The effect of acarbose on the intestinal metabolism of glucose in vitro

The effect of acarbose on the intestinal metabolism of glucose was investigated using an in vitro perfused preparation of the isolated rat small intestine-pancreas. In preparations perfused without intraluminal sucrose administration, the total glucose recovered in the portal effluent and the portal values of lactate, pyruvate and alanine did not depend on whether or not acarbose [1.5 mg/kg body weight (b.w.)] was present in the intestinal lumen. The intestinal glucose and lactate contents were very low at the end of the experiment, and identical with or without acarbose. Insulin and glucagon concentrations remained constant during the whole perfusion period. After intraluminal administration of sucrose a clear increase in portal glucose concentration was observed, which was severely reduced by acarbose administration no changes in portal levels of lactate, pyruvate, alanine, insulin and glucagon were observed. The intestinal content of sucrose at the end of the study was significantly higher in the presence of acarbose (1.5 mg/kg b.w.), while the glucose concentration was low both with and without acarbose (0.20 +/- 0.08 vs 0.29 +/- 0.09 mmol/l respectively). These results suggest that acarbose does not influence the metabolic utilization of the glucose being translocated from the lumen.

Erythrocyte free radical scavenger enzymes in bicycle professional racers. Adaptation to training

This study was designed to investigate the influence of endurance training on the activities of the scavenger enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) measured in erythrocytes from sedentary subjects, amateur bicycle racers and in professional bicycle racers who were cycling in two real cyclist contests including the top-class race Vuelta a España (VCE). Under resting conditions the SOD activity was higher (p less than 0.01) in cyclists than in controls. The activities of CAT and GSH-Px were higher (p less than 0.05 and p less than 0.01, respectively) under resting conditions in professional cyclists versus measured both in sedentary subjects and amateur cyclists. The enzyme activities were not modified significantly in professional cyclists after a bout of exercise of 22 km in 5 hrs, but the SOD activity was increased (p less than 0.05) and CAT activity reduced (p less than 0.05) after 2800 km in 20 days (VCE). The present results shown that aerobic endurance training, when at a professional level, produces an increase in the erythrocyte activities of the main free radicals scavenger enzymes.

Subcutaneous cyclosporin prevents the development of complete Freund's adjuvant-streptozotocin-induced diabetes in the rat

The effect of subcutaneous cyclosporin administration (20 mg/kg) on the development of complete Freund's adjuvant (CFA)-streptozotocin-induced diabetes and on the induction of the so called cyclosporine diabetes like syndrome, were examined in Wistar rats. During and 5 weeks after the cyclosporin A treatment (21 days) the rats remained normoglycaemic. Three injections of 30 mg/kg streptozotocin given at weekly intervals, 24 hr after the administration of CFA, produced a persistent hyperglycaemia, an impairment of glucose tolerance and a drastic reduction in the pancreatic insulin content. The development of the diabetic state was prevented by cyclosporin treatment. The present results suggest that the cyclosporin diabetes like syndrome could not appear when cyclosporin was administered subcutaneously at the recommended doses for immunosuppression and that at such therapeutic doses, cyclosporin inhibits the development of CFA-Streptozotocin-induced diabetes in the Wistar rat.

Plasma lipid concentrations in professional cyclists after competitive cycle races

Plasma lipid concentrations were measured in professional cyclists at the beginning of the training season and both before the start and at the end of two cycle races of similar length (800 and 900 km in 6 days). Plasma concentrations of triglyceride, total and low density lipoprotein-cholesterol (LDL-C) and total cholesterol: high density lipoprotein-cholesterol (HDL-C) ratio were significantly lower and HDL-C concentrations significantly higher in cyclists compared to values in matched sedentary controls. At the end of the races, plasma concentrations of triglyceride and LDL-C were further reduced and HDL-C concentrations had increased compared to values at the start. At the end of the races, plasma concentrations of HDL-C were inversely correlated (r = -0.28, n = 45, P less than 0005) with triglyceride plasma concentrations. Body fat content, assessed as the sum of skinfold thicknesses was slightly reduced at the end of the race compared to the starting values. There was no significant correlation between skinfold thickness and plasma concentrations of HDL-C. Total plasma fatty acid concentrations were reduced and nonesterified fatty acids concentrations were increased at the end of the race compared to resting values. Consequently, the plasma concentrations of esterified fatty acids were significantly reduced after the race and there was a redistribution of the nonesterified fatty acids. The relative amounts of single fatty acids in the total fatty acid pool remained, however, remarkably constant. In conclusion, the results presented suggested that physical exercise, performed at the level of professional cyclists in a race, was an independent modifier of plasma lipid concentrations.

