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O R Rebolledo

Publications and source records attributed to O R Rebolledo.

At least 19 recordsLinked to original sources
PubMed2000

A useful model to study the effect of high sugar concentrations upon growth and enzymic activities of toad embryos and larvae.

The aim of this study was to develop an oviparous model suitable for studying the differential effects and mechanisms by which a high concentration of extracellular glucose and other sugars produce diabetes complications, particularly body growth retardation during development. Hence, we studied the experimental conditions necessary to obtain measurable effects of high sugar concentrations (5-mM glucose, mannitol, fructose and galactose) upon body growth and development of Bufo arenarum embryos and larvae, and upon the activity of aspartate aminotransferase (AST), gamma-glutamyltransferase (GGT), and alkaline phosphatase (APP). Unfed animals kept in glucose showed lower body weight than controls at all stages, a condition only observed at stage 26 for animals kept in galactose and fructose. All animals reached the same stage of development regardless of the solution in which they were kept. Glucose and fructose significantly decreased the activity of all enzymes tested, while galactose only affected GGT activity. The model provides the first experimental evidence for the deleterious effect exerted in vivo by different sugars upon developing embryos and larvaes of Bufo arenarum. The results prove that this model might help to elucidate the effects and the pathogenic mechanisms of hyperglycemia upon growth and development of embryos exposed to environments with high sugar concentrations. It might also become a useful tool for testing the effectiveness of drugs designed to prevent the deleterious effect of such exposure.

Alkaline Phosphatase↗
PubMed2000

[Lipoprotein glycation and glycoxidation: their importance in diabetes mellitus].

Chronic hyperglycemia induces an increase in the non enzymatic glycation of circulating and structural proteins together with a glucose-generated oxidative and carbonyl stress, known as glycoxidation. The physicochemical characteristics and the metabolism of lipoproteins are altered by glycation/glycoxidation and resemble those of other body proteins, except for the fact that there is a simultaneous glycoxidation of both protein and phospholipid components generating an oxidative stress that increases lipoxidation. Information gathered during the last few years suggests that, among lipoproteins, modified LDL would principally contribute to developing diabetic micro-macrovascular complications. The control and the prevention of the progress of such complications are difficult to attain due to the irreversibility of glycoxidation. As glycation/glycoxidation is related to mean blood glucose, the goal in diabetes treatment must be the achievement of a close to normal metabolic control. This review summarizes advances in the importance of lipoprotein glycation/glycoxidation in diabetes mellitus.

Cardiovascular Diseases↗
PubMed1990

Early changes in the rat pancreatic B cell size induced by glucose.

The perimeter, cell area and volume density (Vvi) of B cells and exocytotic images present in these cells were measured in rat pancreas perfused with 3.3 or 16.6 mM glucose. Four minutes after the beginning of 16.6-mM glucose perfusion and coincident with the appearance at the apex of the first phase of insulin secretion, all these parameters underwent a significant increase. The changes observed in the perimeter, the cell area and the Vvi of B cells suggest an increase in their surface area. An imbalance in the rate of endocytosis:exocytosis processes with a relative predominance of the latter would increase the length of the plasma membrane and could be responsible, at least partly, for the changes in the B cell size.

Animals↗
PubMed1988

Effect of verapamil and trifluoperazine upon glucose-induced calcium distribution within B cells.

Insulin secretion and B-cell calcium distribution, assessed with the pyroantimonate precipitation technique, were studied in rat pancreases perfused with glucose (3.3 or 16.6 mM) alone or together with verapamil or trifluoperazine (TFP). Total calcium pyroantimonate precipitates (CPP), and those bound to every B cell structure, at every sampling period, were larger at 16.6 mM glucose concentration. The largest percentage of CPP was located, at early stages of the glucose stimulatory period, mainly within the clear halo of the B granules, while later on they shifted to the plasma membrane. Verapamil and TFP diminished the second phase of glucose-induced insulin release and greatly affected the above mentioned pattern of B cell CPP distribution. The main changes consist in a diminution in the total number of CPP all throughout the perfusion-time as well as an alteration in the percentage distribution of the CPP within the different B cell organelles, i.e., an early diminution in the CPP present in the B granules and of those attached to the plasma membrane and to the mitochondria at the end of the perfusion, were the most striking changes observed. The results suggest that during the glucose stimulus, different B cell structures take over the control of available calcium within the cell, following a chronological sequence. Such sequence might be determined by the different Ca2(+)-set point of those structures. Intracellular provision of calcium might be sufficient to maintain the early phase of insulin secretion when the cation entrance is blocked. Conversely, this substitution might not be enough to sustain the second phase of insulin release. The different amounts of CPP in every B cell organelle, besides their buffering capacity to control free Ca2+ availability, might also be coupled to a regulatory role of the cation upon their respective metabolic functions. In some cases, this latter effect may be the main role for the cation distribution. Our results support the concept that the level of free calcium, acting as the coupler for the stimulus:secretion process, might be regulated by different calcium pools located in the B cell.

