Acetylsalicyclic acid restores acute insulin response reduced by furosemide in man.

Prostaglandin E (PGE) infusion in normal man inhibits the acute insulin response to glucose. In order to determine whether endogenously released PGE might also inhibit insulin secretion, glucose-stimulated insulin responses were investigated in normal volunteers after furosemide (40 mg i.v.), a stimulator of endogenous PGE synthesis. Acute insulin response to glucose (20 g i.v.) was significantly reduced by furosemide (response before furosemide: 36 +/- 5 muU/ml; after furosemide: 26 +/- 5 muU/ml, m +/- SE, mean change 3--10 min, N = 8, P less than 0.01), whereas glucose disappearance rates were not modified after furosemide. Infusion of lysine acetylsalicylate (LAS), an inhibitor of endogenous PGE synthesis, completely reversed the inhibitory effect of furosemide on insulin secretion and also augmented acute insulin response to glucose (response before furosemide + LAS: 41 +/- 6 muU/ml; during furosemide + LAS: 50 +/- 7 muU/ml, N = 10, P less than 0.02). This effect was associated with an increase in glucose disappearance rates (P less than 0.05). These findings demonstrate that (1) furosemide inhibits glucose-induced acute insulin responses and (2) LAS completely reverses the inhibitory effect of furosemide and also accelerates glucose disposal. It is suggested that furosemide acts via the release of endogenous PGEs, which are known to inhibit insulin responses in man.     

Insulin constitutively secreted by beta-cells is necessary for glucose-stimulated insulin secretion

Four hypotheses have been posited on the role of insulin in glucose-stimulated insulin secretion; available evidence has supported insulin as being 1) essential, 2) a positive modulator, 3) a negative modulator, or 4) not necessary. Because circulating insulin levels in mice, before or after intraperitoneal glucose injection, are sufficient to elicit insulin responses in insulin-sensitive tissues, it is likely that beta-cell insulin receptors are continuously exposed to stimulating concentrations of insulin. To determine whether constitutively secreted insulin is necessary for glucose-stimulated insulin secretion, CD1 male mouse islets were incubated for 30 min at 4 degrees C in the absence (control) or presence of anti-insulin (1 micro g/ml) or anti-IgG (1 micro g/ml). Then islets were exposed to 3, 11, or 25 mmol/l glucose or to 20 mmol/l arginine. Nontreated islets exhibited first- and second-phase glucose-stimulated insulin secretion. Control and anti-IgG-treated islets, after a 5-min lag phase, increased their insulin secretion in 25 mmol/l glucose. Anti-insulin-treated islets secreted insulin at a basal rate in 3 or 25 mmol/l glucose buffers. Insulin secretion stimulated by 20 mmol/l arginine was the same in islets pretreated with either antibody and showed no lag phase. Taken together, these data suggest that constitutively secreted insulin is required and sufficient for beta-cells to maintain sensitivity to glucose.     

Transient stimulatory effect of sustained hyperglucagonemia on splanchnic glucose production in normal and diabetic man.

Insulin can modulate glucagon-stimulated hepatic glucose production and is considered to be the major factor acting in vivo to exert a couterregulatory action to glucagon. The insulin-dependent diabetic, therefore, might be especially vulnerable to enhanced hepatic glucose production promoted by glucagon. To investigate this hypothesis, low-dose glucagon infusions were administered to normal and diabetic men to compare the effects of glucagon on net splanchnic glucose production (NSGP). Four normal and three insulin-dependent, ketosis-prone, hyperglycemic diabetic men (insulin withheld for 24 hours) underwent brachial-artery-hepatic-vein catheterization. Each received a 90-minute glucagon infusion at 5 ng/kg./min. Glucagon levels rose four-to-fivefold in both groups, plateauing at 300-600 pg./ml. In the normals, NSGP rose from 92+/-12 to 211+/-31 mg./min. at 15 minutes and returned to basal levels by 45 minutes. Insulin measured in the hepatic vein rose from 19+/-6 to 33+/-11 muU/.ml., while plasma glucose rose 17 mg./dl. In the insulin-dependent diabetics, NSGP rose from 78+/-24 to a peak of 221+/-33 mg./min. at 30 minutes and then fell sharply to 113+/-15 mg./min. at 60 minutes despite continuing hyperglucagonemia. Plasma glucose in the diabetics rose 21 mg./dl. These data suggest a mechanism that acts to rapidly diminish glucagon-induced hepatic glucose production in diabetic man but does not appear to be mediated by increased insulin secretion.     

