Pathogenesis of hypoglycemia in insulinoma patients: suppression of hepatic glucose production by insulin

Evaluation of plasma cortisol during fasting test in patients with endogenous hyperinsulinemic hypoglycemia. Fifteen years experience

BACKGROUND

Endogenous hyperinsulinemic hypoglycemia (EHH) is a rare clinical condition. The aim of this study was to evaluate baseline plasma cortisol concentration and its concentration during hypoglycemic crisis in fasting tests (FT) performed in our center. Secondarily, the aim was to establish the relationship between baseline cortisol and the time of evolution of EHH.

MATERIAL AND METHODS

A retrospective, observational, descriptive study was carried out which included patients with hypoglycemic disorder with positive FT.

RESULTS

Of a total of 21 patients, 16 presented insulinoma, 1 nesidioblastosis, 2 malignant insulinoma and 2 EHH without pathological diagnosis. The time from the onset of symptoms to diagnosis was 2 years (Q1=1.5-Q2=5.5). The comparison between median baseline cortisol (BC)=11.8 mcg/dl (nmol/L 340.68) (Q1=9-Q3=14.1) and median cortisol during hypoglycemic episode (HC)=11.6 mcg/dl (nmol/L: 303.44) (Q1=7.8-Q3=16.1) showed no differences (Z=-0.08; P>.05). When correlating BC with HC, no significant relationship was observed (r=0.16; P>.05). When correlating the glycemic value in the crisis and the HC, a slight negative trend was found (r=-0.53; P=.01). In addition, we found that recurrent hypoglycemic disorder is associated with lower baseline cortisol values ​​the longer the time of its evolution.

CONCLUSION

We confirmed that cortisol values ​​remain low during hypoglycemic episodes, reinforcing the hypothesis of lack of response of this counterregulatory hormone in cases of recurrent hypoglycemia.

A Rare Case of Insulinoma in a Thin, Lean Adult Male: A Case Report

Insulinoma is an insulin-secreting tumor that causes hypoglycemia due to inappropriately high insulin secretion. The Whipple's triad, which comprises indications of hypoglycemia (tremor, sweating, irritability, uneasiness, and weakness), plasma glucose concentration <55 mg/dL (3.0 mmol/L), and resolution of symptoms after administration of glucose, is utilized for the determination of insulinoma. In this report, we present the case of a thin, lean, adult male with a BMI of 22, who presented with repetitive episodes of tremor, sweating, weariness, and perplexity that occurred amid fasting and settled with meals, fulfilling Whipple's triad criteria for the determination of insulinoma. The episodes frequently led to seizures. Supervised fasting was carried out, which revealed raised C-peptide levels, low blood glucose, and negative sulfonylurea screen. A computed tomography (CT) scan localized the tumor, and surgical resection was planned.

Unusual presentation of an insulinoma in an elderly male patient

Insulinoma is a rare neuroendocrine tumor originating from hypersecreting beta-cells of islets of Langerhans in the pancreas. We report a case of 72-year-old male, with chronic alcohol abuse, presenting with atypical features like refractory recurrent secondary generalized seizures and behavioral disturbances with increased irritability, initially mistreated as alcohol withdrawal. Detailed history, particularly the relationship of the symptoms with food intake, made us think of other causes of seizures. Fasting biochemical investigations and localizing studies helped clinch the diagnosis. The tumor was localized with the help of endoscopic ultrasonography and whole-body Ga68-DOTANOC PET-CT. The patient was treated conservatively with diazoxide and is doing well on follow-up. The present case report emphasizes the importance of detailed clinical history, more so in atypically presenting cases of refractory seizures. Insulinoma can be medically managed despite surgery being the gold standard curative treatment.

Diagnostic Evaluation of Hypoglycemia Due To an Insulinoma in a Deployed Infantryman: Significance of Neuroglycopenia and the Role of the Military Health System

Insulinoma, the prototype of endogenous hyperinsulinemic hypoglycemia, is a very rare condition, with an incidence of four cases per million person-years. Its rate of occurrence in the U.S. military population is unknown. Two cases of insulinomas involving active duty service members have been published. However, there has been no reported case of an insulinoma in a deployed service member. We report the case of a 21-year-old infantryman with clinical hypoglycemia of insidious onset, manifesting with overt neuroglycopenic symptoms during his deployment as a combatant soldier, and the ultimate diagnosis of an insulinoma as the underlying cause. The series of multiple clinical evaluations and the unique circumstances leading to the formal evaluation of the patient's hypoglycemia and treatment are chronicled. The significance of neuroglycopenia and the diagnostic approach to any suspected case of hypoglycemia, the potential challenges and opportunities, and educational aspects of evaluation and management of the insulinoma are elaborated. The potential role of the Military Health System in facilitating the detection and treatment of this rare condition in the service member is discussed as well.

