Rise In Plasma Glucagon Concentration Research Articles

Combination Therapy With Canagliflozin Plus Liraglutide Exerts Additive Effect on Weight Loss, but Not on HbA1c, in Patients With Type 2 Diabetes.

OBJECTIVETo examine the effect of combination therapy with canagliflozin plus liraglutide on HbA1c, endogenous glucose production (EGP), and body weight versus each therapy alone.RESEARCH DESIGN AND METHODSForty-five patients with poorly controlled (HbA1c 7–11%) type 2 diabetes mellitus (T2DM) on metformin with or without sulfonylurea received a 9-h measurement of EGP with [3-3H]glucose infusion, after which they were randomized to receive 1) liraglutide 1.2 mg/day (LIRA), 2) canagliflozin 100 mg/day (CANA), or 3) liraglutide 1.2 mg plus canagliflozin 100 mg (CANA/LIRA) for 16 weeks. At 16 weeks, the EGP measurement was repeated.RESULTSThe mean decrease from baseline to 16 weeks in HbA1c was −1.67 ± 0.29% (P = 0.0001), −0.89 ± 0.24% (P = 0.002), and −1.44 ± 0.39% (P = 0.004) in patients receiving CANA/LIRA, CANA, and LIRA, respectively. The decrease in body weight was −6.0 ± 0.8 kg (P < 0.0001), −3.5 ± 0.5 kg (P < 0.0001), and −1.9 ± 0.8 kg (P = 0.03), respectively. CANA monotherapy caused a 9% increase in basal rate of EGP (P < 0.05), which was accompanied by a 50% increase (P < 0.05) in plasma glucagon-to-insulin ratio. LIRA monotherapy reduced plasma glucagon concentration and inhibited EGP. In CANA/LIRA-treated patients, EGP increased by 15% (P < 0.05), even though the plasma insulin response was maintained at baseline and the CANA-induced rise in plasma glucagon concentration was blocked.CONCLUSIONSThese results demonstrate that liraglutide failed to block the increase in EGP caused by canagliflozin despite blocking the rise in plasma glucagon and preventing the decrease in plasma insulin concentration caused by canagliflozin. The failure of liraglutide to prevent the increase in EGP caused by canagliflozin explains the lack of additive effect of these two agents on HbA1c.

Hypothalamic glucagon signaling inhibits hepatic glucose production

Glucagon activates hepatic protein kinase A (PKA) to increase glucose production, but the gluco-stimulatory effect is transient even in the presence of continuous intravenous glucagon infusion. Continuous intravenous infusion of insulin, however, inhibits glucose production through its sustained actions in both the liver and the mediobasal hypothalamus (MBH). In a pancreatic clamp setting, MBH infusion with glucagon activated MBH PKA and inhibited hepatic glucose production (HGP) in rats, as did central glucagon infusion in mice. Inhibition of glucagon receptor-PKA signaling in the MBH and hepatic vagotomy each negated the effect of MBH glucagon in rats, whereas the central effect of glucagon was diminished in glucagon receptor knockout mice. A sustained rise in plasma glucagon concentrations transiently increased HGP, and this transiency was abolished in rats with negated MBH glucagon action. In a nonclamp setting, MBH glucagon infusion improved glucose tolerance, and inhibition of glucagon receptor-PKA signaling in the MBH enhanced the ability of intravenous glucagon injection to increase plasma glucose concentrations. We also detected a similar enhancement of glucose concentrations that was associated with a disruption in MBH glucagon signaling in rats fed a high-fat diet. We show that hypothalamic glucagon signaling inhibits HGP and suggest that hypothalamic glucagon resistance contributes to hyperglycemia in diabetes and obesity.

Surgical removal of insulinoma restores glucose recovery from hypoglycaemia but does not normalize insulin action.

