Biomedical subjects

D Nelson

Publications and source records attributed to D Nelson.

At least 199 records · Page 11Linked to original sources

PubMed1992

Structure activity studies of tryptophan30 modified analogs of Ac-CCK-7.

Cholecystokinin represents a family of gut hormones which among other activities, have been proposed to participate in satiety signaling. Ac-CCK-7[Ac-Tyr(SO3H)-Met-Gly-Trp30-Met-Asp-Phe-NH2 (2)] possesses the full spectrum of activity and potency of the intact hormone; thus analogs of 2 may be useful as anorectic agents. A series of derivatives has been prepared in which the tryptophan indole moiety of 2 has been modified. The new compounds were assayed in CCK binding assays using homogenated rat pancreatic membranes and bovine striatum as a source of CCK-A and CCK-B receptors respectively and in vivo in rats for anorectic activity. Although previous studies have concluded that the indole ring of Trp30 is a critical pharmacophore for the interaction of CCK with both its A and B type receptors, we find 2-Nal30-Ac-CCK-7 (20) to be nearly equipotent to 2 in both CCK binding and as an anorectic agent sensitive to blockade by the Merck CCK-A receptor antagonist MK-329. The extreme structural sensitivity of this anorectic activity is illustrated by the 1-naphthylalanine30 (19) and (benzo[b]thien-2-yl)alanine30 (21) analogs which are 30 and 100 times less potent than 2 respectively. Other mono- and bicyclic Trp30 replacements, including substituted phenylalanines, 3-quinolinylalanine, and 2-(5,6,7,8-tetrahydro)naphthylalanine, gave inactive compounds.

Amino Acid Sequence↗

PubMed1992

Synthesis and properties of polymerized, diaspirin cross-linked hemoglobins.

During the course of our studies it became clear that there were therapeutic applications for which a polymeric hemoglobin having an extended half-life in circulation would be appropriate. Therefore, a process for the glutaraldehyde-polymerization of diaspirin cross-linked hemoglobin (DCLHb) was developed and used to prepare glutaraldehyde-polymerized DCLHb (GP-DCLHb) in lactated Ringer's solution in sufficient quantities for biological testing. Both isovolemic exchange-transfusion and "top-load" studies (rats; primates and swine, respectively) were completed in which a broad spectrum of physiologic, histopathologic and analytical parameters were monitored and assessed. In general, GP-DCLHb in lactated Ringer's solution was well-tolerated physiologically. When compared to DCLHb, GP-DCLHb offers the advantages of reduced renal clearance of hemoglobin and an extended half-life in circulation. GP-DCLHb has the disadvantages that (1) glutaraldehyde is an ineffective virucidal agent under the conditions of the polymerization reaction and a separate virus inactivation step is required; (2) low-endotoxin (LAL-negative) GP-DCLHb solutions are pyrogenic (rabbits); and (3) unusual deposition of hemoglobin-containing material in the small arterioles of the liver and kidney (rats) was sometimes seen even after a period of time (2 weeks) during which treatment-related organ pathologies are usually resolved, a finding peculiar to GP-DCLHb among the various hemoglobin derivatives we have tested.

Animals↗

PubMed1992

Preparation and characterization of diaspirin cross-linked hemoglobin solutions for preclinical studies.

During 1990 and 1991 the capability for repetitive, consecutive production of DCLHb solution to meet a rigorous and complete set of product criteria was demonstrated. In addition, through periodic monitoring of product stored under controlled conditions, the stability of all lots of DCLHb solution during frozen storage was demonstrated for more than a year. In this way, assurance was provided that the DCLHb solution used in preclinical testing met all product criteria throughout the biological testing period.

Aspirin↗

PubMed1991

Depolarization-induced changes in cellular energy production.