Deletion of interleukin 1 receptor-associated kinase 1 (Irak1) improves glucose tolerance primarily by increasing insulin sensitivity in skeletal muscle

Chronic inflammation may contribute to insulin resistance via molecular cross-talk between pathways for pro-inflammatory and insulin signaling. Interleukin 1 receptor-associated kinase 1 (IRAK-1) mediates pro-inflammatory signaling via IL-1 receptor/Toll-like receptors, which may contribute to insulin resistance, but this hypothesis is untested. Here, we used male Irak1 null (k/o) mice to investigate the metabolic role of IRAK-1. C57BL/6 wild-type (WT) and k/o mice had comparable body weights on low-fat and high-fat diets (LFD and HFD, respectively). After 12 weeks on LFD (but not HFD), k/o mice (versus WT) had substantially improved glucose tolerance (assessed by the intraperitoneal glucose tolerance test (IPGTT)). As assessed with the hyperinsulinemic euglycemic glucose clamp technique, insulin sensitivity was 30% higher in the Irak1 k/o mice on chow diet, but the Irak1 deletion did not affect IPGTT outcomes in mice on HFD, suggesting that the deletion did not overcome the impact of obesity on glucose tolerance. Moreover, insulin-stimulated glucose-disposal rates were higher in the k/o mice, but we detected no significant difference in hepatic glucose production rates (± insulin infusion). Positron emission/computed tomography scans indicated higher insulin-stimulated glucose uptake in muscle, but not liver, in Irak1 k/o mice in vivo Moreover, insulin-stimulated phosphorylation of Akt was higher in muscle, but not in liver, from Irak1 k/o mice ex vivo In conclusion, Irak1 deletion improved muscle insulin sensitivity, with the effect being most apparent in LFD mice.

Giant pancreatic insulinoma. The bigger the worse? Report of two cases and literature review

INTRODUCTION

Giant pancreatic insulinomas are rare endocrine tumors. We describe 2 cases reviewing the current literature.

PRESENTATION OF CASE

We report herein 2 female patients affected by giant insulinomas of 14cm and 6cm, respectively. Symptomatic hypoglycemia episodes occurred during 4 months in first case and 3 years in the second one until diagnosis. Both patients were successfully treated performing a distal pancreatectomy with splenic preservation in the first case and a Whipple's procedure in the second one.

DISCUSSION

Up to now only 7 cases have been reported previously. Insulinomas larger than 3cm accounts for less than 5% of all. This literature review shows that despite the size hypoglycemic symptoms varies from 1 day to 3 years and only 1 out of 9 cases reported presented lymph nodes metastases. No recurrences have been described.

CONCLUSION

One of the cases here described (14cm) is the largest presented in the literature. Despite the size, giant insulinoma is related apparently neither to metastases nor to the recurrences.

Outcomes of community-dwelling adults without diabetes mellitus who require ambulance services for hypoglycemia

OBJECTIVE

We evaluate the prevalence, etiology, and outcomes of hypoglycemia requiring emergency medical services (EMS) in patients without diabetes mellitus (non-DM).

METHODS

We reviewed medical records of all ambulance calls for non-DM with blood glucose <70 mg/dl in Olmsted County, Minnesota, between January 1, 2003, and December 31, 2009.

RESULTS

A total of 131 patients (age 51 ± 19 years; 54 % females) made 142 EMS calls, while 10 patients made repeated calls. Causes of hypoglycemia were critical illness (42; 32%), alcohol and polysubstance use (36; 27.5 %), insulinoma/bariatric surgery (10; 8%), restricted oral intake (7; 5%), and multiple factors (3; 27.5 %). Patients with alcohol and polysubstance abuse were younger (p = .002). A total of 54 patients had additional hypoglycemia predisposing comorbidities/factors [adrenal insufficiency (2), end-stage renal disease (11) and chronic liver disease (7), beta blockers use (34), and pentamidine use (1)]. Repeated calls and emergency room transportation were similar, but hospitalization varied across the etiologies, with the lowest proportion in the multiple-factor-related hypoglycemia group (p = .01). Duration of follow-up was 1.28 (interquartile range 0.13-2.70) years. A total of 38 patients died, and age-adjusted mortality varied across different etiologies (p < .001), with highest among critically ill. Cancer caused the highest number of deaths (7/38; 18%), while 1 death was due to hypoglycemia.

CONCLUSIONS

There were multiple etiologies for hypoglycemic episodes in community-dwelling non-DM that required EMS. Critical illness, multifactorial causes, and alcohol/polysubstance abuse were common causes. Hospitalization and mortality were higher with critical illnesses.

