Effect of the enteroinsular axis on both the A- and B-cell response to arginine after oral glucose in man

Summary Studies were made on the effect of the enteroinsular axis on amino acid-induced insulin and glucagon secretion during hyperglycaemia in man. The responses of plasma immunoreactive insulin, C-peptide, and immunoreactive glucagon to arginine infusion were investigated in nine healthy subjects after induction of hyperglycaemia by an oral glucose load and by intravenous glucose infusion to produce similar glucose concentrations in the arterialised blood. The plasma immunoreactive insulin and C-peptide levels increased to higher levels after an oral glucose load than after an intravenous infusion of glucose. The incremental areas under the immunoreactive insulin and C-peptide curves during arginine infusion were significantly greater (p<0.01) after oral than after intravenous glucose administration. The plasma immunoreactive glucagon level was suppressed equally after oral and intravenous glucose loads. However, during subsequent arginine infusion, the plasma immunoreactive glucagon level rose more in the presence of hyperglycaemia induced by oral than intravenous glucose. The incremental area under the plasma immunoreactive glucagon curve during arginine infusion was 1.6-fold greater after glucose ingestion than after intravenous glucose infusion. These results suggest that the enteroinsular axis has a stimulatory effect on the responses of pancreatic A and B cells to arginine after oral glucose administration.     

The metabolic and hormonal responses to glucose infusion in anaesthetized normal and diabetic dogs controlled by an artificial B-cell

Summary The metabolic response to glucose infusion in anaesthetized normal and pancreatectomized dogs has been assessed. Normoglycaemia was achieved in the diabetic dogs with an external artificial B-cell which administered insulin into the peripheral circulation. No differences were found in the levels of blood glucose, glucagon, lactate, pyruvate and plasma non-esterified fatty acids, either in the fasting state or in response to glucose infusion. However, compared to normal animals normoglycaemic diabetic dogs had significantly elevated circulating levels of insulin and alanine at all times. Fasting levels of the same hormones and metabolites were also measured in conscious dogs. Blood pyruvate levels were higher, and plasma non-esterified fatty acid levels lower, in the anaesthetized animals. There were also minor but consistent changes in blood glucose and plasma insulin while glucagon, lactate and alanine levels were unaffected by anaesthesia. In conclusion, controlled barbiturate anaesthesia has relatively minor effects on the metabolic and hormonal status of the dog. The metabolic and hormonal response to glucose infusion in pancreatectomized dogs treated with an artificial B-cell was almost entirely normalized, except for peripheral hyperinsulinaemia and hyperalaninaemia.     

Dose-kinetics of pancreatic glucagon responses to arginine and glucose in subjects with normal and impaired pancreatic B cell function

Summary Pancreatic glucagon responses to different amounts of intravenous arginine and glucose were studied in 10 insulin-dependent diabetics, 14 healthy controls (high insulin responders) and 15 subjects with decreased insulin response to glucose but normal intravenous glucose tolerance (low insulin responders). The dose-kinetics of the glucagon response was studied by using four different arginine doses. The suppressive effect of glucose was evaluated by infusing three glucose doses during a submaximal stimulation with arginine. The diabetics were tested first when under fair metabolic control and then following intensive treatment with insulin to produce near-normalisation of blood glucose. Finally, five subjects underwent insulin-induced hypoglycaemia. The changes in plasma glucagon and blood -amino-nitrogen in response to the four arginine doses were significantly correlated in all groups but the slope of the dose response curve was steeper in the poorly controlled-diabetics than in the non-diabetics. These diabetics displayed higher fasting plasma glucagon values than healthy controls (high insulin responders) (224±4 versus 151±22 pg/ml, p<0.01), higher plasma glucagon responses to arginine and an absence of inhibition by glucose of the arginine-stimulated glucagon release. In strictly controlled diabetic patients, fasting plasma glucagon levels (176±16 pg/ml) were not significantly different from healthy controls, the glucagon response to arginine returned to the normal range, A cell suppressibility by glucose was restored and A cell stimulation by hypoglycaemia reappeared. In the low insulin responders, fasting plasma glucagon was not different from that of high responders (107±12 pg/ml), the slope of the dose response curve to arginine was similar in both groups and the A cells were inhibited by glucose to a similar extent. These results support the concept that islet A cell dysfunction in diabetes is not a primary phenomenon.     