In the present study we have evaluated the effects of chronic hyperinsulinaemia secondary to insulinoma, on insulin sensitivity and on counter-regulatory responses to hypoglycaemia. We studied six patients (M/F = 3/3; age = 40 +/- years), before and 6-9 months after surgical ablation of the neoplasia, by means of an euglycaemic-hyperinsulinaemic clamp (1 mU kg-1 min-1). Seven normal subjects (M/F = 4/3; age = 38 +/- 6 years) underwent the same experimental study as the control subjects. In insulinoma patients after 100 min of the euglycaemic-hyperinsulinaemic clamp, glycaemia was allowed to drop to a minimum value of 1.9 mmol L-1, and recovery evaluated after interrupting insulin infusion. During the entire study, 3-3H-glucose was infused to determine hepatic glucose production and glucose utilization. Surgical removal of the pancreatic adenoma was followed by a reduction in body weight (BMI = 25.7 +/- 1.9 vs. 23.0 +/- 1.6 kg m-2; P < 0.05), normalization of fasting plasma levels of glucose (2.94 +/- 0.16 vs. 4.83 +/- 0.11 mmol L-1), insulin (162 +/- 24 vs. 48 +/- 12 pmol L-1) and of basal hepatic glucose production (7.6 +/- 0.7 vs. 12.2 +/- 1.11 mumol kg-1 min-1). Before the operation, insulin-mediated glucose disposal was significantly lower than in the controls (30.8 +/- 3.1 vs. 49.1 +/- 3.1 mumol kg-1 min-1). Six to nine months after surgical removal of the adenoma, glucose utilization was unchanged (30.5 +/- 3.3 mumol kg-1 min-1) and still significantly lower than in controls (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Improvement in blunted glucagon response to insulin-induced hypoglycemia by strict glycemic control in diabetics

To elucidate the mechanism of impaired pancreatic A cell function in hypoglycemia in diabetics, the effect of long-term strict glycemic regulations on hypoglycemia-induced glucagon secretion was studied. Firstly, the effect of plasma insulin concentrations on suppressing A cell was studied in healthy volunteers by injecting insulin at doses of 0.1 U/kg and 0.3 U/kg. With 0.3 U/kg of insulin, the rate of fall in glycemia and the nadir of blood glucose were made similar to those with 0.1 U/kg of insulin by glucose infusion with artificial endocrine pancreas. Plasma glucagon response after 0.3 U/kg of insulin was significantly suppressed as compared to that after 0.1 U/kg of insulin, demonstrating that not only hypoglycemic stimulus but also plasma insulin concentration were important determinants responsible for glucagon secretion in insulin-induced hypoglycemia. Secondly, effect of strict glycemic control was studied. Short-acting insulin at a dose of 0.1 U/kg was injected in an intravenous bolus form into 12 insulin-dependent (IDDM) and 9 non-insulin-dependent (NIDDM) diabetics before and 1–3 months after strict glycemic control with multiple insulin injections therapy. Before strict glycemic regulations in IDDM, no significant rise in plasma glucagon concentrations was observed during the insulin-induced hypoglycemia. In NIDDM, a rise in plasma glucagon concentrations was observed, though the response was delayed. After strict glycemic regulations, in patients with residual endogenous insulin secretion, the glucagon response to hypoglycemia improved considerably in IDDM and normalized in NIDDM. In IDDM and NIDDM, improvement in glucagon response to hypoglycemia related positively to daily urinary secretion rate of C-peptide. From these experiments, it is clearly shown that blunted hypoglycemia induced glucagon secretion in diabetics is secondary to poor glycemic control, and that the existence of endogenous insulin secretion is essential to glucagon response to hypoglycemia.

Dominant role of glucagon in the initial induction of phosphoenolpyruvate carboxykinase mRNA in cultured hepatocytes from fetal rats.

