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Biomedical subjects

M Welsh

Publications and source records attributed to M Welsh.

At least 127 records · Page 7Linked to original sources
PubMed1984

The stimulus-secretion coupling of amino acid-induced insulin release. Secretory and oxidative response of pancreatic islets to L-asparagine.

L-Asparagine (2-10 mM) failed to affect insulin secretion from rat pancreatic islets incubated in the absence of exogenous nutrient or presence of D-glucose, but caused a dose-related and progressive enhancement of insulin release evoked by L-leucine, 2-aminobicyclo[2,2,1]heptane-2-carboxylate, or 2-ketoisocaproate. The secretory response to the combination of L-asparagine and L-leucine was augmented by theophylline and inhibited in the absence of extracellular Ca2+ or presence of either menadione or methylamine. L-Asparagine augmented leucine-stimulated 45Ca net uptake. The ATP content, rate of O2 uptake, and malate/pyruvate ratio were not significantly different in islets exposed to L-leucine alone or to both L-asparagine and L-leucine, respectively. In the sole presence of L-asparagine, however, the malate/oxalacetate ratio was decreased and the malate/pyruvate ratio increased, relative to basal values. It is proposed that the enhancing action of L-asparagine upon insulin release evoked by L-leucine might be due to an accelerated generation rate of cytosolic NADPH, rather than to any sizable increase in either islet respiration or steady-state cytosolic NADPH/NADP+ ratio.

Amino Acids↗
PubMed1984

Glucose induced inhibition of radioactive nucleotide efflux from mouse pancreatic islets is dissociated from an increase in islet oxygen uptake.

Glucose at 1.7 and 5.6 mmol/l, pyruvate (30 mmol/l) and glutamine (10 mmol/l) all stimulated islet respiration slightly. More marked stimulation was achieved with glucose 8.3 mmol/l. When pyruvate (30 mmol/l) was added to islets respiring in the presence of different concentrations of glucose (1.7, 3.3 or 5.6 mmol/l), a stimulatory effect was only observed at the highest glucose concentration. Stimulation of islet oxygen uptake was also achieved when glucose 8.3 (but not 5.6) mmol/l was added to islets respiring in glutamine 10 mmol/l. Radioactive nucleotide efflux was, however, progressively inhibited by increasing the glucose concentration up to 5.6 mmol/l both in the absence or presence of glutamine 10 mmol/l. It is concluded that the glucose-induced inhibition of radioactive nucleotide efflux is not obligatorily linked to respiration.

Adenine Nucleotides↗
PubMed1983

The effects of glibenclamide on rat islet radioactive nucleotide efflux, ATP contents and respiratory rates.

In order to assess the effects of sulphonylurea on islet function, changes in radioactive nucleotide efflux, ATP contents and oxygen uptake of low or high glucose cultured rat islets in response to glibenclamide were determined. It was observed that: (1) low glucose cultured islets displayed a prompt increase in radioactive efflux in response to glibenclamide when perfused in the presence of 1.7, 5.6 and 11.1 mM glucose. The response was most prominent in the presence of 5.6 mM glucose. (2) High glucose cultured islet did not respond to glibenclamide with increased radioactive efflux in the presence of 11.1 mM glucose, in contrast to the effects in the presence of 1.7 or 5.6 mM glucose. The sulphonylurea-induced changes could be delayed by adding glibenclamide in parallel with a decrease in glucose from 20 to 1.7 mM. (3) No effects of glibenclamide on radioactive nucleotide efflux from either low or high glucose cultured islets could be observed in the absence of extracellular Ca2+. (4) Glibenclamide decreased the islet ATP content of low glucose cultured islets in the presence of 5.6 mM glucose. On the contrary, the ATP content of high glucose cultured islets was increased by glibenclamide with 1.7 mM glucose present. (5) Islet respiration was increased by adding glucose in both high or low glucose cultured islets, although respiration in the presence of both 5.6 and 11.1 mM glucose was higher in high glucose cultured islets. (6) The addition of glibenclamide decreased oxygen uptake of low glucose cultured islets in the presence of 5.6 and 11.1 mM glucose and that of high glucose cultured islets at all glucose concentrations tested (1.7, 5.6 and 11.1 mM). It is concluded that glibenclamide-induced changes in radioactive nucleotide efflux may reflect metabolic and ionic changes of importance to islet functions.

