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J T Tildon

Publications and source records attributed to J T Tildon.

At least 55 records · Page 3Linked to original sources
PubMed1986

Thyroid hormone actions on a cholinergic neuroblastoma cell line (S-20Y).

Thyroid hormone (T3) has a multiplicity of effects on the developing nervous system. We have investigated T3 action using a cholinergic neuroblastoma cell line (S-20Y) as a model. S-20Y contains a nuclear receptor for T3 with binding properties similar to those of other T3 target tissues. In addition, these cells can carry out 5'-deiodination, which is necessary to produce active thyroid hormone in vivo. The enzyme involved in this process appears to be a type I deiodinase, based on its reaction kinetics and its susceptibility to inhibition by propylthiouracil. S-20Y cells maintained in T3-depleted medium showed decreased choline acetyltransferase (ChAT) activity. ChAT activity was restored to the control level in a dose-dependent manner by T3 repletion. Neither cell density nor viability was influenced by the hypothyroid state. The presence of a T3 receptor and the enzyme activity for T3 production, together with an effect of T3 on ChAT activity, demonstrate that S-20Y cells are a target for T3 action and suggest that these cells represent an excellent model system for studies of T3 effects on nervous tissues.

Animals↗
PubMed1986

A developmental study of glycerol oxidation by rat brain.

The rates of oxidation of several concentrations of [1,3-14C]glycerol to 14CO2 were measured in whole homogenates of brain from rats of different ages. The rates of oxidation of glycerol at concentrations from 0.1 to 20 mM were significantly lower with brains of neonatal animals than with adult rats, and increased to adult levels during the second to third week of life. The addition of unlabelled glucose decreased the rate of [1,3-14C]glycerol oxidation by about 40% at all ages and glycerol concentrations. Increasing the initial concentration of glycerol 200-fold from 0.1 to 20 mM resulted in more than a 100-fold increase in the rate of glycerol oxidation. This pattern of an increased rate of oxidation with increasing substrate concentration was in marked contrast to that previously found with other brain energy substrates which levelled off with increasing concentration. The data suggest that glycerol could be an important energy substrate in certain areas or cell types in adult rat brain, or that the ability to oxidize high concentrations of glycerol is a detoxification mechanism to prevent accumulation of excess free glycerol.

Aging↗
PubMed1985

Transport of 2-deoxy-D-glucose by dissociated brain cells.

The characteristics of glucose transport into dissociated cells from rat brain were determined using [1,2-3H]2-deoxyglucose as substrate. The rate of net uptake exhibited biphasic saturation kinetics with increasing substrate concentration; two values each for Km (8.85 and 1.05 mM) and Vmax (20.41 +/- 5.99 nmol/min/mg protein) were obtained, indicating the presence of two transport systems. D-glucose competed with [1,2-3H]2-deoxyglucose as shown by increasing degrees of inhibition of uptake of labeled substrate with increasing concentrations of D-glucose. The presence of an accelerative exchange mechanism was demonstrated by enhanced rates of uptake of labeled substrate by cells pre-loaded with high levels of unlabeled 2-deoxyglucose. Transport was inhibited by cytochalasin B, phloretin and phloridzin in a manner suggesting that the system is sodium-independent. Transport was also inhibited by sodium cyanide, potassium cyanide and dinitrophenol, but not by sodium arsenite or ouabain. Insulin status of the animals had no effect on the rate of transport of this substrate. Net transport was significantly lower in neonatal (4-day-old) rats than in either older sucklings (14-16-day-old) or adult animals; no significant difference between the latter two groups was observed. These findings demonstrate that two carrier-mediated systems for glucose transport are present on the membranes of these mixed brain cells suggesting that the kinetic characteristics of glucose transport may differ between neurons and glial cells. The age change in transport rate may reflect age-associated glial cell proliferation and/or an age-dependent increase in the number of transporters per cell in one brain cell type.

2,4-Dinitrophenol↗
PubMed1985

Substrate oxidation by isolated rat brain mitochondria and synaptosomes.