Animals↗
PubMed1988

Effect of extracellular alkalosis upon calcium distribution within the B cells.

Insulin secretion and the pattern of calcium distribution in B cells, assessed with the pyroantimonate precipitation technique, were simultaneously studied in rat pancreases perfused with 3.3 and 16.6 mM glucose solutions of pH 7.4 and 7.8. We have previously demonstrated the blocking effect of the latter pH upon glucose-induced insulin secretion. Glucose (16.6 mM) caused an increase in the total number of calcium pyroantimonate precipitates (CPP), as well as their number bound to different B cell structures, at every sampling period studied, with respect to the 3.3 mM glucose experiments. Extracellular alkalosis strongly inhibited both phases of the B cell response to the glucose stimulus, and greatly affected the distribution of CPP in the cells with respect to the pH 7.4 ones. During the first phase of glucose induced-insulin secretion, most of the CPP appeared within B granules at pH 7.4, while on the development of the second phase of secretion, they appeared mainly attached to the cell plasma membranes. Conversely, in pH 7.8 experiments, at the first minutes of the glucose challenge, CPP appeared principally located in the cytoplasm, being almost absent from the plasma membrane during the second phase of insulin secretion. These observations suggest that during the glucose stimulus, the cell calcium distribution within the B cells followed a clear chronological sequence. Such sequence might be determined, at least in part, according to the different Ca2(+)-set points of the different B cell structures. In our case, the extracellular alkalosis might interfere with the normal intracellular calcium fluxes, which in consequence might impair release of insulin by affecting several B cell functions.

Acid-Base Equilibrium↗
PubMed1986

Quantitative ultrastructural changes induced by glucose in pancreatic B cells.

The acute ultrastructural changes induced by glucose upon the B cells were studied in normal rat pancreas perfused with 3.3 and 16.6 mmol/l glucose. A significant increment in the volume of the RER, microtubule, mitochondria, lysosomes and B granules was induced by 16.6 mmol/l glucose, while no significant changes were detected in the total B cell volume or in the size of the nucleus, cytoplasm and Golgi complex. The number of secretory granules was greatly reduced in B cells obtained from pancreas perfused with 16.6 mmol/l glucose, while its diameter was significantly enhanced. In these cells both, the number of pale granules as well as those attached to the cell membrane, were increased. All these data suggest that the increase in the extracellular glucose concentration produces not only the classical biphasic secretion on insulin, but also induces significant and measurable changes in the volume of several B cell organelles. Such ultrastructural changes correlate well with the well-known effect of glucose upon the metabolism of these cells.

Animals↗
PubMed1985

Ultracytochemical nuclear calcium distribution in pancreatic B cells: its relation to glucose-stimulated insulin secretion.

Calcium distribution in pancreatic B cells was studied, with the aid of the pyroantimonate technique, at different times of glucose-induced secretory activity in the perfused rat pancreas. Specificity of the pyroantimonate precipitates for calcium was assessed by EGTA cross-incubation. Quantitative studies for these calcium pyroantimonate precipitates were performed by a morphometric technique. Pyroantimonate precipitates within the B cell show both time and glucose dependence. At any time-point studied, in the nucleus as well as in other organelles, they were more numerous when glucose was increased in the medium from 3.3 to 16.6 mmol/l. The total number of nuclear calcium pyroantimonate precipitates rose sharply at the time corresponding to the refractory period, falling after that to almost the number found at the prestimulatory period. Otherwise, glucose significantly modifies the temporal distribution of precipitates bound to euchromatin, heterochromatin and perichromatin. These changes in nuclear calcium pyroantimonate precipitates during different periods of B cell secretory activity may indicate an active role of the cation in some nuclear regulatory function during glucose-induced release of insulin.

Animals↗
PubMed1985

Glucagon secretion and intracellular calcium distribution in pancreatic A cells.

Quantitative changes in the distribution of intracellular calcium in A cells from perfused rat pancreas in relation to the secretory state of A cells were studied with the pyroantimonate technique for calcium precipitation. A cells stimulated with a 3.3 mM glucose concentration in the perfusate presented numerous calcium precipitates attached to cell membranes, nucleus, cytoplasm and secretion granules. Independently of the length of treatment, inhibition of glucagon release with 16.6 mM glucose decreased the calcium precipitates in every cell organelle studied. These results suggest that intracellular calcium rearrangement might be important in coupling stimulus to secretion in A cells, as it has been demonstrated for pancreatic B cells.

Animals↗
PubMed1984

Sequential determination of calcium distribution in B cells at the various phases of glucose-induced insulin secretion.