Adenine Nucleotides↗
PubMed1983

Mechanism of 3-phenylpyruvate-induced insulin release. Secretory, ionic and oxidative aspects.

1. 3-Phenylpyruvate caused a dose-related stimulation of insulin release from rat pancreatic islets deprived of exogenous nutrient or incubated in the presence of 5.6 or 8.3 mM-D-glucose. 2. 3-Phenylpyruvate inhibited insulin release evoked by high concentrations of D-glucose (16.7 or 27.8 mM) or 4-methyl-2-oxopentanoate (10.0 mM). This inhibitory effect appeared to be attributable to impairment of 2-oxo-acid transport into the mitochondria, with resulting inhibition of D-glucose, pyruvate or 4-methyl-2-oxopentanoate oxidation. 3. 3-Phenylpyruvate failed to affect the oxidation of, and secretory response to, L-leucine, and did not augment insulin release evoked by a non-metabolized analogue of the latter amino acid. 4. L-Glutamine augmented 3-phenylpyruvate-induced insulin release. The release of insulin evoked by the combination of 3-phenylpyruvate and L-glutamine represented a sustained phenomenon, abolished in the absence of extracellular Ca2+ or the presence of menadione and potentiated by theophylline. 5. Whether in the presence or in the absence of L-glutamine, the secretory response to 3-phenylpyruvate coincided with an increase in O2 uptake, a decrease in K+ conductance, a stimulation of both Ca2+ inflow and 45Ca2+ net uptake and an increase in cyclic AMP content. 6. It is concluded that the release of insulin induced by 3-phenylpyruvate displays features classically encountered when the B-cell is stimulated by nutrient secretagogues, and is indeed attributable to an increase in nutrient catabolism.

Animals↗
PubMed1983

Mechanism of 3-phenylpyruvate-induced insulin release. Metabolic aspects.

1. The metabolism and metabolic effects of 3-phenylpyruvate were examined in rat pancreatic islets. 2. Islet homogenates catalysed transamination reactions between 3-phenylpyruvate and L-glutamate, L-leucine, L-norleucine or L-valine. 3-Phenylpyruvate failed to activate glutamate dehydrogenase. 3. 3-Phenylpyruvate rapidly entered into islet cells, was extensively converted into phenylalanine but slowly oxidized. 4. The conversion of phenylpyruvate into phenylalanine coincided with a fall in the content of several amino acids (especially glutamate and aspartate) in the islets and incubation medium, the accumulation of 2-oxoglutarate and a modest fall in the NH4+ production rate. 5. 3-Phenylpyruvate failed to affect 14CO2 output from islets prelabelled with [U-14C]palmitate, but augmented 14CO2 output from islets prelabelled or incubated with L-[U-14C]glutamine. 6. In the presence of L-glutamine, 3-phenylpyruvate augmented the ATP/ADP ratio and NAD(P)H islet content, and caused a rapid and sustained decrease in the outflow of radioactivity from islets prelabelled with [2-3H]adenosine. 7. These data support the view that the insulin-releasing capacity of 3-phenylpyruvate coincides with an increase in the catabolism of endogenous amino acids acting as 'partners' in transamination reactions leading to the conversion of 3-phenylpyruvate into phenylalanine.

Adenine Nucleotides↗
PubMed1983

Effects of glucose, leucine and adenosine on insulin release, 45Ca2+ net uptake, NADH/NAD ratios and oxygen consumption of islets isolated from fed and starved mice.