Addition of high concentrations of KC1 to preparations of rat brain synaptosomes incubated with either glucose or pyruvate caused a transient stimulation of oxygen uptake. This increased respiration was insensitive to 1 mM ouabain and 10 microM ruthenium red but was dependent upon the presence of calcium. With 40 mM KCl in the incubation medium, the levels of high-energy phosphate compounds in the synaptosomes were unaltered, whereas pyridine nucleotides underwent a rapid, albeit small and temporary, oxidation. It is postulated that there is a calcium-dependent mechanism in synaptosomes through which the function of the mitochondrial respiratory chain or of oxidative phosphorylation is stimulated directly without the involvement of either adenine nucleotides or mitochondrial dehydrogenases.

Adenosine Triphosphate↗

PubMed1991

Relationships between energy level and insulin secretion in isolated rat islets of Langerhans. A study at various pH values.

To define better the role of [ATP]/[ADP] in insulin release from pancreatic islets, changes in the adenine nucleotide ratios elicited by alterations in external pH were correlated with the secretion profiles produced by administration of two metabolic secretagogues, 16 mM glucose and 10 mM alpha-ketoisocaproic acid. Experiments were carried out in buffers with and without bicarbonate, in the pH range 6.5-7.7. Insulin release was dependent on pHe irrespective of the secretagogue used. Secretion profiles for alpha-ketoisocaproic acid were the same both with and without bicarbonate; the release was decreased below pH 7.1 but maintained at 7.4-7.7. The same pattern was seen with glucose in media buffered with Hepes. With bicarbonate present, secretion caused by high glucose showed a bell-shaped dependence on [H+], with reductions at the acid and alkaline sides of pH 7.1-7.4. [ATP] and [ADP] were higher when Hepes was the buffer, at all pH values studied. The [ATP]/[ADP] declined with increasing pH under both basal and stimulated conditions; the values were always larger after stimulation although at pH 7.7 with bicarbonate present and glucose as the stimulant the difference was very small. It is concluded that: (i) the [ATP]/[ADP] in pancreatic islets is markedly dependent on pHe; (ii) there is no straight-forward correlation between either [ATP] or the absolute value for [ATP]/[ADP] and insulin secretion; and (iii) a rise in [ATP]/[ADP] is necessary for glucose-stimulated insulin release although it is not always the rate-determining event.

Adenosine Diphosphate↗

PubMed1991

(-)threo-chlorocitric acid decreases sham feeding of sucrose in rats.

The contribution of changes in rate of gastric emptying to the anorectic effect of (-)-threo-chlorocitric acid (chlorocitrate) was assessed by examining the effect of this drug in sham feeding rats, a preparation where gastric distention does not occur. Gavage administration of chlorocitrate (100-400 mg.kg-1) decreased sham and real feeding of 20% sucrose in a dose-related manner. In sham-feeding rats, the minimal effective dose was 200 mg.kg-1. The anorectic effect was evident at 60 min after 200 mg.kg-1 and 30 min after 400 mg.kg-1. In real-feeding rats, the minimal effective dose was 100 mg.kg-1 and for all doses tested the effect was apparent at the 15-min time point. In a second experiment, the effect of chlorocitrate (100-400 mg.kg-1) on gastric emptying of 20% sucrose was examined. Chlorocitrate (200 and 400 mg.kg-1) had a modest but significant inhibitory effect on gastric emptying; however, the effect was not dose-related. Inasmuch as chlorocitrate decreased sham feeding, its anorectic effect cannot be solely attributed to inhibition of gastric emptying. However, because chlorocitrate was more potent in the real-feeding condition relative to sham feeding, and the time course of the response in the two feeding conditions was different, part of chlorocitrate's anorectic effect may depend on postingestive cues such as gastric distention.

Animals↗

PubMed1991

Evolution and distribution of (GT)n repetitive sequences in mammalian genomes.

