Response of plasma somatostatin-like immunoreactivity to the administration of alloxan in dogs.

The present study was designed to examine the effects of intravenously injected alloxan (75 mg/kg) upon plasma somatostatin-like immunoreactivity (SLI), glucagon (IRG), insulin (IRI) and glucose levels in 6 dogs. Within 2 hours of the injection of alloxan, SLI and IRI levels decreased significantly below their respective baselines, while IRG and plasma glucose concentrations increased. At 8 hours SLI levels had increased significantly by 55 pg/ml, together with a rise in IRI and a decrease in IRG and glucose concentrations. After 24 hours, marked hyperglycemia and hyperglucagonemia had developed whereas SLI levels were not different from preinjection values.     

Response of extrapancreatic immunoreactive glucagon to intraluminal nutrients in pancreatectomized dogs

To investigate the response of extrapancreatic glucagon to intraluminal stimuli, nutrients were administered to normal and pancreatectomized dogs through a stomach tube in a fully conscious state after an overnight fast. Plasma immunoreactive glucagon was determined with antisera specific and nonspecific to glucagon and was designated as IRG and total IRG, respectively. Oral glucose load elicited a decrease in plasma IRG and a remarkable rise of plasma total IRG in a group of 6 pancreatectomized dogs, as in the control dogs. When arginine was given, both plasma IRG and total IRG significantly increased in a group of 5 pancreatectomized dogs, while only total IRG rose significantly in the normal control dogs. Butter load did not reveal any changes in plasma IRG and total IRG in a group of 5 pancreatectomized dogs, whereas only total IRG increased in the normal control dogs. It is concluded that extrapancreatic glucagon responds to intraluminal administration of nutrients, as pancreatic glucagon does. In addition, gut glucagon-like immunoreactivity increased following glucose or arginine ingestion in pancreatectomized dogs. Furthermore, the failure in response of plasma IRG and total IRG to butter load in pancreatectomized animals suggests that its intraluminal hydrolysis is important in the secretion of extrapancreatic immunoreactive glucagon.     

Effect of acute ethanol load on plasma immunoreactive insulin and glucagon.

The effect of a single large dose of ethanol (5 mg/kg body weight) on plasma glucagon (IRG) and insulin (IRI) concentrations was studied in rats fasting for 24 hr. Hepatic cAMP concentration and blood glucose were also estimated and correlated with hormonal changes. Plasma IRG concentrations had doubled by the first sampling time (2 hr) and remained at this level up to 16 hr after ethanol administration. Plasma IRI concentrations were not affected by ethanol. Hepatic cAMP concentrations reflected changes in the plasma insulin/glucagon ratio, which seems to be the major determining factor for hepatic cAMP even during ethanol oxidation. Hypoglycemia was not found in the ethanol group during the experimental period of 24 hr, and it was therefore concluded that ethanol may stimulate glucagon secretion in rats even without concurrent hypoglycemia. Possible mechanisms for the action of ethanol on the endocrine pancrease are discussed.     

The effect of long-distance running on plasma immunoreactive glucagon levels

Twelve highly conditioned long-distance runners were studied to determine the effects of marathon (42 km) and 10,000 m running on plasma immunoreactive glucagon (IRG), serum immunoreactive insulin (IRI), and serum glucose (G) levels. Blood samples were drawn just prior to and immediately upon completion of the run. Marathon running resulted in no significant change in G, IRI, or IRG levels. After running 10,000 m, plasma IRG levels did not change significantly, while IRI and G increased significantly. In evaluating the pooled data from both runs, a significant inverse correlation was observed between delta G and delta IRG. This relationship between delta G and delta IRG suggests that glucagon plays a role in maintaining normal blood glucose levels during strenuous exercise.     

Lack of effect of thyrotropin-releasing hormone (TRH) on the peripheral plasma levels of pancreatic glucagon in man

Based on the fact that human pancreas has thyrotropin-releasing hormone (TRH) immunoreactivity and bioactivity, we studied the effect of TRH on peripheral plasma levels of pancreatic glucagon (IRG) and insulin (IRI) in healthy subjects. During the infusion of 400 micrograms TRH for 120 min basal plasma IRI and IRG levels did not change significantly. In addition, intravenous infusion of 400 micrograms TRH did not affect the increments in the plasma IRG levels and the decrements in the blood glucose during insulin hypoglycemia.     