Localization and quantification of calcium pyroantimonate precipitates within the B cells, and determination of insulin secretion were performed in rat pancreas perfused with 3.3 and 16.6 mmol/l glucose. Observations were carried out during the peak, the refractory period, and at 10 and 20 min in the second phase of glucose secretion after the start of a glucose challenge. Specific calcium pyroantimonate precipitates, assessed by EGTA cross-incubation, appeared attached to plasma membrane, Golgi complex, mitochondria, cytoplasmic matrix and secretory granules. The total number of cellular calcium pyroantimonate precipitates increased with perfusion time, being significantly higher at every time-point with the higher concentration of glucose (16.6 mmol/l) than with the 3.3 mmol/l glucose concentration. Calcium pyroantimonate precipitates showed a progressive increment both in plasma membranes and mitochondria. In the cytoplasmic matrix, B granules and Golgi complex, a sharp increase in the number of precipitates was detected at the refractory period, followed by a continuous decrease until the end of the experiment. These results show that the number of calcium pyroantimonate precipitates, localized in different organelles, changes according to the functional state of B cells. They stress the importance of intracellular readily exchangeable pools as regulators of calcium availability for insulin stimulus-secretion coupling.

Animals↗
PubMed1983

Stereological-ultrastructural study of pancreatic B cells in metabolic alkalosis.

The secretion of insulin in response to glucose and the changes in the B cell at the ultrastructural level were studied in rat pancreas perfused at pH 7.4 and 7.8 with different concentrations of glucose. Raising the extracellular pH from 7.4 to 7.8 significantly inhibits glucose-induced insulin secretion. Coincidentally, morphometric studies showed significant evidences of low secretory activity in B cells from pancreas submitted to high glucose stimulation under alkalosis, namely lower number of emiocytotic figures and microtubules as well as a decrease in the volume density of the granular endoplasmic reticulum and the Golgi complex. On the other hand, a significant increment in the number of images of granulolysis was also demonstrated. These secretory and ultrastructural results confirm the inhibitory effect of pH 7.8 upon B cell secretory activity induced by glucose. Moreover, they lend further support to the role of intracellular hormone degradation as a regulator of B cell insulin content.

Alkalosis↗
PubMed1983

Characteristics of the inhibitory effect of alkalosis on insulin secretion.

Glucose-induced insulin secretion by the perfused sodium pentobarbital-anesthetized-rat pancreases was studied under different extracellular pH ranging from 7.4 to 7.8. Under our experimental conditions the amount of insulin released was inversely correlated to the pH increase. Besides, metabolic (CO2H- excess) or gaseous (low pCO2) type of alkalosis, were equally effective inhibiting insulin secretion. During a 16.6 mM glucose stimulus, sequential modifications of extracellular pH (7.4-7.8-7.4) caused a dramatic decrease in insulin secretion during alkalosis and an enhancement of its release during the second 7.4 period. The installment and remotion of the inhibition followed almost immediately the changes in the pH of the perfusates. These findings indicate that extracellular diminution of H+ concentration produces a gradual and quickly reversible decrease upon glucose-induced insulin secretion. These characteristics suggest that the inhibitory effect may be mediated through changes in intracellular and/or transmembrane ion fluxes coupled to the variations in H+ concentration.

Acid-Base Equilibrium↗
PubMed1979

Ultrastructural responses of pancreatic beta cells to metabolic alkalosis.

The ultrastructural changes in pancreatic beta cells were studied following glucose-induced insulin secretion in vitro, at two different extracellular pH (7.4 and 7.8). The pancreata perfused at pH 7.4 exhibited a biphasic insulin response to glucose challenge together with signs of increased emiocytotic activity and numerous microtubules in the beta cells. Conversely, the pancreata perfused at pH 7.8 showed a significant decrease in insulin secretion, and their beta cells revealed scarce emiocytotic images and a marked increase of intracellular granulolysis. These results represent the ultrastructural correlate of the reduced insulin secretion produced by metabolic alkalosis in the perfused rat pancreas.

Alkalosis↗
PubMed1978

Insulin secretion during acid-base alterations.

Insulin secretion under extracellular acid-base alterations (metabolic acidosis or alkalosis) was studied, by challenging in vitro perfused sodium pentobarbital-anesthetized-rat pancreases with glucose, arginine, and tolbutamide. Under our experimental conditions, the amount of insulin released was lower at pH 7.8 than the amount corresponding to the pH 7.4 control, in spite of the agent used to stimulate the pancreas. The effect of pH 7.0 on insulin secretion, however, depends on the type and concentration of the stimulus used. It enhances the secretion elicited by glucose (6.6 mM) and glucose plus arginine (6.6 and 10 mM, respectively). On the other hand, it reduces the beta cell response to glucose plus tolbutamide (3.3 mM and 400 microgram/ml, respectively), whereas the response to high glucose (16.6 mM) is reduced in the first phase and not affected in the second. According to these results, modifications of the extracellular pH, mainly at high levels, may interfere with a common process involved in insulin secretion, namely beta cell emiocytosis.

Acidosis↗