A rare case of non-insulinoma pancreatic hypoglycaemia syndrome (niphs) in an adult due to localised islet cell hyperplasia-successfully managed by enucleation

Persistent hyperinsulinemic hypoglycaemia is caused most commonly by an insulinoma in adults or by nesidioblastosis in neonates. In adults, localised islet cell hyperplasia is a rare disorder characterised by localised proliferation of islet cells. The authors present the case of a previously healthy non-obese middle aged female with new-onset severe hypoglycaemia. Laboratory findings confirmed a case of hyperinsulinemic hypoglycaemia. Endoscopic ultrasonography, intra-arterial calcium stimulation test and intraoperative ultrasonography showed a lesion in the uncinate process that was enucleated. Rest of the pancreas was normal. Histological examination and immunostaining of the resected tissue revealed pancreatic tissue with maintained acinar pattern consistent with diagnosis of localised islet cell hyperplasia. The patient did not have further episodes of hypoglycaemia following the procedure. Localised islet cell hyperplasia with such a very high insulin level is exceedingly rare in adult populations and not reported in literature. This diagnosis cannot be easily made through routine diagnostic laboratory or radiological procedures and likely requires a histological diagnosis. Management of this rare entity is by enucleation.

Optimizing the replacement of basal insulin in type 1 diabetes mellitus: no longer an elusive goal in the post-NPH era

In physiology, insulin is released continuously by the pancreas at a nearly constant rate between meals and in the fasting state (basal insulin secretion). The pivotal role of basal insulin is to restrain release of glucose from the liver and free fatty acids from adipose tissue, thus preventing hyperglycemia and ketosis. In type 1 diabetes mellitus (T1DM) (absolute insulin deficiency), the replacement of basal insulin is challenging because the currently available pharmacological preparations of long-acting insulin do not exactly reproduce the fine physiology of flat action profile of basal insulin of subjects without diabetes. NPH and NPH-based insulin mixtures no longer have a place in the treatment of T1DM because of their early peak effects and relatively short duration of action, which result into risk of nocturnal hypoglycemia and fasting hyperglycemia, respectively, after the evening injection. Only continuous subcutaneous (s.c.) insulin infusion (CSII) or long-acting analogs such as glargine (>24 h in duration, once a day) and detemir (<24 h in duration, once or more often twice a day) should be used as basal insulin in T1DM in combination with mealtime rapid-acting analogs. CSII and the long-acting analogs are nearly peakless and therefore reduce the risk for hypoglycemia (especially at night), blood glucose (BG) variability, and lower A1C with similar or less hypoglycemia. CSII is the "gold standard" of replacement of basal insulin because of better reproducibility of subcutaneous absorption of soluble insulin. Although CSII is not superior to multiple daily insulin injections in the general T1DM population, CSII might be indicated in subsets of T1DM (long-term T1DM with insulin "supersensitivity" and needs for low-dose insulin, some individuals with variable subcutaneous absorption of long-acting analogs) to minimize BG variability, reduce hypoglycemia, and benefit A1C.

Beta-cell adenomas without hyperinsulinemia with use of highly specific insulin radioimmunoassays: case report and review of literature

OBJECTIVE

To report a case of a proinsulin-secreting islet cell adenoma in which the diagnosis was obscured by an ultraspecific insulin assay.

METHODS

We describe the case of a 46-year-old woman, who presented with fasting hypoglycemia and appropriately low insulin values.

RESULTS

A prolonged supervised fast produced symptomatic hypoglycemia (20 mg/dL) after only 7 hours. During the entire fasting test, highly specific insulin remained at <3 mIU/L, with a median value (and interquartile range) of 0.9 (0.8 to 2.3) mIU/L, when the glucose concentration was <50 mg/dL. The serum C-peptide level remained high normal (mean +/- SD, 2.7 +/- 0.6 ng/mL; normal fasting levels, 0.8 to 3.9), and no evidence of sulfonylurea use was detected in the patient's urine. Circulating proinsulin levels were persistently high (>200 pmol/L in all determinations when hypoglycemia was present; expected value, <5 pmol/L). Magnetic resonance imaging and endoscopic ultrasonography confirmed the presence of a 2.5-cm tumor in the head of the pancreas. A proinsulin-secreting islet cell tumor was diagnosed. Surgical resection of the tumor was successfully accomplished, but diabetes mellitus developed 4 months postoperatively.

CONCLUSION

The diagnosis of a hypoglycemia-producing pancreatic adenoma can be missed when an ultraspecific insulin assay is used. The direct measurement of proinsulin established the diagnosis in this case.

Evaluation and management of adult hypoglycemic disorders: an Endocrine Society Clinical Practice Guideline

OBJECTIVE

The aim is to provide guidelines for the evaluation and management of adults with hypoglycemic disorders, including those with diabetes mellitus.