The acute effects of glucosidase inhibition on post-meal glucose increments in insulin-dependent diabetics

The effects of glucosidase inhibition on postprandial glucose tolerance was studied in 11 insulin-dependent diabetics. In comparison with placebo, 50 mg miglitol was able to lower the incremental glucose response significantly at 30 minutes and 60 minutes when insulin was injected: (i) 30 minutes before the meal (2,3 +/- 0,5 mmol/l v. 0,37 +/- 0,2 mmol/l; P less than 0,001; and 5,0 +/- 0,7 mmol/l v. 1,1 +/- 0,8 mmol/l; P less than 0,001); and (ii) immediately before the meal (2,3 +/- 0,5 mmol/l v. 2,2 +/- 0,9 mmol/l; P less than 0,001) respectively. The incremental glucose area under the curve when insulin was injected 30 minutes before breakfast was also significantly reduced on miglitol in comparison with placebo (0,67 +/- 0,15 mmol/l v. 0,16 +/- 0,14 mmol/l; P less than 0,01). The effect of miglitol was more evident when insulin was injected 30 minutes before rather than immediately before the meal. No significant adverse effects were encountered. It is concluded that: (i) miglitol safely reduces the early post-meal glucose increments in insulin-dependent diabetics; and (ii) its effect enhances the hypoglycaemic response of an appropriately timed injection of insulin.     

Postprandial plasma-glucose and -insulin responses to different complex carbohydrates

We have studied the effects of dextrose, rice, potato, corn, and bread on postprandial plasma glucose and insulin responses in 16 subjects. All carbohydrate loads were calculated to contain 50 gm. of glucose. The data demonstrate (1) that dextrose and potato elicited similar plasma glucose responses whereas rice, corn, and bread elicited lower responses; (2) similarly, dextrose and potato elicited similar and greater plasma insulin responses than rice and corn, with the response to bread being intermediate; (3) when the study group was divided in half, on the basis of each subject's one-hour plasma glucose response to dextrose, the differences in the plasma glucose and insulin responses were greater in the subjects with the highest glucose response to dextrose than in the low responders. In conclusion, there is a range of plasma-glucose and insulin responses to different complex carbohydrates, with rice and corn producing the lowest response curves. Furthermore, these differences are accentuated in patients with reduced glucose tolerance.     

Continuous infusion of subcutaneous compared to intravenous insulin for tight glycaemic control in medical intensive care unit patients

The aim of this randomised controlled study was to compare continuous subcutaneous insulin infusion using an insulin pump with the traditional continuous intravenous infusion method for tight glycaemic control. Sixty patients admitted to our University Hospital medical intensive care unit with an initial blood glucose level over 6.1 mmol/l, were enrolled and randomised into two treatment groups: the subcutaneous insulin group received continuous subcutaneous insulin infusion and the intravenous group received insulin by traditional intravenous infusion with infusers. Three patients died in the first 24 hours and were excluded from the final analysis. Insulin therapy was administered to both groups according to the previously designed and used protocol in the department. The target glucose level was 4.4 to 6.1 mmol/l. There was no significant difference in mortality between the groups. However mean blood glucose level was found to be lower (6.56+/-0.82 mmol/l vs. 7.85+/-1.6 mmol/l, P=0.00055) in the subcutaneous insulin group. According to Vogelzang's hyperglycaemic index, better glycaemic control was achieved in the subcutaneous insulin group while there was no significant difference in terms of hypoglycaemic events. Daily insulin bolus and infusion requirements were also significantly lower in the subcutaneous insulin group. Despite the small number of patients involved in this study in a medical intensive care unit, strict blood glucose control using a subcutaneous insulin pump was achieved more efficiently than the traditional intravenous infusion method without increasing hypoglycaemic events.     

Insulin and growth-hormone responses in neonatal hyperglycemia.