Effect of a long acting glucagon selective somatostatin analogue on plasma glucose,insulin and glucagon levels in the anaesthetized rat during arginine infusion

Summary The effects of somatostatin and a long acting, glucagon selective somatostatin analog (des-Ala¹Gly²[His^4,5-D-Trp⁸]-somatostatin), were studied during arginine tolerance tests in normal anaesthetized rats. Arginine infusion in control animals resulted in a rapid increase in plasma insulin and glucagon, and an increase of 15±5 mg/dl in plasma glucose. Somatostatin infusion (1 mg/kg/h) resulted in suppression of basal insulin secretion and a decrease in arginine-induced insulin and glucagon release. Glucose levels increased rapidly during the combined arginine-somatostatin infusion reaching a peak of 72±10 mg/dl above basal levels. Similar results were obtained when somatostatin was injected SC (1 mg/kg) at times 0, 15, 30, and 45 minutes (arginine infused from 30–60 minutes). A single injection (1 mg/kg) of the long-acting somatostatin analogue resulted in significant inhibition of basal insulin and glucagon release; during arginine infusion glucagon levels rose only slightly, the insulin response was, however, nearly normal, and only a small arginine-induced increase in glucose levels was observed. Carbohydrate absorption was not influenced by either somatostatin or the analogue.     

Determination of immunoreactive somatostatin in rat plasma and responses to arginine,glucose and glucagon infusion

Summary A method for the determination of immunoreactive somatostatin in rat plasma is described. Blood specimens were collected into aprotinin and EDTA. Plasma was separated, immediately diluted with acidified acetone and ultrasonicated. The resultant supernatant was lyophilised. The dilution curve of the material thus extracted was parallel to that of synthetic somatostatin. The material was eluted mainly in a similar position to that of synthetic somatostatin on Sephadex G-25 (f) column chromatography. The somatostatin immunoreactivity was degraded significantly from the pre-incubated value of 846±86 pg/ml (n=4, mean±SEM) to 102±16 pg/ml in the same manner as that of synthetic somatostatin when incubated with one ml of fresh rat plasma at 37 °C for 30 min. The mean recovery in quadruplicate of immunoreactive somatostatin at concentrations of 100, 200 and 400 pg/ml was 83±7, 95±4 and 76±4%, respectively. Using this method, plasma immunoreactive somatostatin responses to arginine, glucose and glucagon infusion were measured in pentobarbital anaesthetized rats. The mean basal plasma immunoreactive somatostatin concentration in the jugular vein was 35±3 pg/ml (n=7), while that in the hepatic portal vein was 120±17 pg/ml (n=7). Infusion of arginine, glucose and glucagon all resulted in 2–3 fold increases in portal plasma immunoreactive somatostatin concentration.     

Postprandial plasma glucose,insulin, glucagon and triglyceride responses to a standard diet in normal subjects

Summary Postprandial plasma glucose, insulin and triglyceride responses were determined in 12 normal subjects (7 male and 5 female) fed a standard diet composed of typical American foods; the three meals were identical for each subject. A significant post-prandial rise in glucose and insulin was observed. They were closely related temporally in the early post-absorptive period. However, in the late post-absorptive phase insulin decline was generally slower than the glucose decline. A considerable difference in the glucose and insulin response was observed between males and females. Fasting plasma glucose and insulin concentrations were lower in the women. Following each meal the peak plasma glucose was lower in the women, but the difference was significant only following breakfast (p < 0.02). The area under the glucose curve following breakfast was also lower (p < 0.01) in the women. In the men the maximal postprandial glucose concentration and the postprandial glucose area remained stable throughout the day, but there was an increase in peak insulin concentration and insulin area after dinner. In contrast, in the women the maximal postprandial glucose concentration and the postprandial glucose area increased throughout the day, but the peak insulin concentration and insulin area did not change. Plasma triglycerides increased with breakfast and remained elevated throughout the day. Both fasting and postprandial mean triglycerides were higher in the men, but this did not reach statistical significance. The circulating pancreatic glucagon concentration, determined in 4 subjects, was unaffected by meals and remained stable throughout the day.     