The injection of streptozotocin to 18-day-old rat fetuses induced, 2 days later, a 50% fall in plasma insulin and a twofold increase in plasma glucagon concentrations and liver cAMP levels. Phosphoenolpyruvate carboxykinase mRNA that were undetectable in the fetal rat liver, accumulated 48 h after streptozotocin injection, their concentration being 30% of that found in the liver of 1-day-old newborn rats in whom liver phosphoenolpyruvate carboxykinase gene expression is maximal. Physiological concentrations of glucagon (0.7 +/- 0.2 nM) induced, within 2 h, phosphoenolpyruvate carboxykinase mRNA accumulation in cultured hepatocytes from 20-day-old fetuses. The addition of insulin (0.01-100 nM) inhibits, by no more than 30%, the glucagon-induced phosphoenolpyruvate carboxykinase mRNA accumulation. Exposure of fetal hepatocytes to insulin for 24 h did not change the glucagon dose/response curve and did not lead to a more efficient inhibition of the glucagon-induced phosphoenolpyruvate carboxykinase mRNA accumulation, despite a clear stimulatory effect on the rate of lipogenesis. In contrast, when hepatocytes were cultured in the presence of dexamethasone, the glucagon-induced phosphoenolpyruvate carboxykinase mRNA accumulation can be totally inhibited by pharmacological concentrations of insulin (10 nM). From these in-vivo and in-vitro studies, it is concluded that, under physiological conditions, the postnatal rise in plasma glucagon concentration is more important than the fall in the plasma insulin concentration for the primary induction of liver phosphoenolpyruvate carboxykinase gene expression.

Symptomatic reactive hypoglycemia during glucose tolerance test in lithium-treated patients

Glucose, insulin, glucagon, and cortisol responses during a five-hour oral glucose tolerance test (GTT) were evaluated in nine patients with bipolar affective disorders who were receiving lithium treatment and in seven control patients with bipolar affective disorders who were not receiving any treatment. Both the lithium-treated and the control patients were in stable mood at the time of GTT. During GTT mean nadir serum glucose of 48 ± 2 mg/dL in the lithium-treated patients was significantly lower ( P < 0.001) than mean nadir serum glucose of 62 ± 2 mg/dL observed in the control subjects. Seven of these nine lithium-treated patients, but none of the control patients, experienced hypoglycemic symptoms coinciding with low serum glucose concentration. In response to hypoglycemia, mean serum cortisol significantly rose ( P < 0.01) to 22 ± 3 μg/dL in the lithium-treated patients, whereas mean serum cortisol levels gradually declined to 10 ± 2 μg/dL in the control patients at 300 minutes. Despite symptomatic postglucose hypoglycemia, plasma glucagon levels in the lithium-treated patients were similar to those observed in the control patients. These findings suggest that chronic lithium treatment is associated with a symptomatic and biochemical hypoglycemia during GTT, which is characterized by a rise in serum cortisol but by lack of appropriate rise in plasma glucagon concentrations.

Pancreatic endocrine responses to physiological changes in plasma neurotensin concentration in the calf.

1. Plasma neurotensin concentration was found to increase by between 3 and 18 pmol/l 20 min after feeding in conscious 2-6 week old calves. 2. Synthetic bovine neurotensin was infused I.V. at a dose which reproduced the rise in the plasma concentration (1 pmol. kg-1 min-1), in calves of the same age, which were also receiving a continuous I.V. infusion of glucose (0.03 mmol. kg-1. min-1) to mimic alimentary hyperglycaemia. Under these conditions neurotensin caused a significant rise in the mean concentration of both insulin and pancreatic polypeptide (PP), but not that of glucagon, in the arterial plasma. 3. The rise of plasma insulin concentration, but not that of PP, in response to the same dose of neurotensin was strongly potentiated during infusions of exogenous amino acids. There was also a significant rise in plasma glucagon concentration in response to neurotensin in the calves given amino acids. 4. It is concluded that neurotensin is a physiological incretin in the calf.

The effect of glucagon infusion on kidney function in short-term insulin-dependent juvenile diabetics.

Kidney function was studied in nine, metabolically well controlled, short-term insulin-dependent male diabetics before and during glucagon infusion of 4 to 5 and 8 to 10 ng/kg/min. Glomerular filtration rate, effective renal plasma flow (steady-state infusion technique, with urinary collections, using 125I-iothalamate and 131I-iodohippurate), and urinary albumin and beta 2-microglobulin excretion rates were measured. The mean plasma glucagon concentration increased during infusion from 254 +/- 19 pg/ml to 440 +/- 31 pg/ml (low dose) and 730 +/- 52 pg/ml (high dose). Glomerular filtration rate increased in all subjects from 133 +/- 5 before the glucagon infusion to 141 +/- 4 with the low dose, and 148 +/- 7 ml/min/1.73 m2 with the high dose (p < 0.01). The increase in glomerular filtration rate correlated with the rise in plasma glucagon concentration (r = 0.67; p < 0.01). Renal plasma flow increased from 530 +/- 21 before the glucagon infusion to 555 +/- 20 with the low dose and 572 +/- 29 ml/min/1.73 m2 with the high dose (p < 0.01). Urinary beta 2-microglobulin excretion rate rose from 5.8 +/- 1.0 before infusion to 8.7 +/- 1.7 with the low dose, and 17.9 +/- 5.7 micrograms X 10(-2)/min with the high dose (p < 0.01). Urinary albumin excretion remained unchanged during the glucagon infusion. These results suggest that glucagon may contribute to the reversible elevation of glomerular filtration rate typically found in poorly regulated insulin-dependent diabetics, but not to the moderate elevation found in well controlled diabetics.

