Chemical characterization of persistent immunoreactive glucagon in eviscerated rats

Summary Extraction of rat submaxillary salivary glands and ileal mucosa yielded a single immunoreactive glucagon component of 25,000 daltons and a major peak of approximately 9,000 daltons respectively. Eviscerated rats with and without functional livers were found to have decreased, but persistent levels of immunoreactive glucagon and total immunoreactive glucagon, as measured with a pancreatic specific and cross reacting antiserum respectively. Gel filtration of serum samples on Sephadex G-50 fine and G-200 superfine demonstrated that there was no measurable 3485, 9000 or 25,000 dalton glucagon immunoreactivity. The persistent immunoreactive glucagon in the serum of eviscerated rats is a heterogeneous mixture of nonspecific materials and does not contain submaxillary or intestinal glucagon-related materials. These findings suggest caution in the interpretation of glucagon immunoreactivity in serum and demonstrate the necessity for chromatographic analysis of circulating IRG.     

Studies on persistent circulating immunoreactive glucagon (IRG) and immunoreactive insulin (IRI) found in eviscerated rats with a functional liver

Summary Eviscerated rats (animals without gastrointestinal tract or pancreas, but with intact liver and kidneys) are diabetic with blood glucose levels of 287 ± 10 mg% (n = 35) 24 h after surgery. Immunoreactive insulin (IRI) and immunoreactive glucagon (IRG) persisted in these animals at plasma levels of 36 ± 4 U/ml and 0.29 ± 0.02 ng/ml, respectively. Twenty-four h fasted sham-operated controls, on the other hand, had blood glucose levels of 101 ± 3mg%, plasma IRI levels of 62 ± 8 U/ml and plasma IRG levels of 0.38 ± 0.05 ng/ml (n = 21). IRG levels were not increased in eviscerated animals by surgical stress, fasting, arginine infusion, or insulin-induced hypoglycaemia, nor did they decrease following somatostatin infusion. IRI levels were similarly unresponsive. An unexplained decrease in IRG followed arginine infusion. Gel filtration studies showed plasma IRI and IRG to consist mainly of the larger molecular weight components with little of the smaller native hormone species. The disappearance rates of injected ¹²⁵I-insulin and ¹²⁵I-glucagon did not differ from sham-operated controls. Removal of the submaxillary glands from eviscerated animals had no effect on the circulating levels of IRG. Bilateral nephrectomy doubled plasma IRG. It is suggested that persistent IRG and IRI in eviscerated rats represents retained immunoreactive materials with slow rates of degradation, although an unresponsive extravisceral source of IRG can not be ruled out.     

Evidence of glucagon biosynthesis involving protein intermediates in rat salivary glands

Summary In an attempt to determine the ability of rat submaxillary glands to synthesise glucagon via protein intermediates, isolated cells from these glands were incubated in vitro with ³H-L-tryptophan and the acid-ethanol extracts of the cells were purified on Bio-Gel P-30 columns. Aliquots of the eluates were incubated with a C-terminal glucagon antiserum (30K) and the radioactivity bound to the glucagon antibody appeared to be distributed among proteins of Molecular weight >40.14 and 3.5 Kdaltons. A similar elution pattern was obtained in the presence of urea (7 mol/l) and guanidine hydrochloride (6 mol/l). To determine the molecular weight of the immunoreactive material eluting before the 3.5 Kdalton polypeptide, aliquots of the cell extracts were immunoprecipitated and analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Polypeptides of 125.8, 63.1, 42.6 and 14.4 Kdaltons were obtained. These polypeptides incorporate more radioactive tryptophan with increase in the time of incubation. Pulse-chase experiments with unlabelled tryptophan, cycloheximide-treatment of isolated cells and limited tryptic digestion of the larger glucagon immunoreactive component, transform it into a 3.5 Kdalton polypeptide with immunological characteristics indistinguishable from pancreatic glucagon. These results suggest that the larger molecule contains glucagon and thus may serve as a precursor or an intermediate of extrapancreatic glucagon biosynthesis.     

Is submaxillary gland immunoreactive glucagon important in carbohydrate homeostasis?