Glucagon and insulin relationships in genetically diabetic (db/db) and in streptozotocin-induced diabetic mice.

An inappropriate molar ratio of circulating insulin to glucagon is frequently associated with the metabolic alterations accompanying diabetes mellitus. Plasma immunoreactive insulin (IRI) and immunoreactive glucagon (IRG) levels were determined and the IRG:IRI ratio calculated at various intervals in overt diabetes in genetically diabetic (db/db) and in streptozotocin-treated mice. Plasma IRI levels in genetic mutants are elevated at nine weeks of age, but are comparable to values found in lean littermates by 21 weeks. The presence of a prevailing hyperglucagonemia is established for the first time in the intact db/db mice. Streptozotocin diabetics are found to have characteristically low plasma IRI and high plasma IRG values. The hormonal imbalance present in these two experimental animal models is accentuated when the data are expressed as the IRG:IRI ratio, which is seen to increase with the progression of diabetes.     

Pancreatic glucagon secretion during a short period of hemorrhage in anesthetized dogs

Glucagon has been implicated in the hormonal metabolic response to hemorrhage. However, evidence for this has been obtained largely from observations of circulating plasma glucagon concentration. A clear increase in the pancreatic glucagon secretion remains to be demonstrated. Plasma concentrations of pancreatic immunoreactive glucagon (IRG) and insulin (IRI) were determined in portal venous and aortic blood, and plasma glucose in aortic blood. Dogs were bled (approximately 15 mL/kg) until aortic systolic blood pressure dropped to approximately 50% (70.5 +/- 8.1 mmHg, n = 7) (1 mmHg = 133.32 Pa) of its control value (135 +/- 7.1 mmHg, n = 7), and the hemorrhagic hypotension was maintained for 10 min. The net portal venous IRG delivery rate rose significantly and continued to increase during the hemorrhagic hypotension despite a significant fall in the portal venous blood flow. Aortic IRG increased significantly along with the increase in portal venous IRG delivery rate (r = 0.838, n = 42, p less than 0.01). The portal venous delivery rate of IRI decreased significantly in response to hemorrhage. The aortic IRG/IRI concentration ratio increased significantly during the hemorrhage-induced hypotension. Aortic glucose concentration increased significantly 5 min after hemorrhage and continued to rise until the end of the hemorrhagic hypotension. The present study demonstrates that the secretion of pancreatic glucagon actually increases during the early phase of hemorrhage. The results also indicate that the increase in aortic IRG during the hemorrhagic hypotension is due to the increased pancreatic glucagon secretion. It is suggested that the pancreatic glucagon may be involved in the early hyperglycemic response to hemorrhage.     

Islet-activating protein (IAP)-induced adrenergic modulation of pancreatic A and B cell in dogs

Islet-activating protein (IAP) is a substance purified from the culture medium of Bordetella pertussis, and its main action is characterized by the enhancement of secretory response to glucose and other stimuli in pancreatic islet. In this experiment, the effect of IAP on epinephrine-induced secretion of immunoreactive insulin (IRI) and glucagon (IRG) was investigated in normal dogs. Epinephrine suppressed IRI secretion and it had a little increment to IRG secretion in control group, while IRI and IRG secretions were significantly increased by epinephrine in IAP pretreated group. Using beta-blocker (Propranolol) with epinephrine, these increments of IRI and IRG secretions in IAP pretreated group were abolished. However, using alpha-blocker (Phentolamine) with epinephrine, these secretions of IRI and IRG in IAP pretreated group were much more increased than epinephrine alone induced secretions. Blood glucose levels were lower in IAP pretreated group than in control group throughout the loading tests in all of the experiments. These findings suggest that (1) IAP decreases blood glucose level and (2) IAP enhances epinephrine-induced secretion of insulin and glucagon by acceleration of beta-adrenergic effect and by reduction of alpha-adrenergic suppression in dogs.     