Oscillations in insulin secretion during constant glucose infusion in normal man: relationship to changes in plasma glucose

Peripheral plasma or serum concentrations of glucose, insulin, C-peptide, glucagon, and cortisol and insulin secretory rates (ISR) were determined at 15-min intervals in eight normal subjects during a constant iv infusion of 4.5 mg glucose/kg.min for a 24-h period. During each sampling interval, the secretory rate of insulin was calculated by deconvolution of the peripheral plasma C-peptide concentration using C-peptide kinetic parameters derived after bolus injections of C-peptide in individual subjects. Periodogram analysis of the individual glucose curves demonstrated a circadian rhythm in all subjects, with a major nocturnal acrophase occurring at an average clock time of 0228 h (range, 0045-0350 h). In five of the eight subjects, a minor acrophase occurred at an average time of 1774 h (range, 1530-2045 h). This diurnal variation in plasma glucose levels was not paralleled by a similar pattern in insulin secretion. Although glucose was infused at a constant rate, significant pulses were found in glucose, insulin, and C-peptide levels and ISR; the pulse durations of these parameters were 182 +/- 30 (+/- SE), 89 +/- 5, 100 +/- 8, and 85 +/- 5 min, respectively, and their periodicities were 208 +/- 33, 106 +/- 7, 114 +/- 10, and 106 +/- 7 min. The durations and frequencies for pulses of insulin, C-peptide, and ISR were not significantly different, whereas glucose pulses had a longer duration and were less frequent (P less than 0.05, by analysis of variance). On the average, 54 +/- 9% of the C-peptide pulses and 47 +/- 8% of the ISR pulses were concomitant with a pulse in glucose levels. Moreover, approximately half of the C-peptide and ISR pulses that were not concomitant with a glucose pulse occurred in synchrony with a shoulder on the up-stroke or down-stroke of glucose pulses. Analysis of glucagon and cortisol profiles revealed no significant associations with the insulin and glucose oscillations. In conclusion, during a constant glucose infusion in normal subjects, regular oscillations of insulin secretion occur at 80- to 120-min intervals. Their tight coupling with glucose oscillations and the lack of association with fluctuations of glucagon and cortisol suggest that these oscillations represent a dynamic property of the insulin-glucose feedback loop.     

Studies on insulin degradation inside the pancreatic B-cell: evidence for a regulating role of glucose

The present study aimed at testing whether insulin degradation inside the pancreatic B-cell is regulated by insulin release or by glucose per se. Radioactively prelabelled isolated rat islets were cultured in unlabelled medium for 24 h. During that chase period the media contained (a) 50 or 300 mg glucose/dl alone or (b) together with 100 micrograms diazoxide/ml and (c) 50 mg glucose/dl without or with 10 mM L-leucine or 300 mg glucose/dl. The content of labelled (pro-)insulin in islets and media was measured and related to degradation. No degradation was found at the high glucose concentration, not even when insulin release was blocked by diazoxide. Degradation was also inhibited in the presence of leucine. The results suggest that glucose per se or its metabolism prevents insulin from being degraded inside the B-cell.     

Effects of recombinant human insulin-like growth factor I and insulin on counterregulation during acute plasma glucose decrements in normal and Type 2 (non-insulin-dependent) diabetic subjects

