in the degree of saturation induced by ethanol is not an adaptation mechanism but is caused by an inhibitory effect of the compound on the biosynthesis of saturated fatty acids.     

Effect of nifedipine and S-adenosylmethionine in the liver of rats treated with CCl4 and ethanol for one month.

An experimental model of toxic liver injury in rats was employed to assay the effect of Nifedipine (a calcium antagonist blocker) and S-Adenosylmethionine (a precursor of glutathione). An important decrease in both perivenular fibrosis and cirrhosis was found. Furthermore, a significant decrease in lactic acid levels was found in the group of animals treated with pharmacologic therapy, although no correlation was seen between lactic acid levels and the different degrees of perivenular fibrosis. No significant variations in ALT and AST enzymes were observed between both groups, as opposed to a significant decrease in LDH enzyme in the Nifedipine+S-Adenosylmethionine group. The results indicate an improvement in the histologic picture of the liver in rats treated by means of pharmacological association, without any change in inflammatory infiltrate and with a slight decrease in necrosis, indicating an action mechanism via creeping fibrosis (instead of a hepatitis pathway).     

Ovine prolactin and human growth hormone derivatives. Specific modification of their alpha-amino groups

The alpha-amino group of ovine prolactin (oPRL) and human growth hormone (hGH) was selectively modified by transamination with glyoxylic acid. No difference was found in the binding capacity of transaminated oPRL to rat liver lactogenic receptors with respect to its control, although both samples showed a decrease in its binding capacity with reference to the native hormone. This decrease was due to conformational changes caused by the reaction conditions and not by the transamination itself, as shown by the circular dichroism spectra. Transaminated hGH retained the full binding capacity of the hormone. These results suggest that the alpha-amino group is not relevant for the binding to lactogenic liver receptors in both lactogenic hormones.     

Salt tolerance of Agaricus bisporus in relation to water stress and toxicity of sodium ions

Using NaCl or polyethylene glycol (PEG) solutions to progressively decrease the external osmotic potential of the peat casing of the growing medium used to culture the mushroom Agaricus bisporus resulted in proportionately decreased yields of sporophores. Over the range of -0.07 to -0.37 MPa, the extent of decrease in yield was similar with both types of osmoticum. However, with further decrease in external osmotic potential (from -0.37 to -0.62 MPa) there was a further proportional decrease in sporophore yield with PEG but a complete suppression of sporophore production with NaCl. Treatments with both NaCl and PEG decreased the concentrations of P, Mg, K, Fe and Mn, but not N and Cu, in sporophore dry matter. Treatment with NaCl solutions increased the concentrations of Na and CI ions in sporophore dry matter and decreased the concentration of Ca; PEG solutions had no effect. Ion toxicity associated with excessive accumulation of Na and C1 ions, or ionic imbalance associated with the concomittant decrease in Ca ions appear to be additional factors to osmotic stress in decreasing yield of sporophores when the growing medium becomes highly saline. The critical concentration of NaCl which caused 10% reduction in sporophore yield was 28 mM; A. bisporus is, therefore, moderately salt-sensitive.     

Influence of gender on tamoxifen-induced biochemical changes in serum of rats

Tamoxifen, the widely prescribed drug in the prevention and therapy of breast cancer, may cause side effects which may be influenced by gender. The present study was undertaken to investigate the impact of gender on tamoxifen-induced toxic and biochemical changes following oral administration of tamoxifen at high dose level of 20 mg/kg once daily for a 2-week period in both male and female rats. The results showed marked increases in serum activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in female rats. In contrast, treatment with tamoxifen in male animals significantly decreased the activity of ALT, with a tendency for a decrease in serum AST levels. In female rats, a significant reduction in the serum activity of acid phosphatase (ACP) was noted, compared with a non-significant decrease in males. Non-significant changes in serum levels of alkaline phosphatase (ALP) were seen in both sexes. Tamoxifen lowered serum contents of total lipid and total cholesterol in both male and female rats. Serum levels of triglycerides were reduced in female rats as compared to a non-significant decrease in male animals. The serum albumin concentration was decreased in both male and female rats, while total protein was decreased only in female animals. Tamoxifen markedly increased serum levels of creatinine in female rats, compared with a non-significant rise in males. Total serum contents of calcium were similarly reduced in both males and females. This is the first study which points to gender-related differences in tamoxifen-induced toxic and metabolic changes in rats. The results indicated that females are more susceptible than males to tamoxifen toxicity, probably due to the ability of tamoxifen to antagonize the action of estrogen in females.     

Lipoprotein lipase and hepatic lipase activities in a hypercholesterolaemic (RICO) strain of rat. Effect of dietary cholesterol.