The rates of [6-14C]-glucose oxidation by reconstituted systems of cytosol and mitochondria or cytosol and synaptosomes were essentially the same as the rate of oxidation of [3-14C]-3-hydroxybutyrate. However, the rate of [U-14C]-glutamine oxidation by mitochondria was 2.5 times that by synaptosomes. The addition of glutamine (5 mM) caused a reduction in the rates of oxidation [6-14C]-glucose of 20% and 40% by mitochondria and synaptosomes, respectively. Conversely, the addition of glucose (5 mM) had little or no effect on the rate of [U-14C]-glutamine oxidation by either organelle. Amino-oxyacetate decreased [U-14C]-glutamine oxidation by mitochondria more than 35% but had little or no effect on the rate of glutamine oxidation by synaptosomes. When glucose (5 mM) was added to [3-14C]-3-hydroxybutyrate, the rates of oxidation by the mitochondria and synaptosomes were increased by 65% and 77%, respectively. However, in the reverse situation the addition of 3-hydroxybutyrate decreased [6-14C]-glucose oxidation by synaptosomes (35%) but did not decrease the rate by mitochondria. These results suggest that differences in the rates of substrate utilization by mitochondria and synaptosomes and differences in substrate interactions in these two subcellular organelles may contribute to metabolic compartmentation in the brain.

Animals↗
PubMed1985

Glucose transport in astrocytes: regulation by thyroid hormone.

Primary cultures of astrocytes from newborn rat brain showed evidence of a substrate-saturable process for glucose transport. The system shows a relatively high affinity for the substrate, with an apparent Km of approximately 1 mM. Maintenance of the cells in medium containing thyroid-hormone-free serum for 3, 6, or 9 days resulted in significantly reduced rates of hexose transport. Addition of exogenous triiodothyronine to the transport incubation medium of these "hypothyroid" cells markedly increased the net rate of 2-deoxyglucose uptake within 60 s to values equal to or above those of control cultures (cells maintained in normal serum). These findings support a key role for thyroid hormone in the transport of glucose across plasma membranes of brain cells and demonstrate the presence of this regulatory system in astrocytes.

Animals↗
PubMed1984

Mode of death effect on rat liver iodothyronine 5' deiodinase activity: role of adenosine 3',5' monophosphate.

Liver thyronine 5'-deiodinase activity assayed in crude homogenates in the absence of dithiothreitol (DTT) is increased in rats killed by asphyxia when compared to that of animals killed by phenobarbital injection or decapitation. The addition of cyclic adenosine monophosphate leads to a consistent decrease in observed deiodinase activity, suggesting the possible involvement of this nucleotide in the regulation of this enzyme. The addition of DTT eliminates this effect and suggest a dual regulation of the enzyme by cAMP and physiological sulfhydryl compounds.

1-Methyl-3-isobutylxanthine↗
PubMed1984

Mode of death and post-mortem time effects on 3,3',5-triiodothyronine levels--relevance to elevated post-mortem T3 levels in SIDS.

Post-mortem T3 levels have been reported to be increased in victims of SIDS. Recent animal studies suggest, however, that elevated T3 in SIDS may be a non-specific post-mortem phenomenon. Therefore, we studied the possible effects of post-mortem time on T3 levels in 10- and 20-day-old rats killed by various methods including: Sodium pentobarbital overdose, injection of KCl, cervical dislocation or asphyxia with 100% N, 95% N-5% CO2 or 100% CO2. In both age groups T3 remained unchanged or increased slightly when the animals were killed with Na Pentobarbital or KCl. Greater increases were observed when rats were killed by cervical dislocation or asphyxia (100% N, 95% N-5% CO2 or 100% CO2). T3 levels did not become elevated in asphyxiated adult rats in which the inferior vena cava was ligated immediately following death. By extension to the human infant, the results of this study support the possibility that elevated T3 levels in SIDS victims may result from post-mortem processes. However, these results also suggest that the post-mortem elevation in T3 levels may be directly related to the mode of death.

Animals↗
PubMed1984

Decreased oxidation of labeled glucose by dissociated brain cells in the presence of fetal bovine serum.