EVIDENCE

Using the recommendations of the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system, the quality of evidence is graded very low (plus sign in circle ooo), low (plus sign in circle plus sign in circle oo), moderate (plus sign in circle plus sign in circle plus sign in circle o), or high (plus sign in circle plus sign in circle plus sign in circle plus sign in circle).

CONCLUSIONS

We recommend evaluation and management of hypoglycemia only in patients in whom Whipple's triad--symptoms, signs, or both consistent with hypoglycemia, a low plasma glucose concentration, and resolution of those symptoms or signs after the plasma glucose concentration is raised--is documented. In patients with hypoglycemia without diabetes mellitus, we recommend the following strategy. First, pursue clinical clues to potential hypoglycemic etiologies--drugs, critical illnesses, hormone deficiencies, nonislet cell tumors. In the absence of these causes, the differential diagnosis narrows to accidental, surreptitious, or even malicious hypoglycemia or endogenous hyperinsulinism. In patients suspected of having endogenous hyperinsulinism, measure plasma glucose, insulin, C-peptide, proinsulin, beta-hydroxybutyrate, and circulating oral hypoglycemic agents during an episode of hypoglycemia and measure insulin antibodies. Insulin or insulin secretagogue treatment of diabetes mellitus is the most common cause of hypoglycemia. We recommend the practice of hypoglycemia risk factor reduction--addressing the issue of hypoglycemia, applying the principles of intensive glycemic therapy, and considering both the conventional risk factors and those indicative of compromised defenses against falling plasma glucose concentrations--in persons with diabetes.

Mini-Mental State Examination is superior to plasma glucose concentrations in monitoring patients with suspected hypoglycaemic disorders during the 72-hour fast

OBJECTIVE

To determine whether systematic evaluation of cognitive function by the Mini-Mental State Examination (MMSE) allows the objective detection and documentation of cognitive deterioration in patients referred for evaluation of suspected hypoglycaemic disorders by the 72-h fast.

DESIGN

Prospective case series.

METHODS

In 50 patients referred for evaluation of suspected hypoglycaemic disorders, the MMSE score (maximum 30 points) was assessed at the start and at the end of the fast.

RESULTS

The fast was terminated before 72 h in 14 patients because they developed neuroglycopenic symptoms due to hypoglycaemic disorders. Their MMSE score fell from a median of 29 points (range 20-30) at the beginning to 17 points (range 0-24) at the termination of the fast. The score dropped by > or =6 points in all patients with hypoglycaemic disorders. Median (range) plasma glucose concentration at the end of the fast was 2.1 (1.1-2.5) mmol/l. Thirty-six individuals developed no neuroglycopenic symptoms throughout the 72-h fast, their MMSE score remained between 27 and 30 throughout the fast and their median plasma glucose concentration dropped to 2.9 (2-3.6) mmol/l.

CONCLUSIONS

Systematic evaluation of cognitive function by the MMSE at the beginning and at the termination of the fast allows objective determination and documentation of the deterioration of the cognitive state in patients with hypoglycaemic disorders. A decline in the cognitive performance by > or =6 points in the MMSE score rather than a distinct plasma glucose concentration should be used as the criterion to terminate the prolonged fast before 72 h.

Post-hypoglycaemic hyperketonaemia does not contribute to brain metabolism during insulin-induced hypoglycaemia in humans

It is controversial as to whether ketone bodies are utilized by the human brain as a fuel alternative to glucose during hypoglycaemia. To clarify the issue, we studied 10 normal volunteers during an experimental hypoglycaemia closely mimicking the clinical hypoglycaemia of patients with Type 1 (insulin-dependent) diabetes mellitus or insulinoma. Hypoglycaemia was induced by a continuous infusion of insulin (0.40 mU.kg-1.min-1 for 8 h, plasma insulin approximately 180 pmol/l) which decreased the plasma glucose concentration to approximately 3.1 mmol/l during the last 3 h of the studies. Subjects were studied on two occasions, i.e. spontaneous, counterregulatory-induced post-hypoglycaemic increase in 3-beta-hydroxybutyrate (from approximately 0.2 to approximately 1.1 mmol/l at 8 h), or prevention of post-hypoglycaemic hyperketonaemia (plasma beta-hydroxybutyrate approximately 0.1 mmol/l throughout the study) after administration of acipimox, a potent inhibitor of lipolysis. In the latter study, glucose was infused to match the hypoglycaemia observed in the former study. The glycaemic thresholds and overall responses of counterregulatory hormones, symptoms (both autonomic and neuroglycopenic), and deterioration of cognitive function (psychomotor tests) were superimposable in the control study in which ketones increased spontaneously after onset of hypoglycaemic counterregulation, as compared to the study in which ketones were suppressed (p = NS). The fact that responses of counterregulatory hormones, symptoms and deterioration in cognitive function were not exaggerated when posthypoglycaemic hyperketonaemia was prevented, indicate that during hypoglycaemia, the counterregulatory-induced endogenous hyperketonaemia does not provide the human brain with an alternative substrate to glucose. Thus, it is concluded that during hypoglycaemia, endogenous hyperketonaemia does not contribute to brain metabolism and function.