Previous investigators have shown rat submaxillary gland extracts to contain large amounts of material immunologically similar to pancreatic glucagon (SM-IRG). The present studies were designed to assess any physiologic contribution of this material to plasma immunoreactive glucagon (IRG) levels and to overall carbohydrate homeostasis in the rat. Bilateral submaxillary glandectomy or sham surgery was performed on adult male rats. After 2–4 wk, these animals were subjected to arginine or epinephrine infusion, fasting, insulin-induced hypoglycemia, or oral glucose loads. No measurable differences could be found between animals with or without submaxillary glands with respect to basal plasma levels of IRG, immunoreactive insulin (IRI), blood glucose (BG), or to the response of these parameters to any of the conditions tested. Furthermore, when eviscerated animals (without gastrointestinal tract or pancreas, but with intact liver and kidneys) were studied with or without submaxillary glands, no significant differences were found in either basal or stimulated levels of plasma IRG and BG. We conclude that SM-IRG makes no significant contribution to either plasma IRG or the metabolism of carbohydrates in the rat, even when other known sources of IRG have been surgically removed. While being unable to document any apparent role for SM-IRG in the maintenance of carbohydrate homestasis, we did observe dynamic changes in the glandular content of SM-IRG that occurred with the onset of puberty in both male and female weanling rats. The possibility, thus, remains that SM-IRG may be physiologically important, but in areas not necessarily related to carbohydrate metabolism.     

Presence of insulin-like immunoreactivity and its biosynthesis in rat and human parotid gland

Summary Extracts from homogenates of rat and human parotid glands contained insulin-like immunoreactivity. The values were 5.6±2.8 ng/g wet tissue in six groups of rat parotid glands and 23.8 and 39.7 ng/g wet tissue in two human extracts. Upon gel filtration immunoreactive insulin of rat origin was eluted in a peak corresponding to the elution volume of isotopically labelled insulin. The material obtained from the two peak fractions showed an immunoassay dilution curve identical with that of rat insulin. Furthermore, biosynthesis of insulin-like immunoreactivity in rat and human parotid glands was confirmed in vitro by a specific separation method using anti-insulin antibody. These findings suggest that the parotid gland may be a further extrapancreatic source of insulin, and that insulin biosynthesis does occur in extrapancreatic tissues.     

Immunologic characterization of plasma glucagon components in a patient with malignant glucagonoma

Plasma immunoreactive glucagon (IRG) components were analyzed by gel filtration on either a Bio-Gel P-30 or a Sephadex G-150 column (1.0 X 68 cm) in a 47-year-old male with biopsy-proven malignant glucagonoma. Plasma samples were obtained before and after 20 courses of streptozotocin treatment as well as after administration of a somatostatin-derivative (SRIF-D, 0.38 mg, subcutaneous), regular insulin (0.2 U/kg, intravenous), and secretin (2 U/kg, intravenous). The fractions from the columns were assayed for IRG by simultaneous radioimmunoassay with C-terminal (Unger 30 K) and N-terminal (OAL 196) antibodies to glucagon. Four IRG components were observed. The largest had a molecular weight of approximately 150,000 daltons and cross-reacted much more strongly with the N-terminal antibody than with the C-terminal. The second IRG component appeared to be about 9000 daltons and cross-reacted more strongly with the N-terminal antibody. The third and major IRG component comprised 51.8% to 88.1% of the total IRG as measured with C-terminal antibody, corresponded in molecular weight to synthetic 3500 dalton glucagon, and reacted roughly equally with each of the two antibodies. The fourth IRG component cross-reacted only with N-terminal antibody and appeared to be smaller than 3500 daltons. The plasma IRG level decreased from 8829 pg/mL to 1421 pg/mL (averages of five consecutive determinations) after 20 courses of treatment with streptozotocin with significant clinical improvement. A marked (74%) but transient decrease in plasma IRG was observed after the SRIF-D injection, whereas secretion and insulin caused increases in plasma IRG level of 53% and 22%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Un dosage radioimmunologique du glucagon pancréatique dans le plasma humain

Résumé Le dosage radioimmunologique est effectué pour le glucagon grâce à l'obtention d'antisérum anti-glucagon chez le lapin. La séparation du glucagon libre et du glucagon lié se fait par immunoprécipitation en présence de sérum anti-gammaglobuline de lapin. Deux sortes d'antisérum ont été obtenues, l'un spécifique du glucagon pancréatique qui ne réagit pas avec les extraits de jéjunum et d'estomac. L'ajout d'anti-enzyme au milieu d'incubation prévient toute dégradation de l'hormone et permet le dosage plasmatique sans extraction. La glucagonémie moyenne est de 219 pg/ml ± 148 DS avec l'antisérum spécifique chez les sujets normaux, de 392 pg/ml chez les diabétiques. L'administration de tyrosine p.o. entraîne une élévation de la glucagonémie à la 30^ème min.

