Abnormalities of glucagon metabolism in diabetes mellitus

Frequency and Causes of False-Positive Elevated Plasma Concentrations of Fasting Gut Hormones in a Specialist Neuroendocrine Tumor Center

INTRODUCTION

In the UK, the fasting plasma concentrations of a panel of gut hormones (comprising vasoactive intestinal peptide (VIP), gastrin, pancreatic polypeptide (PP), glucagon, somatostatin and chromogranin A) are measured to evaluate patients who have or who (due to unexplained and compatible symptoms) are suspected of having neuroendocrine tumors (NETs). False positive elevated hormone concentrations are sometimes found.

OBJECTIVE

To evaluate the frequency and implications of false positive fasting gut hormone results.

METHODS

Retrospective audit of fasting gut hormone profile results at a large UK university teaching hospital over 12 months.

RESULTS

Fasting gut hormone concentrations were measured in 231 patients during 2017. No NETs were found in the 88 patients who had this test performed only to investigate symptoms. 31 false positive gastrin, 8 false positive chromogranin A, two false positive glucagon, three false positive somatostatin, one false positive PP, and one false positive VIP results were found. We extended the audit for glucagon and somatostatin for an additional two years and found seven probable false-positive raised glucagon concentrations and four probable false-positive elevated plasma somatostatin concentrations in total.

CONCLUSIONS

False-positive elevations of plasma gastrin and chromogranin A were common and causes such as proton pump inhibitor use or inadequate fasting accounted for most cases. Elevated plasma concentrations of the other gut hormones were also detected in patients who had no other evidence of NET. Other diagnoses (e.g. cirrhosis and medullary thyroid carcinoma for hypersomatostatinemia and type 2 diabetes mellitus, pancreatitis, liver or renal impairment for hyperglucagonemia) may cause these false positive results.

Insulin and glucagon response of the diabetic Chinese hamster in the Asahikawa colony

The relationship between pancreatic hormone content and pattern of hormone release has not been completely elucidated because of heterogeneity in diabetes. Accordingly, this study was performed to establish the relationship, using spontaneously diabetic Chinese hamsters in the Asahikawa colony, a newly discovered experimental model resembling insulin-deficient diabetes in humans. As a result of investigations of insulin and glucagon responses to glucose or arginine in vivo and in vitro using isolated islets obtained by the collagenase procedure, a decreased insulin response and paradoxical glucagon response to glucose, and an excessive glucagon response to arginine were found in the diabetic animals. While the yield of isolated islets tended to decrease, a decreased pancreatic insulin content and increased pancreatic glucagon content were found as the diabetic state advanced. It may be suggested, therefore, that the relationship between pancreatic hormone content and pattern of hormone release in diabetic animals in the Asahikawa colony is based on the disruption of islets, disruption or dysfunction of B-cells and hyperplasia or hypertrophy of A-cells by some cause genetically determined.

Paradoxical glucagon response in perifused islets of the diabetic Chinese hamster

Dynamic insulin and glucagon response to glucose was examined in the perifusion system to investigate the relationship between pancreatic hormone content and the pattern of hormone secretion in diabetic Chinese hamsters of the Asahikawa colony (CHA). Isolated islets of normals and diabetics from the CHA were perifused. When the medium was changed to high glucose (500 mg/dl), a low insulin response and paradoxical glucagon response were seen in diabetics compared with normals. Positive correlations were found between pancreatic insulin and the amount of perifusate insulin, and glucagon content and glucagon release, respectively. It is suggested, accordingly, that pancreatic hormone content is related to the amount of hormone release in CHA. A negative correlation between the amount of perifusate insulin and glucagon release was found. It is suggested, therefore, that an impaired suppression of glucagon release in the diabetic CHA animals could be attributed at least to insulin deficiency. These findings agree with the histological discovery of decreased B-cells and increased A-cells in the diabetic islets. Both decreased B-cells and islet numbers could be the cause of the low insulin response to glucose. Increased numbers of A-cells with hyperfunction resulting from local insulin deficiency could be the cause of the paradoxical glucagon response.

Plasma glucagon and glucagon-like immunoreactive components in Type 1 (insulin-dependent) diabetic patients and normal subjects before and after an oral glucose load