Gliclazide increases glucose utilization by rat intestine in vitro

The effect of gliclazide (a hypoglycemic sulphonylurea; 200 micrograms/ml) on the absorption and utilization of glucose and lactate production was investigated by using an in vitro perfused intestine-pancreas preparation isolated from fed rats, after intraluminal or arterial glucose administration. In the absence of intraluminal glucose administration, both glucose utilization and lactate production seem to be dependent on the arterial glucose concentration. The glucose utilization by the intestine was significantly increased in the presence of gliclazide (200 micrograms/ml) at three arterial concentrations of glucose (2.75, 5.5 and 11.0 mmol/l) without increasing the lactate production. The translocation of glucose from the lumen to the blood after intraluminal sugar administration was reduced when the glucose concentration was increased in the perfusate. In the presence of gliclazide (200 micrograms/ml) the translocation of glucose from the lumen to the blood was significantly reduced at the three arterial concentrations of glucose without affecting the intestinal absorption rate. In conclusion, gliclazide 200 micrograms/ml, increases the metabolic utilization of both arterially or intraluminally supplied glucose in isolated and perfused rat intestine-pancreas.

Increased arachidonic acid uptake by platelets from insulin-dependent diabetics and diabetic rats

14C-Arachidonic acid uptake was measured in platelets obtained from 15 insulin-dependent diabetic and 17 control subjects and in 12 streptozotocin-diabetic and 21 control rats. The 14C-arachidonic acid uptake, expressed as pmol/10(8) platelets/min, mean +/- SEM, was significantly higher in platelets from diabetic subjects (2.80 +/- 0.23) and diabetic rats (1.73 +/- 0.20) than in the control subjects (2.29 +/- 0.15) and the control rats (1.35 +/- 0.08). No significant correlations were found between arachidonic acid uptake and glucose, total cholesterol or triglyceride plasma levels in either rats or humans. Arachidonic acid uptake was inhibited by indometacin but not by nordihydroguaiaretic acid, in diabetic as well as in control subjects. The present results suggest that the increased arachidonic acid uptake by platelets from insulin-dependent diabetic patients and streptozotocin-diabetic rats depends on their increased platelet arachidonic acid utilization through the cyclooxygenase pathway.

In vitro study on the contribution of the rat intestine-pancreas to glucose homeostasis

Insulin release, glucose utilisation and lactate production were investigated using an in vitro perfused rat intestine-pancreas preparation after intraluminal or arterial glucose administration. In the absence of intraluminal glucose administration, both glucose utilisation and lactate production seem to be dependent on the arterial glucose concentration. Despite the different proportions in the portal values of glucose and lactate found at the various arterial glucose concentrations, the percentage of the total carbon atoms from infused glucose recovered in the portal vein remained constant. A significant (p less than 0.01) increase in insulin secretion was observed when the arterial glucose concentration was increased from 5.5 to 16.7 mmol/l. After intraluminal administration of glucose (4 g/kg body weight) both as a bolus or as an infusion, the lactate produced and the insulin released by the preparation were not significantly increased with respect to values measured in the absence of intraluminal glucose load. After intraluminal administration of glucose (1 g/kg body weight) as a bolus, the net translocation of glucose from the lumen to the vascular circuit was apparently reduced when the glucose concentration was increased in the perfusate from 2.75 to 11.0 mmol/l; this reduction could be dependent on an increase in the metabolism of absorbed glucose. In conclusion, the functional unit intestine-pancreas seems to play an important role in glucose homeostasis by elaborating the adequate mixture of glucose and lactate that must reach the liver under the various metabolic conditions.