A case with glucagonoma syndrome--heterogeneity of glucagon and insulin

The heterogeneity of glucagon and insulin in plasma and tissue extracts from a 57-year-old female with glucagonoma syndrome with surgically and autopsy verified islet-cell tumors was studied by Bio-Gel P-10 filtration. The preoperative plasma immunoreactive glucagon (IRG) level was 20.2 ng/ml, and plasma glucagon-like immunoreactivity(GLI) 25.8 ng/ml. The column chromatography of the preoperative plasma revealed three or four IRG components and four GLI components. Among these, peak II, the large glucagon immunoreactivity (LGI) peak, considered a candidate for proglucagon, was prominent, along with peak III. The resected metastatic liver tumor contained an enormous amount of IRG and an appreciable amount of immunoreactive insulin (IRI), indicating that the elevated plasma IRG was mainly of tumor origin. The IRG pattern of the tumor tissue extract revealed a small quantity of IRG in peaks I and II, and a large amount in peak III; control pancreatic tissue extract manifested a similar elution pattern. The IRI elution pattern of the tumor tissue extract revealed two major IRI peaks which migrated close to the elution volume of cytochrome C and insulin, respectively. This is a quite different pattern from the control pancreatic tissue extract in which the RI peak was localized in the elution volume of the insulin. We conclude that the present metastatic liver tumor produced not only enormous amounts of glucagon but heterogeneous peptides which contained immunological insulin determinants within their.     

Effects of serotonin, of its biosynthetic precursors and of the anti-serotonin agent metergoline on the release of glucagon and insulin from rat pancreas.

We have evaluated the effect of serotonin (5-HT) and of its biosynthetic precursors 5-Hydroxytryptophan (5-HTP) and tryptophan (TRP) on the release of immunoreactive glucagon (IRG) and insulin (IRI) from isolated islets and pieces of pancrease of the rat. In isolated islets, 5-HT inhibited the IRI response to a high glucose concentration (3.0 mg/ml), without affecting the IRG response to either a low (0.5 mg/ml) or a high glucose concentration; TRP stimulated the IRG and IRI response to the low glucose concentration, while 5-HTP was ineffective. When pieces of pancreas were used, 5-HT and 5-HTP inhibited IRG response to both glucose concentrations, while IRI release was inhibited only by 5-HT. The anti-5-HT agent metergoline enhanced the release of IRG and IRI by pieces of pancreas at both glucose concentrations. The results indicate that exogenous and endogenous 5-HT inhibit basal as well as glucose-mediated IRG and IRI release; that isolated islets are less sensitive than pieces of pancreas to the inhibitory effect of 5-HT and that TRP acts as an amino acid and not as a precursor of 5-HT.     

Increase by somatostatin of the arginine induced rise in blood glucose in untreated insulin requiring diabetics.

We have demonstrated previously that cyclic somatostatin (GH-RIH) exerts a diabetogenic action in healthy subjects. To further examine the impact of this phenomenon studies of blood glucose (BG), immunoreactive insulin (IRI), glucagon (IRG) and growth hormone (GH) were performed in insulin requiring diabetics (n = 6) receiving i.v. arginine (0.5 g/kg) both in the absence and presence of i.v. GH-RIH (500 microgram/h). The infusion of GH-RIH-resulted in a persistent diminution in plasma IRI, IRG and GH. BG fell during i.v. GH-RIH during the initial 30 min and was below control values up to 45 min after initiation of i.v. arginine, but subsequently exceeded control levels (p less than 0.05 - less than 0.025). The excess rise in BG occurred in spite of suppression by somatostatin of the ariginine induced release of IRG, IRI and GH. A fall in BG was seen following cessation of i.v. GH-RIH and during a rebound of insulin release with glucagon levels remaining in the basal range. These findings indicate a diabetogenic action of somatostatin also in insulin requiring diabetics as long as some residual capacity for insulin release is retained.     