The dinucleotide repetitive sequence, (GT)n, is highly interspersed in eukaryotic genomes and may have functional roles in genetic recombination or the modulation of transcriptional activity. We have examined the distribution and conservation of position of GT repetitive sequences in several mammalian genomes. The distribution of GT repetitive sequences in the human genome was determined by the analysis of over 3700 cosmid clones containing human insert DNA. On average, a GT repetitive sequence occurs every 30 kb in DNA from euchromatic regions. GT repetitive sequences are significantly underrepresented in centric heterochromatin. The density of GT repetitive sequences in the human genome could also be estimated by analyzing GenBank genomic sequences that include introns and flanking sequences. The frequency of GT repetitive sequences found in GenBank human DNA sequences was in close agreement with that obtained by experimental methods. GenBank genomic sequences also revealed that (GT)n repetitive sequences (n greater than 6) occur every 18 and 21 kb, on average, in mouse and rat genomes. Comparative analysis of 31 homologous sequences containing (GT)n repetitive sequences from several mammals representing four orders revealed that the positions of these repeats have been conserved between closely related species, such as humans and other primates. To a lesser extent, positions of GT repetitive sequences have been conserved between species in distantly related groups such as primates and rodents. The distribution and conservation of GT repetitive sequences is discussed with respect to possible functional roles of the repetitive sequence.

Animals↗

PubMed1991

Carboxylic acids and tetrazoles as isosteric replacements for sulfate in cholecystokinin analogues.

A series of analogues of the satiety-inducing peptide cholecystokinin (CCK-8) was prepared in which the sulfated tyrosine required for activation of peripheral receptors was replaced with a carboxy(alkyl)- or tetrazolyl(alkyl)-phenylalanine to investigate whether an organic acid could serve the role of the sulfate group at the receptor. The necessary intermediates were prepared by previously reported procedures or by alkylation of carboxy(alkyl)- or tetrazolyl(alkyl)phenylmethyl bromides with a glycine-derived anion followed by protecting-group manipulations, and these were incorporated into derivatives of acetyl-CCK-7 using solid-phase synthesis. Peptide analogues were evaluated in a CCK-binding assay for affinity for either peripheral (CCK-A) receptors using homogenated rat pancreatic membranes as the receptor source or for central (CCK-B) receptors using bovine striatum as the receptor source. They were further evaluated for effects on food intake in rats after intraperitoneal (ip) injection. A number of the compounds reported are active in the CCK-A receptor binding assay although less potent than acetyl-CCK-7 and decrease food intake with comparable potency to acetyl-CCK-7. In a meal feeding model designed to assess appetite suppressant activity, acetyl-CCK-7 has an ED50 of 7 nmol/kg ip, while the ED50s of Ac-Phe(4-CH2CO2H)-Met-Gly-Trp-Met-Asp-Phe-NH2 (28) and Ac-Phe[4-(tetrazol-5-yl)]-Met-Gly-Trp-Met-Asp-Phe-NH2 (34) were 9 and 11 nmol/kg ip, respectively. An analogue of 28 lacking the N-terminal acetamido group, 3-[4-(carboxymethyl)-phenyl]propanoyl-Met-Gly-Trp-Met-Asp-Phe-NH2 (50), was also active in the meal feeding assay with an ED50 of 3 nmol/kg ip. Its anorexic effect was blocked by simultaneous administration of the CCK-A receptor antagonist MK 329, indicating that the observed anorexic activity is mediated by CCK-A receptors. We conclude from this work that the requirement for a negative charge at the CCK-A receptor provided in the natural substrate by a sulfate group can be satisfied by organic acids.

Animals↗

PubMed1991

Age-dependent changes in thiamin concentrations in whole blood and cerebrospinal fluid in infants and children.