Biogel P-30 filtration of plasma from Type 1 (insulin-dependent) diabetic patients and normal subjects in basal state and after an oral glucose load was assayed with a C-terminal (30 K) and a glucagon-like immunoreactivity-cross-reacting antiserum (R8). Up to four immunoreactive peaks of approximate molecular sizes of greater than 20,000 (fraction I), 9000 (fraction II), 3500 (fraction III) and 2000 (fraction IV) were detected with the two antisera in both groups. In the basal state, the only significant difference observed between both groups was a higher R8-reactivity in fraction II in the group of diabetic patients, although the R8 minus 30 K values for this fraction did not show a significant difference between both groups. After glucose the only significant differences were an increase of R8-reactivity in fraction II in both groups (p less than 0.01) and a decrease of 30 K-reactivity in fraction III (IRG3500) in normal subjects (p less than 0.05). In seven out of 12 diabetic patients, 30 K-reactivity in fraction II (IRG9000) and III (IRG3500) increased above their basal values. The gut-glucagon-like immunoreactivity response to oral glucose (delta R8-delta 30 K values in fraction II) was similar in both the diabetic and normal subjects. These results indicate that the paradoxical rise in plasma immunoreactive glucagon after oral glucose in diabetic patients may be due to an increase of both IRG3500 and/or IRG9000, the gut-glucagon-like immunoreactivity released during glucose absorption has a molecular weight of approximately 9000, and no differences in plasma gut-glucagon-like immunoreactivity were observed in Type 1 diabetic patients when compared with normal subjects, either in the basal state or after glucose ingestion.

Defective glucose counterregulation after subcutaneous insulin in noninsulin-dependent diabetes mellitus. Paradoxical suppression of glucose utilization and lack of compensatory increase in glucose production, roles of insulin resistance, abnormal neuroendocrine responses, and islet paracrine interactions

To characterize glucose counterregulatory mechanisms in patients with noninsulin-dependent diabetes mellitus (NIDDM) and to test the hypothesis that the increase in glucagon secretion during hypoglycemia occurs primarily via a paracrine islet A-B cell interaction, we examined the effects of a subcutaneously injected therapeutic dose of insulin (0.15 U/kg) on plasma glucose kinetics, rates of glucose production and utilization, and their relationships to changes in the circulating concentrations of neuroendocrine glucoregulatory factors (glucagon, epinephrine, norepinephrine, growth hormone, and cortisol), as well as to changes in endogenous insulin secretion in 13 nonobese NIDDM patients with no clinical evidence of autonomic neuropathy. Compared with 11 age-weight matched nondiabetic volunteers in whom euglycemia was restored primarily by a compensatory increase in glucose production, in the diabetics there was no compensatory increase in glucose production (basal 2.08 +/- 0.04----1.79 +/- 0.07 mg/kg per min at 21/2 h in diabetics vs. basal 2.06 +/- 0.04----2.32 +/- 0.11 mg/kg per min at 21/2 h in nondiabetics, P less than 0.01) despite the fact that plasma insulin concentrations were similar in both groups (peak values 22 +/- 2 vs. 23 +/- 2 microU/ml in diabetics and nondiabetics, respectively). This abnormality in glucose production was nearly completely compensated for by a paradoxical decrease in glucose utilization after injection of insulin (basal 2.11 +/- 0.03----1.86 +/- 0.06 mg/kg per min at 21/2 h in diabetics vs. basal 2.08 +/- 0.04----2.39 +/- 0.11 mg/kg per min at 21/2 h nondiabetics, P less than 0.01), which could not be accounted for by differences in plasma glucose concentrations; the net result was a modest prolongation of hypoglycemia. Plasma glucagon (area under the curve [AUC] above base line, 12 +/- 3 vs. 23 +/- 3 mg/ml X 12 h in nondiabetics, P less than 0.05), cortisol (AUC 2.2 +/- 0.5 vs. 4.0 +/- 0.7 mg/dl X 12 h in nondiabetics, P less than 0.05), and growth hormone (AUC 1.6 +/- 0.4 vs. 2.9 +/- 0.4 micrograms/ml X 12 h in nondiabetics, P less than 0.05) responses in the diabetics were decreased 50% while their plasma norepinephrine responses (AUC 49 +/- 12 vs. 21 +/- 5 ng/ml X 12 h in nondiabetics, P less than 0.05) were increased twofold (P less than 0.05) and their plasma epinephrine responses were similar to those of the nondiabetics (AUC 106 +/- 17 vs. 112 +/- 10 ng/ml X 12 h in nondiabetics). In both groups of subjects, increases in plasma glucagon were inversely correlated with plasma glucose concentrations (r = -0.80 in both groups, P less than 0.01) and suppression of endogenous insulin secretion (r = -0.57 in nondiabe

Plasma glucagon in diabetes of haemochromatosis: too low or too high?