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Summary Radioimmunoassay of glucagon has been achieved by using antiglucagon antiserum obtained from rabbits and separating the free and bound glucagon by immunoprecipitation in the presence of antirabbit gammaglobulin serum. Two kinds of antiserum were obtained: one specific for pancreatic glucagon, which did not react with extracts of jejunum and stomach, and the other, which reacted equally well with pancreas and stomach extracts. The addition of antienzyme to the incubation medium prevented any degradation of the hormone, thus permitting the assay in plasma without extraction. The mean plasma glucagon proved to be 219 pg/ml ± 148 SD with the specific antiserum in normal subjects and 392 pg/ml in diabetics. Oral tyrosine induced a rise in plasma glucagon after 30 min.

Attachée de Recherches à l'INSERM.     

The alpha cell response to glucose change during perfusion of anti-insulin serum in pancreas isolated from normal rats

Summary To determine the effect of neutralization of endogenous insulin upon the glucagon response to a rise and fall of glucose concentration, pancreata isolated from normal rats were perfused with either a potent anti-pork insulin guinea pig serum or a nonimmune guinea pig serum for 30 min. During this period glucose concentration was changed from 100 mg/dl to either 130, 180 or 80 mg/dl for 10 min. Antiserum perfusion at 100 mg/dl caused an approximately two-fold increase in glucagon which was not suppressed by an increase in glucose concentration to either 130 or 180 mg/dl, although glucagon secretion was significantly suppressed in the control experiments in which nonimmune serum was perfused. However, the 0.38±0.21 ng/min rise in glucagon secretion in response to a reduction in glucose concentration to 80 mg/dl in the control experiments was not abolished by antiserum perfusion but, instead, was enhanced (2.66±0.60 ng/min). These findings suggest that insulin may be required for glucose-mediated suppression of glucagon in the isolated pancreas of normal rats but not for stimulation of glucagon secretion by mild glucopenia. Alternatively, neutralization of insulin-mediated release-inhibition of glucagon secretion may simply have altered alpha cell responsiveness in a direction that desensitized it nonspecifically to suppression and sensitized it to stimulation.Senior Medical Investigator, Dallas Veterans Administration     

Possible involvement of the cholinergic system in hormonal secretion by the perfused pancreas from ventromedial-hypothalamic lesioned rats

Summary Total arginine-induced secretion of insulin, glucagon and somatostatin was studied during a 20 min period in isolated perfused pancreases from control and non-hyperphagic ventromedial hypothalamic (VMH) lesioned rats. Compared to controls pancreases from VMH-lesioned rats secreted more insulin (82±13ng vs 36±9ng) and more glucagon (130±23ng vs 73±14ng) but less somatostatin (0.58±0.18ng vs 1.12±0.14ng). These abnormalities were restored to normal by perfusion with atropine (25 mol/l). Pancreases of both groups were perfused with the cholinergic agonist methacholine (100 mol/l). Again pancreases from VMH-lesioned rats secreted more insulin (157±19ng vs 33±6ng) and more glucagon (95±13 ng vs 57±9 ng) but less somatostatin (0.80±0.15 ng vs 1.30±0.18 ng). These results support the concept that, in pancreases isolated from VMH-lesioned rats increased cholinergic activity may prevail via increased release of endogenous acetylcholine from islet-postsynaptic ganglion cells together with increased numbers of muscarinic receptors on postsynaptic ganglion cells as well as on endocrine cells.     