We determined pediatric age-specific normative ranges for total, phosphorylated, and nonphosphorylated thiamin in whole blood (n = 323) and cerebrospinal fluid (CSF; n = 208). Whole-blood total thiamin decreased from 258 +/- 63 (mean +/- SD; age 0-3 mo group) to 214 +/- 44 nmol/L (age 3-12 mo group) in the first year of life and was stable at 187 +/- 39 nmol/L after 12 mo of age. The overall decline in whole-blood total thiamin was mainly due to a drop in phosphorylated thiamin, the biologically active form. Mean CSF total thiamin decreased from 135 +/- 42 (age 0-9-mo group) to 107 +/- 34 nmol/L (age 9-18-mo group) in the first 1.5 y of life and was stable at 84 +/- 51 nmol/L thereafter. This overall decline was due initially to a drop in nonphosphorylated thiamin and later to a drop in phosphorylated thiamin. The changes in whole blood and CSF occurred independently and probably represent metabolic and neurological maturation of the infant. Whole-blood total and phosphorylated thiamin concentrations were lower in blacks only after pubarche. Age-specific norms should be used for determining the thiamin status in infancy because thiamin concentrations are significantly higher in the first few months of life.

Age Factors↗

PubMed1991

Monoclonal antibodies as probes for detecting lipopolysaccharide expression on Escherichia coli from different growth conditions.

Monoclonal antibody (mAb) probes were used to investigate the expression of lipopolysaccharide (LPS) on four Escherichia coli strains, grown under a variety of conditions in batch culture which mimicked some of the in vivo environmental conditions of an infected host. Techniques of silver staining, immunoblotting, whole cell ELISA and flow cytometry were all used to monitor the expression of LPS on the bacteria and the binding of the anti-LPS mAbs. Growth in heat-inactivated sheep serum and magnesium-depleted conditions demonstrated increased expression of LPS core and subsequent increased binding of anti-core mAbs. Magnesium-depleted conditions also resulted in decreased production of O-polysaccharide material. Iron-depleted bacteria showed only minor changes in LPS expression, although increased binding of anti-core mAbs was observed. Nitrogen-deficient/high-carbon conditions, chosen to promote capsule production, resulted in increased expression of O-polysaccharide and decreased binding of anti-core mAbs.

Antibodies, Monoclonal↗

PubMed1991

Glutamate dehydrogenase reaction as a source of glutamic acid in synaptosomes.

The role of the glutamate dehydrogenase reaction as a pathway of glutamate synthesis was studied by incubating synaptosomes with 5 mM 15NH4Cl and then utilizing gas chromatography-mass spectrometry to measure isotopic enrichment in glutamate and aspartate. The rate of formation of [15N]glutamate and [15N]aspartate from 5 mM 15NH4Cl was approximately 0.2 nmol/min/mg of protein, a value much less than flux through glutaminase (4.8 nmol/min/mg of protein) but greater than flux through glutamine synthetase (0.045 nmol/min/mg of protein). Addition of 1 mM 2-oxoglutarate to the medium did not affect the rate of [15N]glutamate formation. O2 consumption and lactate formation were increased in the presence of 5 mM NH3, whereas the intrasynaptosomal concentrations of glutamate and aspartate were unaffected. Treatment of synaptosomes with veratridine stimulated reductive amination of 2-oxoglutarate during the early time points. The production of ([15N]glutamate + [15N]aspartate) was enhanced about twofold in the presence of 5 mM beta-(+/-)-2-aminobicyclo [2.2.1]heptane-2-carboxylic acid, a known effector of glutamate dehydrogenase. Supplementation of the incubation medium with a mixture of unlabelled amino acids at concentrations similar to those present in the extracellular fluid of the brain had little effect on the intrasynaptosomal [glutamate] and [aspartate]. However, the enrichment in these amino acids was consistently greater in the presence of supplementary amino acids, which appeared to stimulate modestly the reductive amination of 2-oxoglutarate. It is concluded: (a) compared with the phosphate-dependent glutaminase reaction, reductive amination is a relatively minor pathway of synaptosomal glutamate synthesis in both the basal state and during depolarization; (b) NH3 toxicity, at least in synaptosomes, is not referable to energy failure caused by a depletion of 2-oxoglutarate in the glutamate dehydrogenase reaction; and (c) transamination is not a major mechanism of glutamate nitrogen production in nerve endings.

