Oxytocin increases extrapancreatic glucagon secretion and glucose production in pancreatectomized dogs

Infusion of oxytocin into normal dogs increases plasma levels of insulin and glucagon and glucose production and uptake. To determine whether infused oxytocin also increases glucagon secretion from extrapancreatic sites, pancreatectomized dogs, off insulin for 18 hr, were infused with oxytocin and plasma glucagon, and glucose production and uptake were measured using the [6-3H]glucose primer-infusion technique. The diabetic dogs, in the control period, had elevated plasma glucose and glucagon levels, an increased rate of glucose production, and a relative decrease in glucose uptake (decreased clearance). Infusion of oxytocin (500 microU/kg/min) caused a rise in plasma glucagon and glucose levels, increased glucose production, and further decreased glucose clearance. It is concluded that oxytocin can stimulate secretion of extrapancreatic glucagon, which contributes to the increased glucose production.     

Response of gastric inhibitory polypeptide (GIP) to oral administration of nutrients in normal and pancreatectomized dogs

In order to clarify the response of plasma gastric inhibitory polypeptide (GIP) to various nutrients and to investigate the relationship between the pancreas and GIP secretion, an experimental study was performed using normal and pancreatectomized dogs. Oral administration of glucose (2 g/kg) or butter (2 g/kg) resulted in an increase of plasma GIP in five normal dogs. In contrast, oral administration of arginine (1 g/kg) did not produce any discernible changes in plasma GIP in normal dogs. In a group of nine pancreatectomized dogs, the fasting level of plasma GIP did not differ from that of the control group. Furthermore, glucose ingestion in the pancreatectomized group resulted in the same pattern and the same degree of change in plasma GIP as it did in the normal controls. In contrast, plasma GIP did not change at all following fat loading in the pancreatectomized group. However, butter with pancreatic enzymes elicited a significant rise of plasma GIP in the pancreatectomized dogs. The present study indicates that plasma GIP increases following oral administration of glucose or fat but not arginine. Furthermore, it is demonstrated that GIP secretion following fat ingestion occurs only after fat digestion by pancreatic enzymes. In addition, the findings observed in the present study do not support the existence of feedback effect of insulin on GIP secretion.     

Kaluresis independent K-homeostasis: glucagon and B receptor blockade in pancreatectomized dogs

Seventy minutes post pancreatectomy, in dogs that are K loaded - made abruptly hyperkalemic and "life threatened" - by infusion with 2 mEgKC1/kg-/hr until prelethal ECG changes of hyperkalemic cardiotoxicity appear, a kaluresis independent K homeostatic mechanism transfers about 2/3 of administered K to intracellular fluid. Treatment of K loaded pancreatectomized dogs with glucagon or a B receptor blockading dosage of propranolol does not alter the proportion transferred, but treatment with glucagon and propranolol reduces it. It appears that in pancx dogs there is a reciprocal relation between insulin and B receptor mediated K transfer and that glucagon is involved in activity of the kaluresis independent K homeostatic mechanism.     

The effect of insulin-induced hypoglycaemia on the secretion of glucagon and hepatic glucose production in pancreatectomized dogs

The concentration of plasma glucose in insulin deprived pancreatectomized dogs was decreased from the basal 385 +/- 44 to 65 +/- 12 mg/dL by the infusion of 7 mU X kg-1 X min-1 insulin. During the infusion, the plasma concentration of immunoreactive glucagon (IRG) did not change and hepatic glucose production was decreased. This is in contrast to earlier findings in alloxan diabetic dogs in which plasma IRG decreased in hypoglycaemia. The hypothesis is put forward that, in contrast to pancreatic alpha cells in which the effect of insulin prevails, neither insulin nor a decrease in the ambient concentration of glucose exerts any effect on the secretion of glucagon from extrapancreatic alpha cells.     

Cardiovascular response to glucagon in hypovolemic dogs.

Glucagon in a dose of 50 mug/kg body weight was studied for its cardiovascular effects in hypovolemic dogs in which coronary blood flow was reduced to an average 40% of its control value and cardiac depression was evident. Myocardial contractility, as judged mainly by dP/dt and acceleration of aortic blood flow, was brought to a normal level for a short time. Systemic and coronary vascular resistances were markedly reduced. These effects were similar in normovolemic dogs. The inotropic, chronotropic, and peripheral vascular effects of glucagon can be evoked also in hypovolemic dogs in which coronary blood flow is less than normal and myocardial metabolism is impaired.     

Response of pancreatic immunoreactive somatostatin to arginine

Perfusion of isolated dog pancreases with arginine (20 mM) was associated with a prompt and sustained increase in immunoreactive somatostatin (IRS) in the venous effluent while insulin and glucagon rose promptly but soon receded from their peak levels. These results are compatible with a postulated feedback relationship between somatostatin-, glucagon-, and perhaps insulin-secreting cells of the islets in which somatostatin, stimulated by local glucagon, restrains glucagon secretion and perhaps glucagon-mediated insulin release as well.The demonstration that D-cells of the pancreatic islets contain immunoreactive somatostatin (1, 2, 3) which is probably biologically active (4), and are situated topographically between the A-cells and B-cells in the heterocellular region of the islet (5) has suggested a functional role for these components of the islet of Langerhans (6). In view of the inhibitory action of somatostatin upon both insulin and glucagon secretion (7, 8, 9), it was postulated that the D-cell might serve to restrain glucagon and/or insulin secretion (6). We have since reported that the release of IRS from the isolated dog pancreas increases promptly during the perfusion of high concentrations of glucagon whereas high concentrations of insulin do not appear to stimulate IRS release (10). In this study we examine the effect of perfusion with arginine, a potent stimulus of both glucagon and insulin secretion, upon pancreatic IRS release.     