The effect of serum on the rate of substrate oxidation by dissociated brain cells in vitro was examined. At a serum protein concentration of approximately 0.55 milligram per milliliter, oxidation of [6-14C]glucose to 14CO2 was decreased more than 50 percent. Oxidation of [3-14C]-3-hydroxybutyrate and [U-14C]glutamine was decreased much less. Serum from cows, rats, horses, and humans produced similar effects, as did serum from young and old animals and from both sexes. The effect on [6-14C]glucose oxidation was proportional to serum protein concentration, and significant inhibitory activity was obtained with dialyzed serum. Heating (80 degrees C for 10 minutes) significantly reduced the inhibitory activity. These results suggest the presence of a factor in serum that can preferentially decrease glucose oxidation. Such a factor would have profound implications for metabolic regulation in vivo and for studies of cells in vitro in which serum is included in the growth medium.

Animals↗
PubMed1984

Competition among oxidizable substrates in brains of young and adult rats. Whole homogenates.

The rates of conversion into 14CO2 of D-(-)-3-hydroxy[3-14C]butyrate, [3-14C]acetoacetate, [6-14C]glucose and [U-14C]glutamine were measured in the presence and absence of unlabelled alternative oxidizable substrates in whole homogenates from the brains of young and adult rats. The addition of unlabelled glutamine resulted in decreased 14CO2 production from [6-14C]glucose in brain homogenates from both young and adult rats. In contrast, glucose had no effect on [U-14C]glutamine oxidation. In suckling animals, both 3-hydroxybutyrate and acetoacetate decreased the rate of oxidation of [6-14C]glucose, but in adults only 3-hydroxybutyrate had an effect, and to a lesser degree. The addition of unlabelled glucose markedly enhanced the rates of oxidation of both ketone bodies in adult brain tissue and had little or no effect in the young. The rate of production of 14CO2 from [U-14C]glutamine was increased by the addition of unlabelled ketone bodies in brain homogenates from young, but not from adult rats. In the converse situation, unlabelled glutamine added to 14C-labelled ketone bodies diminished 14CO2 production in young rats, but had no effect in adult animals. These results revealed a complex age-dependent pattern of interaction in which certain substrates apparently competed with each other, whereas an enhanced rate of 14CO2 production was found with others.

3-Hydroxybutyric Acid↗
PubMed1984

Competition among oxidizable substrates in brains of young and adult rats. Dissociated cells.

The rates of conversion of D-(-)-3-hydroxy[3-14C]butyrate, [3-14C]acetoacetate, [6-14C]glucose and [U-14C]glutamine into 14CO2 were measured in the presence and absence of alternative oxidizable substrates in intact dissociated cells from the brains of young and adult rats. When unlabelled glutamine was added to [6-14C]glucose or unlabelled glucose was added to [U-14C]glutamine, the rate of 14CO2 production was decreased in both young and adult rats. The rate of oxidation of 3-hydroxy[3-14C]butyrate was also decreased by the addition of unlabelled glutamine in both age groups, but in the reverse situation, i.e. unlabelled 3-hydroxybutyrate added to [U-14C]glutamine, only the brain cells from young rats were affected. No significant effects were seen when glutamine and acetoacetate were combined. The addition of either of the two ketone bodies to [6-14C]glucose markedly lowered the rate of 14CO2 production in young rats, but in the adult only 3-hydroxybutyrate was effective and the magnitude of decrease in the rate of [6-14C]glucose oxidation was much lower than in young animals. Unlabelled glucose decreased the rate of [3-14C]acetoacetate oxidation to a minor extent in brain cells from both age groups; when added to 3-hydroxy[3-14C]butyrate, glucose had no effect in young rats and greatly enhanced 14CO2 production in adult brain cells. Many of these patterns of substrate interaction in dissociated brain cells differ from those in whole homogenates; they may be a function of the plasma membranes and the role of a carrier-mediated transport system or a reflection of a difference in the population of cell types or subcellular organelles in these two preparations.

3-Hydroxybutyric Acid↗
PubMed1984

Metabolic fate of [14C]-glutamine in mouse cerebral neurons in primary cultures.