Plasma immunoreactive glucagon fractions in four cases of glucagonoma: Increased “Large glucagon — immunoreactivity”

Summary Immunoreactive glucagon (IRG) fractions from plasma of 8 normal subjects and 4 patients with glucagon secreting tumors were studied by gel filtration techniques on Bio Gel P-30 and Sephadex G-50 columns. The pancreatic glucagon specific anti serum (30K) of Unger was utilized to measure IRG. Columns were calibrated with labelled albumin, proinsulin, insulin and glucagon. Four peaks were defined in normal and tumor bearing patients: peak I (>20000 mol. wt.), peak II (primarily 9000 mol. wt.), peak III pancreatic glucagon (3500 mol. wt.) and peak IV small glucagon (<3500 mol. wt.). Glucagonoma patients differed from our normal and reported normal subjects in that peak II contained most of the circulating IRG. The percent of IRG associated with peak II was 9.5–31.5% in normals and 39.1–61.2% in glucagonomas. Glucagon-like biological activity in an isolated hepatocyte system was demonstrated for all peaks. However, relative to immunoreactivity, peak II showed reduced activity (25–33%). Immunoassay of dilutions of all peaks revealed the probability of immuno determinants identical with porcine pancreatic glucagon. The presence of heterogeneous IRG peaks with biological glucagon-like activity suggest that the larger molecules may be prohormones. Further, it is possible that specific elevation of peak II may be a diagnostic feature of glucagonomas.Supported in part by NIH Grant #AM 17431-02.     

Enhanced glucagon secretion by pancreatic islets from prednisolone-treated mice

Summary This work was undertaken to study the effect of prednisolone on glucagon release in mouse pancreatic islets isolated by the collagenase technique. Pretreatment of the donors with prednisolone (0.2–0.3 mg daily) induced an increase in glucagon release both in the absence (1005±75, SEM, vs. 796±46 pg/10 islets/60 min, p = 0.019) and in the presence of 7.5 mM arginine (1500±119 vs. 1236±61 pg/10 islets/60 min, p = 0.05). The glucagon content of the islets was not modified by the treatment (28.6±1.1 vs. 28.0±1.1 ng/50 islets). The addition of prednisolone (5 · 10^–5 M) into the medium, failed to affect significantly glucagon secretion. In agreement with previous human studies, our data indicate that chronic glucocorticoid administration augments the secretory activity of the A-cell. This does not seem to be a result of increased glucagon synthesis nor a direct effect of glucocorticoids on the glucagon-releasing mechanism. Rather, environmental changes induced by these hormones could be responsible for A-cell hyperfunction.Presented at the 11th Annual Meeting of the European Association for the Study of Diabetes, September 4, 1975, Munich, Federal Republic of Germany (Abstract # 32, Diabetologia 11, 334, 1975).Supported in part by a research grant (12-895-74) from the Instituto Nacional de Previsión, Spain, by a research contract (No. 1551/RB) from the International Atomic Energy Agency, Vienna, Austria, and by a gift from the Alexander von Humboldt Stiftung, Bonn-Bad Godesberg, Federal Republic of Germany.     

Nature and biologic activity of “extrapancreatic glucagon”: Studies in pancreatectomized cats

After total pancreatectomy concentrations of circulating immunoreactive glucagon (IRG) were elevated (255 ± 37 pg/ml, mean ± SEM; n = 20) in comparison to unoperated cats (119 ± 27 pg/ml). Plasma glucagon concentrations were determined in an assay regarded as specific for pancreatic glucagon. The nature of this extrapancreatic IRG was further examined in the following studies. Arginine (0.45 gm/kg i.v.) caused a marked elevation of IRG in normal animals but did not cause a consistent elevation of IRG in 6 pancreatectomized cats. Whereas somatostatin (20 μg/kg/hr i.v. for 1 hr) in 10 pancreatectomized cats caused a reduction in IRG from 195 ± 45 to 64 ± 22 pg/ml (p < 0.02), blood glucose did not change. Moreover, insulin (0.22 U/kg/hr i.v. for 1 hr) failed to reduce blood glucose levels in 6 pancreatectomized cats despite a fall in IRG from 269 ± 87 to 150 ± 62 pg/ml (p < 0.05). Glucagon (4 ng/kg/min i.v. for 1 hr) given during the second hour of somatostatin infusion failed to raise blood glucose in 7 untreated pancreatectomized cats. However, when euglycemia was achieved by prolonged insulin therapy in 2 pancreatectomized animals, extrapancreatic IRG became completely suppressed and a hyperglycemic response to exogenous glucagon was restored. Although extrapancreatic IRG appeared identical to pancreatic glucagon by immunoassay, Sephadex G50 chromatography of plasma from 4 pancreatectomized animals showed that 40%–90% of the IRG was of approximately 9000–10,000 molecular weight. Only 10%–60% was of molecular weight corresponding to pancreatic glucagon, i.e., 3500. This contrasted with normal cats, in whom more than 90% of IRG was of molecular weight 3500. The excessive secretion of extrapancreatic IRG is probably related to insulin deficiency since it is reversed by prolonged insulin therapy. The circulating material is heterogeneous and would correspond in molecular size to pancreatic glucagon and a larger molecular weight glucagon precursor. The lack of a consistent response to arginine and predominance of 9000–10,000 molecular weight material could be due to chronic hyperstimulation of true A cells situated in the upper gastrointestinal tract or other extrapancreatic sites; on the other hand, these results could suggest that the cell of origin of extrapancreatic IRG is distinct from the A cell. A major role for extrapancreatic glucagon in the hyperglycemia of diabetes is not evident in these studies, though hepatic glycogen depletion and a reduced rate of peripheral glucose utilization in the operated animals may have reduced the impact on blood glucose levels of changes in IRG. It is possible that extrapancreatic IRG contributes to the poor response to exogenous insulin and glucagon seen in untreated pancreatectomized animals.     

