Glucagon responses to hypoglycemia in adrenalectomized man

Roles of Pancreatic Islet Catecholamine Neurotransmitters in Glycemic Control and in Antipsychotic Drug-Induced Dysglycemia

Catecholamine neurotransmitters dopamine (DA) and norepinephrine (NE) are essential for a myriad of functions throughout the central nervous system, including metabolic regulation. These molecules are also present in the pancreas, and their study may shed light on the effects of peripheral neurotransmission on glycemic control. Though sympathetic innervation to islets provides NE that signals at local α-cell and β-cell adrenergic receptors to modify hormone secretion, α-cells and β-cells also synthesize catecholamines locally. We propose a model where α-cells and β-cells take up catecholamine precursors in response to postprandial availability, preferentially synthesizing DA. The newly synthesized DA signals in an autocrine/paracrine manner to regulate insulin and glucagon secretion and maintain glycemic control. This enables islets to couple local catecholamine signaling to changes in nutritional state. We also contend that the DA receptors expressed by α-cells and β-cells are targeted by antipsychotic drugs (APDs)-some of the most widely prescribed medications today. Blockade of local DA signaling contributes significantly to APD-induced dysglycemia, a major contributor to treatment discontinuation and development of diabetes. Thus, elucidating the peripheral actions of catecholamines will provide new insights into the regulation of metabolic pathways and may lead to novel, more effective strategies to tune metabolism and treat diabetes.

Effects of sitagliptin on counter-regulatory and incretin hormones during acute hypoglycaemia in patients with type 1 diabetes: a randomized double-blind placebo-controlled crossover study

AIMS

To assess whether the dipeptidyl peptidase-4 (DPP-4) inhibitor sitagliptin affects glucagon and other counter-regulatory hormone responses to hypoglycaemia in patients with type 1 diabetes.

METHODS

We conducted a single-centre, randomized, double-blind, placebo-controlled, three-period crossover study. We studied 16 male patients with type 1 diabetes aged 18-52 years, with a diabetes duration of 5-20 years and intact hypoglycaemia awareness. Participants received sitagliptin (100 mg/day) or placebo for 6 weeks and attended the hospital for three acute hypoglycaemia studies (at baseline, after sitagliptin treatment and after placebo). The primary outcome was differences between the three hypoglycaemia study days with respect to plasma glucagon responses from the initialization phase of the hypoglycaemia intervention to 40 min after onset of the autonomic reaction.

RESULTS

Sitagliptin treatment significantly increased active levels of glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1. No significant differences were observed for glucagon or adrenergic counter-regulatory responses during the three hypoglycaemia studies. Growth hormone concentration at 40 min after occurrence of autonomic reaction was significantly lower after sitagliptin treatment [median (IQR) 23 (0.2-211.0) mEq/l] compared with placebo [median (IQR) 90 (8.8-180) mEq/l; p = 0.008].

CONCLUSIONS

Sitagliptin does not affect glucagon or adrenergic counter-regulatory responses in patients with type 1 diabetes, but attenuates the growth hormone response during late hypoglycaemia.

Neural control of the endocrine pancreas

The autonomic nervous system affects glucose metabolism partly through its connection to the pancreatic islet. Since its discovery by Paul Langerhans, the precise innervation patterns of the islet has remained elusive, mainly because of technical limitations. Using 3-dimensional reconstructions of axonal terminal fields, recent studies have determined the innervation patterns of mouse and human islets. In contrast to the mouse islet, endocrine cells within the human islet are sparsely contacted by autonomic axons. Instead, the invading sympathetic axons preferentially innervate smooth muscle cells of blood vessels. This innervation pattern suggests that, rather than acting directly on endocrine cells, sympathetic nerves may control hormone secretion by modulating blood flow in human islets. In addition to autonomic efferent axons, islets also receive sensory innervation. These axons transmit sensory information to the brain but also have the ability to locally release neuroactive substances that have been suggested to promote diabetes pathogenesis. We discuss recent findings on islet innervation, the connections of the islet with the brain, and the role islet innervation plays during the progression of diabetes.

