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Biomedical subjects

J Marchand

Publications and source records attributed to J Marchand.

At least 37 records · Page 2Linked to original sources
PubMed1987

32P, 86Rb+ and 45Ca2+ handling by tumoral insulin-secreting cells (RINm5F line).

In perifused tumoral islet cells (RINm5F line), which were prelabelled with either [32P]orthophosphate, 86Rb+ or 45Ca2+, the administration of D-glucose (1.4, 2.8 or 16.7 mM) increased the efflux of 32P, decreased the outflow of 86Rb, increased slightly the efflux of 45Ca from cells perifused in the presence of Ca2+, and decreased modestly the outflow of 45Ca from cells perifused in the absence of Ca2+. D-glucose also stimulated the net uptake of 45Ca2+. When Ba2+ (2 mM) was used, in the absence of Ca2+, instead of D-glucose as an insulin secretagogue, the efflux of 32P was little affected, but the outflow of 45Ca was dramatically increased. These changes are qualitatively similar to those occurring in normal islet cells. Nevertheless, the ionic response to D-glucose appeared, as a rule, less marked in tumoral than normal islet cells. Moreover, the concentration-response relationship was shifted to a lower range of hexose concentrations in the RINm5F cells.

Animals↗
PubMed1987

Production and partial characterization of monoclonal antibodies against 3,3',5-triiodo-L-thyronine.

Spleen cells of Biozzi HL mouse (selection V) immunized with bovine albumin-triiodothyronine conjugate were fused with P3-X63-Ag8.653 mouse myeloma cells. Thirteen monoclonal antibodies, selected by an enzyme-linked immunosorbent assay and a radioimmunoassay, were produced in mouse ascites fluid, purified and analyzed. All of them were IgG1 (kappa). The cross-reactivity of all these monoclonal antibodies with thyroxine (T4) was less than 0.2%. The association constant determined by Scatchard analysis ranged from 1.5 x 10(9) M-1 to 2.7 x 10(10) M-1.

Animals↗
PubMed1987

Anomeric specificity of the insulin and glucagon secretory responses to D-glucose in lean and obese Zucker rats.

The perfused pancreas of lean and obese Zucker rats was exposed, in the presence of L-leucine, to the anomers of D-glucose, which were administered on four successive occasions in the alpha/beta/alpha/beta or beta/alpha/beta/alpha sequence. In 5 lean and 6 obese rats, alpha-D-glucose was more efficient than beta-D-glucose in both stimulating insulin secretion and suppressing glucagon release. Although D-glucose evoked a greater release of insulin and, during prolonged exposure to the hexose, a less pronounced suppression of glucagon secretion in obese than lean rats, the anomeric specificity of these secretory responses was not different in the two groups of animals. In one lean rat, however, alpha-D-glucose, while efficiently stimulating insulin release, failed on two occasions to inhibit glucagon secretion. This isolated observation raises the possibility that the anomeric specificity of functional events evoked by D-glucose in the endocrine pancreas may occasionally be perturbed.

Animals↗
PubMed1985

Is glucokinase responsible for the anomeric specificity of glycolysis in pancreatic islets?

At a low concentration of D-glucose (3.3 mM), the phosphorylation rate of this hexose in rat pancreatic islet homogenates incubated at 8 degrees C is higher with the beta- than with the alpha-anomer, as expected from the anomeric specificity of hexokinase. In the presence of a high concentration of glucose 6-phosphate (3.0 mM), which inhibits hexokinase but not glucokinase, the phosphorylation rates of the two anomers are not significantly different from one another. Nevertheless, in intact islets exposed at 8 degrees C to the same low concentration of D-glucose, the alpha-anomer augments, more than the beta-anomer, the production of lactic acid and net uptake of 45Ca. At the same concentration (3.3 mM), the alpha-anomer is also more potent than the beta-anomer in enhancing insulin release from perfused pancreases stimulated at 37 degrees C by L-leucine or by the combination of Ba2+ and theophylline. It is concluded that the participation of glucokinase is not essential for the anomeric specificity of glycolysis and insulin release in rat pancreatic islets.

Animals↗
PubMed1985

Insulin and glucagon release from the ventral and dorsal parts of the perfused pancreas of the rat. Effects of glucose, arginine, glucagon and carbamylcholine.

The ventral and the dorsal parts of the rat pancreas were perfused separately via either the superior mesenteric artery (0.6 ml/min) or the coeliac artery (1.4 ml/min). Control perfusions were performed via both arteries (2 ml/min). Expressed relative to the weight of tissue, the insulin content was comparable in the ventral and dorsal parts whereas the glucagon content was 2.5 times lower in the ventral than dorsal part. In comparison to the dorsal or total pancreas, the insulin secretory activity of the ventral pancreas was markedly decreased in response to either an elevation of the glucose concentration or the administration of carbamylcholine or arginine. The difference between the ventral and dorsal response was less marked at low glucose concentrations (3.3 or 7.0 mmol/l) and, possibly, in response to glucagon. In the case of glucagon release, a decreased response of the ventral pancreas was only observed when glucagon output was fully stimulated by the administration of arginine at a low glucose concentration. These results indicate that the B cell in the ventral pancreas responds poorly to several stimuli. There was little evidence to support the involvement of endogenous glucagon in the diminished sensitivity of the ventral B cells.

Animals↗
PubMed1985

Multiple effects of leucine on glucagon, insulin, and somatostatin secretion from the perfused rat pancreas.