Insulin resistance in a case of coexisting insulinoma and type 2 diabetes

Hyperinsulinaemia due to pancreatic beta-cell tumours has been reported to lead to insulin resistance. A possible contribution of dysregulated insulin receptors to the impaired insulin action of insulinoma has not been explored. Therefore, we studied insulin receptor function in a patient with insulin-producing adenoma. This patient was rather unusual in that she was found to have a very large tumour and strikingly high circulating levels of insulin. In addition, her previous history included type 2 (non-insulin-dependent) diabetes mellitus. We confirmed decreased glucose utilization and metabolic clearance rate for glucose in presence of marked endogenous hyperinsulinaemia (approximately 2000 pM). 125I-labelled insulin binding capacity and receptor affinity for insulin were normal in her intact blood monocytes and erythrocytes. Insulin receptors were purified from the patient's tumour as well as from the pancreas, omental fat, liver and erythrocytes. All parameters of insulin binding to these receptors were normal. Thus, no evidence of receptor downregulation due to the marked hyperinsulinaemia was found. As expected, addition of insulin in vitro stimulated receptor autophosphorylation and tyrosine kinase activity of the receptors isolated from the liver, fat and erythrocytes. However, the basal tyrosine kinase activities of the tumour and pancreatic receptors were very high when isolated and further addition of insulin in vitro increased the protein kinase activity only slightly.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypoglycemia in infants

Because the infant's brain is to a large extent dependent on glucose utilization, hypoglycemia of infants can have grave effects on brain function, and it is important to diagnose it and, when possible, treat it promptly. Causes of hypoglycemia in infants are (a) excess insulin secretion, (b) factitious hyperinsulinemia, (c) GH or ACTH deficiency, (d) primary glucocorticoid deficiency, (e) defects of the enzymes involved in hepatic glucose production, or (f) defects in hepatic fatty acid oxidation.

Adrenergic mechanisms contribute to the late phase of hypoglycemic glucose counterregulation in humans by stimulating lipolysis

Three studies were performed on nine normal volunteers to assess whether catecholamine-mediated lipolysis contributes to counterregulation to hypoglycemia. In these three studies, insulin was intravenously infused for 8 h (0.30 mU.kg-1.min-1 from 0 to 180 min, and 0.40 mU.kg-1.min-1 until 480 min). In study I (control study), only insulin was infused; in study II (direct + indirect effects of catecholamines), propranolol and phentolamine were superimposed to insulin and exogenous glucose was infused to reproduce the same plasma glucose (PG) concentration of study I. Study III (indirect effect of catecholamines) was the same as study II, except heparin (0.2 U.kg-1.min-1 after 80 min), 10% Intralipid (1 ml.min-1 after 160 min) and variable glucose to match PG of study II, were also infused. Glucose production (HGO), glucose utilization (Rd) [3-3H]glucose, and glucose oxidation and lipid oxidation (LO) (indirect calorimetry) were determined. In all three studies, PG decreased from approximately 4.8 to approximately 2.9 mmol/liter (P = NS between studies), and plasma glycerol and FFA decreased to a nadir at 120 min. Afterwards, in study I plasma glycerol and FFA increased by approximately 75% at 480 min, but in study II they remained approximately 40% lower than in study I, whereas in study III they rebounded as in study I (P = NS). In study II, LO was lower than in study I (1.69 +/- 0.13 vs. 3.53 +/- 0.19 mumol.kg-1.min-1, P less than 0.05); HGO was also lower between 60 and 480 min (7.48 +/- 0.57 vs. 11.6 +/- 0.35 mumol.kg-1.min-1, P less than 0.05), whereas Rd was greater between 210 and 480 min (19 +/- 0.38 vs. 11.4 +/- 0.34 mumol.kg-1.min-1, respectively, P less than 0.05). In study III, LO increased to the values of study I; between 4 and 8 h, HGO increased by approximately 2.5 mumol.kg-1.min-1, and Rd decreased by approximately 7 mumol.kg-1.min-1 vs. study II. We conclude that, in a late phase of hypoglycemia, the indirect effects of catecholamines (lipolysis mediated) account for at least approximately 50% of the adrenergic contribution to increased HGO, and approximately 85% of suppressed Rd.