The metabolic fate of L-[14C]-glutamine was followed in cerebral cortical neurons in primary cultures, a GABAergic preparation. Part of the glutamine was converted to GABA (0.3 nmol/min per mg protein), which is consistent with the presence of glutaminase and glutamate decarboxylase activity in the cells and with findings by other authors in vivo or in brain slices. However, an even larger part (1.8 nmol/min per mg protein) was converted to CO2 and succinate via an oxidative deamination to alpha-ketoglutarate. This is not consistent with the concept that transfer of glutamine from astrocytes to neurons should replenish neuronal GABA stores quantitatively after release of GABA and its partial accumulation into astrocytes, but it is well compatible with the recent demonstration of a net glutamine uptake by the brain.

Absorption↗
PubMed1984

Stimulatory effects of follicle-stimulating hormone and luteinizing hormone upon secretion of progesterone and inhibin activity by cultured infant human ovarian granulosa cells.

Ovarian tissue obtained from three human infants (60, 120, and 210 days of age) was separated into cell types and cultured. Granulosa cells from two of three subjects were viable and grew in culture. The cells had the potential to secrete low levels of progesterone and responded to luteinizing hormone and follicle-stimulating hormone added in culture with greatly enhanced ability to secrete progesterone. Granulosa cells could also secrete inhibin activity in culture and responded to luteinizing hormone and follicle-stimulating hormone with enhanced inhibin secretion. The granulosa cells also had the potential to secrete estrogen in the presence of testosterone. Serum levels of gonadotropin in the human infant are elevated for a period between 1 and 4 months; yet only follicular growth, not luteinization, occurs. It can be concluded that infant human granulosa cells, like adult human granulosa cells, have the potential of responding in vitro to gonadotropin.

Androstenedione↗
PubMed1984

Glutamine oxidation by dissociated cells and homogenates of rat brain: kinetics and inhibitor studies.

The rates of [U-14C]glutamine oxidation to 14CO2 were determined under a variety of experimental conditions using whole homogenates and dissociated cells from rat brain. The pattern of glutamine oxidation by homogenates differed from that by dissociated brain cells in several respects. The rates of glutamine oxidation by dissociated brain cells showed saturation kinetics with an apparent Km of 0.30 mM. Lineweaver-Burk plots of glutamine oxidation by homogenates revealed two linear segments with two apparent Km values (0.58 mM and 3.0 mM). In the presence of aminooxyacetate, however, the Lineweaver-Burk plots for homogenates were linear with a single Km of 0.47 mM. The oxidation of glutamine by homogenates was inhibited by both rotenone and antimycin A (80-85%), as were glutamate and glucose oxidation, suggesting that a significant amount of glutamine is oxidized via the tricarboxylic acid cycle. In the presence of aminooxyacetate, glutamine oxidation was inhibited less than 40%, whereas the oxidation of glutamate was inhibited 75%; in contrast, glucose oxidation was enhanced 50%. The rates of glutamine oxidation by homogenates were highest in the presence of high levels of potassium (50 mM) and low levels of sodium (2.5 mM). Varying ionic composition, however, had little or no effect on the rates of glutamine oxidation by dissociated brain cells. Measurements of glutamine oxidation by homogenates prepared from 2-, 10-, 15-, 25-, and 90-day-old rats revealed little or no age-dependent difference. In contrast, the oxidation by dissociated brain cells from 2-day-old animals was significantly less than that obtained for animals 10 days or older (7.76 vs. 15.6 nmol/h/mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Aminooxyacetic Acid↗
PubMed1983

Differential substrate oxidation by dissociated brain cells and homogenates during development.

The rates of oxidation of 3-hydroxy[3-14C]butyrate, [3-14C]acetoacetate and [6-14C]glucose were compared by using two different preparations of brain from the same animals (i.e. whole homogenates and dissociated brain cells) at various ages during development. In homogenates the rates of oxidation of 3-hydroxy[3-14C]butyrate and [3-14C]acetoacetate were high in young rats and low in adults, and were significantly higher at most ages during development than those obtained for intact cells. In contrast, rates of [6-14C]glucose oxidation by homogenates and intact cells were essentially the same at early ages; however, the rate by homogenates did not change throughout development, whereas that by intact cells increased severalfold by adulthood. In adult animals the initial glucose concentration affected the rate of glucose oxidation in homogenates, but not in intact cells. These data suggest a role for the intact cell membrane in the regulation of alternative substrate utilization by brain cells and that this process changes during development. However, the data may reflect selective differences in the cellular and subcellular components in these two preparations.