Novel approaches to studying the role of innervation in the biology of pancreatic islets

The autonomic nervous system helps regulate glucose homeostasis by acting on pancreatic islets of Langerhans. Despite decades of research on the innervation of the pancreatic islet, the mechanisms used by the autonomic nervous input to influence islet cell biology have not been elucidated. This article discusses how these barriers can be overcome to study the role of the autonomic innervation of the pancreatic islet in glucose metabolism. It describes recent advances in microscopy and novel approaches to studying the effects of nervous input that may help clarify how autonomic axons regulate islet biology.

Redundant parasympathetic and sympathoadrenal mediation of increased glucagon secretion during insulin-induced hypoglycemia in conscious rats

Both the parasympathetic and sympathoadrenal inputs to the pancreas can stimulate glucagon release and are activated during hypoglycemia. However, blockade of only one branch of the autonomic nervous system may not reduce hypoglycemia-induced glucagon secretion, because the unblocked neural input is sufficient to mediate the glucagon response, ie, the neural inputs are redundant. Therefore, to determine if parasympathetic and sympathoadrenal activation redundantly mediate increased glucagon secretion during hypoglycemia, insulin was administered to conscious rats pretreated with a muscarinic antagonist (methylatropine, n = 7), combined alpha- and beta-adrenergic receptor blockade (tolazoline + propranolol, n = 5) or adrenergic blockade + methylatropine (n = 7). Insulin administration produced similar hypoglycemia in control and antagonist-treated rats (25 to 32 mg/dL). In control rats (n = 9), plasma immunoreactive glucagon (IRG) increased from a baseline level of 125 +/- 11 to 1,102 +/- 102 pg/mL during hypoglycemia (delta IRG = +977 +/- 98 pg/mL, P < .0005). The plasma IRG response was not significantly altered either by methylatropine (delta IRG = +677 +/- 141 pg/mL) or by adrenergic blockade (delta IRG = +1,374 +/- 314 pg/mL). However, the IRG response to hypoglycemia was reduced to 25% of the control value by the combination of adrenergic blockade + methylatropine (delta IRG = +250 +/- 83 pg/mL, P < .01 v control rats). These results suggest that the plasma glucagon response to hypoglycemia in conscious rats is predominantly the result of autonomic neural activation, and is redundantly mediated by the parasympathetic and sympathoadrenal divisions of the autonomic nervous system.

An analysis of the glucagon response to hypoglycaemia in patients with type 1 diabetes and in healthy subjects

The study aimed to analyse the glucagon response during hypoglycaemia in relation to gender, level of hypoglycaemia, and hyperinsulinaemia as well as its relation to other counterregulatory hormones in patients with Type 1 diabetes and in nondiabetic subjects. Mild hypoglycaemia was induced by an i.v. insulin infusion (244 pmol kg-1h-1) for 180 min in 43 Type 1 diabetic patients and 22 nondiabetic subjects. Venous blood glucose, plasma free insulin, glucagon, adrenaline, noradrenaline, growth hormone, and cortisol were measured every 15-30 min. The hormonal responses during hypoglycaemia were evaluated from the incremental areas under their respective curves. There was a linear correlation between the glucagon response and the decremental area of blood glucose (p < 0.005), but the slope of the regression line in the diabetic group was less steep than in the controls (p < 0.5), and, in spite of the deeper hypoglycaemia in the diabetic groups, their glucagon response was diminished (p < 0.05). Plasma, adrenaline, growth hormone and cortisol all increased during hypoglycaemia. The glucagon response correlated with the responses of growth hormone and cortisol in both groups, while it was positively correlated with the adrenaline response (p < 0.001) and inversely with the plasma insulin (p < 0.001) only in the diabetic patients. Although the insulin infusion rate was identical, the female diabetic patients had a lower metabolic clearance rate of insulin as compared with the males (p < 0.05). There was no statistical difference in the counterregulatory hormone responses between males and females in neither of the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Pancreatic and pituitary hormonal responses to insulin-induced hypoglycaemia during muscarinic cholinergic blockade in man