Glucose, insulin, and growth hormone values were studied prospectively in 75 premature infants during the first five days after birth. Intravenous glucose was given at a mean rate of 4.7-4.9 mg./kg./min. (range 3-7). Mean birth weight was 1,394+/-47 gm. (mean+/-S.E.M.). Blood glucose values were significantly higher on days 1 and 2 than on days 3 to 5. Hypoglycemia (blood glucose less than 20 mg./100 ml.) occurred in two SGA and one AGA infants. On the other hand, hyperglycemia (greater than 125 mg./100 ml.) was found in 32 of the 75 (42.7 per cent) infants. A significantly greater number of deaths occurred in infants with hyperglycemia (19/32) than in those with normoglycemia (19/32) than in those with normoglycemia (5/43). Mean plasma insulin values were significantly higher on days 1 and 2 (15+/-3 and 18+/-4 muU./ml.) than on days 3 and 4-5 (6+/-1 and 7+/-2 muU./ml.). In addition, mean insulin levels were significantly higher during hyperglycemic than during normoglycemic glucose levels at similar postnatal age. Growth hormone values were higher during the first three days than subsequently, but the values were similar in normoglycemic and hyperglycemic groups. Significant negative correlations were seen between glucose values on the first two days of postnatal life and birth weight, gestational age, and Apgar scores, whereas positive correlations were found with FiO2 and respiratory distress score (RDS).     

Pulsatile insulin release from islets isolated from three subjects with type 2 diabetes

Plasma insulin in healthy subjects shows regular oscillations, which are important for the hypoglycemic action of the hormone. In individuals with type 2 diabetes, these regular variations are altered, which has been implicated in the development of insulin resistance and hyperglycemia. The origin of the change is unknown, but derangement of the islet secretory pattern has been suggested as a contributing cause. In the present study, we show the dynamics of insulin release from individually perifused islets isolated from three subjects with type 2 diabetes. Insulin release at 3 mmol/l glucose was 10.5 +/- 4.5 pmol.g(-1).s(-1) and pulsatile (0.26 +/- 0.05 min(-1)). In islets from one subject, 11 mmol/l glucose transiently increased insulin release by augmentation of the insulin pulses without affecting the frequency. Addition of 1 mmol/l tolbutamide did not increase insulin release. In islets from the remaining subjects, insulin release was not affected by 11 mmol/l glucose. Tolbutamide transiently increased insulin release in islets from one subject. Insulin release from four normal subjects at 3 mmol/l glucose was 4.3 +/- 0.8 pmol.g(-1).s(-1) and pulsatile (0.23 +/- 0.03 min(-1)). At 11 mmol/l glucose, insulin release increased in islets from all subjects. Tolbutamide further increased insulin release in islets from two subjects. It is concluded that islets from the three individuals with type 2 diabetes release insulin in pulses. The impaired secretory response to glucose may be related to impaired metabolism before mitochondrial degradation of the sugar.     

Insulin treatment of the insulin-dependent diabetic patient undergoing minor surgery

In a prospective randomised study in 20 insulin-dependent diabetics who had minor surgery under general anaesthesia we compared the metabolic responses to intravenous glucose-insulin-potassium infusion with those who had conventional subcutaneous insulin administration. The former treatment resulted in lower blood glucose levels both during the infusion period (p less than 0.05) as well as the entire observation period (operative, first and second postoperative days; p less than 0.01). More blood glucose values were within the intended range of 5 to 10 mmol/litre in the glucose-insulin-potassium as compared to the conventional group (48% versus 24%; p less than 0.01). The levels of lactate, 3-hydroxybutyrate, glycerol, alanine, glucagon, insulin and growth hormone did not differ between the two groups. The infusion regimen resulted in better glycaemic control both peri-and postoperatively than the conventional subcutaneous insulin regimen in insulin-dependent diabetic patients who have minor surgery.     

Differential sensitivity of glycogenolysis and gluconeogenesis to insulin infusions in dogs.