Amino Acids↗

PubMed1991

Transport of asparagine by rat brain synaptosomes: an approach to evaluate glutamine accumulation.

Isolated rat brain synaptosomes accumulated L-asparagine with a Km value of 348 microM and a Vmax value of 3.7 nmol/mg of protein/min at 28 degrees C. Uptake of L-asparagine was inhibited by the presence of L-glutamine, whereas transport of L-glutamine was blocked by L-asparagine. Alanine, serine, cysteine, threonine, and, in particular, leucine were also inhibitory whereas alpha-(methylamino)isobutyrate, ornithine, lysine, arginine, and glutamate were much less effective blockers. Transport of L-asparagine had a substantial sodium-dependent component, whereas that of the D-stereoisomer was almost unaffected by the presence or absence of the cation. L-Asparagine was accumulated to a maximal gradient, [L-Asn]i/[L-Asn]o, of 20-30, and this value was reduced to 5-6 by withdrawal of sodium or addition of high [KCI]. A plot of log [Na+]o/[Na+]i against the log [L-Asn]i/[L-Asn]o had a slope close to I, which indicates that a single sodium ion is transported inward with each asparagine molecule. It is postulated that uptake of L-asparagine occurs, to a large extent, in cotransport with Na+ and that it utilizes the sodium chemical gradient and the membrane electrical potential as the source of energy. The similarity between the L-asparagine and L-glutamine transport systems and the reciprocal inhibition of influx of the two amino acids suggest that the same mechanism is responsible for glutamine accumulation. This could explain the high [Gln]i maintained by the brain in vivo.

Amino Acids↗

PubMed1991

Effect of cyclocreatine feeding on levels of amino acids in rat hearts before and after an ischemic episode.

Feeding Sprague-Dawley rats for 3 wk a diet containing 1% by weight of cyclocreatine increased the reservoir of the high-energy phosphate compounds but also caused alterations in the levels of the two key amino acids, aspartate and glutamate. Both were decreased by approximately 50% in the presence of an unaltered content of glutamine. In vitro exposure of these hearts to sequential perfusion, global ischemia, and reperfusion in the absence of added amino acids resulted in changes in aspartate, glutamate, and glutamine that were different from those in hearts from control rats. In the cyclocreatine-fed group, aspartate concentration ([aspartate]) and [glutamate] fell after global ischemia, whereas [glutamine] was unaltered. [Glutamine] decreased, however, in the reperfusion period. In control hearts, the predominant effect was a steady decline in glutamine, which was accompanied by either less than 10% (after global ischemia) or 30-50% fall (after reperfusion) in [aspartate] and [glutamate]. The concentration of tissue Pi was smaller in hearts from cyclocreatine-fed rats and appeared to increase more slowly during ischemia. In the presence of rotenone and aminooxyacetate, heart homogenates catalyzed production of glutamate from glutamine, which was markedly stimulated by Pi and inhibited by H+. It is postulated that 1) phosphate-activated glutaminase is an important enzyme that determines cardiac [glutamate], 2) lower [phosphate] in hearts from rats fed cyclocreatine is responsible for the apparently lesser activity of glutaminase, 3) breakdown of the high-energy phosphate compounds and consequent rise in Pi activates glutaminase, and 4) slow breakdown of glutamine during global ischemia is a result of inhibition of glutaminase by H+.

Adenosine Triphosphate↗

PubMed1991

Relations between intracellular ions and energy metabolism: a study with monensin in synaptosomes, neurons, and C6 glioma cells.