Hepatic lipase (HL) and lipoprotein lipase (LPL) were assayed in heparinized plasma from male normocholesterolaemic (SW) and genetically hypercholesterolaemic (RICO) rats. Both strains were fed on either a semi-purified control diet or the same diet enriched with 0.5% or 1% cholesterol. HL activity was similar in both groups of rats fed on the control diet. LPL activity was found to be significantly lower in RICO rats (35% decrease, P less than 0.05). Feeding with a high-cholesterol diet led to a decrease in HL activity (15-23%) in both groups of rats but no change was detected in LPL activity, which remained consistently lower in the RICO rats. Thus, with the control diet, LPL activity is lower in RICO rats but presumably is not rate-limiting for their triacylglycerol clearance, given the normal triacylglycerol levels present. After cholesterol feeding, however, the lower LPL activity may become rate-limiting together with the decrease in HL activity, as in these circumstances hypertriacylglycerolaemia was evident and the hypercholesterolaemia of this strain was further increased.     

The localization of GABA-Transaminase in the striato-nigral system

The localization of gamma-aminobutyric acid transaminase (GABA-T), the degrading enzyme for γ-aminobutyric acid, was examined in the striatum and substantia nigra using biochemical techniques. Selective destruction of the nigrostriatal dopaminergic system with 6-hydroxydopamine had no effect on the activity of GABA-T in either the striatum or the substantia nigra, although striatal tyrosine hydroxylase activity was reduced by half. Intrastriatal injection of kainic acid in adult rats resulted in a significant dose-dependent decrease in GABA-T activity in both the striatum and the substantia nigra. The decrease in both of these regions was significantly correlated with the decrease in the GABA synthetic enzyme glutamate decarboxylase (GAD). The intrastriatal injection of kainic acid in ten day old rats did not affect striatal GAD or GABA-T activities, although striatal choline acetyl-transferase activity was reduced by half.It is concluded that the GABA-T activity in the striatum is predominantly localized in neuronal elements, although not, apparently, in cholinergic neurons. Some GABA-T activity is also present in the terminals of the striatonigral neurons. However, the dopaminergic nigrostriatal neurons do not appear to contain GABA-T. It is suggested that high GABA-T activity may be characteristic of GABA neurons.     

A comparison of the chilling-stress response in two differentially tolerant cultivars of tomato (Lycopersicon esculentum).

The chilling responses of two differentially cold tolerant cultivars of tomato were monitored through in vivo labelling of polypeptides with [35S]methionine, both during a gradual temperature decrease (2 degrees C/day) and also during a rapid cold shock (4 degrees C). The polypeptides were separated by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and revealed by fluorography. Both cultivars showed changes in the polypeptide profiles resulting from either chilling treatment. During the gradual temperature decrease, there were few differences exhibited between the two cultivars. However, during cold shock both cultivars showed the altered synthesis of several unique polypeptides. Both cultivars showed the appearance of a 35-kDa polypeptide during the gradual temperature decrease and also during the cold shock. The appearance of three high relative mass polypeptides was found in both cultivars only during the gradual temperature decrease. Treatments with cycloheximide and chloramphenicol suggested that cold-shock polypeptides are both nuclear and organelle encoded. The cold-shock response in roots was different from the response in leaves and between cultivars. A comparison of the two cultivars showed a number of differences in polypeptide synthesis which may be related to increased cold tolerance.     

Changes in adenosine deaminase and antioxidative enzyme activity in patients with lung diseases of dust etiology]

Activity of purine metabolism enzyme, adenosine deaminase (ADA) in lymphocytes and erythrocytes from patients with pneumoconiosis and chronic bronchitis was determined. ADA activity decrease was found in lymphocytes and erythrocytes for both decreases. The observed decrease of ADA activity indicates that after the long term work in mineral dust industry damage of purine metabolism takes place, that is similar to the disturbance observed under secondary immunodeficiency. Changes in activity of superoxide dismutase and catalase show some decrease of functional activity of anti-radical protection. Therefore the results obtained can be used for the selection of a group with highest risk of predisposition to these diseases.     

Behavioral activity during prolonged hypoxemia in fetal sheep

Experiments were conducted in unanesthetized, chronically catheterized pregnant sheep to determine the fetal behavioral response to prolonged hypoxemia produced by restricting uterine blood flow. Uterine blood flow was reduced by adjusting a vascular occluder placed around the maternal common internal iliac artery to decrease fetal arterial O2 content from 6.1 +/- 0.3 to 4.1 +/- 0.3 ml/dl for 48 h. Associated with the decrease in fetal O2 content, there was a slight increase in fetal arterial PCO2 and decrease in pH, which were both transient. There was an initial inhibition of both fetal breathing movements and eye movements but no change in the pattern of electrocortical activity. After this initial inhibition there was a return to normal incidence of both fetal breathing movements and eye movements by 16 h of the prolonged hypoxemia. These studies indicate that the chronically catheterized sheep fetus is able to adapt behaviorally to a prolonged decrease in arterial O2 content secondary to the restriction of uterine blood flow.     

