Properties of immunoreactive glucagon fractions of canine stomach and pancreas

Interaction between insulin and counterregulatory hormones in control of substrate utilization in health and diabetes during exercise

In summary, the appropriate balance of glucagon and insulin at the liver and the catecholamines and insulin in the periphery provide the most optimal balance of substrate fluxes to the working muscle. When the hormonal balance is perturbed such as is seen in diabetes or with glucagon suppression, or when the effect of a hormone is impaired such as with beta blockade, optimal substrate balance is lost. The effects of these hormones can be overridden by metabolic factors in muscle, as evidenced by the uncoupling of the normal catecholamine antagonism of glucose uptake from the actual glucose uptake observed during exercise under conditions of tissue hypoxia.

Characterization of a chemically tritiated large molecular weight glucagon immunoreactive protein species by lectin-affinity column chromatography and reaction with anti-glucagon antibodies

High molecular weight glucagon immunoreactive material, obtained by gel-filtration (in the presence of 6 M guanidine hydrochloride) of fetal bovine pancreatic extracts, was tritiated by reductive methylation. Concanavalin-A-Sepharose column chromatography of the radiolabeled preparation yielded a discrete Concanavalin-A-reactive, alpha-methyl-mannoside-displaceable radioactive peak, coinciding with the glucagon immunoreactive peak. Submission of the Con-A-reactive material to wheat germ agglutinin-Sepharose column chromatography yielded a lectin-reactive, N-acetyl-glucosamine-displaceable radioactive peak, coinciding with the glucagon immunoreactive peak. The tritiated Con-A-reactive component interacted specifically with anti-glucagon antibodies. Sephacryl S-200 gel-filtration (in the presence of guanidine hydrochloride) dissociated a approximately 40 kDa radioactive species from the antibody-antigen complex. These data provide direct evidence for the existence of a large molecular weight glycosylated glucagon-related protein species from the fetal bovine pancreas.

Effects of total pancreatectomy on the secretion of gut glucagon in humans

To determine how total pancreatectomy influences the secretion of gut glucagon in man, 15 totally pancreatectomized patients (Px), 14 distally gastrectomized patients (Gx), and 15 healthy subjects were investigated by intravenous arginine infusion test and oral glucose tolerance test. Blood glucose, plasma insulin (IRI), and C-peptide (CPR) levels were determined. Plasma immunoreactive glucagon (IRG) and total glucagon-like immunoreactivity (total GLI) were also measured. Gut glucagon-like immunoreactivity (gut GLI) was calculated to be the difference between total GLI and IRG. In the Px group, arginine infusion did not significantly alter the levels of IRI, CPR, IRG, and gut GLI. Mean basal value of gut GLI in the Px group of 356 +/- 40 pg/ml was significantly higher than 179 +/- 26 pg/ml of the healthy (p less than 0.01) and 182 +/- 24 pg/ml of Gx group (p less than 0.01). Oral glucose loading led to the highest increase of gut GLI in the Px group (p less than 0.01). Thus, extrapancreatic IRG may not be secreted into the plasma in totally pancreatectomized humans in response to arginine stimulation. Complete absence of the pancreas and the deficiency of insulin-effect may lead to a hypersecretion of gut GLI, both in the basal state and after oral glucose loading.

State of metabolic control determines role of epinephrine-glucagon interaction in glucoregulation in diabetes

Epinephrine (0.1 micrograms.kg-1.min-1) was infused with or without somatostatin (0.1 microgram.kg-1.min-1) in six depancreatized dogs, studied under normo- and hypoinsulinemia to determine whether the participation of glucagon in epinephrine-induced hepatic glucose overproduction is governed by the degree of metabolic control. When normoglycemia was achieved by basal intraportal insulin replacement, insulin levels remained constant during the epinephrine infusion, and there was a twofold increase in extrapancreatic immunoreactive glucagon (eIRG) and glucose production (Ra). Although eIRG increments were prevented by somatostatin, the increase in Ra was undiminished, indicating that epinephrine can act independently of glucagon as in normal animals. During subbasal intraportal insulin infusion in the depancreatized dogs, insulin levels remained 35% lower than with basal replacement, and the animals were hyperglycemic. Epinephrine induced a similar twofold increase in eIRG as during normoglycemia, and again this rise was prevented by somatostatin. There was a significantly greater, threefold increase in Ra with epinephrine when the animals were hyperglycemic. This exaggerated response to epinephrine was not seen during eIRG suppression by somatostatin, suggesting that glucagon participated in the epinephrine-induced hepatic glucose overproduction when the depancreatized dogs were in poor metabolic control, as seen previously in alloxan-diabetic dogs. However, in the depancreatized, unlike in the alloxan-diabetic dogs, epinephrine-induced glucagon release was small. Thus, hypoinsulinemia appears to sensitize the liver to eIRG during epinephrine infusion. The fact that epinephrine induces hyperglycemia both in physiology and diabetes could indicate an important role in enhancing glucose transport in insulin-insensitive tissues.