3-Hydroxybutyric Acid↗
PubMed1983

Alterations of catecholamine enzymes in several brain regions of victims of sudden infant death syndrome.

Dopamine-beta-Hydroxylase (DBH) activity is decreased and tyrosine hydroxylase activity is increased in three brain regions (hypothalamus, putamen, and caudate nucleus) from victims of Sudden Infant Death Syndrome (SIDS) when compared to values in the same regions from infants dying of known causes. No stastically significant difference was detected in tyrosine hydroxylase activity in the thalamus and brain stem although DBH was 20% lower in the former region of the SIDS victims. Two other enzymes of biogenic amine metabolism, catechol-o-methyl transferase and Dopa-decarboxylase, were essentially the same in both groups. These data are consistent with the hypothesis that an alteration in the central nervous system may be a factor in the pathophysiology of SIDS.

Brain↗
PubMed1982

Utilization of ketone bodies and glucose by established neural cell lines.

The rates of utilization of [3-14C]-acetoacetate, [3-14C]-3-hydroxybutyrate, and [6-14C]-glucose were measured in four established cell lines from neuroblastoma of rat (B103) and mouse (N4TG1) and from rat astrocytoma (RGC6) and mouse oligodendroglia (G2620). The rates of incorporation of acetoacetate into lipid were 3-5 times higher than glucose in all cell lines. The incorporation of 3-hydroxybutyrate was similar to that of glucose. Thin-layer chromatography of the total lipid extracts showed the same relative rates of use of these substrates for synthesis of various phospholipids and neutral lipids. The rates of incorporation into neutral lipids and phosphatidylcholine were essentially linear for 12 hr; however, that into phosphatidylethanolamine was markedly higher in the second 6 hr interval than in the first. In all cases, the greatest percentage of label (35-50%) appeared in the phosphatidylcholine fraction. The distribution of label from each of the three substrates among the various lipids was similar in the glial cells, but there were marked differences in distribution of the two ketone bodies in the neuroblastoma lines. These cells also synthesized lipids that migrated to the same area on the chromatogram as cholesterol esters and free fatty acids. In three of the four cell lines the rates of oxidation were highest for glucose, intermediate for acetoacetate, and lowest for 3-hydroxybutyrate. The ratios of the rate of incorporation to the rate of oxidation were higher for ketone bodies (3.32 for 3-hydroxybutyrate and 5.29 for acetoacetate) than for glucose (0.41). This indicates that in these cells ketone bodies are directed toward lipid synthesis rather than oxidation, and glucose is preferentially used as an energy source.

3-Hydroxybutyric Acid↗
PubMed1982

Antiketonemic effect of glycerol during development of the rat.

Glycerol, which decreased circulating levels of ketone bodies in adults, was tested for its antiketonemic action in developing rats. Following intraperitoneal injection of glycerol in rats from 2 to 90 days of age, blood levels of 3-hydroxybutyrate (beta HOB) decreased and reached minimum values in 35-40 minutes. The pattern of recovery in suckling animals (2, 7 and 14 days of age) differed from that of 24-, 35- and 90-day-old rats. Glycerol did not change blood acetoacetate (Ac2) levels in suckling rats but caused marked reductions in fasted older animals. The effect of glycerol on the ration of beta HOB:Ac2 was strikingly different for 90-day-old rats compared to all other groups. Glycerol did not raise blood glucose levels in neonatal or suckling rats. These developmental patterns of response to glycerol differed remarkedly from those to alanine, suggesting differential antiketonemic mechanisms for these two compounds on in vitro rats of beta HOB synthesis in liver homogenates from rats injected with either glycerol or alanine.

3-Hydroxybutyric Acid↗