The suppressive effect of insulin on hepatic glucose production is generally recognized. Though it is well established that this effect is at least partially due to inhibition of glycogenolysis, controversy still exists about insulin's effect on gluconeogenesis. The present study was undertaken to determine whether insulin could affect gluconeogenesis from alanine in the intact dog and to compare the effect of insulin on glycogenolysis and gluconeogenesis. In anesthetized dogs fasted overnight, blood samples were drawn simultaneously from a femoral artery and hepatic vein. Alanine-U-14C, 10 mu Ci./kg., was infused over 110 minutes. A constant insulin infusion at either 1 or 5 mU./kg./min. was begun at 50 minutes, and blood glucose concentration was maintained by a variable glucose infusion. When insulin was infused at 1 mU./kg./min., resulting in plasma immunoreactive insulin (IRI) levels of 73 +/- 10 muU./ml., the net splanchnic glucose production (NSGP) was suppressed from 2.7 +/- 2 mg./kg./min. to virtually zero. In constrast, this small increment in insulin concentration had no demonstrable effect on the net splanchnic uptake of alanine or on the conversion of plasma alanine to glucose (7.9 +/- 0.3 mu mol/min.). Insulin infused at 5 mU./kg./min. resulted in IRI levels of 240 +/- 25 muU./ml. This higher insulin concentration was associated with a marked suppression of both the NSGP (100 per cent) and the conversion of plasma alanine to glucose (90 per cent) but did not affect the extraction of alanine by the splanchnic bed. Doses of both 1 and 5 mU./kg./min. were associated with a 35 per cent fall in immunoreactive glucagon levels. These data demonstrate that (1) glycogenolysis is more sensitive than gluconeogenesis to the inhibitory effect of small increments in insulin concentrations, (2) gluconeogenesis could be suppressed by insulin but only at higher insulin concentrations, (3) this suppression of gluconeogenesis from alanine by insulin was due to an intrahepatic effect rather than an effect on the splanchnic extraction of alanine, and finally, (4) that insulin can suppress glucagon in the absence of hyperglycemia.     

Enhanced stimulation of glucose uptake by insulin increases exercise-stimulated glucose uptake in skeletal muscle in humans: studies using [15O]O2, [15O]H2O, [18F]fluoro-deoxy-glucose, and positron emission tomography

In vitro studies have shown that insulin and exercise stimulate glucose uptake in part via distinct mechanisms. We determined whether a high rate of insulin-stimulated glucose uptake (good insulin sensitivity) is associated with an enhanced ability of exercise to increase glucose uptake in vivo in humans. In our study, 22 normal subjects performed one-legged isometric exercise for 105 min (45-150 min) under intravenously maintained euglycemic-hyperinsulinemic conditions (0-150 min). Rates of oxygen consumption, blood flow, and glucose uptake were quantitated simultaneously in skeletal muscle of both legs using [15O]O2, [15O]H2O, [18F]fluoro-deoxy-glucose, and positron emission tomography. The one-legged exercise, performed at an intensity of 11% of maximal isometric force, was designed to induce similar increases in oxygen consumption in both groups. In the entire group, exercise increased oxygen consumption from 2.3 +/- 0.3 ml x kg(-1) muscle x min(-1) (insulin) to 34.2 +/- 3. ml x kg(-1) muscle x min(-1) (insulin and exercise) (P < 0.001) and muscle glucose uptake from 60 +/- 6 pmol x kg(-1) muscle x min(-1) (insulin) to 220 +/- 22 micromol x kg(-1) muscle x min(-1) (insulin and exercise) (P < 0.001). The exercise-induced increase in glucose uptake was due to marked increases in blood flow (36 +/- 5 ml x kg(-1) muscle x min(-1) [insulin] vs. 262 +/- 20 ml x kg(-1) muscle x min(-1) [insulin and exercise], P < 0.001) rather than glucose extraction, which decreased from 2.0 +/- 0.2 mmol/l (insulin) to 1.0 +/- 0.1 mmol/1 (insulin and exercise) (P < 0.001). The subjects were classified according to their mean rate of whole-body insulin-stimulated glucose uptake into those with high (49 +/- 3 micromol x kg(-1) x min(-1)) and normal (27 +/- 2 micromol x kg(-1) x min(-1)) rates of insulin-stimulated glucose uptake. Both insulin-stimulated (2.4 +/- 1.1 vs. 2.3 +/- 1.2 ml x kg(-1) muscle x min(-1), normal vs. high insulin sensitivity) and exercise- and insulin-stimulated (33 +/- 6 vs. 34 +/- 4 ml x kg(-1) muscle x min(-1)) rates of oxygen consumption were comparable between the groups. Exercise increased glucose uptake more in the group with high insulin sensitivity (195 +/- 25 pmol x kg(-1) muscle x min(-1)) than in the group with normal insulin sensitivity (125 +/- 19 micromol x kg(-1) muscle x min(-1)) (P < 0.05). Muscle blood flow was closely correlated with the rate of oxygen consumption (r = 0.91, P < 0.0001), and insulin-stimulated (30 +/- 5 vs. 35 +/- 6 ml x kg(-1) muscle x min(-1)) and exercise-induced increments (222 +/- 31 vs. 228 +/- 23 ml x kg(-1) muscle x min(-1)) in muscle blood flow were similar between the groups. Glucose extraction remained higher in the group with high insulin sensitivity (1.2 +/- 0.2 mmol/l) than in the group with normal insulin sensitivity (0.7 +/- 0.1 mmol/l, P < 0.05). We conclude that whereas acute exercise per se increases glucose uptake via increasing glucose delivery, good insulin sensitivity modulates exercise-induced increases in glucose uptake by enhancing cellular glucose extraction.     

