Factors controlling gastric-glucagon release.

A system consisting of an isolated dog stomach perfused with whole blood has been designed to study gastric glucagon secretion. Under basal conditions, gastric glucagon release was 0.0-3.1 ng glucagon/100g of stomach per min. Arginine, at an arterial plasma concentration averaging 10 mM, elicited a rapid glucagon release. This gastric glucagon release was almost completely abolished by somatostatin (100 ng/ml). The release of gastric glucagon was not affected by hyperglycemia alone but was reduced by about 40% when hyperglycemia was concomitant with an hyperinsulinemia within the physiological range. These observations support the concept that adequate concentrations of insulin are necessary in order for hyperglycemia to inhibit gastric glucagon secretion. Furthermore, it is suggested that the isolated perfused dog stomach might provide a unique tool permitting investigation of alpha-cell function in the absence of endogenously released insulin.

Neurotransmitters and glucagon release from the isolated, perfused canine stomach.

The isolated, perfused, canine stomach was used to investigate the effect of three neurotransmitters--norepinephrine, acetylcholine (or its analogue carbamylcholine), and VIP (vasoactive intestinal peptide)--on gastric glucagon release. Norepinephrine at the two concentrations tested (3.10-8 and 7.10-7 M) did not influence gastric glucagon release. In contrast, acetylcholine or carbamylcholine (5.10-6 M) as well as VIP (46-60 ng/ml) unequivocally stimulated gastric glucagon release, an effect apparently independent of the changes in blood flow. These results are in sharp contrast with the previously reported lack of effect of an electric stimulation of the vagus nerves on the release of glucagon from the dog stomach. An absence of innervation of the canine gastric A-cell would probably best explain this situation.

Similar metabolic effects of pulsatile versus continuous human insulin delivery during euglycemic, hyperinsulinemic glucose clamp in normal man.

Seven normal volunteers were studied on two different occasions during which 4-h pulsatile (PULS: 0.8 mU X kg-1 X min-1, 7.5 min of 15) and continuous (CONT: 0.4 mU X kg-1 X min-1) intravenous (i.v.) infusions of human insulin (Actrapid HM, Novo) were randomly compared. A euglycemic glucose clamp was performed and a 3-3H-glucose infusion was used for determination of endogenous glucose production (EGP) and metabolic clearance rate (MCR) of glucose. Plasma glucose was similar in both conditions; plasma insulin was stable at about 29 mU/L (CONT) and fluctuated between 10 and 45 mU/L (mean: 28, PULS). Exogenous glucose infused was 1.137 +/- 0.058 and 1.088 +/- 0.099 g X kg-1 X 4 h-1 in CONT and PULS, respectively (NS). EGP was totally suppressed in both conditions. Glucose MCR increased similarly to a maximum of 6.71 +/- 0.19 (CONT) and 6.79 +/- 0.59 (PULS) ml X kg-1 X min-1 during the fourth hour. C-peptide plasma levels remained stable, whereas plasma glucagon, free fatty acids, and 3-hydroxybutyrate were similarly suppressed in both tests. Thus, under these conditions, pulsatile and continuous insulin infusions have similar metabolic effects. These data contrast with those of Matthews et al. (1983) who reported that, at lower plasma concentrations (5-19 mU/L), pulsatile insulin had greater hypoglycemic effect than did continuous delivery. It is concluded that pulsatile insulin shows no greater activity under normoglycemic, moderately hyperinsulinemic conditions in man.

Utilization of oral sucrose load during exercise in humans. Effect of the alpha-glucosidase inhibitor acarbose.

