Control of gastric glucagon secretion in the acutely pancreatectomized rat

Absence of islet alpha cell function in pancreatectomized patients

Plasma immunoreactive glucagon, C-peptide and substrates (glucose, lactate, and alanine) were measured in 21 pancreatectomized patients and 28 patients with chronic calcifying pancreatitis during arginine infusion. Results were compared with those obtained in control and in insulin-dependent diabetic subjects, and in pancreatectomized subjects receiving a combined infusion of glucagon and arginine or somatostatin and arginine. Plasma immunoreactive glucagon in the pancreatectomized patients was 230 +/- 26 pg/ml (control subjects 100 +/- 13 pg/ml, p less than 0.001), but was unchanged following arginine or somatostatin. Following ethanol extraction of plasma it became undetectable. Similar results were obtained in patients with chronic pancreatitis. In contrast to the insulin-dependent diabetic subjects, no changes in blood glucose, lactate, and alanine concentrations were found during arginine infusion in the pancreatectomized or pancreatitis patients. Addition of glucagon restored the metabolic response to arginine in the pancreatectomized patients. Our results confirm previous smaller studies that in pancreatectomized patients, A cell function is absent or insignificant.

The effect of streptozotocin-induced diabetes on the early steps of glucagon action in isolated rat liver cells

This study was undertaken to investigate the effect of experimental diabetes on the early steps of glucagon action. The binding of glucagon and glucagon-stimulated cyclic AMP accumulation in the presence of a potent phosphodiesterase inhibitor (IBMX, 0.1 mmol/l) were studied in liver cells isolated from control and streptozotocin-induced (65 mg/kg) diabetic rats. Comparative studies of insulin binding indicated that hepatocytes of diabetic rats bound twice as much 125I-insulin (10.8 +/- 2.0%) as those of control rats (5.7 +/- 1.3%). Scatchard analysis and the competition plots of the data suggested that this was due to an increased number of receptors rather a change in their affinity. No significant change was observed in 125I-glucagon binding of diabetic liver cells (5.8 +/- 0.5%( as compared to controls (6.8 +/- 0.4%). The number of molecules of glucagon bound to high and low affinity binding sites of control liver cells was (51 +/- 2) X 10(3) and (1300 +/- 134) X 10(3) sites/cell, respectively. The corresponding numbers in streptozotocin-treated rats were (45 +/- 5) X 10(3) and (1000 +/- 167( X 10(3) sites/cell, respectively. Cyclic AMP response to concentration of glucagon below 1 nmol/l was significantly lower in diabetics than in normals: for 0.3 nmol/l and 0.6 nmol/l of glucagon, cyclic AMP production was 48 +/- 7 pmol/10(6) cells and 78 +/- 8 pmol/10(6) cells in diabetics, as compared to 72 +/- 9 and 110 +/- 9 pmol/10(6) cells in normals. At concentrations of glucagon that are maximally efficient (greater than or equal to 7 nmol/l) cyclic AMP production was higher in diabetic (202 +/- 20 pmol/10(6) cells) than in normal rats (156 +/- 7 pmol/10(6) cells). Thus, diabetes seems to increase the quantity of adenylate cyclase and decrease its affinity for glucagon. Those changes are not related to a modification of the glucagon binding sites and are associated to an increase of insulin receptors.