Changes in plasma glucose, insulin (IRI), glucagon (IRG) and free fatty acids (FFA) following alanine loading in hyperthyroid patients

The responses of plasma glucose, insulin (IRI), glucagon (IRG) and free fatty acids (FFA) following alanine loading (0.1 g/kg) were observed in 9 control subjects and 7 hyperthyroid patients, before and after restoration of thyroid function to normal. Despite the persistence of impaired glucose response to alanine, the blunted IRI and IRG responses in the hyperthyroid state were improved with a significant reduction in fasting IRI and IRG after treatment. Markedly increased FFA following alanine loading in hyperthyroid patients was reduced after treatment, but the FFA concentration remained greater than in the control subjects. We tentatively conclude that the impaired alpha and beta-cell responses to alanine were temporarily induced by the direct and/or indirect effects of thyroid hormone excess.     

Effect of subcutaneous pancreatic tissue transplants on streptozotocin-induced diabetes in rats. II. Endocrine and metabolic functions.

The present study examines the effect of subcutaneous pancreatic tissue grafts (SPTG) on endocrine and metabolic functions in streptozotocin (STZ)-induced diabetic rats using radioimmunoassay and biochemical techniques. SPTG survived even after 15 weeks of transplantation and significantly improved the weight of STZ-diabetic rats over a 15-week period. Although blood glucose-, cholesterol-, and glycosylated-haemoglobin (GHb) levels were not significantly lower in STZ-diabetic rats treated with SPTG, the values of these biochemical parameters were lower than those in untreated diabetic rats. Plasma and pancreatic immunoreactive C-peptide (IRCP) levels did not improve after SPTG (IRCP expressed as mean +/- standard deviation were 0.22 +/- 0.07, 0.072 +/- 0.02 and 0.08 +/- 0.03 pg ml-1 in the plasma non-diabetic diabetic and treated rats respectively, while IRCP levels in the pancreas of the non-diabetic, diabetic and treated rats were 433.8 +/- 0.1, 22.9 +/- 0.01 and 10.4 +/- 0.01 pg mg tissue-1 respectively). SPTG, however, improved plasma immunoreactive insulin (IRI) levels in both plasma and pancreas. IRI values in plasma were 54.7 +/- 13.6, 18.0 +/- 5.0 and 22.1 +/- 4.3 microUI ml-1 in non-diabetic, diabetic and treated rats respectively and were 277.3 +/- 37.1, 14.7 +/- 1.8 and 30.3 +/- 15.9 microIU micrograms tissue-1 in the pancreas of non-diabetic, diabetic and treated rats respectively. There was improvement in immunoreactive glucagon (IRG) levels after SPTG. IRG values in the plasma of non-diabetic, diabetic and treated rats were 147.0 +/- 10.7, 408.0 +/- 76.5 and 247.7 +/- 3 pg ml-1 respectively whereas, IRG measured in the pancreas was 1642.25 +/- 424.23, 1899.0 +/- 290.4 and 1714.1 +/- 301.98 pg micrograms tissue-1 in non-diabetic, diabetic and treated rats, respectively. The pancreas:plasma ratio of pancreatic hormones was deranged in untreated diabetes but improved after SPTG. In conclusion, SPTG significantly improved the weight gain, pancreatic insulin content, plasma IRG and pancreas: plasma ratio of IRCP, IRI and IRG. It also reduced blood glucose-, cholesterol-, and glycosylated-hemoglobin levels in STZ-diabetic rats.     

Plasma glucagon, insulin and glucose responses to intravenous arginine infusion in the rat

Plasma glucagon (IRG), insulin and glucose responses to intravenous arginine infusion in the rat were studied. Three doses of arginine hydrochloride were infused into fasted rats: 0.2 gm/kg b.w., 0.5 gm/kg b.w., and 1 gm/kg b.w. The 0.2 gm/kg dose did not result in significant elevation of plasma IRG or insulin. Both the 0.5 and 1 gm/kg doses produced a significant increase in glucagon and insulin levels within 5 minutes of starting the infusion. The 1 gm/kg dose was most effective in stimulating secretion of both hormones. This dose produced a 250% rise in the plasma IRG compared to 80% peak rise with the 0.5 gm/kg dose (p less than .01) and 1055% rise in insulin levels compared to a peak level of 225% above baseline with the 0.5 gm/kg dose (p less than .001). These results demonstrate the effectiveness of intravenous arginine in the stimulation of glucagon and insulin secretion in the rat.     