Treatment of rat brain synaptosomes with 10 microM monensin stimulated activity of the Na/K pump, which enhanced oxygen consumption and lactate production. Glycolytic flux was also increased independently of the pump activation by a fall in [H+]i. Under such conditions, glycolysis provided 26% of ATP for the ouabain-sensitive ATPase, a value substantially greater than the 4% obtained in veratridine-treated preparations (Erecińska and Dagani, 1990). In C6 glioma cells, a glia-derived line endowed with high rates of aerobic lactate synthesis, the cytosolic and mitochondrial ATP generation contributed 50% each for the support of the pump in the presence of 10 microM monensin. The fraction of energy utilized by the pump was greater in synaptosomes than in C6 cells. Enhancement of ion movements was accompanied by changes in the levels of high-energy phosphate compounds. Measurements with ion-sensitive microelectrodes in C6 cells and cultured neurons showed that monensin caused an increase in pHi by 0.4-0.5 unit and a parallel rise in [Na+]i. The increases in [Na+]i were about twofold in both types of cells, but the absolute values attained were much higher in neurons (40-50 mM) than in C6 cells (10-12 mM). Membrane potentials transiently declined by less than 10 mV and returned to their original values after 20 min of treatment. Rises in [Ca2+]i were small in neurons as well as in C6 cells. These changes could be explained by the known mechanism and/or consequences of monensin action. In contrast, in synaptosomes monensin caused an internal alkalinization of 0.1-0.15 pH unit, a large depolarization of the plasma membrane, and massive leakage of potassium into the external medium. The decrease in plasma membrane potential was accompanied by an increase in [Ca/+]i and release of the neurotransmitter amino acids GABA, aspartate, and glutamate. The depolarization and loss of K+ were unaffected by calcium withdrawal, replacement of chloride with gluconate, and addition of 1 mM 4-acetamido-4'-isothiocyanostilebene-2,2'-disulfonic acid (SITS), but was markedly attenuated by elimination of Na+. It is proposed that in synaptosomes monensin and/or the consequences of its action open a nonspecific cation channel that allows Na+ entry and K+ exit, with a consequent decrease in membrane potential.

Animals↗

PubMed1991

Corneal topography as a predictor of refractive change in the prospective evaluation of radial keratotomy (PERK) study.

The first operated eyes of 435 patients undergoing radial keratotomy in the Prospective Evaluation of Radial Keratotomy (PERK) study were evaluated by photokeratography to document the preoperative and postoperative corneal shape. We determined by regression analysis and analysis of variance that the corneal shape preoperatively improved the prediction of the corneal shape 6 months postoperatively in the 3-mm-clear-zone population. The reduction of myopia in all 435 eyes ranged from 1.25 to 9.75 diopters. We studied the effect of the preoperative corneal shape on this variability in the outcome of the surgery using rings 2 and 7 on photokeratography and corneal diameter. In the 3-mm-clear-zone group, eyes with flat prolate corneas had a greater reduction in myopia (4.65 D); those with steeper, more spherical corneas had less reduction in myopia (3.48 D). In addition, eyes with a 3-mm clear zone and flat central corneas alone (8.0 mm = 42.19 D) flattened approximately 0.75 D more than those with steep central corneas (7.0 mm = 48.21 D). In the 3.5-mm and 4.0-mm clear zone groups, the change in corneal curvature was not related to the preoperative curvature. A stepwise regression analysis of the 151 eyes in the 3.0-mm-clear-zone population demonstrated the following predictive equation for radial keratotomy; change in cycloplegic refraction = -14.55 + [-2.097 x average ring-2 radius] + [3.605 x average ring-7 radius] + [0.69 x horizontal corneal diameter] + [0.079 x age] + [-0.379 x spherical equivalent cycloplegic refraction]. There was a 1.17-D observed difference in the effect of radial keratotomy between those eyes with a steep/steep corneal topography (7.2% of the 3.0-mm-clear-zone population) and the flat/flat topography (29% of the 3.0-mm-clear-zone PERK population). A knowledge of corneal topography provides an additional tool for understanding the operative variability of radial keratotomy.