To investigate the role of muscarinic cholinergic mechanisms in mediating the pancreatic and pituitary hormonal responses to hypoglycaemia, six normal subjects were studied during acute insulin-induced hypoglycaemia under control conditions, and during blockade with intravenous atropine. During atropine blockade the response of pancreatic polypeptide was suppressed while the maximum response of plasma glucagon was significantly higher. The increment in plasma vasopressin was also increased significantly during cholinergic blockade. During blockade with atropine the responses of plasma prolactin was reduced, with a slight but significant reduction in the growth hormone response, and although a similar maximum response of plasma ACTH was achieved, this rise was delayed. These results implicate involvement of a cholinergic muscarinic inhibitory and stimulatory mechanisms in regulating the responses of pancreatic and pituitary hormones to hypoglycaemia.

Inadequate adrenergic response to disopyramide-induced hypoglycemia

OBJECTIVE

To report a case of disopyramide-induced hypoglycemia and to discuss the observed inadequate adrenergic response in this patient. Risk factors, possible etiologies, and preventive measures are also discussed.

DATA SOURCES

References from case reports and review articles as identified by MEDLINE.

DATA SYNTHESIS

A wide variety of drugs has been implicated as causing hypoglycemia. The mechanism for drug-induced hypoglycemia is known for the majority of these agents. Case reports of disopyramide-induced hypoglycemia have been reported in the literature, but the mechanism of action is unclear. We report a case of disopyramide-induced hypoglycemia in which counter-regulatory hormones, serum insulin, and C-peptide concentrations were obtained. From these data, it appears that disopyramide-induced hypoglycemia results from endogenous insulin secretion, with concomitant inadequate counterregulatory response.

CONCLUSIONS

Although a rare occurrence, disopyramide-induced hypoglycemia is potentially life-threatening. Patients at risk for this reaction need to be identified prior to the institution of disopyramide therapy. Patients at risk for hypoglycemia should be monitored while on disopyramide and disopyramide blood concentrations should be maintained at the lower end of the therapeutic range, or alternative agents should be considered.

Indomethacin and salicylate modulate effect of insulin on glucose kinetics in dogs

We studied insulin's effects on glucose production (Ra) and utilization (Rd) in trained, conscious dogs before and during treatment with indomethacin (Indo) and salicylate (S). Ra and Rd (mg X kg-1 X min-1) were calculated by isotope dilution using [3-3H]glucose. Animals were treated with either oral Indo or acetylsalicylic acid for 1 day before the respective studies. On the study day, experimental animals were given a continuous infusion of either saline (control), Indo (5 mg/kg bolus followed by 0.05 mg X kg-1 X min-1), or sodium salicylate (0.45 mg X kg-1 X min-1) for 330 min on separate days; each animal participated in all three protocols. After establishing steady-state specific activity, control (C) and experimental animals (n = 6/group) received insulin, 0.275 mU X kg-1 X min-1 for 150 min, raising serum insulin levels two- to threefold above basal. During insulin infusion in C, plasma glucose (G) fell from 99 +/- 2 to 82 +/- 6 ml/dl (P less than 0.01), associated with a transient fall in Ra from 2.5 +/- 0.3 to 1.9 +/- 0.2 (P less than 0.01) at 30 min, returning to base line at 45 min; Rd did not change. In the Indo and S groups, G also fell by a similar extent. In contrast to C, however, the fall in G was associated with a rise in Rd, commencing at 30 min in the Indo group (P less than 0.05) and at 45 min in the S group (P less than 0.01); Ra did not fall and actually rose above basal (P less than 0.05), although it did not match the rise in Rd.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of parasympathetic nervous system in glucagon response to insulin-induced hypoglycemia in normal and diabetic rats