The temporal relationship between endogenously secreted stress hormones and metabolic decompensation in diabetic man.

Stress-induced diabetic ketoacidosis is characterized by an elevation in stress hormone concentration. Whether metabolic decompensation induces or results from the secretion of stress hormones has not been examined. Our study examined the temporal relationship between the onset of stress (pyrogen-induced shaking chills and fever); the elevation in stress hormone concentation; and the rise in plasma glucose, ketone bodies, and nonesterified fatty acid concentration. Insulin deficiency, which may itself induce stress hormone secretion, was prevented by the continuous infusion of insulin (0.01 U/kg.h). Pyrogen administration induced malaise and fever in all diabetic volunteers and the rapid endogenous secretion of all stress hormones. The rise in plasma GH, catecholamines, and cortisol preceded the rise in plasma nonesterified fatty acid and ketone body concentrations by at least 30 min. The rise in plasma glucagon concentration preceded the rise in plasma glucose concentration by at lease 1 h. Thus, these studies support a primary role for stress hormones in initiating metabolic decompensation in stressed diabetic man.

The role of the autonomic nervous system in the control of pancreatic endocrine responses to milk ingestion in the calf.

1. Pancreatic endocrine responses to ingestion of milk have been investigated in conscious unweaned calves, 3-5 weeks after birth. Passage of gastric content from abomasum to small intestine was prevented by means of a cannula placed in the duodenum adjacent to the pylorus and food was witheld for at least 22 h in order to deplete liver glycogen. 2. Under these conditions ingestion of milk was followed by a prompt rise in the concentrations of pancreatic glucagon, PP and gastrin in the arterial plasma but the usual rises in plasma glucose and insulin concentration were absent. 3. Evidence was obtained to show that absorption of glucose from the small intestine occurs sufficiently rapidly to account for the initial rise in plasma glucose concentration after feeding in normal animals. However, the rise in plasma glucagon concentration was sufficient to contribute to alimentary hyperglycaemia by promoting hepatic glycogenolysis in calves with abundant liver glycogen. 4. None of the neuroendocrine responses to ingestion of milk was affected by prior section of the splanchnic nerves whereas each was blocked by atropine (0.2 mg/kg), showing that all depend upon muscarinic, parasympathetic rather than sympathetic activity, in the absence of extraneous stress.

Adrenal and pancreatic endocrine responses to hypoxia and hypercapnia in the calf.

1. Adrenal and pancreatic endocrine responses to hypoxia and hypercapnia, of differing degrees of intensity, have been examined in conscious, unrestrained calves 3-5 weeks after birth. 2. The outputs of cortisol and corticosterone from the right adrenal gland were found to vary inversely with arterial Po2 between 17 and 55 mmHg. Significant increase in mean adrenal blood flow was not observed at arterial oxygen tensions above about 30 mmHg. 3. Release of physiologically effective amounts of catecholamines from the adrenal medulla occurred only in response to intense hypoxia (arterial Po2 17-1 +/- 2-8 mmHg) and was effectively abolished by section of both splanchnic nerves. Release of pancreatic glucagon in response to such intense hypoxia was unaffected by section of both splanchnic nerves and administration of atropine. In contrast, the rise in plasma pancreatic glucagon concentration during less intense hypoxia was abolished by autonomic blockade. 4. Hypercapnia produced by inhalation of either 5% or 10% CO2 for 30 min stimulated maximal release of adrenal glucocorticoids and caused a substantial rise in plasma glucagon concentration. In contrast, the adrenal medulla was found to be extremely resistant to hypercapnia. Significant release of catecholamines was only observed during intense hypercapnia (inhalation of 10% CO2) and noradrenaline was invariably found to be the predominant amine. 5. The results of these experiments show how endocrine responses to hypoxia and hypercapnia are graded in the conscious calf. Of the mechanisms we have examined the pituitary-adrenal cortical axis is the most sensitive and the adrenal medulla the most resistant, while the pancreatic alpha cell occupies an intermediate position.