Cornea↗

PubMed1991

Immunoregulation of asthma: control of T-lymphocyte activation in the respiratory tract.

Allergic asthma results ultimately from inappropriate responses to non-pathogenic airborn antigens by the respiratory tract T-cell system. In order to understand how sensitization to inhaled antigens develops, it is necessary to precisely define the tissue microenvironments within which T-cells occur in the respiratory tract, and to analyse the factor(s) which regulate their local activation. This review focuses upon recent data on the distribution of T-cells and antigen presenting cells within the lung and airway tissues of man and experimental animals, and examines the available information on their responses to antigenic stimulation. We argue that in the steady state, respiratory tract T-cells are tightly regulated by a series of inherent and acquired immunosuppressive control mechanisms, which normally limit local T-cell activation to situations where antigenic exposure is accompanied by an inflammatory stimulus, such as the case with incoming pathogenic microorganisms.

Allergens↗

PubMed1990

A comparison of immunoblotting, flow cytometry and ELISA to monitor the binding of anti-lipopolysaccharide monoclonal antibodies.

This study was designed to assess the use of flow cytometry to observe the binding, under physiological conditions, of anti-lipopolysaccharide (LPS) monoclonal antibodies (mAbs) to whole bacteria, and to compare this with the more conventional whole cell ELISA and immunoblotting techniques. The bacteria consisted of two clinical isolates of E. coli 018:K1 and 06:K5 and two isogenic mutants of the 018 parent: a non-capsulate (018:K-) and a rough mutant (018rf). Two cross-reactive anti-core mAbs and one 018 0-antigen-specific mAb were used. ELISA and flow cytometry showed that capsule and O-polysaccharide influenced the binding of mAbs to the bacteria, whilst the latter technique demonstrated that sub-populations existed. Immunoblotting showed the two anti-core mAbs to be different, one bound only to core which was not substituted with O-antigen, whilst the other bound both to substituted and unsubstituted core. This comparison for monitoring the binding of anti-LPS mAbs demonstrates the potential use of flow cytometry in bacterial cell surface research, and complements results obtained by ELISA and immunoblotting.

Animals↗

PubMed1990

Oxygen and temperature dependence of stimulated insulin secretion in isolated rat islets of Langerhans.

The effects of lowered O2 tension on insulin secretion and changes in cellular energy parameters were investigated in isolated rat pancreatic islets perifused with buffers equilibrated with 21, 9, 5, and 1% oxygen and containing 5 mM glucose. Decreasing the external [O2] reduced the amount of insulin released in response to 16 mM glucose, 20 mM alpha-ketoisocaproic acid, and 40 mM KCl. Secretion elicited by high glucose or KCl had declined significantly at 9% oxygen, whereas that caused by alpha-ketoisocaproic acid became inhibited below 5% O2. Lowering the oxygen tension also decreased the ability of islets to respond with a rise in [ATP]/[ADP] upon stimulation with metabolic secretagogues. This reduction in the evoked increase in the nucleotide ratios paralleled the inhibition of stimulated insulin secretion. Addition of 2 mM amytal markedly decreased the islet energy level and eliminated the secretory response to 16 mM glucose. The results suggest that enhancement of B-cell energy production and a consequent rise in [ATP] (or [ATP]/[ADP]) are a necessary event for the hormone release elicited by high glucose and alpha-ketoisocaproic acid. A decrease in temperature inhibited insulin secretion with all three secretagogues tested. The energies of activation were similar for high glucose and KCl-induced secretion, about 20 kcal/mol, but were higher for alpha-ketoisocaproic acid, about 35 kcal/mol. At 28 degrees C, the [ATP]/[ADP] was larger than that at 38 degrees C (8 versus 5) and was not increased further upon addition of 16 mM glucose. It is suggested that a decrease in the rate of energy production at lowered temperatures may contribute to the inhibition of insulin release caused by metabolic secretagogues.

Animals↗