We investigated the hormonal and metabolic response to a 100-g sucrose load given 15 min after adaptation to moderate-intensity (50% VmaxO2) long-duration (4-h) exercise in healthy volunteers. The effect of a 100-mg dose of the alpha-glucosidase inhibitor Acarbose ingested with the sucrose load was also investigated. "Naturally labeled [13C] sucrose" was used to follow the conversion to expired-air CO2 of the sugar ingested by isotope-ratio mass spectrometry. Circulating hormone and metabolite data were obtained in nine subjects, and indirect calorimetry and stable isotope methodology were applied to six of them. Under placebo, 93 +/- 4 g sucrose were entirely oxidized during the 4 h of exercise, total carbohydrate utilization was 235 +/- 14 g, endogenous carbohydrate utilization was 142 +/- 13 g, and total lipid oxidation was 121 +/- 7 g. A single oral dose of 100 mg Acarbose ingested with the sucrose load did not significantly modify total carbohydrate (239 +/- 2 g/4 h) or lipid (122 +/- 6 g/4 h) oxidation. In contrast, sucrose oxidation was reduced to 53 +/- 6 g/4 h and endogenous carbohydrate utilization increased to 186 +/- 7 g/4 h. Reduction of the rises in blood glucose and fructose and of the increases in plasma insulin and C peptide under Acarbose confirmed these effects, whereas lower circulating levels of alanine suggested a higher rate of gluconeogenesis. These data show that a 100-g glucose load ingested soon after initiation of exercise is a perfect available metabolic substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic alterations after a two-hour nocturnal interruption of a continuous subcutaneous insulin infusion.

In order to evaluate the metabolic consequences of a 2-h nocturnal interruption of continuous subcutaneous insulin infusion (CSII), seven insulin-dependent diabetic patients without residual insulin secretion were investigated. The changes in blood glucose, plasma free insulin, glucagon, free fatty acids, and 3-hydroxybutyrate (3 OH-B) concentrations have been compared during two randomized tests carried out either during the normal functioning of a Mill-Hill pump from 10 p.m. to 8 a.m. (1.00 +/- 0.06 U insulin/h, keeping adequate metabolic control) or during the same conditions but with a deliberate arrest of the pump between 11 p.m. and 1 a.m. Considering the value recorded at 11 p.m. as reference, interruption of the insulin infusion resulted in: (1) a rapid (already significant after 1 h) and sustained (maximal fall: --12.5 +/- 2.5 mU/L at 3 a.m.) decrease in plasma free insulin; (2) a delayed (significant after 4 h) and linear rise in blood glucose (maximal increase: + 4.0 +/- 1.3 mmol/L at 5 a.m.); (3) an early (significant at midnight) and prolonged rise in plasma free fatty acids (+ 387 +/- 148 mumol/L at 3 a.m.); (4) a delayed (significant after 3 h) and sustained increase in plasma 3 OH-B (+ 347 +/- 88 mumol/L at 3 a.m.); and (5) no significant changes in plasma glucagon. Thus, a 2-h interruption of CSII in resting nocturnal conditions is sufficient to induce significant, delayed, and sustained metabolic alterations in C-peptide-negative patients despite good baseline blood glucose control. Resetting the pump at its basal rate is insufficient to quickly restore adequate circulating insulin levels and effectively counteract the metabolic disturbances. The efficacy of a bolus insulin injection in these conditions should be evaluated.

Glucose and insulin in the regulation of glucagon release from the isolated perfused dog stomach.

The respective roles of glucose and insulin in the regulation of glucagon release from the canine stomach were investigated using an isolated blood-perfused preparation. At normal blood glucose and plasma insulin levels, the stomach released small amounts of glucagon. Such basal gastric glucagon release was not modified by hyperglycemia. In contrast, gastric glucagon release was increased by hypoglycemia or 2-deoxy-D-glucose-induced cytoglycopenia. Antibody neutralization of basal circulating concentrations of insulin (10 +/- 1 microU/ml) doubled the stimulation induced by hypoglycemia alone. It is concluded that: 1) suppression of gastric glucagon release is observed with very low concentrations of insulin; 2) basal gastric glucagon release is not further suppressed by hyperglycemia; and 3) that hypoglycemia and cytoglycopenia stimulate gastric glucagon secretion.

Influence of ketone body infusion on plasma growth hormone and glucagon in man.