Contribution of adrenergic mechanisms to glucose counterregulation in humans

To assess the role of adrenergic mechanisms during prolonged hypoglycemia, eight normal subjects were studied on six occasions. In study 1, insulin was infused subcutaneously (15 mU.m-2.min-1 for 12 h), and plasma glucose concentration (PG) decreased from 89 +/- 2 to 50 +/- 1 mg/dl. In study 2 (insulin as in study 1 + propranolol and phentolamine + variable glucose to maintain PG as in study 1), the rate of hepatic glucose production (HGO, [3-3H]glucose) was approximately 30% lower after 1.5 h, and the rate of peripheral glucose utilization (GU) was approximately 15% greater after 5 h. To quantitate the effects of adrenergic mechanisms on glucose counterregulation, in a control study (study 3), glucoregulatory hormone secretion was blocked, and the hormones were reinfused to reproduce study 1. When alpha- and beta-blockade plus variable glucose were superimposed to study 3 (study 4), HGO was approximately 25% lower (after 2 h), and GU was approximately 10% greater (after 6 h) vs. study 3. When glucose was not infused to match PG of study 3 (study 5), severe hypoglycemia developed (PG at 7 h 36 +/- 2 vs. 62 +/- 3 mg/dl). Finally, when glucose was not infused during alpha- and beta-blockade of study 2 (study 6), PG was 49 +/- 3 mg/dl at 7 h vs. 65 +/- 3 mg/dl of the control study (study 1), despite greater secretion of glucagon, growth hormone, and cortisol. It is concluded that adrenergic mechanisms play a key counterregulatory role, even in the presence of appropriate responses of glucagon and that greater increases in glucagon (and other counterregulatory hormones) cannot compensate fully for absent contribution of adrenergic mechanisms to counterregulation.

Evidence against important catecholamine compensation for absent glucagon counterregulation

To assess the counterregulatory role of glucagon and to test the hypothesis that catecholamines can largely compensate for an impaired glucagon response, four studies were performed in seven normal volunteers. In all studies, insulin was infused subcutaneously (15 mU.m-2.min-1) and increased circulating insulin approximately twofold to levels (26 +/- 1 microU/ml) observed with intensive insulin therapy. In study 1, plasma glucose fluxes (D-[3-3H]glucose) and plasma substrate and counterregulatory hormone concentrations were simply monitored; plasma glucose decreased from 87 +/- 2 mg/dl and plateaued at 51 +/- 2 mg/dl for 3 h. In study 2 [pituitary-adrenal-pancreatic (PAP) clamp], secretion of insulin and counterregulatory hormones (except for catecholamines) was prevented by somatostatin (0.5 mg/h i.v.) and metyrapone (0.5 g/4 h per os), and glucagon, cortisol, and growth hormone were reinfused to reproduce the concentrations of study 1. In study 3 (lack of glucagon response), the PAP clamp was performed with maintenance of plasma glucagon at basal levels, and glucose was infused whenever needed to reproduce plasma glucose concentration of study 2. Study 4 was identical to study 3, but exogenous glucose was not infused. The PAP clamp (study 2) reproduced glucose concentrations and fluxes observed in study 1. In studies 3 and 4, isolated lack of glucagon response did not affect glucose utilization but caused an early and persistent decrease in hepatic glucose production (approximately 60%) that caused plasma glucose to decrease to 38 +/- 2 mg/dl (P less than 0.01 vs. control 62 +/- 2 mg/dl), despite compensatory increases in plasma epinephrine. We conclude that, in a model of clinical hypoglycemia, glucagon's effect on hepatic glucose production is a dominant counterregulatory factor in humans and that its absence cannot be compensated for by increased epinephrine secretion.

Evaluation of a euglycaemic clamp procedure as a diagnostic test in insulinoma patients