Summary Insulin-like growth factor I (65 μg/kg) or insulin (0.1 IU/kg) were injected i.v. on two separate occasions in random order in normal and in Type 2 (non-insulin-dependent) diabetic subjects. Insulin-like growth factor I and insulin injection resulted in identical decrements of plasma glucose concentrations after 30 min but in delayed recovery after insulin-like growth factor I as compared to insulin in both groups (p<0.05 insulin-like growth factor I vs insulin). Counterregulatory increases in plasma glucagon, adrenaline, cortisol and growth hormone concentrations after hypoglycaemia (1.9±0.2 mmol/l) in normal subjects were blunted after insulin-like growth factor I administration compared to insulin (p<0.05). Plasma glucose in Type 2 diabetic subjects did not reach hypoglycaemic levels but the acute glucose decrease to 4.5±0.8 mmol/l was associated with significantly lower responses of plasma glucagon and adrenaline but higher cortisol levels after insulin-like growth factor I compared to insulin (p<0.003). Plasma concentrations of non-esterified fatty acids and leucine decreased similarly after insulin-like growth factor I and insulin in both groups. The present results demonstrate that insulin-like growth factor I is capable of mimicking the acute effects of insulin on metabolic substrates (plasma glucose, non-esterified fatty acids, leucine). The decreases of plasma glucose were similar after both peptides in normal and in diabetic subjects who were presumably insulin resistant. Counterregulatory hormone responses to plasma glucose decrements differed, however, between insulin-like growth factor I and insulin and in the diabetic and the control subjects. After insulin-like growth factor I the increases in adrenaline, cortisol, growth hormone and glucagon were blunted in normal subjects despite slightly lower plasma glucose concentrations.     

糖耐量正常者和糖耐量低减者互相转化过程中胰岛素敏感性和胰岛β细胞分泌功能的改变

目的了解胰岛素敏感性和胰岛B细胞功能在2型糖尿病发病中的作用。方法以静脉葡萄糖耐量试验刺激后急性胰岛素反应（AIR2-5）表示第一时相胰岛素分泌功能指数,采用口服葡萄糖耐量试验30min与空腹时胰岛素差值与血糖差值比（△I30／△G30）反映早期相胰岛素分泌功能;Cederholm提出的胰岛素敏感性指数（ISI）评估胰岛素敏感性。分析70例非糖尿病者3年追踪结果,其中糖耐量正常（NGT）转变为糖耐量低减（IGT）组（进展NGT组）9例,NGT无进展组45例,IGT逆转为NGT组（IGT好转组）16例。结果（1）AIR2-5进展NGT组与NGT无进展组间基线时比较差异无统计学意义;3年后两组AIR2-5均无明显变化,且与基线时比较差异仍无统计学意义;IGT好转组3年后较基线时升高但差异无统计学意义。（2）△I30／△G30进展NGT组与NGT无进展组间基线时比较差异无统计学意义,3年后两组均无明显变化,组问比较差异仍无统计学意义;IGT好转组3年后与基线比较差异亦无统计学意义。（3）ISI：基线时进展NGT组与NGT无进展组间比较差异无统计学意义;3年中进展NGT组的ISI明显下降,3年后与基线时比差异有统计学意义;而NGT无进展组基线时与3年后的ISI差异无显著意义。NGT进展组和NGT无进展组间追踪后比较差异有统计学意义。IGT好转组追踪后ISI较基线时明显好转,前后差异有统计学意义。（4）logistic回归分析显示,AIR3-5、△I30／△G30、ISI3个指标中,仅ISI对NGT向IGT转变的影响有统计学意义。结论本组人群由NGT向IGT进展过程中,胰岛素敏感性明显下降,而胰岛B细胞功能改变不明显;而由IGT逆转为NGT的过程中,胰岛素敏感性显著改善,而胰岛B细胞功能无明显改变。提示在2型糖尿病发病的早期阶段,即由NGT向IGT的进展过程中,胰岛素抵抗起主要作用。     

Effect of insulin on glucagon secretion mediated via glucose metabolism of pancreatic a cells in ducks