Effects of cholinergic mechanisms on glucagon and epinephrine responses to insulin-induced hypoglycemia were examined in diabetic and age-matched control male rats. Atropine did not affect plasma glucose levels or plasma glucagon concentrations, in the basal state, in normal or short-term diabetic rats (10 to 15 days following streptozotocin injection). However, atropine blocked the glucagon response to insulin hypoglycemia in both normal and short-term diabetic rats. Subcutaneous injection of carbachol also failed to alter basal plasma glucose, glucagon, or epinephrine values in both normal and diabetic rats. The lack of glucagon and epinephrine responses to insulin hypoglycemia in long-term diabetic rats (80 to 100 days after streptozotocin injection) was reversed with a single dose of carbachol. Carbachol exaggerated the glucagon response to insulin hypoglycemia in normal and short-term diabetic rats. These results demonstrate that the parasympathetic nervus system plays an important role in the glucagon release in response to insulin hypoglycemia in rats. The lack of glucagon response to insulin hypoglycemia observed in long-term diabetic rats could be due to deteriorated parasympathetic nervous system and also could be corrected with carbachol.

Glucose counterregulation during prolonged hypoglycemia in normal humans

To study glucose counterregulation under conditions approximating those of clinical disorders in which hypoglycemia develops gradually and is reversed over a prolonged period, we injected regular insulin subcutaneously, in a dose (0.15 U/kg) selected to produce two- to threefold increases in plasma insulin, in 11 normal human volunteers and measured plasma glucose, insulin, C-peptide, and counterregulatory hormone concentrations as well as rates of glucose production, glucose utilization, and insulin secretion over 12 h. The data suggest that the mechanisms of gradual recovery from prolonged hypoglycemia may differ from those of rapid recovery from short-term hypoglycemia produced by intravenous injection of insulin in that 1) both stimulation of glucose production and limitation of glucose utilization contribute to recovery from prolonged hypoglycemia; 2) increases in glucagon, epinephrine, growth hormone, and cortisol secretion as well as a decrease in insulin secretion may all participate in glucose counterregulation during prolonged hypoglycemia; 3) epinephrine may play a more important role than glucagon during prolonged hypoglycemia. The latter two conclusions are based primarily on the temporal relationships between changes in the rates of glucose turnover and changes in plasma hormone concentrations and should not be considered proved. However, they provide the basis for testable hypotheses concerning the physiology of gradual recovery from prolonged hypoglycemia that can be expected to be relevant to the pathophysiology of clinical hypoglycemia.

Hormonal response to insulin-induced hypoglycemia in patients with Shy-Drager syndrome

We examined the response of plasma glucose concentration and glucose counterregulatory factors (eg, glucagon, epinephrine, growth hormone, cortisol, and norepinephrine) to insulin-induced hypoglycemia in four patients with Shy-Drager syndrome and in five control subjects to determine if glucose counterregulation occurred in the patients with sympathetic and parasympathetic nervous system defects. The recovery of plasma glucose from hypoglycemia in a slower phase in the patients appeared to be almost similar to that in the control subjects, along with the absence of an initial rapid recovery phase; that is, there was no significant difference in the plasma glucose levels observed at any point between the patients and the control subjects. Although the insulin-induced hypoglycemia in the control subjects provoked a rapid release of epinephrine, followed by an increase in the plasma glucagon, growth hormone, and cortisol levels, it did not cause a significant increase in any of the glucose counterregulatory factors in the patients. Our findings that the restoration of normoglycemia after insulin-induced hypoglycemia occurred despite no significant increase in the counterregulatory hormonal factors suggest that other glucose counterregulatory mechanisms (eg, increased glucose release from the liver by the intrinsic effect of hypoglycemia on the liver) than the hormonal glucose counterregulatory factors might play an important role in the recovery of plasma glucose from insulin-induced hypoglycemia in a state of chronic deficiency of hormonal factors.