Beta-cell-targeted expression of a dominant-negative mutant of hepatocyte nuclear factor-1alpha in mice: diabetes model with beta-cell dysfunction partially rescued by nonglucose secretagogues

We studied islet function in mice with beta-cell-targeted expression of a dominant-negative mutant of hepatocyte nuclear factor (HNF)-1alpha. At age 2-3 months, anesthetized transgenic and wild-type male mice underwent an intravenous glucose (1 g/kg) tolerance test (IVGTT). It was found that transgenic mice had an abolished insulin response in association with severe glucose intolerance. In other tests, the 5-min insulin response to intravenous arginine was impaired by 79% (P=0.032) and the 15-min insulin response to gastric glucose was suppressed by 97% (P=0.006). In islets incubated for 60 min, the insulin response to glucose (3.3-22.2 mmol/l) was impaired by >80% in transgenic mice. In contrast, insulin responses to nonglucose secretagogues were only partially suppressed (to GLP-1 [100 nmol/l] by 40%, to carbachol [1 micromol/l] by 20%, and to palmitate [0.5 mmol/l] by 15%), whereas the response to depolarization by KCl (50 mmol/l) was not reduced. Finally, the IVGTT data insulin sensitivity in transgenic mice was not significantly different from that of wild-type mice. Thus, mice with targeted suppression of beta-cell HNF-1alpha represent a good diabetes model exhibiting severely impaired insulin secretion after glucose with marked glucose intolerance. In contrast, the insulin responses to nonglucose stimuli are not suppressed when the islet insulin content is taken into account.     

Glucose-induced [Ca2+]i abnormalities in human pancreatic islets: important role of overstimulation

Chronic hyperglycemia desensitizes beta-cells to glucose. To further define the mechanisms behind desensitization and the role of overstimulation, we tested human pancreatic islets for the effects of long-term elevated glucose levels on cytoplasmic free Ca2+ concentration ([Ca2+]i) and its relationship to overstimulation. Islets were cultured for 48 h with 5.5 or 27 mmol/l glucose. Culture with 27 mmol/l glucose obliterated postculture insulin responses to 27 mmol/l glucose. This desensitization was specific for glucose versus arginine. Desensitization was accompanied by three major [Ca2+]i abnormalities: 1) elevated basal [Ca2+]i, 2) loss of a glucose-induced rise in [Ca2+]i, and 3) perturbations of oscillatory activity with a decrease in glucose-induced slow oscillations (0.2-0.5 min(-1)). Coculture with 0.3 mmol/l diazoxide was performed to probe the role of overstimulation. Neither glucose nor diazoxide affected islet glucose utilization or oxidation. Coculture with diazoxide and 27 mmol/l glucose significantly (P < 0.05) restored postculture insulin responses to glucose and lowered basal [Ca2+]i and normalized glucose-induced oscillatory activity. However, diazoxide completely failed to revive an increase in [Ca2+]i during postculture glucose stimulation. In conclusion, desensitization of glucose-induced insulin secretion in human pancreatic islets is induced in parallel with major glucose-specific [Ca2+]i abnormalities. Overstimulation is an important but not exclusive factor behind [Ca2+]i abnormalities.     

Effects of differing durations of antecedent hypoglycemia on counterregulatory responses to subsequent hypoglycemia in normal humans