In order to elucidate further the effects of starvation on islet metabolism and insulin release, pancreatic islets of mice were isolated and incubated in the presence of various nutrient secretagogues. Starvation for 60 h completely blocked the insulin release in response to either 16.7 mM glucose or 10 mM leucine. The further addition of 20 mM adenosine partly restored the insulin response. Glucose, adenosine, glucose + adenosine, glucose + leucine or leucine + adenosine all increased the NADH/NAD ratios over basal values in islets from both fed and starved mice. No effects of starvation were observed on islet NADH/NAD ratios in any of the above media, but when islets of starved animals were incubated in the absence of any metabolic substrates the NADH/NAD ratios were decreased. In the absence of exogenous substrates the respiratory rate was also lower in islets from starved animals. Respiratory stimulation evoked by either 16.7 mM glucose or 10 mM leucine + 10 mM glutamine was lower after starvation, whereas glucose + adenosine, glucose + leucine and adenosine all induced normal respiratory responses. No differences between the 45Ca2+ uptake of islets from either starved or fed mice were observed under any conditions. It is concluded that, in starvation, a dissociation between islet insulin release and metabolism (measured as NADH/NAD ratios, oxygen consumption and 45Ca2+ uptake) may exist in the presence of certain nutrient secretagogues.

Adenosine↗
PubMed1983

Streptozotocin-induced impairment of islet B-cell metabolism and its prevention by a hydroxyl radical scavenger and inhibitors of poly(ADP-ribose) synthetase.

The possible protective effects in vitro of the hydroxyl radical scavenger dimethyl urea (6 mg/ml) and the poly(ADP-ribose)synthetase inhibitors theophylline (5 mM) and nicotinamide (0.75 mg/ml) against streptozotocin (SZ) induced deterioration of islet metabolism were investigated using isolated mouse pancreatic islets. All these compounds counteracted to different extents the deleterious effects of SZ (4.4 mM) on glucose-stimulated (pro)insulin biosynthesis, dimethyl urea protecting least. No protective effects against SZ were obtained by adding 16.7 mM glucose or 5 mM dibuturyl cAMP. The islet NADH + NAD content decreased drastically when exposed to SZ. Again, nicotinamide and theophylline protected better against the SZ-effects on pyridine nucleotides than dimethyl urea. Furthermore, the maintenance of a linear rate of oxygen uptake was lost after SZ-exposure of the islets, and there was no increase of the respiratory rate when these islets were challenged with high glucose. Also in these islet respiratory studies a partial or total protection by dimethyl urea, theophylline and nicotinamide against SZ was observed. In perifusion experiments SZ rapidly decreased insulin release together with a slightly delayed increased radioactive nucleotide efflux. Later (about 20 min.) a massive leakage of both radioactive nucleotides and insulin occurred in most of the experiments. It is concluded that all the observed impairments of islet metabolism after SZ-exposure can be related to islet NAD depletion, which may depend on poly(ADP-ribose)synthetase activation due to DNA damage. The SZ-induced DNA injury may be mediated by free radicals as suggested by the protective effects of dimethyl urea.

Animals↗
PubMed1982

Respiration and insulin release in mouse pancreatic islets. Effects of L-leucine and 2-ketoisocaproate in combination with D-glucose and L-glutamine.

In order to further evaluate the importance of B-cell metabolism for the stimulation of insulin release, respiration and insulin release were studied in mouse pancreatic islets. Leucine and 2-ketoisocaproate stimulated insulin release during an initial 1-h period, whereas there was no stimulation during two subsequent 1-h periods. This effect was in contrast to that of 16.7 mM glucose, which was a potent stimulator through all the 3 h. Furthermore, the presence of glucose (5.6 mM) or glutamine together with either leucine or 2-ketoisocaproate enhanced the insulin release and prolonged the stimulation. When the kinetics of islet respiration were studied both leucine and 2-ketoisocaproate exerted an initial stimulation on the O2 uptake which, however, was short-lived (less than 30 min). The presence of 5.6 mM glucose strongly delayed the respiratory retardation seen after the initial stimulation. Similarly, glutamine enhanced the leucine- and 2-ketoisocaproate-stimulated respiratory rates and prevented the respiratory retardation otherwise observed. Leucine (20 mM) and 2-ketoisocaproate (10 and 20 mM) stimulated the oxidation of glucose (5.6 mM). It is concluded that there is a strong correlation between respiratory stimulation and the enhancement of insulin release and that leucine and 2-ketoisocaproate depend on the presence of endogenous fuels for their ability to stimulate islet functions in vitro.