Carboxylmethylation of insulin and glucagon in vitro

We studied the methyl acceptor capacity of insulin and glucagon in vitro. The levels of carboxylmethylation of pancreatic hormones (dpm x 10(3], when incubated with S-adenosyl-L-(3H-methyl)-methionine as methyl donor and purified protein carboxylmethylase, were: insulin (n = 6) 8.1 +/- 0.2 and 11.1 +/- 1.5 (mean +/- SEM) for 0.25 and 1.0 mg/ml, respectively; glucagon (n = 6) 17.0 +/- 3.2 and 40.2 +/- 2.5 (mean +/- SEM) for 0.5 and 1.0 mg/ml, respectively. On a molar basis, the methyl acceptor capacity was 1.0 dpm/pmol for insulin and 9.5 dpm/pmol for glucagon. Polyacrylamide gel electrophoresis of carboxylmethylated hormones showed a radioactivity (3H-methyl) peak that co-migrated with the corresponding 125I-hormone. Glucagon, but not insulin, seems to be a relatively good substrate for carboxylmethylation.

Influence of inorganic phosphate on glucose-induced insulin release in vitro

The effect of various extracellular phosphate concentrations on glucose induced insulin secretion has been investigated in two experimental systems the isolated perfused rat pancreas and the isolated rat pancreatic islets incubated in vitro. In both systems, total insulin secretion in response to 16.7 mmol/l glucose increased as extracellular phosphate concentration increased from 0 to 3.6 mmol/l. In perfusion experiments insulin secretion was significantly reduced at 4.8 mmol/l phosphate. In incubation experiments insulin secretion was inhibited only at 9.6 mmol/l phosphate concentration. When IBMX 1 mmol/l was used in incubation experiments glucose induced insulin secretion increased as extracellular phosphate increased from 0 to 3.6 mmol/l, but was also inhibited at 4.8 mmol/l.

Inorganic phosphate-insulin relationships in normal subjects and in patients with moderate glucose intolerance

The relationship between serum insulin and serum inorganic phosphate levels was investigated in normal subjects (NGT) and in patients with moderate impairment of glucose tolerance (IGT1 with subnormal and IGT2 with excessive insulin secretion) fasting and after oral glucose. Insulin and phosphate fasting levels were similar in all groups. In NGT subjects, a significant correlation between fasting insulin and inorganic phosphate levels are observed. In NGT and in IGT1 subjects, oral glucose administration was followed by a fall in serum phosphate level that was well correlated with the total insulin released. The phosphate fall was severely impaired in IGT2 patients, despite the increased insulin secretion. The plasma ionized calcium levels remain unchanged throughout the OGTT. The present results support the hypothesis that in IGT1 patients a reduced glucose-induced insulin release and in IGT2 patients, a peripheral resistance to insulin action could be the determinant of impaired glucose tolerance.

Effect of phosphate omission on the glucose-induced insulin release in vitro in fed and fasted rats

Isolated perfused rat pancreases from fed and 20-h fasted rats were used to investigate the effect of phosphate omission on the insulin response to 16.7 mmol/l glucose. The insulin response to continuous glucose stimulation was biphasic. Both phases were significantly reduced when pancreases were perfused in the absence of extracellular phosphate in fasted, but not in fed rats.

Effect of bicarbonate on the arginine-induced insulin and glucagon secretion in vitro

The isolated perfused rat pancreas was used to investigate the effect of extracellular bicarbonate concentration (25 and 40 mmol/l) on the arginine-induced insulin and glucagon release with or without 5.5 mmol/l glucose in the perfusate. In the absence of glucose, the insulin response to arginine was increased at 40 mmol/l bicarbonate, while no potentiation by glucose of the arginine-induced insulin release, at this bicarbonate concentration, was observed. At 40 mmol/l bicarbonate, glucose inhibition of basal glucagon release was abolished. In contrast, the glucagon response to arginine was not affected by the bicarbonate concentration in the perfusion medium. These results confirm that the bicarbonate concentration in the medium markedly influences the insulin release from the isolated perfused rat pancreas, while the glucagon response to arginine seems to be less sensitive to changes in extracellular bicarbonate concentration.