Summary A possible action of insulin via glucose metabolism on the pancreatic A cell response to glucose, was studied in ducks. 2-Deoxyglucose, a non-metabolizable analogue of glucose was used. In normal ducks, the hyperglycaemia induced by 2-deoxyglucose (IV: 0.5 g/kg) resulted in hyperglucagonaemia, while the same degree of hyperglycaemia, induced by glucose infusion (IV injection 25 mg/kg, and infusion 5 mg/kg/min) immediately suppressed glucagon secretion. In diabetic ducks, two days after subtotal pancreatectomy, glucose responsiveness of the A cell was abolished, but could be restored by insulin treatment before (IM 0.2 U/kg insulin+8 g/kg glucagon every 6 h) and during (IV 3.6 mU/kg+infusion 0.9 mU/kg/min) the glucose test (IV: 0.5 g /kg). The normal response of the A cell to glucose was not observed in diabetic insulin-treated ducks after the administration of 2-deoxyglucose (IV: 0.5 g/kg). These data suggest an inhibitory effect of the metabolism of glucose on the release of glucagon. In addition, the action of insulin on the A cell may be mediated by its effect on glucose metabolism within the A cell.     

Liraglutide,a once‐daily human GLP‐1 analogue,improves pancreatic B‐cell function and arginine‐stimulated insulin secretion during hyperglycaemia in patients with Type 2 diabetes mellitus

Aims To assess the effect of liraglutide, a once‐daily human glucagon‐like peptide‐1 analogue on pancreatic B‐cell function. Methods Patients with Type 2 diabetes (n = 39) were randomized to treatment with 0.65, 1.25 or 1.9 mg/day liraglutide or placebo for 14 weeks. First‐ and second‐phase insulin release were measured by means of the insulin‐modified frequently sampled intravenous glucose tolerance test. Arginine‐stimulated insulin secretion was measured during a hyperglycaemic clamp (20 mmol/l). Glucose effectiveness and insulin sensitivity were estimated by means of the insulin‐modified frequently sampled intravenous glucose tolerance test. Results The two highest doses of liraglutide (1.25 and 1.9 mg/day) significantly increased first‐phase insulin secretion by 118 and 103%, respectively (P < 0.05). Second‐phase insulin secretion was significantly increased only in the 1.25 mg/day group vs. placebo. Arginine‐stimulated insulin secretion increased significantly at the two highest dose levels vs. placebo by 114 and 94%, respectively (P < 0.05). There was no significant treatment effect on glucose effectiveness or insulin sensitivity. Conclusions Fourteen weeks of treatment with liraglutide showed improvements in first‐ and second‐phase insulin secretion, together with improvements in arginine‐stimulated insulin secretion during hyperglycaemia.     

In vivo and in vitro increased pancreatic beta-cell sensitivity to glucose in normal rats submitted to a 48-h hyperglycaemic period

Summary We investigated the importance of the level and the duration of glucose stimulation on the in vivo and in vitro insulin response to glucose in normal rats previously submitted to hyperglycaemia. Rats were made hyperglycaemic by a 48-h glucose infusion. Glucose-induced insulin secretion was investigated in vivo by a 20-min hyperglycaemic clamp and in vitro by the isolated perfused pancreas technique, 3 h after the end of the in vivo glucose infusion. In glucose-infused rats, as compared to controls, in vivo incremental plasma insulin values above baseline integrated over the 20-min hyperglycaemic clamp (I) were five times higher during 8 mmol/l glucose clamp, only two times higher in 11 mmol/l glucose clamp and no different in 16.5 mmol/l. Compared to the controls, in vitro incremental plasma insulin concentration above baseline integrated over a 20-min period (I) in glucose-infused rats was 16 times higher in response to 2.8 mmol/l glucose, two times higher in response to 5.5 mmol/l, similar in response to 8.3 mmol/l and significantly lower in response to 16.5 mmol/l. In conclusion, our data suggest that a 48-h hyperglycaemic period results in an increased response of the pancreatic beta cell to low glucose. The response is immediately maximal and can not be increased with higher glucose concentrations. This situation could explain the apparent minimal effect of high concentrations on in vitro insulin secretion in previously hyperglycaemic rats and may provide insights into the sequence of events leading to the impairment of beta-cell function in Type 2 (non-insulin-dependent) diabetes mellitus.     