Size heterogeneity of immunoreactive glucagon during bile-duct obstruction in the rabbit

The influence of bile-duct obstruction upon basal plasma glucagon levels and the relationship between glucagon-like substance in bile and postobstructive plasma glucagon were examined in the rabbit. Immunoreactive glucagon (IRG) was measured with antiserum 30 K (Unger). Bile-duct obstruction was followed by a prompt rise within 60 minutes in plasma IRG which was four times the basal value, but had little influence on plasma immunoreactive insulin and blood sugar. The biliary IRG and the elevated plasma IRG during bile-duct obstruction were filtered with a Bio-Gel P-10 column. Most of the postobstructive plasma IRG appeared in the void volume area (plasma large IRG), while almost all of the biliary IRG was recovered in the position equivalent to approximately 2000 daltons (biliary IRG 2000). Both IRGs of different molecular sizes revealed similar dilution curve in radioimmunoassay to that with porcine glucagon. After incubation of bile with preobstructive plasma, the IRG elution profile of the mixture contained an increased amount of large molecular size IRG similar to that of postobstructive plasma in regard to 30K specificity and elution position. The disappearance of IRG in the void volume area was observed when the bile-plasma mixture or the postobstructive plasma was filtered with acidic buffer. These results suggest that plasma large IRG contributing to hyperglucagonemia during bile-duct obstruction may be derived from biliary IRG 2000.     

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.     

Long-term normoglycemia in pancreatectomized dogs transplanted with frozen/thawed pancreatic islets

Storage of pancreatic islets by cryopreservation would greatly facilitate a large scale program of clinical islet transplantation. We report success on long-term follow-up with autotransplantation of frozen/thawed canine pancreatic fragments. Total pancreatectomy and islet isolation by collagenase ductal perfusion and mechanical disruption preceded either acute autotransplantation or cryogenic preservation prior to autotransplantation. Cryopreservation was by dimethylsulfoxide equilibration, cooling at 0.25 degrees C/min to -75 degrees C, storage in liquid N2 and thawing at 3.5 degrees C/min. Four of five acutely autotransplanted dogs remained normoglycemic for 20 months, with three of four maintaining normal K values on intravenous glucose tolerance test (IVGTT) and nondiabetic values on oral GTT. Four of four dogs transplanted with frozen/thawed islets remained normoglycemic for 15 months with three of four maintaining nondiabetic IV GTT K values and normal oral GTTs for 15 months. Both acutely transplanted and frozen/thawed islets are capable of maintaining long-term metabolic control. Cryopreservation preserved viability of sufficient canine pancreatic islets to reverse diabetes with autotransplantation. Function of the frozen-thawed islets showed minimal deterioration during a follow-up of 15 to 18 months.     

Properties of immunoreactive glucagon fractions of canine stomach and pancreas.

The present study was designed to identify the physicochemical, immunologic, and biologic properties of the immunoreactive glucagon (IRG) moieties of canine gastric fundus and to compare them with those of the canine pancreas. Acid-alcohol extracts of the gastric fundus and pancreas of dogs were subjected to Bio-Gel P-10 chromatography, The elution profiles of extracts of both organs revealed IRG peaks in the Mr = 2,000 3,500, and 9,000 zones; in the gastric extracts, a void volume peak was also present. On the basis of Sephadex G-150 rechromatography and sucrose density gradient ultracentrifugation the latter IRG was estimated to have a Mr = 65,000. Incubation of fundic IRG65,000 in 8 M urea failed to alter its elution position. Its pI was 6.4, while fundic IRG3,500 had a pI of 6.15 and pancreatic glucagon 6.25.Fundic IRG9,000 had a pI of 4.5 and pancreatic IRG9,000 4.65. Dilution curves of these three fundic and two pancreatic IRGs were parallel to crystalline beef-pork glucagon. The glycogenolytic activity of fundic IRG3,500 and IRG65,000, measured in the isolated rat liver system, was not different from that of immunoequivalent amounts of dog pancreatic glucagon or crystalline beef-pork glucagon. Both fundic and pancreatic IRG9,000 were devoid of glycogenolytic activity and lacker adenylate cyclase stimulating activity and 125I-glucagon displacing activity when tested on partially purified rat liver membranes. Fundic IRG65,000, however, stimulated adenylate cyclase and displaced 125I-glucagon to the same degree as immunoequivalent amounts of pancreatic glucagon. Fundic IRG3,500 was more active than pancreatic glucagon in stimulating adenylate cyclase activity. This was not clearly attributable to differences in binding to liver cell membranes.