The aim of this study was to determine whether the duration of antecedent hypoglycemia regulates the magnitude of subsequent counterregulatory failure. A total of 31 lean healthy overnight-fasted individuals (16 men/15 women) were studied. There were 15 subjects (8 men/7 women) who underwent two separate 2-day randomized experiments separated by at least 2 months. On day 1, 2-h hyperinsulinemic (9 pmol x kg(-1) x min(-1)) euglycemic (5.2 +/- 0.1 mmol/l) or hypoglycemic (2.9 +/- 0.1 mmol/l) glucose clamps (prolonged hypoglycemia) were carried out in the morning and afternoon. Of the other subjects, 16 participated in a 2-day study in which day 1 consisted of morning and afternoon short-duration hypoglycemia experiments (hypoglycemic nadir of 2.9 +/- 0.1 mmol for 5 min), and 10 of these individuals underwent an additional 2-day study in which day 1 consisted of morning and afternoon intermediate-duration hypoglycemia (hypoglycemic nadir of 2.9 +/- 0.1 mmol for 30 min). The next morning (day 2) all subjects underwent an additional 2-h hyperinsulinemic-hypoglycemic clamp (2.9 +/- 0.1 mmol/l). The rate of fall of glucose (0.07 mmol/min) was carefully controlled during all hypoglycemic studies so that the glucose nadir was reached at 30 min. Despite equivalent day 2 plasma glucose and insulin levels, there were significant differences in counterregulatory physiological responses. Steady-state epinephrine, glucagon, growth hormone, cortisol, and pancreatic polypeptide levels were similarly significantly blunted (P < 0.01) by the differing duration day 1 hypoglycemia compared with day 1 euglycemia. Muscle sympathetic nerve activity and endogenous glucose production were also similarly blunted (P < 0.01) by day 1 hypoglycemia (relative to day 1 euglycemia). Day 2 hypoglycemic symptoms were significantly reduced (P < 0.01) after day 1 prolonged intermediate- but not short-duration hypoglycemia. In summary, two episodes of short-duration moderate hypoglycemia can produce significant blunting of key neuroendocrine and metabolic counterregulatory responses. Hypoglycemic symptom scores are reduced by prolonged but not short-duration prior hypoglycemia. We conclude that in healthy overnight fasted humans, 1) neuroendocrine, autonomic nervous system, and metabolic counterregulatory responses are sensitive to the blunting effects of even short-duration prior hypoglycemia, and 2) the duration of antecedent hypoglycemia results in a hierarchy of blunted physiological responses with hypoglycemic symptom awareness less vulnerable than neuroendocrine responses.     

In vivo and in vitro glucose-induced biphasic insulin secretion in the mouse: pattern and role of cytoplasmic Ca2+ and amplification signals in beta-cells

The mechanisms underlying biphasic insulin secretion have not been completely elucidated. We compared the pattern of plasma insulin changes during hyperglycemic clamps in mice to that of glucose-induced insulin secretion and cytosolic calcium concentration ([Ca(2+)](c)) changes in perifused mouse islets. Anesthetized mice were infused with glucose to clamp blood glucose at 8.5 (baseline), 11.1, 16.7, or 30 mmol/l. A first-phase insulin response consistently peaked at 1 min, and a slowly ascending second phase occurred at 16.7 and 30 mmol/l glucose. Glucose-induced insulin secretion in vivo is thus biphasic, with a similarly increasing second phase in the mouse as in humans. In vitro, square-wave stimulation from a baseline of 3 mmol/l glucose induced similar biphasic insulin secretion and [Ca(2+)](c) increases, with sustained and flat second phases. The glucose dependency (3-30 mmol/l) of both changes was sigmoidal with, however, a shift to the right of the relation for insulin secretion compared with that for [Ca(2+)](c). The maximum [Ca(2+)](c) increase was achieved by glucose concentrations, causing half-maximum insulin secretion. Because this was true for both phases, we propose that contrary to current concepts, amplifying signals are also implicated in first-phase glucose-induced insulin secretion. To mimic in vivo conditions, islets were stimulated with high glucose after being initially perifused with 8.5 instead of 3.0 mmol/l glucose. First-phase insulin secretion induced by glucose at 11.1, 16.7, and 30 mmol/l was decreased by approximately 50%, an inhibition that could not be explained by commensurate decreases in [Ca(2+)](c) or in the pool of readily releasable granules. Also unexpected was the gradually ascending pattern of the second phase, now similar to that in vivo. These observations indicated that variations in prestimulatory glucose can secondarily affect the magnitude and pattern of subsequent glucose-induced insulin secretion.     