Relation of birthweight to maternal plasma glucose and insulin concentrations during normal pregnancy

Summary Maternal diabetes mellitus is complicated by fetal macrosomia and predisposes the offspring to diabetes, but recent evidence indicates that a low, not high, birthweight is associated with a higher incidence of Type 2 (non-insulin dependent) diabetes in adult life. To clarify the relationships between maternal glucose and insulin levels and birthweight, we measured oral glucose tolerance and neonatal weight in a large group (n = 529) of women during the 26th week of pregnancy. Women with gestational diabetes (n = 17) had more familial diabetes, higher pre-pregnancy body weight, and tended to have large-for-gestational-age babies. In contrast, women with essential hypertension (n = 10) gave birth to significantly (p <0.01) smaller babies. In the normal group (without gestational diabetes or hypertension, n = 503), maternal body weight before pregnancy and at term, maternal height, week of delivery, gender of the newborn, and parity were all significant, independent predictors of birthweight, together explaining 23% of the variability of neonatal weight. In addition, both fasting (p <0.006) and 2-h post-glucose (p = 0.03) maternal plasma glucose concentrations were positively associated with birthweight independent of the other physiological determinants, accounting, however, for only 10% of the explained variability. In a subgroup of 134 normal mothers with prepregnancy body mass index of less than 25 kg · m^–2, in whom plasma insulin measurements were available, the insulin area-under-curve was inversely related to birthweight (p <0.02) after simultaneously adjusting for physiological factors and glucose area. When glucose and insulin measurements were combined in the I/G ratio (ratio of insulin to glucose area), this was still inversely related to birthweight. Furthermore, maternal insulinaemia was directly related to blood pressure levels (p <0.001) independently of body weight. We conclude that in normal pregnancy, whereas physiological factors account for most of the explainable variability of infant weight, the influence of the maternal metabolic milieu is dual, positive for glucose levels but negative for insulin concentrations. Maternal hyperinsulinaemia during pregnancy may be one trait linking low birthweight with predisposition to diabetes in adult life.     

Effect of furosemide on insulin and glucagon responses to arginine in normal subjects

Summary This study aimed at evaluating the influence of furosemide upon insulin and glucagon responses to arginine in healthy subjects. For this purpose, six normal subjects received two consecutive arginine pulses (3 g), 60 min apart, before and after the administration of furosemide (40 mg, IV). The acute insulin response (mean change from 3–10 min) to the second arginine pulse was significantly inhibited by furosemide (mean increase: 14.8 ±3.0 U/ml versus 11.7±2.5 U/ml, p<0.01). By contrast, the acute glucagon response was significantly increased (mean increase: 77±18 pg/ml versus 105±21 pg/ml, p<0.01). No significant changes in plasma glucose levels occurred. In control experiments, in which saline rather than furosemide was administered, the acute insulin and glucagon response to the first arginine pulse did not differ from that observed with the second pulse. The effect of furosemide on insulin and glucagon secretion might be mediated through enhanced release of endogenous prostaglandin E.     

Metasomatotrophic diabetes and its induction: Basal insulin secretion and insulin release responses to glucose,glucagon, arginine and meals

Summary Growth hormone treatment produced somatotrophic diabetes, with hyperglycaemia, polyuria, glycosuria and elevation in serum non-esterified fatty acids (NEFA) in dogs. Early in this diabetes, fasting serum immunoreactive insulin (IRI) rose 20-fold, the insulin/glucose (I/G) ratio rose 10-fold and in response to glucose infusion, the rise in IRI was twice the normal. In the latter half of the continued growth hormone treatment, the intensity of the diabetes increased, serum IRI declined to the normal level and the I/G ratio became subnormal. Late in the treatment, following glucose infusion, there was no change in serum IRI, no fall in NEFA and further depression of glucose tolerance. In metasomatotrophic diabetes, in which hyperglycaemia, glycosuria and high NEFA level persisted, fasting serum IRI was normal during several months, then became subnormal and the I/G ratio was diminished further. Following glucose IV there was no change in serum IRI, no fall in NEFA and low glucose tolerance. The normally-occurring rises in serum IRI following arginine and glucagon IV and after the ingestion of a meal were absent. These permanently diabetic dogs were responsive to insulin IV. The insulin content of the pancreas was reduced to about 1.2% of the normal after 14 months of this diabetes. From the sequence of change it is concluded that growth hormone induced metasomatotrophic diabetes by causing excessive secretion of insulin under basal and stimulative conditions, leading to permanent loss of function of the beta cells of the pancreatic islets, to such an extent that basal insulin secretion was low and the ability to secrete extra insulin in response to stimuli was lost.     