Effect of phosphate on the arginine-induced insulin release by the isolated perfused rat pancreas

The isolated perfused rat pancreas was used to investigate the effect of extracellular phosphate on the arginine-induced insulin release. In the absence of any metabolic substrate, the insulin response to arginine was monophasic. In the absence of phosphate in the medium, the insulin release as unaffected until the 15th minute of the stimulation period, but was significantly augmented from that time onward. In the presence of oleic acid in the perfusate, the insulin response to arginine was also monophasic but occurred earlier than in controls. In this conditin, phosphate omission resulted in an increase of the insulin response to arginine from the 3rd minute of the stimulatory period onward. In the presence of glucose 5.5 mM in the medium the insulin response to argnine was biphasic and was not affected by extracellular phosphate omission.

Effect of oleic acid on arginine-induced glucagon secretion by the isolated perfused rat pancreas

The isolated perfused rat pancreas was used to investigate the effect of oleic acid on glucagon secretion in response to 10 mmol/l arginine. In the absence of oleic acid and at 2.5 mmol/l calcium, arginine induced a biphasic glucagon secretion. At lower extracellular calcium concentration (1.0 mmol/l), the second phase of glucagon release was reduced, the first phase being unchanged. In the presence of 1,500 mumol/l oleic acid, the glucagon response to arginine was also biphasic, but second phase release was markedly inhibited, the first phase glucagon release being unchanged. Such an effect was not obtained when oleic acid concentration in the medium was 750 mumol/l. These results demonstrate that high concentrations of oleic acid inhibit glucagon secretion in response to arginine from the isolated perfused rat pancreas and support the concept that circulating free fatty acid levels are involved in the control of glucagon secretion.

Effect of phosphate omission on glucose-induced insulin release in vitro

In the isolated perfused rat pancreas, omission of extracellular phosphate (H2PO-4) significantly reduces the insulin secretion in response to 16.7 mM glucose.

Effect of oleic acid on insulin secretion by the isolated perfused rat pancreas

The isolated perfused rat pancreas was utilized to investigate the effect of oleic acid on insulin secretion. In the absence of glucose, a continuous infusion of oleic acid (1500 micromol/l) induced a biphasic insulin release. This effect was reduced at low extracellular calcium concentration. In the presence of oleic acid 1500 micromol/l, the insulin response to 10 mmol/l arginine occurred earlier, the total amount of insulin released in response to the amino acid being unchanged. Such an effect was not obtained when oleic acid in the medium was 750 micromol/l, but it was observed in the presence of oleic acid 1500 micromol/l when the concentration of albumin in the perfusate was increased from 2 g/100 ml to 4 g/100 ml. The insulin response to a continuous infusion of glucose (4.4 mmol/l and 16.7 mmol/l) was potentiated by the presence of oleic acid 1500 micromol/l in the perfusate. No modification of the biphasic pattern of insulin response to glucose 16.7 mmol/l was observed. These results demonstrate that high concentrations of oleic acid stimulate insulin release from the isolated perfused rat pancreas and modulate the insulin response to arginine or glucose.

Effect of somatostatin on the potentiating action of glucagon, cyclic adenosine monophosphate and theophylline on glucose-induced insulin release

The effect of glucagon on the inhibition of the insulin response to glucose induced by somatostatin was investigated in humans and in the isolated perfused rat pancreas. Both in vivo and in vitro somatostatin suppressed glucose-induced insulin release. This inhibitory effect of somatostatin was overcome by glucagon. Similar results have been observed in vitro by the infusion of theophylline or cyclic adenosine monophosphate.

Effect of various concentrations of calcium on arginine-induced insulin and glucagon release in vitro

The effect of extracellular calcium concentration on the insulin and glucagon release in response to arginine from the isolated perfused rat pancreas, has been studied. All the experiments were carried out in the absence of glucose in the perfusate. Arginine 10 mM elicited a biphasic glucagon release, and a monophasic insulin response. In the presence of calcium 2.5 mM an increase of total insulin and glucagon in response to arginine were obtained. The increase in glucagon release was only detectable during the second phase, while first phase was not modified by the concentration of calcium present in the perfusate. The results of this study show that extracellular calcium concentration influences positively insulin and glucagon responses to arginine in vitro.