Counterregulation in Type 2 (non-insulin-dependent) diabetes mellitus. Normal endocrine and glycaemic responses,up to ten years after diagnosis

Summary We have examined hormonal and metabolic responses to insulin-induced hypoglycaemia in 10 Type 2 (non-insulin-dependent) diabetic patients treated with tablets and 10 age, sex and weight matched control subjects. Diabetic patients were under 110% ideal body weight, had no autonomie neuropathy and were well controlled (HbA₁, 7.1±0.2%). After the diabetic patients were kept euglycaemic by an overnight insulin infusion, hypoglycaemia was induced in both groups by intravenous insulin at 30 mU·m^–2·min^–1 for 60 min and counterregulatory responses measured for 150 min. There were no significant differences between diabetic patients and control subjects in the rate of fall (3.3±0.3 vs 4.0±0.3 mmol·1^–1·h^–1), nadir (2.4±0.2 vs 2.3±0.1 mmol/l) and rate of recovery (0.027±0.002 vs 0.030±0.003 mmol·1^–1·min^–1) of blood glucose. Increments of glucagon (60.5±5.7 vs 70±9.2 ng/l) and adrenaline (1.22±0.31 vs 1.45±0.31 nmol/l) were similar in both groups. When tested using this model, patients with Type 2 diabetes, without microvascular complications and taking oral hypoglycaemic agents show no impairment of the endocrine response and blood glucose recovery following hypoglycaemia.     

Effect of glucagon antibodies on plasma glucose,insulin and somatostatin in the fasting and fed rat

Summary A potent high-titre glucagon antibody pool was used to induce a state of acute glucagon deficiency in order to investigate the importance of glucagon in maintaining euglycaemia in the fed and fasted anaesthetised rat. Binding characteristics of the antiserum and evidence of its neutralisation of the biological effects of exogenous glucagon are described. The amount of antibody administered was capable of neutralising up to 12 times the total content of glucagon (approximately 1nmol) in the rat pancreas. The hyperglycaemic response to 1.43 nmol exogenous glucagon was significantly inhibited in the rat by glucagon antibodies given intravenously or intraperitoneally (p < 0.001). However, no changes in plasma glucose occurred in rats fasted 16 h (4.35±0.1 mmol/l or 24 h (4.0±0.05 mmol/l) after antibody administration. The same dose of glucagon antibodies produced no change in plasma glucose (6.1±0.2 mmol/l), immunoreactive insulin (1.85±0.05 g/l) or immunoreactive somatostatin (110±30 ng/l) in rats after antibody administration. Antibody excess, equivalent to a binding capacity for glucagon of 40 nmol/l in the plasma of recipient animals, was demonstrable at all times after passive immunisation. The absence of any affect on glucose concentrations following immunoneutralisation of glucagon suggests that glucagon secretion may not be a major factor in the maintenance of euglycaemia in the rat.     