The glucoregulatory response to intravenous glucose infusion in normal man: Roles of insulin and glucose

In order to differentiate the roles of hyperinsulinemia and hyperglycemia per se in the homeostatic response to i.v. glucose administration, two groups of normal subjects were given either glucose alone (3.5 mg kg^?1 min^?1) or glucose (3 mg kg^?1 min^?1) in conjunction with somatostatin (500 μg hr^?1), insulin (0.15 mU kg^?1 min^?1) and glucagon (1 ng kg^?1 min^?1). Glucose kinetics were measured by the primed-constant infusion of 3-³H-glucose. During the infusion of glucose alone, plasma glucose stabilized at levels 45–50 mg/dl above the fasting values. Endogenous glucose output was markedly suppressed by 85%–90% while glucose uptake rose to values very close to the infusion rate of exogenous glucose. Glucose clearance remained unchanged. Plasma insulin rose three-fourfold while plasma glucagon fell by 25%–30%. When glucose was infused with somatostatin, insulin, and glucagon, plasma insulin was maintained at levels 50% above baseline while glucagon remained at preinfusion levels. Under these conditions, the infusion of exogenous glucose resulted in a progressive increase of plasma glucose which did not stabilize until the end of the study period (190 mg/dl at 120 min). Endogenous glucose production was consistently suppressed (52%) but significantly less than observed with the infusion of glucose alone (p < 0.01). Glucose uptake increased to the same extent as with glucose alone, despite the more pronounced hyperglycemia. Thus, glucose clearance fell significantly below baseline (25%–30%; p < 0.01). These data demonstrate that hyperglycemia per se (fixed, near basal levels of insulin and glucagon) certainly contributes to the glucoregulatory response to i.v. glucose administration by both inhibiting endogenous glucose output and increasing tissue glucose uptake. However, the extra-insulin evoked by hyperglycemia is necessary for the glucoregulatory system to respond to the glucose load with maximal effectiveness.     

Abnormal glucagon response to arginine and its normalization in obese hyperinsulinaemic patients with glucose intolerance: importance of insulin action on pancreatic Alpha cells

Summary An excessive glucagon secretion to intravenous arginine infusion was found in obese hyperinsulinaemic patients with glucose intolerance. This study was designed to determine whether the glucagon hyperresponsiveness to arginine in these patients would improve by insulin infused at a high enough dose to overcome insulin resistance. By infusing high dose insulin during arginine infusion, the previously exaggerated glucagon response to arginine could be normalized. To normalize the abnormal glucagon response, insulin doses of 4.2±0.7 and 3.8±0.5 IU were required during arginine infusion in obese hyperinsulinaemic patients with impaired glucose tolerance and Type 2 (non-insulin-dependent) diabetes mellitus, respectively. This achieved plasma peak insulin levels 3 to 4 times higher than those observed in non-obese healthy subjects. Furthermore, we clarified whether or not the effect of normalizing insulin action and/or glycaemic excursions contributed to normalizing the exaggerated glucagon response to arginine in these patients. Blood glucose was clamped while high dose insulin was infused at the same levels as observed during the arginine infusion test with no insulin infusion. As a result, normalization of the exaggerated plasma glucagon response was achieved, whether hyperglycaemia existed or not. These results clearly demonstrate that, similar to non-obese hypoinsulinaemic Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetic patients, the exaggerated Alpha-cell response to arginine infusion in obese hyperinsulinaemic patients with glucose intolerance is secondary to the reduction of insulin action on the pancreatic Alpha cell, and that the expression of insulin action plays an important part in normalizing these abnormalities.