The influence of pH on substrate form specificity of phosphoenolpyruvate carboxylase purified from Crassula argentea

Purified phosphoenolpyruvate carboxylase from both the crassulacean acid metabolism plant Crassula argentea and the C4 plant Zea mays was shown by kinetic studies at saturating fixed-varying concentrations of free mg2+ to selectively use the metal-complexed form of phosphoenolpyruvate when assayed at pH 8.0. A similar response to added magnesium at high free phosphoenolpyruvate concentrations was obtained for both enzymes, consistent with the use of the complex as the substrate. Kinetic studies at pH 7.0 indicated that at this pH the total concentration of phosphoenolpyruvate (including both free and metal-complexed forms) could be used by the enzyme from C.argentea while the C4 enzyme still utilized the complex. The loss of specificity induced by the decrease in the pH of the assay medium was accompanied by a decrease in the Km of this enzyme for phosphoenolpyruvate whatever the form considered and an increase in Vmax/Km. In contrast, a similar decrease of pH led to an increased Km of the C4 enzyme for phosphoenolpyruvate and a decrease of Vmax/Km. For the enzyme from C. argentea (previously shown to contain an essential arginine at the active site), protection of activity by the different forms of substrate against inactivation by the specific arginyl reagent 2,3-butanedione changes markedly with pH. At pH 8.1, the metal complex is the better protector while at pH 7.0 free phosphoenolpyruvate gives the best protection consistent with the observed kinetic changes in substrate form utilization. The relationship between the enzyme affinity for substrate, substrate specificity, and the requirement for magnesium for substrate turnover is discussed.     

Ezetimibe inhibits the incorporation of dietary oxidized cholesterol into lipoproteins

Oxidized cholesterol is present in significant quantities in the typical Western diet. When ingested, oxidized cholesterol is absorbed by the small intestine and incorporated into both chylomicrons and LDL, resulting in LDL that is more susceptible to further oxidation. Feeding studies in animal models and epidemiological studies in humans have suggested that oxidized cholesterol in the diet increases the development of atherosclerosis. In this study, we determined the effect of ezetimibe, a drug that inhibits small intestinal absorption of cholesterol, on the levels of oxidized cholesterol in the serum after a test meal containing oxidized cholesterol. We demonstrate that ezetimibe, 10 mg per day for 1 month, markedly reduced the levels (50% decrease) of oxidized cholesterol in the serum after feeding a test meal containing either alpha-epoxy cholesterol or 7-keto cholesterol, two of the predominant oxidized cholesterols found in the diet. Moreover, the decrease in oxidized cholesterol in the serum was attributable to a decrease in the incorporation of dietary oxidized cholesterol into both chylomicrons and LDL. Because there was no decrease in postprandial triglyceride levels, we conclude that this decrease in oxidized cholesterol levels in the serum is attributable to decreased absorption and not to enhanced clearance. Whether this decrease in oxidized cholesterol absorption prevents or delays the development of atherosclerosis remains to be determined.     

Influence of benomyl on photosynthetic capacity in soybean leaves

This investigation was performed to study the influence of benomyl on photosynthetic pigments and enzymes in soybean leaves. Chlorophyll and pheophytin levels were reduced by benomyl 45 days after greening. These results indicate that chlorophylla andb, and pheophytin must be controlled by benomyl. SDS-PAGE analysis showed that 50 and 14.5 kD polypeptides represented as the large and small subunits of rubisco. In the both of these subunits, the band intensity of the control was significantly higher than that after benomyl treatment, indicating that these two subunits are affected by benomyl. Benomyl strongly inhibited both the activity and content of rubisco as its concentration was gradually increased. However, it remains unclear whether this reduction of rubisco level was due to a reduced level of rubisco activase. Two major polypeptides of 46 and 42 kD were identified as rubisco activase subunits by SDS-PAGE. The intensity of these two bands was shown to be higher in the control than after benomyl treatment. These results indicate that the rubisco decrease resulting from increased benomyl concentrations was caused by rubisco activase. A significant decrease in both the activity and content of rubisco activase by benomyl was also observed. These results suggest that the decrease in rubisco level caused by benomyl is accompanied by a decrease in both the activity and content of rubisco activase.