Effect of Environmental Temperature on Glucose-induced Insulin Response in the Newborn Rat

Blood glucose and plasma insulin and glucagon concentrations were determined in full-term rats delivered by cesarean section and exposed to 37 degrees C. or 24 degrees C. environmental temperature during the first hours of extrauterine life. When newborn rats were maintained at thermal neutrality (37 degrees C.), a transient period of hypoglycemia of two hours occurred, associated with a rapid fall in plasma insulin and a rise in plasma glucagon concentrations. During cold exposure (24 degrees C.), the blood glucose level remained stable over the four hours studied; the decrease of plasma insulin was sluggish while the rise of plasma glucagon was unchanged. In newborn rats maintained at 37 degrees C., an intraperitoneal glucose load one hour after delivery produced a marked rise in blood glucose and plasma insulin concentrations one hour later. The distribution of experimental points suggested a sigmoidal dose-response curve. By contrast in newborn rats kept at room temperature (24 degrees C.) the same glucose load did not induce any increase in plasma insulin in spite of hyperglycemia. However, phentolamine resulted in pronounced plasma insulin rise in hypothermic newborns in response to glucose administration. From these observations it is concluded that the in-vivo unresponsiveness of the beta cells to glucose at birth, reported by others, is mainly due to the experimental conditions.

The release of pancreatic glucagon and inhibition of insulin in response to stimulation of the sympathetic innervation.

The changes in the concentration of glucagon and insulin in arterial plasma which occur in response to splanchnic nerve stimulation have been investigated in adrenalectomized dogs, cats and sheep. 2. In dogs, stimulation of both splanchnic nerves at a low frequency (2-0 c/s) for 10 min produced a small but statistically significant increase in plasma glucagon concentration and appeared to inhibit the release of insulin. Stimulation at a higher frequency (10-0 c/s) produced a much greater increase in plasma glucagon concentration, which was normally accompanied by a rise in plasma glucose concentration. 3. Qualitatively similar changes in plasma glucagon and insulin concentration were observed in both sheep and cats in response to adrenergic stimulation. 4. Intramesenteric infusions of glucagon at a dose of 5-0 ng kg-1 min-1 in dogs produced a comparable rise in plasma glucagon concentration to that elicited by splanchnic nerve stimulation at high frequency (10-0 c/s) and invariably caused a rise in plasma glucose concentration. 5. In dogs given exogenous glucose, release of glucagon in response to splanchnic nerve stimulation was unaffected by induced hyperglycaemia. Secretion of insulin was partially inhibited by stimulation at 2-0 c/s and completely suppressed at higher frequency (10-0c/s). 6. It is concluded that stimulation of the sympathetic innervation to the pancreatic islets, at frequencies within thephysiological range, stimulates the release of glucagon and inhibits that of insulin in each of these species.

Endocrine responses to insulin hypoglycaemia in the young calf.