The serum glucose response to glucagon suppression with somatostatin,insulin or antiglucagon serum in depancreatized rats

Summary Total immunoreactive glucagon (IRG) and immunoreactive glucagon of A cell origin (IRG_a) were measured in the serum of normal, sham-operated and depancreatized rats, after the administration of three glucagon antagonists: insulin (5–200 mU/rat/h), somatostatin (SRIF; 100 g/kg/h) and antiglucagon serum (AGS, enough to bind three times the calculated total amount of circulating IRG). Since no differences were noted between the responses of normal and sham-operated animals, the values were pooled and used as controls. Pancreatectomy caused a significant increase in serum glucose, IRG_a and total IRG and a significant decrease in serum insulin. AGS and SRIF significantly decreased serum glucose in control, but not in depancreatized rats, even though SRIF caused a significant decrease of IRG_a in all animals. SRIF significantly decreased plasma insulin in control rats, but did not modify total IRG secretion in either group. In control rats the minimum effective hypoglycaemic dose of insulin (5 mU/rat/h) may have decreased serum IRG_a, but not total IRG. At higher doses (20 mU/rat/h) insulin stimulated glucagon secretion. In depancreatized animals, higher doses of insulin (200 mU/rat/h) were needed to lower serum glucose. On the other hand, a dose of 100 U/rat/h was sufficient to lower the serum IRG. We conclude that although hyperglucagonaemia may contribute to the hyperglycaemia of the untreated depancreatized rats, the excessive secretion of glucagon is secondary to insulin insufficiency and that, at least in this animal model, the hypoglycaemic action of insulin is only minimally dependent upon its ability to suppress glucagon secretion.     

The acute metabolic effects of glucagon and its interactions with insulin in forearm tissue

Summary The acute effects of glucagon (mol. wt. 3500) and its interactions with insulin were studied in the forearm during eight studies in seven normal, post-absorptive males. The protocol consisted of a 2 h baseline, 1 h glucagon perfusion (mean glucagon increment, 691±50 pg/ml), 1 h perfusion of both insulin and glucagon (mean insulin increment of 105 ±13 mU/l) and a 30 min recovery period. Simultaneous arterial (A), deep venous (DV), and superficial venous (SV) blood samples were obtained at 30 min intervals. Perfusion of glucagon resulted in a decrease in (A-DV) non-esterified fatty acids of-0.128±0.057 mmol/l (n=7, p<0.05) and (A-SV) non-esterified fatty acids of -0.081±0.036 mmol/l (n=7, p<0.05), as well as a change in deep compartment uptake of glycerol after 60 min of -0.044±0.019 mol/min/100 ml of forearm tissue (n=6, p<0.05), indicating increased lipolysis. There was also a decrease in net glucose uptake as reflected by a change in (A-DV) of -0.24±0.09 mmol/l (n=7, p<0.025) and (A-SV) of 0.10± 0.05 mmol/l (n=7, p<0.05). There was also a net decrease in deep arteriovenous differences of potassium in six of seven subjects. Insulin levels, similar to those found after a meal, rapidly reversed the effects of glucagon on non-esterified fatty acid, glucose and potassium. These effects persisted throughout the recovery period.     

Hyperglucagonemia in liver cirrhosis with portal-systemic venous anastomoses: responses of plasma glucagon and gastric inhibitory polypeptide to oral or intravenous glucose in cirrhotics with normal or elevated fasting plasma glucose levels.

Plasma immunoreactive glucagon (IRG) was examined in volunteers with biopsy-proven cirrhosis of the liver after recovery from surgical portal--caval anastomosis. A wide range of increased total plasma IRG concentrations was found after overnight fast in groups of cirrhotic subjects with and without fasting hyperglycemia. Gel filtration chromatography of plasma showed a major component in the 3500-mol wt fraction in all cases so studied. Administration of glucose i.v. caused rapid suppression of total plasma IRG in normoglycemic and non-insulin-dependent hyperglycemic cirrhotic subjects. After administration of oral glucose, total plasma IRG was suppressed rapidly in normoglycemic cirrhotic subjects, while non-insulin-dependent hyperglycemic cirrhotic subjects exhibited delayed but prolonged suppression. Chromatography of selected plasma with glucose-suppressed total IRG showed a major decrease in the 3500-mol wt component in every case. Exaggerated increments of plasma gastric inhibitory polypeptide were demonstrable in both groups of cirrhotic individuals after administration of oral glucose, and it is speculated that this peptide may contribute to stimulation of glucagon secretion in liver disease associated with insulin deficiency.     