The influence of ketone body infusion on the serum GH and glucagon response to FFA depression and insulin hypoglycemia was investigated in 10 healthy men. Intravenous infusion of nicotinic acid induced suppression of both FFA and ketone bodies. This was accompanied by a delayed GH increase to 21.1 +/- 6.9 ng/ml (at 300 min). During an additional beta-hydroxybutyrate (OHB) infusion, FFA remained depressed, but ketone bodies were elevated, and the GH response was abolished (maximum 5.6 +/- 1.6 ng/ml). During infusion of OHB alone, FFA were suppressed. GH increased significantly, although less markedly than during suppression of both FFA and ketone bodies (to 9.3 +/- 3.1 ng/ml at 270 min). No GH rise occurred when both FFA and ketone bodies were kept elevated by the addition of a lipid infusion. The GH rise in response to insulin hypoglycemia was not changed by an OHB infusion (43.2 +/- 4.6 vs. 48.0 +/- 7.3 ng/ml). However, OHB increased the net GH output by significantly delaying the return to basal concentrations in the presence of a reduced FFA rebound. An effect of OHB infusion on the plasma glucagon concentration during all experiments was small, and its physiological significance is doubtful. These results confirm that FFA depression induces delayed GH secretion. They suggest that this is not wholly dependent on concomitant depression of ketone bodies. On the other hand, when ketone bodies are elevated, the GH response to FFA depression is diminished or absent. The net GH response to changes in lipid substrates probably depends on the concentration of both FFA and ketone bodies.

Growth hormone, glucagon, and insulin response to depression of plasma free fatty acids and the effect of glucose infusion.

It has previously been shown that nicotinic acid (NA)-induced depression of free fatty acids (FFA) stimulates the secretion of GH and glucagon. To evaluate this hormonal response further, we studied the influence of different doses of glucose administered by continuous iv infusion on the GH and glucagon increase during NA-induced FFA depression. In ten male non-obese volunteers, FFA depression by the infusion of NA (2.3 g over a period of 210 min) resulted in a late rise (from 150 min on) of GH (From 1.1 to 25.9 ng/ml) and an early increase (from 30 min on) of glucagon (from 71.7 to 138.2 pg/ml). When glucose was infused (approximately 60, 120 and 180 g, respectively, over a period of 270 min) during NA-induced FFA depression, the GH rise was reduced and delayed in relation to the amount of glucose infused, but could not be completely abolished (maximal GH concentration during the three NA-plus-glucose infusions: 16.5, 8.0 and 6.1 ng/ml, respectively). The glucagon rise was entirely reversed by the high glucose dose. Insulin did not rise during NA infusion alone. Its secretion in response to glucose infusion was not significantly influenced by FFA depression. Thus, during NA-induced FFA depression the secretion of two lipolytic hormones--GH and glucagon--is stimulated while the secretion of the lipogenetic hormone insulin remains low. Glucose has an inhibitory effect on the GH and glucagon response which, however, is different for each of the hormones.

Growth hormone, cortisol, and glucagon concentrations during plasma free fatty acid depression: different effects of nicotinic acid and an adenosine derivative (BM 11.189).

Two chemically unrelated inhibitors of lipolysis were used in order to differentiate between the effect of FFA depression and a possible FFA-unrelated drug effect, respectively, on the plasma concentrations of GH, cortisol, and glucagon. Saline infusion served as a control experiment. In eight healthy male volunteers, a similar FFA depression by either iv infusion of nicotinic acid (3-pyridine-carboxylic acid, NA) or oral intake of an adenosine derivative, N(6)-allyl-N(6)-cyclohexyl-adenosine (AD-D), was followed by a significant GH increase (to 22.1 +/- 6.2 and 9.6 +/- 2.9 ng/ml at 240 and 270 min, respectively). Due to the large scatter of the GH concentrations during NA infusion, these responses were not significantly different. No GH increase occurred when the FFA depression was prevented by addition of a lipid infusion. In contrast, plasma cortisol and glucagon both increased significantly (by 107.4 micrograms/liter at 270 min and by 48.4 pg/ml at 60 min, respectively) during NA- but not during AD-D-induced FFA depression. Addition of the lipid infusion abolished the cortisol increase during NA infusion but had no influence on basal cortisol concentrations during AD-D intake. It lowered glucagon to values slightly below basal concentrations when added to the NA infusion and more markedly during AD-D administration. The results provide evidence that 1) depression of plasma FFA per se stimulates the secretion of GH, and 2) the increase of cortisol and glucagon during NA infusion is probably unrelated to the FFA depression. Hence, the stimulatory effect of FFA lack on glucagon secretion needs to be reconsidered.