1. Variations in the output of glucocorticoids and catecholamines from the right adrenal gland, in response to insulin hypoglycaemia, have been investigated in calves 2-5 weeks after birth. These have been correlated with changes in the concentration of glucocorticoids and glucagon in arterial plasma. 2. Moderate hypoglycaemia for a limited period (0-1 u. insulin/kg), elicited a prompt increase in steroid output from the adrenal gland followed by a significant rise in plasma glucagon concentration. By comparison, changes in both catecholamine output and peripheral plasma glucocorticoid concentrations were found to be trivial in this group of animals. 3. Administration of a larger dose of insulin (0-5 u./kg) produced a more substantial fall in plasma glucose concentration followed by spontaneous recovery within 2-3 hr. This stimulus elicited the release of greater amounts of both cortisol and corticosterone, followed by a significant increase both in the output of adrenaline and in plasma glucagon concentration. Increase in steroid output was accompanied by an increase in adrenal blood flow and was associated with elevated concentrations of both steroids in arterial plasma. 4. The adrenal cortical response and associated changes in plasma steroid concentration were found to be transient even in response to persistent and intense hypoglycaemia (4 u. insulin/kg). The increase in plasma glucagon concentration in this group of animals was not significantly greater than that produced by smaller doses of insulin. However, substantial amounts of adrenaline (78 plus or minus 14 ng. kg-minus 1 min-minus 1; maximum; n equals 9) together with a little noradrenaline (10 plus or minus 3 ng.kg-minus 1 min-minus 1; maximum; n equals 9) were released from the right adrenal gland under these conditions. 5. Changes in adrenal blood flow could be related to adrenal glucocorticoid output in calves given 0-1 or 0-5 u. insulin/kg. In animals given the largest dose of insulin adrenal blood flow was found to increase coincidentally with rising steroid output but this hyperaemia then persisted after steroid output had subsided to values within the normal range. 6. Calves given the largest dose of insulin (4-0 u./kg) invariably collapsed and convulsed after 2-3 hr, but these symptoms could not be related to any particular endocrine response. No clinical signs of hypoglycaemia were observed in the other animals. 7. The results are discussed in relation to previous studies of adrenal function in this and other species.

Insulin-glucagon substrate interrelationships in the neonatal sheep

The pancreatic alpha and beta cell responses to glucose and deoxyglucose infusion were studied in nine healthy newborn lambs at 24 to 36 hours of age. Steady-state glucose infusion resulted in a significant, though obtunded, increase in plasma insulin concentrations within 45 minutes; glucose/insulin ratios were higher than fetal values observed in similar studies (5.6 vs. 0.88, p < 0.001), indicating a more significant role of insulin in stimulating glucose disposal in the newborn period than in the fetal period. Glucose infusion resulted in a paradoxical rise in plasma glucagon concentrations (360 to 500 pg. per milliliter, p < 0.05). Deoxyglucose infusions did not evoke significant changes in plasma insulin concentrations but there was an increase in plasma glucagon levels (300 to 480 pg. per milliliter, p < 0.05). These data indicate residual immaturity of insulin and glucagon secretion mechanisms in the neonatal period and suggest that such immaturity may be important in the abnormalities of glucose homeostasis in the newborn period.

The role of the autonomic innervation in the control of glucagon release during hypoglycaemia in the calf.

1. The extent to which the autonomic innervation to the pancreas is implicated in the control of glucagon release during hypoglycaemia has been investigated in calves 3-6 weeks after birth.2. A pronounced rise in plasma glucagon concentration occurred in normal conscious calves in response to hypoglycaemia following administration of insulin (0.1 u./kg). Prior treatment with atropine caused no significant change in the hypoglycaemic response to insulin in these animals but the rise in plasma glucagon concentration was delayed.3. Section of both splanchnic nerves produced no significant change in the tolerance of conscious calves to this small dose of insulin and the changes in plasma glucagon concentration in these animals were within the normal range.4. In contrast, the same dose of insulin produced severe hypoglycaemia, accompanied by convulsions, in atropinized calves with cut splanchnic nerves. In spite of the intensity of the hypoglycaemic stimulus the rise in plasma glucagon concentration was both delayed and diminished in these animals.5. Administration of atropine alone (0.2 mg/kg) to normal fasting calves produced a significant fall in the mean plasma concentrations of both glucose and glucagon (P < 0.01) within 30 min, without affecting that of insulin.6. A significant increase in plasma glucagon concentration also occurred in response to stimulation of the peripheral ends of the thoracic vagi in adrenalectomized calves with cut splanchnic nerves under barbiturate anaesthesia. A rise in mean plasma glucose concentration was also observed in these experiments and found to be significantly correlated with the glucagon response.7. It is concluded that changes in either sympathetic or parasympathetic efferent activity may modify plasma glucagon concentration in the conscious calf, but that only the latter mechanism is likely to be implicated in the response to changes in plasma glucose concentration within the physiological range.