Animals↗
PubMed1982

The stimulus-secretion coupling of amino acid-induced insulin release. Metabolic response of pancreatic islets of L-glutamine and L-leucine.

L-Glutamine markedly enhances insulin release evoked by L-leucine in rat pancreatic islets. The metabolic situation found in the islets exposed to both L-glutamine and L-leucine was investigated. L-Leucine slightly decreased the rate of L-glutamine deamidation, inhibited the conversion of glutamate to 2-ketoglutarate by transamination, increased the oxidative deamination of L-glutamate, stimulated the recirculation of 2-ketoglutarate to glutamate and inhibited the further oxidative metabolism of 2-ketoglutarate. L-Glutamine slightly decreased the rate of L-leucine conversion to 2-ketoisocaproate, but inhibited more severely the conversion of 2-ketoisocaproate to acetoacetate and CO2. Several of these findings appeared attributable to activation of glutamate dehydrogenase by L-leucine. When allowance was made for the influence of exogenous amino acids on the oxidation of endogenous fatty acids, a close parallelism was found between the rate of generation of reducing equivalents or O2 uptake and the insulin secretory response to L-leucine and/or L-glutamine. These findings reinforce the view that the process of nutrient-stimulated insulin release coincides with and may be attributable to an increase in catabolic fluxes in the islet cells.

Animals↗
PubMed1982

Efflux of radioactive nucleotides from mouse pancreatic islets prelabelled with 2-3H-adenosine.

Cultured mouse pancreatic islets were prelabelled with 2-3H-adenosine in order to monitor the efflux pattern of radioactivity and insulin. The outflow of radioactivity decreased continuously when the islets were perifused with glucose (1.67 mmol/l). When raising the glucose concentration to 16.7 mmol/l, there was a prompt inhibition of the radioactive efflux concomitant with an increased rate of insulin release. These effects were reversed when the high glucose challenge was withdrawn. Similar radioactive efflux patterns were obtained after addition of alpha-ketoisocaproic acid, leucine or pyruvate to the perifusion medium, and also when the islets were challenged with high glucose concentrations in the absence of calcium. Both antimycin A and glipizide stimulated the efflux of radioactivity, although only the addition of glipizide was accompanied by a stimulation of the insulin release. Nucleotides constituted approximately 90% of the total effluent radioactivity. Decrease in the radioactive AMP and ADP efflux due to high glucose was furthermore found to be the cause of the observed inhibition of the total radioactive efflux. The changes in radioactive efflux induced by glucose probably reflect changes in the intracellular concentrations of AMP and ADP. It is concluded that no simple correlation exists between radioactive efflux and insulin release and that changes in the intracellular concentrations of nucleotides may be an early event in the stimulus-secretion coupling of glucose-induced insulin release.

Adenosine↗
PubMed1980

Respiration of the pancreatic B-cell: effects of glucose and 2-aminonorbornane-2-carboxylic acid.

The rates of oxygen consumption and glucose oxidation were measured in isolated pancreatic islets of obese-hyperglycemic or normal mice. Sufficient analytical sensitivity was achieved by incubating islets in Cartesian divers, allowing accurate measurements of oxygen uptake in the range of 1 to 10 mug dry islet weight. The endogenous islet respiration proceeded at a constant rate for more than one hour. Glucose effected a rapid and lasting elevation of the respiratory rate which corresponded to the observed rate of glucose oxidation. An extended period of starvation led to a reduction in both oxygen uptake and glucose oxidation. Isolated islets maintained for seven days in tissue culture at a glucose concentration of 5.5 mM showed a pronounced increase in oxygen consumption when they were incubated with the nonmetabolizable insulin secretagogue b (+/-) BCH in the absence of glucose. The respiratory stimulation was less marked after culture at 3.3 mM glucose and only faint after culture at 16.7 mM glucose. A common feature of islets exposed to BCH in the absence of glucose was a gradual decline of respiration commencing 30 to 40 minutes after addition of BCH. Islets incubated with BCH in the presence of glucose displayed, however, no respiratory retardation. BCH produced only a weak stimulation of the islet glucose oxidation. It is concluded that BCH stimulates the endogenous substrate oxidation of the B-cells, possibly by affecting a noncarbohydrate pool of substrate. The observations add further support to the idea that the regulation of insulin release is linked to metabolic events in the B-cell.

