Rapidly induced modulation of beta-N-acetylglucosaminidase activity in pancreatic islets.

The aim of this work was to determine the possible rapid modulatory effect of glucose on the activity of pancreatic islet lysosomal enzymes. For this purpose, beta-N-acetylglucosaminidase and beta-galactosidase activities were measured in homogenates of isolated rat islets after a 5, 15, 30 or 60-min exposure to either 3.3 or 16.

Identification of the calmodulin-regulated protein phosphatase, calcineurin, in rat pancreatic islets.

The aim of this work was the identification of the calmodulin-stimulated protein phosphatase, calcineurin, in rat pancreatic islets. For this purpose, a high-affinity calcineurin antibody and the Western blotting technique were used to detect the presence of calcineurin in freshly collagenase-isolated islets. The calcineurin content detected by this method was about 0.

Changes in insulin secretion and calcium distribution within B cells induced by gliclazide.

Using the pyroantimonate technique, the ultracytochemical distribution of calcium within B cells was studied in isolated rat pancreatic islets incubated during 5, 15 and 30 min with 8.3 mM glucose alone or together with 76 microgram glicazide. Glucose alone produced a continuous increment in the total number of calcium pyroantimonate precipitates (CPP) throughout the incubation period studied.

Thyroid hormone binding and deiodination by pancreatic islets: relationship with the in vitro effect upon insulin secretion.

Thyroxine dehalogenation by rat pancreatic islets was studied incubating isolated islets with labelled T4. [125I]T4 added to the incubation medium was deiodinated by the islets with the consequent production of T3, rT3 and iodide. This deiodination process showed a clear glucose-dependence, being significantly increased in the presence of 16.

Islet cells-tight junctions: changes in its number induced by glucose.

Cell-tight junctions were counted in rat isolated islets incubated for different periods of time in the presence of different extracellular glucose concentrations. The number of tight junctions increased as a function of the length of the incubation period and the concentration of glucose. These results would suggest the involvement of tight junctions in the regulatory process of glucose-induced insulin secretion.

Islet cell population changes induced by short term ovariectomy.

Changes induced in the endocrine pancreas were studied in rats 14 days after ovariectomy. The study was performed in age matched control (C) and ovariectomized (O) rats. The pancreases were stained using the p-aldehyde-fuchsin and the peroxidase (using antiinsulin serum) methods.

Role of phospholipase and calmodulin inhibitors on insulin, arachidonic acid and prostaglandin E2 release.

Using several experimental approaches, we have studied simultaneously the effect of glucose upon insulin, arachidonic acid and prostaglandin E2 release by rat pancreatic islets. A 16.6 mmol/l glucose concentration stimulated the release of insulin, arachidonic acid and prostaglandins.

[Hormonal regulation of glucose metabolism in islands of Langerhans].

Insulin secretion and glucose metabolism were simultaneously studied in isolated islets obtained from normal, endocrine-deficient (adrenalectomized, ovariectomized and radiothyroidectomized) rats as well as from this latter group of rats previously submitted to specific substitutive therapy. The islets from all the endocrine-deficient rats showed clear and similar changes in both the insulin secretion and the metabolism of glucose, being the correlation between the degree of these two alterations highly significant. All the above mentioned abnormalities were corrected by the administration of the corresponding substitutive therapy.

Effect of the removal of different endocrine glands upon insulin secretion and B-cell ultrastructure.

Glucose-induced insulin secretion and B-cell ultrastructure were studied in islets obtained from normal, adrenalectomized, radiothyroidectomized, ovariectomized and orchidectomized rats. Both parameters were also studied in the same experimental groups submitted to specific substitutive therapy. Insulin secretion in response to high glucose was significantly diminished in adrenalectomized, hypothyroid and male castrated rats.

Multiple modulators of the glucose-induced net calcium uptake by isolated islets.

Glucose-induced insulin secretion and net calcium uptake were simultaneously studied in isolated islets obtained from normal, adrenalectomized, ovariectomized and radiothyroidectomized rats, as well as from the corresponding hormone deprived rats following the administration of specific substitutive therapy. Both parameters were also studied in islets from normal rats incubated in the presence of Trifluoperazine (TFP). In all these unrelated experimental conditions simultaneous changes were obtained, observed in the release of insulin and the net calcium uptake elicited by glucose.

Functional and ultrastructural changes induced by short term ovariectomy on pancreatic islets.

The effect of short term ovariectomy and combined estrogen-progesterone treatment on insulin secretion was studied and related to the changes observed in the glucose oxidation, calcium uptake and insulin content, as well as the ultrastructure of pancreatic rat islets. It was found that ovariectomy was followed by an enhanced glucose-induced insulin secretion, glucose oxidation, calcium uptake and insulin content together with striking changes at the ultrastructural level located only in the B cell population. They were represented by the appearance of broad cytoplasmic areas containing an homogeneous fine granular material, enclosing sometimes organelles, B secretory granules with their clear halo significantly enlarged and marked dilation of the rough endoplasmic reticulum.

Evidence for the participation of calmodulin in stimulus-secretion coupling in the pancreatic beta-cell.

1. The ability of a range of phenothiazines to inhibit activation of brain phosphodiesterase by purified calmodulin was studied. Trifluoperazine, prochlorperazine and 8-hydroxyprochlorperazine produced equipotent dose-dependent inhibition with half-maximum inhibition at 12mum.