Insulin-stimulated glucose disposal is not increased in anorexia nervosa.

Insulin-stimulated glucose disposal was investigated using the euglycemic hyperinsulinemic glucose clamp technique in six women with anorexia nervosa (27.3 +/- 4.9 yr old; weight, 38.8 +/- 6.6 kg) and compared to results obtained in six normal women (22.6 +/- 1.2 yr old; weight, 58 +/- 2.5 kg) and seven obese women (26.8 +/- 7.7 yr old; weight, 92.5 +/- 13.8 kg). The glucose clamp was performed for 2 h using the Biostator and a continuous insulin infusion of 100 mU kg-1 h-1. Plasma levels of insulin were determined at 30-min intervals. Plasma levels of glucagon, FFA, glycerol, 3-hydroxy-butyrate, and alanine were measured basally. Blood glucose levels were similar in normal subjects and anorectic patients; they were slightly but significantly higher in the obese patients. The indices of insulin sensitivity measured were the MCR of glucose and the ratio of glucose infused to insulin infused (G/I). They were very similar in anorectic subjects [MCR, 13.5 +/- 2.4 (+/- SEM) ml kg-1 min-1; G/I, 5.2 +/- 0.9 mg/mU) and normal subjects (MCR, 13.5 +/- 1.7 ml kg-1 min-1; G/I, 5.2 +/- 0.4 mg/mU), but were significantly reduced in obese patients (MCR, 5.1 +/- 0.8 ml kg-1 min-1; G/I, 2.6 +/- 0.3 mg/mU; P less than 0.0025). Differences in plasma insulin among the three groups were not statistically significant. Plasma alanine levels were higher in anorectic than in normal or obese subjects, suggesting defective gluconeogenesis. Thus, insulin-stimulated glucose disposal is normal in patients with anorexia nervosa, a finding that contrasts with the previously reported increase in erythrocyte insulin receptors in this disease.

Insulin oscillations per se do not affect glucose turnover parameters in normal man.

To compare the metabolic effects of pulsatile vs. continuous iv insulin infusion, normal men had two glucose-controlled iv glucose infusions using the Biostator for 260 min, during which endogenous pancreatic hormone secretion was inhibited by a somatostatin infusion and glucagon was replaced by continuous glucagon infusion. The two tests were performed at 1-week intervals, during which human insulin was infused either continuously at a constant rate of 0.2 mU kg-1 min-1 or in a pulsatile manner at a rate of 1.3 mU kg-1 min-1 with a switching on/off length of 2/11 min. Blood glucose levels and glucose infusion rates (GIR) were continuously monitored, and glucose turnover was estimated using a [3H]glucose infusion. In both tests, plasma C-peptide dropped markedly, whereas plasma glucagon levels were about twice basal values. Plasma insulin averaged 7 mU liter-1 during continuous infusion and oscillated between 1.5 and 35 mU liter-1 during pulsatile delivery. During the first 30-60 min of both tests, the glucose appearance rate and endogenous glucose production (EGP) increased, resulting in moderate hyperglycemia, which completely suppressed GIR. During the last 65 min, EGP declined, while the glucose disappearance rate and the glucose MCR increased, so that GIR increased progressively to maintain the blood glucose clamped at about 5 mmol liter-1. During this period, no significant differences were found between the two modes of insulin administration for any of the parameters studied. Thus, continuous and pulsatile insulin iv infusion, resulting in physiological peripheral plasma insulin levels, altered the glucose turnover parameters equally, in particular inhibiting EGP, which was stimulated by glucagon during the first part of the study, and stimulating peripheral glucose uptake at the end of the study period.