Glucagon and carbohydrate disorder in a totally pancreatectomized man (a study with the aid of an artificial endocrine pancreas)

The effect of insulin withdrawal and exogenous glucagon infusion upon blood glucose concentration was investigated in a totally pancreatectomized patient with the aid of an artificial endocrine pancreas. Blood glucose remained unchanged at about 100 mg/100 ml, when insulin infusion was stopped, but rose up to 300 mg/100 ml, during a 12-h period of exogenous glucagon infusion at a rate of 3 ng/kg/min. Fractionation of whole plasma on Bio Gel P-30 revealed no immunoreactive glucagon in the region of true glucagon. This study seems to reinforce the hypothesis that true glucagon is essential in the fasting condition at least in the short term to produce hyperglycemia in insulin deprived diabetics.

Glucagon levels and ketogenesis in human diabetes following total or partial pancreatectomy and severe chronic pancreatitis

In three groups of patients with insulin-dependent diabetes following total (n = 5) or partial (n = 5) pancreatectomy or chronic pancreatitis (n = 7) and in a group of idiopathic diabetics, ketogenic capacity following insulin withdrawal and during a 24-h fast was studied. Basal glucagon values were significantly increased in all diabetic groups with no significant intergroup differences. Basal ketone body values and their increase during starvation and insulin withdrawal were high and not different in totally pancreatectomized and primary diabetics, both showing unmeasurable C-peptide levels. On the contrary, ketogenesis was reduced in partially pancreatectomized and in pancreatitis diabetics with persistent levels of C-peptide. Our data confirmed the persistence of immunoreactive glucagon after pancreatectomy and demonstrated that ketogenesis is not suppressed in pancreatectomized diabetics and depends above all on residual B-cell function. A possible ketogenic effect of extra-pancreatic glucagon-like substances cannot be excluded.

Role of glucagon in the pathogenesis of diabetes: the status of the controversy

The current controversy concerning the role of glucagon in the pathogenesis of diabetes is reviewed. The traditional "unihormonal abnormality concept," namely, that all of the metabolic derangements of diabetes are the direct consequence of deficient insulin secretion or activity, and the newer so-called bihormonal abnormality hypothesis, proposing that the fullblown diabetic syndrome requires, in addition to the insulin abnormality, a relative glucagon excess, are scrutinized. The relationship of insulin deficiency to the A-cell malfunction of diabetes, the conflicting evidence concerning the essential role of glucagon in mediating the marked overproduction of glucose and ketones in severe insulin deficiency and the contribution of glucagon to the endogenous hyperglycemia of diabetics without insulin deficiency are examined. Finally, the possibility that therapeutic suppression of diabetic hyperglucagonemia may make possible better control of hyperglycemia than is presently attainable by conventional therapeutic methods is considered. It is concluded that (1) although insulin lowers glucagon levels, restoration to normal of the A-cell dysfunction of diabetes requires that plasma insulin levels vary appropriately with glycemic change; (2) that glucagon mediates the severe endogenous hyperglycemia and hyperketonemia observed in the absence of insulin; (3) that in diabetics in whom insulin is present but relatively fixed an increase in glucagon causes hyperglycemia and glycosuria; and (4) that glucagon suppression could be a potentially useful adjunct to conventional antihyperglycemic treatment of diabetics.

Stimulation of gastric-glucagon release by prostaglandin E1

The canine gastric fundus has recently been demonstrated to contain and release a material identical by all criteria to pancreatic glucagon (1, 2). Since exogenous prostaglandins have been reported to stimulate pancreatic glucagon release (3) and endogenous prostaglandins are suspected to play a role in the control of glucagon secretion (4), we were interested in seeing if prostaglandin E1 (PGE1) would affect gastric-glucagon release.

Glucagon and diabetes

We have considered the evidence, first, that the presence of glucagon is essential in the pathogenesis of the full syndrome that results from complete insulin deficiency; second, that in the diabetic in whom insulin levels are relatively fixed, a rise in glucagon concentration contributes to endogenous hyperglycemia; and, third, that conventional methods of treatment of diabetes do not fully correct either the abnormal glucagon levels or the hyperglycemia, but when insulin therapy is supplemented with somatostatin, an agent which suppresses both glucagon and growth hormone, both hyperglycemia and hyperglucagonemia are corrected. These facts may one day provide a rationale for therapeutic efforts to suppress excess glucagon secretion in the management of diabetes in man.

Streptozotocin-induced diabetes in the Chinese hamster. Biochemical and endocrine disorders

Streptozotocin treatment (125 mg/kg) in the Chinese hamster induced hyperglycaemia, hypoinsulinaemia, hyperglucagonaemia and changes in body, liver, pancreas, stomach, kidney and adipose tissue weights. The pancreatic reserves of insulin and glucagon in the diabetic animals were low, but stomach glucagon high. These animals showed high levels of phosphoenolpyruvate carboxykinase and low levels of glucokinase, hexokinase, isocitrate dehydrogenase and malic enzyme, but normal levels of pyruvate kinase in the liver. Increases in lactate dehydrogenase subunit B and isozymes 2, 3 and 4 were also observed in the liver, but not in the epididymal fat pad, of the diabetic animals. N-Acetyl-beta-D-glucosaminidase was elevated in plasma, liver and heart, but not in the kidney of the treated animals. Renal alpha-galactosidase and beta-glucosidase were depressed, whereas beta-galactosidase and alpha-glucosidase remained essentially normal. These features indicated that there were considerable differences between the biochemical disorders associated with streptozotocin-diabetes in the Chinese hamster and the published observations in the rat.