Maintenance of normoglycemia during cardiac surgery

We used the hyperinsulinemic normoglycemic clamp technique, i.e., infusion of insulin at a constant rate combined with dextrose titrated to clamp blood glucose at a specific level, to preserve normoglycemia during elective cardiac surgery. Ten nondiabetic and seven diabetic patients entered the clamp protocols. Perioperative glucose control was also assessed in 19 nondiabetic and 11 diabetic patients (control group) receiving a conventional insulin infusion sliding scale. In patients of the clamp group, a priming bolus of insulin (2 U) was started before the induction of anesthesia followed by infusions of insulin at 5 mU. kg(-1). min(-1) and of variable amounts of dextrose. Arterial blood glucose was measured every 5 min in the clamp group and every 20 min in the control group. Control of normoglycemia was defined as > or =95% of the glucose levels within 4.0-6.0 mmol/L. Glucose concentration was recorded before surgery, 15 min before cardiopulmonary bypass (CPB), during early and late CPB, and at sternal closure. Patients of the control group became progressively hyperglycemic during surgery (late CPB; nondiabetics, 9.0 +/- 3.2 mmol/L; diabetics, 10.1 +/- 3.6 mmol/L), whereas normoglycemia was achieved in the study group (late CPB; nondiabetics, 5.5 +/- 0.7 mmol/L; diabetics, 4.9 +/- 0.6 mmol/L; P < 0.05 versus control group). In conclusion, it seems that normal blood glucose concentration during open heart surgery can be reliably maintained in nondiabetic and diabetic patients by using the hyperinsulinemic normoglycemic clamp technique.     

Effect of peritonitis on insulin and glucose absorption during peritoneal dialysis in diabetic rats

The intraperitoneal route is frequently used for the administration of insulin in diabetic continuous ambulatory peritoneal dialysis patients. However, there is conflicting evidence as to whether the dosage of intraperitoneal insulin should be increased or decreased during peritonitis in these patients. Glucose and insulin absorption and glycaemic control were evaluated in 2-hour exchanges using 15 ml of 2.5% dextrose dialysis solution in diabetic rats with (group 1) and without (group 2) peritonitis. Fasting blood glucose values at the beginning of the study exchanges were mean +/- SD 17.9 +/- 3.3 mmol/l in group 1 and 18.2 +/- 3.5 mmol/l in group 2. Even though group 1 had a higher percentage absorption of dialysate glucose (65 +/- 19 vs. 47 +/- 7%; p less than 0.05) and higher percentage absorption of dialysate insulin (49 +/- 12 vs. 44 +/- 14%; p less than 0.1), the hypoglycaemic response to the standard intraperitoneal dose of insulin was similar in each group. Plasma C peptide levels remained very low in both groups, thus excluding significant endogenous release of insulin. These data indicate that peritonitis per se does not change intraperitoneal insulin requirements during standardized peritoneal dialysis exchanges in diabetic rats. Insulin requirements may also be unaltered during peritonitis in diabetic continuous ambulatory peritoneal dialysis patients, provided that dialysate glucose load and oral carbohydrate intake are kept constant.     

Hyperglycemia inhibits insulin activation of Akt/protein kinase B but not phosphatidylinositol 3-kinase in rat skeletal muscle

Sustained hyperglycemia impairs insulin-stimulated glucose utilization in the skeletal muscle of both humans and experimental animals--a phenomenon referred to clinically as glucose toxicity. To study how this occurs, a model was developed in which hyperglycemia produces insulin resistance in vitro. Rat extensor digitorum longus muscles were preincubated for 4 h in Krebs-Henseleit solution containing glucose or glucose + insulin at various concentrations, after which insulin action was studied. Preincubation with 25 mmol/l glucose + insulin (10 mU/ml) led to a 70% decrease in the ability of insulin (10 mU/ml) to stimulate glucose incorporation into glycogen and a 30% decrease in 2-deoxyglucose (2-DG) uptake, compared with muscles incubated with 0 mmol/l glucose. Glucose incorporation into lipid and its oxidation to CO2 were marginally diminished, if at all. The alterations of glycogen synthesis and 2-DG uptake were first evident after 1 h and were maximal after 2 h of preincubation; they were not observed in muscles preincubated with 25 mmol/l glucose + insulin for 5 min. Preincubation for 4 h with 25 mmol/l glucose in the absence of insulin produced a similar although somewhat smaller decrease in insulin-stimulated glycogen synthesis; however, it did not alter 2-DG uptake, glucose oxidation to CO2, or incorporation into lipids. Studies of insulin signaling in the latter muscles revealed that activation of Akt/protein kinase B (PKB) was diminished by 60%, compared with that of muscles preincubated in a glucose-free medium; whereas activation of phosphatidylinositol (PI) 3-kinase, an upstream regulator of Akt/PKB in the insulin-signaling cascade, and of mitogen-activated protein (MAP) kinase, a parallel signal, was unaffected. Immunoblots demonstrated that this was not due to a change in Akt/PKB abundance. The results indicate that hyperglycemia-induced insulin resistance can be studied in rat skeletal muscle in vitro. They suggest that impairment of insulin action in these muscles is related to inhibition of Akt/PKB by events that do not affect PI 3-kinase.     