In 15 patients with insulinoma, six patients after successful removal of this tumour, two patients with previous pancreas resection because of hypoglycaemia elsewhere, and 10 control subjects, the diagnostic usefulness of euglycaemic clamp procedures (without exogenous insulin) was assessed in comparison with prolonged starvation. Only insulinoma patients developed sustained hypoglycaemia (less than or equal to 2.3 mmol l-1) within 2-44 h without caloric intake, because of inappropriately elevated immunoreactive insulin (IR-insulin) concentrations. IR-proinsulin values were elevated in most (7 out of 10), but not in all insulinoma patients. The steady-state glucose infusion rate necessary to maintain a stable plasma glucose concentration of 4.4-5.0 mmol l-1 was significantly (P less than or equal to 0.001) higher in insulinoma patients (2.5 +/- 0.6 mg kg-1 min-1) than in pancreas resected patients (0.6 +/- 0.2 mg kg-1 min-1), or in control subjects (0.5 +/- 0.1 mg kg-1 min-1). Due to a considerable degree of overlap, sensitivity (0.44) and specificity (0.95) were too low for such a procedure to qualify as a diagnostic test. There was no correlation of glucose infusion rates to IR-insulin values (r = 0.024, P = 0.461). One reason for this was the development of insulin resistance in some, but not in all insulinoma patients. When, in analogy to insulin/glucose ratios, a diagnostic index was derived by multiplying the steady state glucose infusion rate by the steady state IR-insulin concentration, the diagnostic accuracy was greatly increased (sensitivity and specificity 0.94, respectively), but still lower than that of 'amended' insulin/glucose ratios in fasting plasma or at the time of discontinuation of prolonged fasts (1.00). Somatostatin infusions inhibited insulin secretion (IR-C-peptide plasma concentrations) by 52-88% in subjects without insulinoma and in those insulinoma patients whose tumour cells ultrastructurally contained plenty of normal secretory granules, and to a lesser degree when only abnormal or virtually no secretory granules were present, i.e. in more de-differentiated tumours. In contrast to this significant (P = 0.036) association, malignancy, i.e. the presence of metastases, could not be predicted from whether or not insulin secretion was resistant to the inhibitory action of somatostatin. In conclusion, euglycaemic clamp experiments are less reliable for detecting or excluding a functioning insulinoma than the relation of glucose and insulin values during starvation. The inhibition of insulin secretion by somatostatin depends on the presence of normal beta-granules, and does not distinguish adenomas from carcinomas.

Contribution of cortisol to glucose counterregulation in humans

To test the hypothesis that cortisol secretion plays a counterregulatory role in hypoglycemia in humans, four studies were performed in eight normal subjects. In all studies, insulin (15 mU.m-2.min-1) was infused subcutaneously (plasma insulin 27 +/- 1 microU/ml). In study 1, plasma glucose concentration and glucose fluxes [( 3-3H]glucose), substrate, and counterregulatory hormone concentrations were simply monitored, and plasma glucose decreased from 89 +/- 2 to 52 +/- 2 mg/dl for 12 h. In study 2, (pituitary-adrenal-pancreatic clamp), insulin and counterregulatory hormone secretion (except for catecholamines) was prevented by somatostatin (0.5 mg/h, iv) and metyrapone (0.5 g/4 h, per os), and glucagon, cortisol, and growth hormone were infused to reproduce the concentrations of study 1. In study 3 (lack of cortisol increase), the pituitary-adrenal-pancreatic clamp was performed with maintenance of plasma cortisol at basal levels, and glucose was infused, whenever needed, to reproduce plasma glucose concentration of study 2. Study 4 was identical to study 3, but exogenous glucose was not infused. Isolated lack of cortisol increase caused a approximately 22% decrease in hepatic glucose production (P less than 0.01) and a approximately 15% increase in peripheral glucose utilization (P less than 0.01), which resulted in greater hypoglycemia (37 +/- 2 vs. 52 +/- 2 mg/dl, P less than 0.01) despite compensatory increases in plasma epinephrine. Lack of cortisol response also reduced plasma free fatty acid, beta-hydroxybutyrate, and glycerol concentrations approximately 50%. We conclude that cortisol normally plays an important counterregulatory role during hypoglycemia by augmenting glucose production, decreasing glucose utilization, and accelerating lipolysis.

Demonstration of a role for growth hormone in glucose counterregulation

To test the hypothesis that growth hormone secretion plays a counterregulatory role in prolonged hypoglycemia in humans, four studies were performed in nine normal subjects. Insulin (15 mU.M-2.min-1) was infused subcutaneously (plasma insulin 27 +/- 2 microU/ml), and plasma glucose decreased from 88 +/- 2 to 53 +/- 1 mg/dl for 12 h. In study 1, plasma glucose, glucose fluxes (D-[3-3H]glucose), substrate, and counterregulatory hormone concentrations were simply monitored. In study 2 (pituitary-adrenal-pancreatic clamp), insulin and counterregulatory hormone secretions (except for catecholamines) were prevented by somatostatin (0.5 mg/h iv) and metyrapone (0.5 g/4 h po), and glucagon, cortisol, and growth hormone were reinfused to reproduce the concentrations of study 1. In study 3 (lack of growth hormone increase), the pituitary-adrenal-pancreatic clamp was performed with maintenance of plasma growth hormone at basal levels, and glucose was infused whenever needed to reproduce plasma glucose concentration of study 2. Study 4 was identical to study 3, but exogenous glucose was not infused. Isolated lack of a growth hormone response caused a decrease in hepatic glucose production and an increase in glucose utilization that resulted in an approximately 25% greater hypoglycemia despite compensatory increases in plasma catecholamines. Plasma free fatty acid, 3-beta-hydroxybutyrate, and glycerol concentrations were reduced approximately 50%. It is concluded that growth hormone normally plays an important counterregulatory role during hypoglycemia by augmenting glucose production, decreasing glucose utilization, and accelerating lipolysis.