Important role of glucagon during exercise in diabetic dogs

To define the role of immunoreactive glucagon (IRG) during exercise in diabetes, 12 insulin-deprived alloxan-diabetic (A-D) dogs were run for 90 min (100 m/min, 12 degrees) with or without somatostatin (St 0.5 microgram . kg-1 . min-1). Compared with normal dogs, A-D dogs were characterized by similar hepatic glucose production (Ra), lower glucose metabolic clearance, and higher plasma glucose and free fatty acid levels during rest and exercise. In A-D dogs IRG was greater at rest and exhibited a threefold greater exercise increment than controls, whereas immunoreactive insulin (IRI) was reduced by 68% at rest but had similar values to controls during exercise. Basal norepinephrine, epinephrine, cortisol, and lactate levels were similar in normal and A-D dogs. However, exercise increments in norepinephrine, cortisol, and lactate were higher in A-D dogs. When St was infused during exercise in the A-D dogs, IRG was suppressed by 432 +/- 146 pg/ml below basal and far below the exercise response in A-D controls (delta = 645 +/- 153 pg/ml). IRI was reduced by 1.8 +/- 0.2 microU/ml with St. With IRG suppression the increase in Ra seen in exercising A-D controls (delta = 4.8 +/- 1.6 mg . kg-1 . min-1) was virtually abolished, and glycemia fell by 104 to 133 +/- 37 mg/dl. Owing to this decrease in glycemia, the increase in glucose disappearance was attenuated. Despite the large fall in glucose during IRG suppression, counterregulatory increases were not excessive compared with A-D controls. In fact, as glucose levels approached euglycemia, the increments in norepinephrine and cortisol were reduced to levels similar to those seen in normal exercising dogs. In conclusion, IRG suppression during exercise in A-D dogs almost completely obviated the increase in Ra, resulting in a large decrease in plasma glucose. Despite this large fall in glucose, there was no excess counterregulation, since glucose concentrations never reached the hypoglycemic range.     

Modulation of A and B cell functions by tolbutamide and arginine in the pancreas of thiamine-deficient rats

The effects of administration of glucose orally and tolbutamide or arginine intravenously on insulin and glucagon secretion and blood glucose level were studied in normal and thiamine-deficient rats. In thiamine deficiency, insulin secretion and glucose tolerance were impaired during glucose ingestion. Tolbutamide decreased the blood glucose level in both control and thiamine-deficient rats but its stimulatory effect on insulin secretion was minimal in thiamine-deficient rats unlike the control animals. Arginine did not alter substantially the blood glucose or insulin in thiamine-deficient rats, whereas it increased the insulin level in control rats. The fasting plasma glucagon level was high in thiamine deficiency. Tolbutamide increased the plasma glucagon in control rats, but did so only marginally in thiamine-deficient rats. Arginine also increased the glucagon secretion throughout the period of study in control rats. In thiamine-deficient rats the glucagon secretion was pronounced only after 20 min of arginine administration. These results suggest that an unimpaired glucose metabolism is a prerequisite to induce proper insulin secretion. Only proper insulin secretion can check the glucagon secretion rather than the increased glucose level. Hypoglycemia can induce glucagon secretion independent of the insulin level.     

Effect of phenformin on the response of plasma intestinal glucagon-like immunoreactivity (GLI) to oral glucose in gastrectomized subjects.