Amino Acids↗
PubMed1979

Further observations on the incidence and nature of atypical creatine kinase activity.

The interference of atypical creatine kinase (CK; EC 2.7.3.2) with anion-exchange methods for the measurement of the CK-MB isoenzyme is now firmly established. False-positive results from this source are much more common than interferences caused by the BB isoenzyme. Atypical CK, at least in some patients, does not appear to be a genetic variant, nor could we relate it to a specific clinical diagnosis, to hypoxia, or to administration of a particular drug. Its behavior in an immuno-inhibition test for CK-B subunit indicates an immunological difference from the normal M subunit. Thus the change in immunological properties is associated with the altered electrophoretic properties. The variability of electrophoretic patterns suggests that atypical CK may represent multiple forms of creatine kinase rather than a unique entity.

Aged↗
PubMed1976

Atypical increase in serum creatine kinase activity in hospital patients.

We use an ion-exchange column-chromatographic technique for separating creatine kinase isoenzymes in serum, and occasionally observe what appears to be sustained increase in the MB fraction. Most patients whose sera show such behavior have myocardial disease, but not necessarily a recent myocardial infarction. Electrophoretic analysis of a small sampling of such sera revealed that the apparent MB migrates atypically, appearing distinctly between isoezymes MB and MM. In another electrophoretic system, the peak might easily be mistaken for MM. This unusual isoenzyme does not appear to be "macro" creatine kinase. In laboratories that use the ion-exchange technique, the possibility of a falsely positive MB value should be considered in subjects who show persistent increases together with normal or nearly normal values for total creatine kinase activity. A suitable electrophoretic method that clearly demonstrates this unusual isoenzyme should be used in such cases, for confirmation.

Aged↗
PubMedDate not supplied

Long-term use of the low molecular weight heparin tinzaparin in haemodialysis.

Fifty-two patients with chronic renal failure undergoing hospital haemodialysis were given a single bolus dose of tinzaparin (Innohep, Leo Laboratories, UK) into the arterial side of the dialyser, for up to 43 consecutive dialyses. The mean tinzaparin dose at the beginning was 2,139 IU anti-Xa and at the end 2,186 IU anti-Xa. Overall, tinzaparin proved a satisfactory anticoagulant for 1,370 (96.0%) out of 1,427 dialyses. Significant clot formation was prevented in 1,326 (92.8%) out of 1,429 dialyses. The clinically effective dose was associated with a mean plasma anti-Xa activity 1 h after dosing of 0.4 IU/ml and suppressed fibrinopeptide A formation for up to 4 h. Bleeding, from the skin or mucous membranes, was recorded at 27 (1.9%) of 1,408 dialyses. Prolonged fistula bleeding on completion of dialysis was recorded on only 20 occasions. Other haemorrhagic events included haematemesis, bruising and subconjunctival haemorrhage (each in 1 patient) and epistaxis (2 patients). Three patients died during the study of causes considered unrelated to tinzaparin therapy, myocardial infarction (2 patients) and multiple myeloma. Other adverse events reported included vomiting (3 patients) and hypotension (3 patients). Three patients ceased treatment due to haematemesis, prolonged bleeding from fistula puncture and thrombosis of the arteriovenous access, respectively. A small, but statistically significant, increase within the normal reference range was recorded in the mean values for aspartate aminotransferase and alanine aminotransferase.

Adult↗