Glucagon secretion before and during arginine infusions was tested in 11 patients with diabetes associated with haemochromatosis. The results were compared with those obtained in six normal subjects and five patients with haemochromatosis but normal glucose tolerance. The patients with haemochromatosis, regardless of glucose tolerance, exhibited higer level of plasma immunoreactivity for glucagon (antiserum 30-K) suggesting hyperglucagonaemia. However, additional analysis revealed that a considerable amount of this glucagon immunoreactivity was due to cross-reacting material of high molecular weight, the levels of which were significantly higher in patients with idiopathic haemochromatosis. When this was deducted from the total immunoreactivity measured, the resulting values for true glucagon concentrations were similar to those of normal subjects. The data suggest that (1) patients with idiopathic haemochromatosis, whether or not associated with diabetes, exhibit plasma glucagon levels comparable with those of normal subjects; (2) the plasma of the same patients contains significantly more high-molecular-weight substances reacting with glucagon antiserum 30-K than is present in plasma of normal subjects; and (3) 'hyperglucagonaemia' may be erroneously suggested when glucagon is measured with certain antisera reputed to be specific for glucagon.

Glucagon and diabetes. II. Complete suppression of glucagon by insulin in human diabetes

In order to determine whether glucagon levels of diabetic subjects are suppressible, alpha cell responsiveness to acute insulin administration (0.1 units/kg intravenously) was determined in fourteen juvenile onset, healthy diabetic and eight control subjects. In the diabetics, insulin produced a significant but slow fall in blood glucose over 60 min (P less than 0.01). On the other hand, glucagon levels fell dramatically in all diabetics to undetectable levels (P less than 0.001). Only one diabetic became hypoglycaemic and he alone showed a rebound rise of glucagon at 60 min. The rate of fall of blood glucose in the diabetic subjects was not influenced by the basal glucagon level (r=0.13) or the rate of fall of plasma glucagon (r=0.04). The glucose and glucagon responses of control subjects to insulin administration were in sharp contrast to the diabetics: blood glucose levels fell rapidly to hypoglycaemic levels and were associated with a major rise in glucagon levels (mean rise 116 pmol/1, P less than 0.001). We conclude that alpha cell hyperfunction in human diabetes can be completely suppressed by insulin administration and is therefore not autonomous, and that the slow rate of fall of blood glucose following insulin administration in diabetics is not secondary to glucagon excess.

Glucagon levels in normal and diabetic subjects: use of a specific immunoabsorbent for glucagon radioimmunoassay

Non-specific plasma effects may produce major errors in the estimation of true plasma pancreatic glucagon concentrations by radioimmunoassay. This has been circumvented by the production of glucagon-free plasma for each individual investigated, by means of glucagon antibody, coupled to sepharose beads. True fasting pancreatic glucagon levels (mean+/-SEM) in 18 healthy subjects (24+/-3 pg/ml) were significantly lower (p less than .005) than in 10 non-ketotic non-obese diabetics (38+/-3 pg/ml). It is suggested that, in the presence of decreased insulin-effect in the diabetic, this 55% glucagon elevation in diabetics may be of biological importance and contribute to the fasting hyperglycaemia.

Plasma glucagon response to arginine infusion in children and adolescents with diabetes mellitus

Plasma glucagon response to an arginine infusion was studied in children and adolescents belonging to the following groups: (I) twenty-two controls; (II) six subjects with delayed insulin peak during oral GTT; (III) ten diabetics on diet and/or oral therapy; (IV) six newly diagnosed uncompensated diabetics; and (V) eight diabetics on insulin therapy. The fasting glucagon concentrations and rise of glucagon in response to arginine in the patients of Groups II, III and V were similar to those of the controls (Group I). The basal levels and rise of glucagon in the newly diagnosed, uncompensated dibetic children (Group IV) was elevated compared to the other groups but the difference was statistically not significant. The results of this investigation favour the hypothesis that the hyperglucagonaemia in diabetes is a secondary effect to the metabolic derangement, bearing a direct relationship to the degree of homeostastic decompensation.

Glucagon secretion in unaffected monozygotic twins of juvenile diabetics

Glucagon secretion during a 50-g oral glucose tolerance test has been investigated in 16 nondiabetic monozygotic twins of juvenile diabetics and compared with the results in 10 normal controls and 10 untreated, newly diagnosed, maturity-onset diabetics. Normal subjects showed a significant mean fall in glucagon at 15, 30, and 60 min, with a return to the baseline at 120 min. Maturity-onset diabetics showed a significant mean rise 15 min after oral glucose. The mean of the twin group was intermediate between normals and diabetics, although there was considerable individual variation with some showing suppression and others stimulation of glucagon release. When the twins were divided according to the length of discordance it was found that the mean response in the 8 twins who had been discordant for a mean of 19 years was indistinguishable from that of normal subjects, whereas the mean response of twins discordant for a mean of only 4.5 years was similar to that of the diabetic patients. It is possible, therefore, that hypersecretion of glucagon may occur in some subjects predisposed to develop diabetes mellitus, and the finding of lack of suppression of glucagon in the identical twin of a juvenile diabetic may be of prognostic significance. Identical twins who have been discordant for over 10 years are thought on other grounds to be unlikely to develop diabetes, and the finding of a normal glucagon response is further confirmation of their normal metabolic status and reinforces the suggestion that they are not prediabetic.