Defective glucose utilization in patients with functioning beta-cell tumors persists after tumor excision

Glucose utilization was assessed before and after operation in five patients with insulin-secreting tumors using the euglycemic clamp. Two groups of age, sex, and weight-matched controls were studied under conditions of either acute (3 h, N = 7) or chronic (48-72 h, N = 6) hyperinsulinemia (46 +/- 4 microU/mL). The rate of glucose infusion (M = mg/kg/min) required to maintain steady-state euglycemia was taken as index of glucose utilization. M was higher both in postoperative patients and in chronic controls than in preoperative patients (2.1 +/- 0.1 and 1.8 +/- 0.2 vs. 1.0 +/- 0.2, p less than 0.01), yet never achieved levels seen in acute controls (3.3 +/- 0.3, p less than 0.01). Also reported is one subject who had a predominantly proinsulin-producing tumor with little insulin secretion, who also manifested a similar defect in glucose utilization. Excision of this tumor resulted in partial reversal of the peripheral defect in glucose metabolism. In conclusion, chronic endogenous hyperinsulinemia (and hyperproinsulinemia) in humans is associated with a defect in peripheral glucose utilization that is only partially resolved 2 years after tumor removal.

Hyperinsulinaemia and insulin insensitivity: studies in subjects with insulinoma

Hepatic glucose turnover, peripheral insulin sensitivity and insulin receptor binding were measured in four subjects with insulinoma before and 3 months after surgical resection of the insulinoma. Basal hepatic glucose production, quantitated employing a primed constant infusion of tritiated glucose, was low pre-operatively (5.2 +/- 1.7 mumol X kg-1 X min-1) but returned to normal post-operatively (14.9 +/- 2.8; normal subjects 13.9 +/- 0.8 mumol X kg-1 X min-1). Paired euglycaemic dose-response curves were developed for each subject. Insulin sensitivity, expressed as a right shift of the dose-response curve (ED50), was low pre- and post-operatively. However, insulin responsiveness (Vmax) remained normal (pre-operatively 13.9 +/- 2.2, post-operatively 13.8 +/- 0.8, normal subjects 16.7 +/- 0.8 ml X kg-1 X min-1). There was no consistent pattern in monocyte or erythrocyte receptor binding before or after surgery. These data suggest that the chronic hyperinsulinaemia causes suppression of hepatic glucose production, and a state of insulin insensitivity which appears to be due to a post-receptor defect.

Glucose counterregulation during prolonged hypoglycemia in normal humans

To study glucose counterregulation under conditions approximating those of clinical disorders in which hypoglycemia develops gradually and is reversed over a prolonged period, we injected regular insulin subcutaneously, in a dose (0.15 U/kg) selected to produce two- to threefold increases in plasma insulin, in 11 normal human volunteers and measured plasma glucose, insulin, C-peptide, and counterregulatory hormone concentrations as well as rates of glucose production, glucose utilization, and insulin secretion over 12 h. The data suggest that the mechanisms of gradual recovery from prolonged hypoglycemia may differ from those of rapid recovery from short-term hypoglycemia produced by intravenous injection of insulin in that 1) both stimulation of glucose production and limitation of glucose utilization contribute to recovery from prolonged hypoglycemia; 2) increases in glucagon, epinephrine, growth hormone, and cortisol secretion as well as a decrease in insulin secretion may all participate in glucose counterregulation during prolonged hypoglycemia; 3) epinephrine may play a more important role than glucagon during prolonged hypoglycemia. The latter two conclusions are based primarily on the temporal relationships between changes in the rates of glucose turnover and changes in plasma hormone concentrations and should not be considered proved. However, they provide the basis for testable hypotheses concerning the physiology of gradual recovery from prolonged hypoglycemia that can be expected to be relevant to the pathophysiology of clinical hypoglycemia.

[Diagnosis and surgery of an insulinoma using a glucose-controlled insulin infusion system]

A 71-year-old woman with insulinoma was studied. Preoperatively, using the glucose controlled insulin infusion system (GCIIS) for glucose clamping at various blood glucose levels, autonomous insulin production was demonstrated and intravenous glucose needs for maintenance of normoglycaemia were evaluated. The results of a somatostatin suppression test, guided by the GCIIS, supported the postulation of a well differentiated beta cell adenoma with reduced storage capacity. These assumptions were later confirmed by histochemical and ultrastructural investigations. Hypoglycaemia during surgery was avoided by means of the GCIIS. Upon clamping of the plasma glucose at 90 mg/dl, 15.5 g dextrose had to be given until resection of the tumour. Immediately thereafter, a sharp rise in plasma glucose to 140 mg/dl together with a need for 4.1 U insulin showed that the insulinoma tissue had been removed completely.