Loss of the decrement in intraislet insulin plausibly explains loss of the glucagon response to hypoglycemia in insulin-deficient diabetes: documentation of the intraislet insulin hypothesis in humans

The intraislet insulin hypothesis for the signaling of the glucagon secretory response to hypoglycemia states that a decrease in arterial glucose --> a decrease in beta-cell insulin secretion --> a decrease in tonic alpha-cell inhibition by insulin --> an increase in alpha-cell glucagon secretion. To test this hypothesis in humans, a hyperinsulinemic- euglycemic ( approximately 5.0 mmol/l [90 mg/dl] x 2 h) and then a hypoglycemic ( approximately 3.0 mmol/l [55 mg/dl] x 2 h) clamp was performed in 14 healthy young adults on two occasions, once with oral administration of the ATP-sensitive potassium channel agonist diazoxide to selectively suppress baseline insulin secretion and once with the administration of a placebo. The decrement in plasma C-peptide during the induction of hypoglycemia was reduced by approximately 50% in the diazoxide clamps (from 0.3 +/- 0.0 to 0.1 +/- 0.0 nmol/l [0.8 +/- 0.1 to 0.4 +/- 0.1 ng/ml]) compared with the placebo clamps (from 0.4 +/- 0.0 to 0.1 +/- 0.0 nmol/l [1.2 +/- 0.1 to 0.4 +/- 0.1 ng/ml]) (P = 0.0015). This reduction of the decrement in intraislet insulin during induction of hypoglycemia caused an approximately 50% reduction (P = 0.0010) of the increase in plasma glucagon in the diazoxide clamps (from 29 +/- 3 to 35 +/- 2 pmol/l [102 +/- 9 to 123 +/- 8 pg/ml]) compared with the placebo clamps (from 28 +/- 2 to 43 +/- 5 pmol/l [98 +/- 7 to 151 +/- 16 pg/ml]). Baseline glucagon levels, the glucagon response to intravenous arginine, and the autonomic (adrenomedullary, sympathetic neural, and parasympathetic neural) responses to hypoglycemia were not altered by diazoxide. These data indicate that a decrease in intraislet insulin is a signal for the glucagon secretory response to hypoglycemia in healthy humans. The absence of that signal plausibly explains the loss of the glucagon response to falling plasma glucose concentrations, a key feature of the pathogenesis of iatrogenic hypoglycemia, in insulin-deficient (type 1 and advanced type 2) diabetes.     

Nerve growth factor increases insulin secretion and barium current in pancreatic beta-cells

We analyzed the effect of a brief exposure to nerve growth factor (NGF) on insulin secretion and macroscopic barium currents of single adult rat pancreatic beta-cells. After a 1-h exposure to NGF (50 ng/ml), single beta-cells show a 2.5-fold increase in the insulin secretion index in 5.6 mmol/l glucose and a nearly twofold increase in 15.6 mmol/l glucose compared with control cells. We have recently demonstrated that pancreatic beta-cells synthesize and secrete NGF. We analyzed the effect of endogenous NGF on insulin secretion by incubating islet cells in the presence of an anti-NGF monoclonal antibody for 1 h in different glucose concentrations. Although the basal insulin secretion index (5.6 mmol/l glucose) is not affected, glucose-stimulated insulin secretion (15.6 mmol/l glucose) is decreased by 41% in the presence of the antibody. This effect is mediated by the activation of the NGF receptor TrkA because the specific inhibitor of Trk phosphorylation K252a also blocks NGF-induced increase in insulin secretion, both in the presence and absence of exogenous NGF. Using the whole-cell variation of the patch-clamp technique, we found that cells exposed to NGF for 5 min exhibit a 32% increase in the average barium current density. These results suggest that the effects of NGF on insulin secretion are partially mediated by an increase in calcium current through Ca channels. These results further suggest that NGF plays an important autoregulatory role in pancreatic beta-cell function. Two targets of short-term NGF-modulation are insulin secretion and calcium-channel activity.