The effects of increasing concentrations of leucine (0.2, 2.0, and 15.0 mmol/liter) on glucagon secretion from the perfused rat pancreas were examined at various glucose levels (0, 3.3, or 8.3 mmol/liter) and in the absence or presence of either arginine (5.0 mmol/liter) or glutamine (10.0 mmol/liter). At a low glucose concentration (3.3 mmol/liter), leucine caused a dose-related biphasic increase in glucagon output in the absence of arginine, but only a transient increase in the presence of the latter amino acid. These positive responses were markedly reduced and, on occasion, abolished at a high glucose concentration (8.3 mmol/liter). Moreover, at a low glucose concentration (3.3 mmol/liter) and in the presence of arginine, the highest concentration of leucine (15.0 mmol/liter) provoked a sustained and reversible inhibition of glucagon release. Likewise, leucine (15.0 mmol/liter) reversibly inhibited glucagon secretion evoked by glutamine in the absence of glucose. Thus, leucine exerted a dual effect on the secretion of glucagon, the inhibitory effect of leucine prevailing at a high concentration of the branched chain amino acid and when glucagon secretion was already stimulated by arginine or glutamine. At a physiological concentration (0.2 mmol/liter), however, leucine was a positive stimulus for glucagon release, especially in the absence of another amino acid. Concomitantly, leucine was always a positive stimulus for both insulin and somatostatin secretion. The intimate mechanisms involved in the dual effect of leucine on glucagon secretion remain to be elucidated.

Animals↗
PubMed1985

Anomeric dissociation between glucokinase activity and glycolysis in pancreatic islets.

In pancreatic islet homogenates incubated in the presence of a high glucose concentration (40 mM), the beta-anomer of D-glucose is phosphorylated at a higher rate than the alpha-anomer, whether in the absence or presence of exogenous glucose 6-phosphate. However, in intact islets also exposed to 40 mM D-glucose, the production of 3H2O from D-[5-3H] glucose, the oxidation of D-[U-14C] glucose and the glucose-induced increment in either lactate production or 45Ca net uptake, as well as the release of insulin from isolated perfused pancreases, are not higher with beta- than alpha-D-glucose. It is concluded that the rate of glucose utilization by islet cells is not regulated solely by the activity of hexokinase and/or glucokinase.

Animals↗
PubMed1979

The effect of muscimol on hippocampal pyramidal cells.

The effects of muscimol on rabbit hippocampal pyramidal cell firing were studied and compared after iontophoretic, topical, and intravenous administration of the drug. All modes of application resulted in a bicuculline-sensitive, strychnine-insensitive, depression of the monosynaptically activated population spike evoked by micro-stimulation of the contralateral hippocampal field. These findings indicate that systemically administered muscimol selectively activates hippocampal GABA receptors suggesting that this compound may be useful for studying limbic system physiology.

Action Potentials↗
PubMed1979

Interactions of alpha-ketoisocaproate, glucose and arginine in the secretion of glucagon and insulin from the perfused rat pancreas.

The effects of alpha-ketoisocaproate (KIC, 10 mmol/l) on glucagon and insulin release were studied in the in vitro perfused rat pancreas. The experiments were performed at low glucose concentration (3.3 mmol/l) in the absence or presence of arginine (10 mmol/l). In all the experiments KIC induced a marked and not rapidly reversible inhibition of glucagon release. This inhibition was more pronounced in the absence (76 percent) than presence of arginine (61 percent). These inhibitory patterns closely duplicated those which were seen in parallel experiments which included a rise in the concentration of glucose (from 3.3 to 11.1 mmol/l). KIC was also a potent stimulator of insulin release. The results are compatible with the view that the intracellular metabolism of KIC and glucose plays an essential role in the regulation of glucagon release by exogenous substrates.

Animals↗
PubMed1979

Calcium dependency of glucagon release: its modulation by nutritional factors.

The calcium dependency of glucagon release by the perfused rat pancreas was investigated in the presence of different nutrients: glucose, arginine, and a mixture of "fumarate + glutamate + pyruvate" (FGP, 5 mM of each salt). At a 3.3 mM glucose concentration, FGP-induced glucagon release was inhibited by the removal of calcium or addition of verapamil. At a higher glucose concentration (16.6 mM), the glucagonotropic action of FGP was again inhibited by verapamil, but the removal of extracellular calcium enhanced transiently glucagon release. Comparable results were obtained when arginine (10 mM) instead of FGP was used to stimulate the alpha cell. These findings suggest that the glucagonotropic effect of FGP or arginine depends on the availability and inward transport of calcium, whereas extracellular calcium per se may be required for glucose to be sensed by the alpha cell as an inhibitor of glucagon secretion. Thus, the nutritional environment offered to the alpha cell may condition the expression of the different mechanisms involved in the control of glucagon release by calcium.

Animals↗
PubMed1978

The role of calcium in glucagon release. Studies with verapamil.

The role of calcium transport into the pancreatic A2-cell in release of glucagon was studied in the perfused in vitro rat pancreas exposed to the organic calcium-antagonist verapamil (10 and 20 microns). As judged by the inhibitory effect of verapamil, a sufficient influx of calcium was required for glucagon release to be stimulated by either arginine (10 mM) or a lowering of the glucose concentration from 16.6 to 3.3 mM. However, such was not the case for glucose to inhibit the release of glucagon or when the A-2-cell was established in a stimulated state during prolonged exposure to a low, 3.3 mM, glucose concentration. These findings suggest that the role of inwardly directed transport of calcium in the secretory process of the A2-cell is of a complex nature, being dependent on the type of stimulus employed (arginine or glucose) and, in the case of glucose, on the static or dynamic state of the cell. The intimate mechanisms by which calcium exerts such complex effects on the secretory process in the A2-cell remain to be elucidated.

Animals↗