Hormonal and metabolic changes induced by elevated plasma free fatty acids in term pregnancy. I. Effect on maternal blood glucose, insulin and human placental lactogen circulating levels.

The influence of plasma free fatty acid (FFA) concentration on the secretion of human placental lactogen (hPL) was investigated in 16 normal young women during the last month of gestation, in order to determine whether hPL secretion is influenced in the same way as human growth hormone (hGH) during plasma FFA elevation. Maternal blood glucose (BG), plasma triglycerides (TG), FFA, immunoreactive insulin (IRI) and hPL levels were measured during and after a lipid emulsion infusion for 75 min (10 cases). The intravenous injection of 5,000 U of heparin at the 15th min of the lipid infusion was followed by a decrease in plasma triglyceride levels and by an accompanying rise in plasma FFA (rom 468 plus or minus 52 to 2,478 plus or minus 310 mueq/liter). In control experiments lipid infusion alone (3 cases) resulted in a moderate increase in FFA (718 plus or minus 157 to 1,046 plus or minus 255 mueq/liter), and separate iv heparin administration (3 cases) elevated the FFA levels from 728 plus or minus 50 to 1,649 plus or minus 153 mueq/liter). No significant change in either IRI or hPL levels was discernible in any of the tests performed. A tendency of blood glucose to increase was observed after heparin administration. It was concluded that a marked and sustained plasma FFA elevation, achieved through intravenous lipid and heparin infusion cannot alter hPL circulating levels in term human pregnancy.

Effect of acute kidney exclusion by ligation of renal arteries on peripheral plasma glucagon levels and pancreatic glucagon production in the anesthetized dog.

Bilateral kidney exclusion in the anesthetized dog resulted in an immediate and important increase in arterial plasma glucagon. Forty minutes after ligation of the renal arteries, plasma glucagon averaged 200% of the basal values and 90 min after ligation, mean plasma glucagon averaged 357% of the mean basal value. Comparable changes were observed when basal plasma glucagon was markedly suppressed by intravenous infusion of glucose. The rate of production of glucagon by the pancreas was not significantly increased by kidney exclusion. Since the uptake of glucagon by the kidney was previously shown to be quantitatively important, the present findings suggest that abrupt cessation of kidney glucagon uptake is the major factor responsible for the rise in peripheral plasma glucagon levels observed after ligation of renal arteries.

Plasma glucagon after kidney exclusion: experiments in somatostatin-infused and in eviscerated dogs.

Bilateral kidney exclusion in the anesthetized dog is followed by a rapid and sustained increase in arterial plasma glucagon. This occurs even if endogenous glucagon secretion is inhibited by somatostatin or completely suppressed by abdominal evisceration and, in both cases, replaced by a constand infusion of exogenous glucagon. It is concluded that the rise in plasma glucagon occurring after bilateral kidney exclusion is not due to an increase in endogenous glucagon production but results from an abrupt cessation of kidney glucagon uptake.

Influence of elevated plasma free fatty acids on the glucagon response to hypoglycemia in normal and in pregnant women.

We investigated the influence of an insulin-induced hypoglycemia on plasma glucagon in nonpregnant healthy young women and in women during the last month of gestation. Both groups were tested either in the basal state or during a period where free fatty acid plasma levels were increased by infusion of a lipid emulsion supplemented with heparin. Regular insulin was injected intravenously at the dose of 0.1 U/kg body wt in controls and 0.3 U/kg in pregnant women in order to obtain a similar lowering of blood glucose in all groups. In controls, the increase in plasma glucagon was maximum 30 and 45 min after insulin injection and averaged 130 pg/ml; the infusion of triglycerides and heparin which raised plasma FFA to about 1300 muEq/liter decreased basal plasma glucagon levels and reduced, by about 70%, the glucagon response to hypoglycemia. During the last month of pregnancy, the glucagon response to insulin-induced hypoglycemia was reduced by 60% (mean maximal increase 52 pg/ml); furthermore, raising plasma FFA to about 1500 muEq/liter completely abolished the glucagon rise induced by the insulin hypoglycemia. These results support the view that the glucagon release from A-cells can be modulated by the level of circulating plasma FFA.

