The effects of ingested and infused glucose upon circulating glucagon-like immunoreactivity (GLI) were compared in 14 triply catheterized conscious dogs. Within 60 min after the intraduodenal administration of 2 g/kg of glucose, the mean level of glucagon-like immunoreactivity in the vena caval plasma more than doubled, whereas after intravenous infusion of the same dose over a 90 min period no change in the mean vena caval level was observed; during glucose infusion mean glucagon-like immunoreactivity in the pancreatic venous effluent declined, suggesting that hyperglycemia suppresses rather than stimulates pancreatic glucagon secretion. To determine if the rise in glucagon-like immunoreactivity that occurs during glucose absorption was of pancreatic origin, the effect of pancreatectomy performed 1 hr after the intraduodenal administration of glucose was determined. Although circulating insulin disappeared after resection of the pancreas, the level of glucagon-like immunoreactivity continued to rise, establishing its extrapancreatic origin. In other experiments, measurements of Glucagon-like immunoreactivity in plasma obtained simultaneously from pancreaticoduodenal and mesenteric veins and from the vena cava revealed the increment after intraduodenal glucose loading to be greatest in the mesenteric vein in 8 of 12 experiments, favoring the gut as the likely source of the rise. To characterize gut glucagon-like immunoreactivity, acid-alcohol extracts of canine jejunum were compared with similar glucagon-containing extracts of canine pancreas with respect to certain physical and biological properties. On a G-25 Sephadex column the elution volume of the jejunal immunoreactivity was found to be smaller than that of glucagon, which suggested a molecular size at least twice that of pancreatic glucagon. Furthermore, the in vivo and in vitro biological activities of the eluates containing jejunal glucagon-like immunoreactivity appeared to differ from those of eluates containing pancreatic glucagon. The jejunal material lacked hyperglycemic activity when injected endoportally into dogs, was devoid of glycogenolytic activity in the isolated perfused rat liver, and did not increase hepatic 3',5' cyclic adenylate in the perfused liver; however, like glucagon it appeared to stimulate insulin release. It seems quite clear the material in intestinal extracts either is a different substance or a different form from that of true pancreatic glucagon, although it crossreacts in the radioimmunoassay with antibodies to glucagon. It is concluded, (a) that hyperglycemia does not stimulate and probably suppresses the secretion of pancreatic glucagon; (b) that during intestinal absorption of glucose, a rise in glucagon-like immunoreactivity occurs; (c) this immunoreactivity is derived from an extrapancreatic site, probably the gut; (d) that the glucagon-like immunoreactivity extractable from jejunum is not the same as pancreatic glucagon but is a larger molecule devoid of hyperglycemic and glycogenolytic activity, a cross-reactant in radioimmunoassay for glucagon; and (e) that the eluate in which jejunal immunoreactivity is contained can stimulate insulin release in conscious dogs.

Animals↗

PubMed1968

[Diagnostic value of the chemical determination of urinary estrogens and pregnandiol].

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Adolescent↗

PubMedDate not supplied

Repaglinide preserves nutrient-stimulated biosynthetic activity in rat pancreatic islets.

The meglitinide analogue repaglinide is a novel non-sulphonylurea insulinotropic agent which, like hypoglycaemic sulphonylureas, causes the closing of ATP-sensitive K+ channels in islet cells. We have now explored the effect of repaglinide upon proinsulin biosynthesis in rat pancreatic islets. Groups of eight islets each were incubated for 90 min in the presence of L-[4-(3)H]phenylalanine (4 microM) and glucose (2.8 or 16.7 mM), in the absence or presence of repaglinide (10 microM). A rise in glucose concentration caused a four-fold increase of the incorporation of L-[4-(3)H]phenylalanine into TCA-precipitable material. Repaglinide failed to adversely affect protein biosynthesis, whether at low or high glucose concentrations. Further characterization of the biosynthetic response was achieved by separation of the tritiated peptides by gel filtration. In the absence of repaglinide, the (pro)insulin/total ratio of tritiated peptides averaged 33.3 +/- 10.2 and 58.7 +/- 1.7% (n = 6 in both cases) at 2.8 and 16.7 mM D-glucose, respectively. Repaglinide again failed to significantly affect such ratios. In conclusion, repaglinide may offer the advantage over hypoglycaemic sulphonylureas of preserving nutrient-stimulated biosynthetic activity in pancreatic islet cells.

Animals↗

PubMedDate not supplied

Lipolytic action of glucagon-like peptides in isolated rat adipocytes.

The lipolytic effect of GLP-1(1-36)-amide, GLP-1(7-36) amide and GLP-2 [proglucagon(126-159)] has been studied in isolated rat adipocytes. Glycerol release and cyclic AMP content were measured after incubation of adipocytes with GLPs and results have been compared with those obtained in the presence of glucagon. GLP-1(7-36)-amide and GLP-1(1-36)-amide at 10(-8), 10(-7) and 10(-6) M concentrations activated glycerol release, the truncated peptide having a more potent effect. On the other hand, GLP-2 had no effect on glycerol release. Also, it has been found that 10(-6) M GLP-1(7-36)-amide increases cyclic AMP content in adipocytes and does not compete with glucagon binding. These results demonstrate that GLP-1(7-36)-amide has a lipolytic effect on isolated rat adipocytes through different receptors than glucagon.

Adipose Tissue↗

PubMedDate not supplied

Carbohydrate metabolism and plasma levels of insulin and glucagon in patients with atherosclerotic vascular disease.

In non-obese, non-diabetic patients suffering acute myocardial infarction, angina pectoris, previous myocardial infarction and peripheral vascular disease, the plasma levels of glucose, insulin, C-peptide and glucagon were determined in basal condition and during an intravenous glucose tolerance test. In the four groups there was a high frequency of glucose intolerance. Basal hyperinsulinism was present in all groups; in groups; in those which maintained normal glucose tolerance there was a high B-cell response to the sugar. Basal hyperglucagonemia was found in the early stage of acute ischemic heart disease, in patients with previous myocardial infarction and in those with peripheral vascular disease. The elevated plasma glucagon levels may play a role in the complex disturbance of carbohydrate metabolism present in patients with atherosclerotic vascular disease.

Adult↗

PubMedDate not supplied

Plasma glucose, insulin, proinsulin, C-peptide and glucagon before and after a carbohydrate-rich meal in hyperthyroid patients.

The function of the pancreatic B- and A- cell during a carbohydrate-rich meal was investigated in hyperthyroid patients, since these patients frequently present an altered handling of glucose. In basal conditions the plasma levels of glucose, immunoreactive insulin (IRI), C-peptide (CPR), proinsulin were higher in hyperthyroid patients than in normal subjects, whereas plasma glucagon was similar in the two groups. Hyperthyroid patients had high post-breakfast incremental areas of glucose and IRI and those of CPR and glucagon were normal. In post-breakfast plasma, the hyperthyroid patients had high proinsulin and normal insulin levels. The molar ratio between CPR and IRI was low throughout the test in the hyperthyroid group. In conclusion, in the hyperthyroid group the plasma levels of proinsulin were high and those of glucagon were normal; in response to the standard breakfast the levels of insulin and C-peptide were normal. These findings do not explain the altered glucose handling present in these patients.

Adult↗