The effect of phenformin (DBI) on the plasma intestinal glucagon-like immunoreactivity (GLI) and pancreatic glucagon (IRG) responses to oral and intravenous glucose loads were studied in 26 gastrectomized subjects, using a cross-reacting and an IRG-specific anti-serum. The drug produced no significant changes in fasting GLI and IRG levels. Thirty minutes after oral glucose alone, the total GLI level rose to a peak of 1.55 +/- 0.17 ng/ml in the untreated subjects and to a maximum level of 1.67 +/- 0.18 ng/ml in the DBI-pretreated subjects. However, the mean GLI levels obtained 120 and 180 min after oral glucose were significantly higher after treatment with DBI. The blood sugar and IRI responses to oral glucose were lowered significantly by DBI pretreatment. DBI did not alter the glucose, IRI, IRG and GLI response to intravenous glucose. These results suggest that the release of intestinal GLI is not related to the intestinal absorption of glucose.     

Effects of histamine, of histidine and of anti-histaminic agents on the release of glucagon and insulin from the rat pancreas.

We have studied the effect of histamine (HA) and histidine (HIS) on the release of immunoreactive glucagon (IRG) and insulin (IRI) by isolated rat islets and pieces of pancreas. In isolated islets, HA and HIS stimulated IRG release at a glucose concentration of 3.0 mg/ml and IRI release at a glucose concentration of 0.5 mg/ml. In pieces of pancreas incubated in the presence of glucose (3.0 mg/ml), HA at a 2mM concentration stimulated IRG release and had no effect on the release of IRI; however, when the concentration of HA was doubled (4 mM), an inhibition of IRI release could also be demonstrated. HIS was ineffective. Perphenazine and dexchlorpheniramine, two anti-histaminic agents, inhibited IRG and stimulated IRI release. These results indicate that histamine, whether endogenous or exogenous, directly stimulated IRG and inhibits IRI release and suggest that some of the in vivo effects of histamine, such as hyperglycemia and lipid mobilization, may be mediated, at least in part, by these endocrinologic effects.     

Effects of glucosamine on insulin and glucagon secretion in dogs and ducks.

The effects of infusion of glucosamine on immunoreactive glucagon (IRG) and insulin (IRI) secretion were studied in dogs and ducks. During systemic infusion of glucosamine, hyperglycemia developed and insulin secretion was inhibited in both species. An immediate and sustained elevation of peripheral IRG levels was induced in ducks but a transient rise, detectable only in the pancreatic vein blood, was provoked in dogs. Suppression of insulin release and stimulation of glucagon release may be mediated by the inhibition of glucose utilization in beta- and alpha-cells. The very prompt response of IRG in ducks may imply that glucosamine has a specific stimulating effect on the alpha-cells of ducks. Intrapancreatic administration of glucosamine in dogs, however, failed to elicit the rise of IRG, although insulin secretion was inhibited. Thus, it is suggested that the systemic administration of glucosamine in dogs may stimulate IRG secretion by some indirect effect. In one dog, however, a sustained rise of the pancreatic vein IRG was observed. Thus, the possibility cannot be ruled out that the difference in IRG response to glucosamine in dogs and ducks is quantitative rather than qualitative. Glucagon release by glucosamine may provide an additional factor to the hyperglycemic effect of glucosamine, in addition to its effect to suppress insulin release as well as its direct inhibitory effect on glucose utilization in tissues.     

Rate dependent stimulation of insulin and glucagon but not gastrin and somatostatin release during the intestinal phase of a meal

Previous studies have indicated a possible influence of gastric emptying on postprandial pancreatic endocrine function and the present study was designed to determine if the rate at which nutrients enter the small intestine may play a role in the postprandial regulation of insulin, glucagon, somatostatin and gastrin release in conscious dogs. In response to an intraduodenal instillation of a liver extract--sucrose test meal postprandial insulin and glucagon levels increased significantly with increasing infusion rates of the test meal, whereas somatostatin and gastrin levels did not change. The rise of the endocrine factors preceded any increase of peripheral vein plasma glucose levels. The present data demonstrate that during the intestinal phase of a meal the rate of nutrient entry into the duodenum favours insulin and glucagon but not somatostatin and gastrin release. This mechanism could be of importance in the regulation of nutrient homeostasis during the ingestion of certain carbohydrate containing meals.