Remarkable metabolic availability of oral glucose during long-duration exercise in humans.

It was reported previously that glucose ingestion prior to or at the beginning of muscular exercise was a readily available metabolic substrate. The aim of this study was to see what percentage of carbohydrate utilization can be covered by glucose ingested regularly during exercise. Male healthy volunteers exercised for 285 min at approximately 45% of their individual maximal O2 uptake on a 10% uphill treadmill. After 15 min adaptation to exercise they received either 200 g (group G 200) or 400 g (group G 400) glucose (0.25 g X ml H2O-1) orally in eight equal doses repeated every 30 min (G 200 = 8 X 25 g, n = 4; G 400 = 8 X 50 g, n = 4). Indirect calorimetry was used to evaluate carbohydrate and lipid oxidation. Naturally labeled [13C]glucose was used to follow the oxidation of the exogenous glucose. Total carbohydrate oxidation was 341 +/- 22 and 332 +/- 32 g, lipid oxidation was 119 +/- 8 and 105 +/- 5 g, and exogenous glucose oxidation was 137 +/- 4 and 227 +/- 13 g (P less than 0.005) in groups G 200 and G 400, respectively. Endogenous glucose oxidation was about half in G 400 of what it was in G 200: 106 +/- 27 vs. 204 +/- 24 g (P less than 0.02). During the last hour of exercise, exogenous oxidation represented 55.3 and 87.5% of total carbohydrate oxidation for groups G 200 and G 400, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate metabolism in women who used oral contraceptives containing levonorgestrel or desogestrel: a 6-month prospective study.

Blood glucose and pyruvate, plasma insulin, and glucagon levels as well as erythrocyte insulin receptors were measured during an oral glucose tolerance test in 38 normal women before and after 6 months' use of one of three new oral contraceptives containing low doses of 19 nortestosterone-derived progestogens, levonorgestrel, and desogestrel. A slight deterioration of glucose tolerance was observed, with the area under the glucose curve increasing by only 7%, 9%, and 12% after Ovidol (Aaciphar SA, Brussels, Belgium), Marvelon (Organon, SA, Brussels, Belgium), and Trigynon (Schering SA, Brussels, Belgium) administration, respectively. We did not find any argument in favor of the development of a state of insulin resistance in women using these compounds, because erythrocyte receptor binding was not modified and plasma insulin responses to glucose were decreased. The glucose-induced suppression of plasma glucagon levels seemed less effective for treatment with the desogestrel-containing preparations than with the levonorgestrel-containing oral contraceptives.

Effect of phosphate on the arginine-induced insulin release by the isolated perfused rat pancreas.

The isolated perfused rat pancreas was used to investigate the effect of extracellular phosphate on the arginine-induced insulin release. In the absence of any metabolic substrate, the insulin response to arginine was monophasic. In the absence of phosphate in the medium, the insulin release as unaffected until the 15th minute of the stimulation period, but was significantly augmented from that time onward. In the presence of oleic acid in the perfusate, the insulin response to arginine was also monophasic but occurred earlier than in controls. In this conditin, phosphate omission resulted in an increase of the insulin response to arginine from the 3rd minute of the stimulatory period onward. In the presence of glucose 5.5 mM in the medium the insulin response to argnine was biphasic and was not affected by extracellular phosphate omission.

[Extrapancreatic glucagon in the dog (author's transl)]. / Le glucagon extrapancréatique chez le chien.

The analysis of the factors controlling glucagon release by the isolated perfused canine stomach stresses the importance of a metabolic and hormonal control: stimulation by arginine, hypoglycemia, cytoglycopenia or insulin deprivation, inhibition by glucose in the presence of insulin or by somatostatin. In contrast, the secretion of the canine gastric A-cell does not respond to vagal stimulation or local release of noradrenaline.