Heterogeneity of plasma glucagon: patterns in patients with chronic renal failure and diabetes.

Immunoreactive plasma glucagon (IRG) in normal subjects and patients with chronic renal failure, diabetic ketoacidosis and diagetic hyperosmolar syndrome circulates in several forms. In the diabetic patients most IRG eluted coincidentally with the extracted, purified pancreatic hormone (MW3500), while in normal subjects a high molecular weight component predominated. In striking contrast, the major component of plasma IRG in patients with chronic renal failure was of intermediate size (MW +/- 9000), consistent with proglucagon. The accumulation of this form of IRG suggests that the kidney plays an important role in its metabolism. If there are differences in the biological activity of the various circulating components of IRG, the significance of immunoreactive glucagon levels in some disease states will require reassessment.     

Effects of ingested fructose and infused glucagon on endogenous glucose production in obese NIDDM patients,obese non-diabetic subjects,and healthy subjects

Summary Increased endogenous glucose production (EGP) and gluconeogenesis contribute to the pathogenesis of hyperglycaemia in non-insulin-dependent diabetes mellitus (NIDDM). In healthy subjects, however, EGP remains constant during administration of gluconeogenic precursors. This study was performed in order to determine whether administration of fructose increases EGP in obese NIDDM patients and obese non-diabetic subjects. Eight young healthy lean subjects, eight middle-aged obese NIDDM patients and seven middle-aged obese non-diabetic subjects were studied during hourly ingestion of ¹³C fructose (0.3 g · kg fat free mass^–1 · h^–1) for 3 h. Fructose failed to increase EGP (measured with 6,6 ²H glucose) in NIDDM (17.7±1.9 mol · kg fat free mass^–1 · min^–1 basal vs 15.9±0.9 after fructose), in obese non-diabetic subjects (12.1±0.5 basal vs 13.1±0.5 after fructose) and in lean healthy subjects (13.3±0.5 basal vs 13.8±0.6 after fructose) although ¹³C glucose synthesis contributed 73.2% of EGP in lean subjects, 62.6% in obese non-diabetic subjects, and 52.8% in obese NIDDM patients. Since glucagon may play an important role in the development of hyperglycaemia in NIDDM, healthy subjects were also studied during ¹³C fructose ingestion + hyperglucagonaemia (232±9 ng/l) and during hyperglucagonaemia alone. EGP increased by 19.8% with ingestion of fructose + glucagon (p<0.05) but remained unchanged during administration of fructose or glucagon alone. The plasma ¹³C glucose enrichment was identical after fructose ingestion both with and without glucagon, indicating that the contribution of fructose gluconeogenesis to the glucose 6-phosphate pool was identical in these two conditions. We concluded that during fructose administration: 1) gluconeogenesis is increased, but EGP remains constant in NIDDM, obese non-diabetic, and lean individuals; 2) in lean individuals, both an increased glucagonaemia and an enhanced supply of gluconeogenic precursors are required to increase EGP; this increase in EGP occurs without changes in the relative proportion of glucose 6-phosphate production from fructose and from other sources (i. e. glycogenolysis + gluconeogenesis from non-fructose precursors).Abbreviations EGP Endogenous glucose production - CHO carbohydrate - APE atom percent excess - GRd glucose rate of disappearance - FFM fat-free mass     

Lowering of fasting and food stimulated serum immunoreactive gastric inhibitory polypeptide (GIP) by glucagon.

The effect of intravenous glucagon infusion on serum levels of immunoreactive GIP (IR-GIP), insulin (IRI), gastrin (IRG), and on blood glucose has been investigated in six healthy volunteers in the fasting state and during ingestion of a mixed standard meal. Glucagon (500 ng/kg/min) lowered significantly serum levels of IR-GIP and IRG below the fasting values and increased the levels of IRI and blood glucose. Glucagon (50 ng/kg/min) infused 30 minutes before and continued 90 minutes after ingestion of a test meal abolished the IR-GIP response, suppressed significantly the IRG response, and left the IRI response unchanged. The same glucagon dose infused 60 minutes after ingestion of the test meal decreased significantly the raised levels of IR-GIP and IRG to fasting levels without changing IRI values. It is concluded that exogenous glucagon inhibits Gip release at the level of the GIP-producing cells.