Release of glucagon in male alcoholics with vagal neuropathy

There is evidence supporting involvement of the parasympathetic nervous system in the control of glucagon secretion. We have investigated the possible role of vagal neuropathy in alcoholics as a cause of alcoholic hypoglycemia. Slow infusions of insulin (2.4 U/hr) were carried out in ten male alcoholics, four with and six without evidence of vagal neuropathy, and in six male controls. The fall in blood glucose levels and the rise in serum glucagon levels in the alcoholics with or without vagal neuropathy were not significantly different from controls. We conclude that vagal neuropathy in alcoholics has no effect on the glucagon response to hypoglycemia.

Neural mechanisms involved in the recovery from insulin hypoglycemia in dogs

The contribution of the central nervous system to recovery from insulin hypoglycemia was studied in dogs. Animals with spinal transection just above the sympathetic outflow (to isolate it from encephalic influences), bilateral vagotomy or both types of lesion received an i.v. insulin injection. Also dogs in which the entire central nervous system had been inactivated by osmotic shock were submitted to this test. The results, compared to those obtained from control groups, showed that either spinal transection or severance of the vagi alone did not prevent full recovery from hypoglycemia. When both surgical procedures were combined or the entire central nervous system had been functionally destroyed normal blood glucose concentration was not regained.

Hormonal, metabolic and cardiovascular responses to hypoglycaemia in Type 1 (insulin-dependent) diabetes with and without residual B cell function

Hormonal, metabolic and cardiovascular responses to insulin induced hypoglycaemia were investigated in seven Type 1 (insulin-dependent) diabetic patients with residual B cell function, eight Type 1 diabetic patients without B cell function and six healthy subjects. No differences were found between the diabetic groups regarding nadir of glucose and rate of recovery to normoglycaemia. The patients with residual B cell function had a glucagon response to hypoglycaemia which was close to that of normal subjects. In patients without B cell function, the glucagon response to hypoglycaemia was present, albeit significantly smaller than in the patients with preserved B cell function (0.025 ng/ml, range 0.007-0.042 versus 0.054 ng/ml, range 0.029-0.087). The group without B cell function had signs of an exaggerated rate of lipolysis and ketogenesis compared with the patients with B cell function and the normal subjects.

Lack of glucagon response in glucose counter-regulation in type 1 (insulin-dependent) diabetics: absence of recovery after prolonged optimal insulin therapy

Mild hypoglycaemia was induced using an artificial pancreas in five normal subjects (from 5.00 +/- 0.15 to 2.83 +/- 0.15 mmol/l) by infusing 28 mU/m2 per min soluble insulin for 60 min. Six Type 1 (insulin-dependent) diabetic patients were stabilized for 14h using an artificial pancreas. They were then rendered hypoglycaemic (from 4.94 +/- 0.09 to 2.89 +/- 0.11 mmol/l) by infusing 28 mU/m2 per min plus 16 +/- 3.8 mU/min insulin for 60 min. Before the study, the diabetic patients were in optimal blood glucose control (mean blood glucose 6.72 +/- 0.11 mmol/l over the previous 14-20 days; HbA1 8.3 +/- 0.1%). During the insulin infusion test, blood glucose decrement was slower in the diabetic patients than in the control subjects. The blood glucose nadir was delayed in the diabetics until 75 min compared with 55 min in the control subjects. Blood glucose recovery rate in the diabetic subjects was severely impaired. In Type 1 diabetes, the counter-regulatory hormonal response to insulin induced hypoglycaemia is similar to that of non-diabetics, except for that of glucagon, the blunted response of which is not reversed by prolonged optimisation of blood glucose control. This impaired response of the A cell does not seem to be a consequence of insulin deficiency.

Autonomic neural control mechanisms of substrate and hormonal responses to acute hypoglycaemia in man

The contributions of adrenergic and cholinergic mechanisms to recovery from acute hypoglycaemia induced by insulin (0.15 units/kg i.v.) were examined in eleven normal subjects, six subjects with a pre-ganglionic sympathectomy (adrenergic denervation) and six sympathectomized subjects given atropine (combined adrenergic denervation and cholinergic blockade). Blood glucose recovery was impaired only in the sympathectomized subjects given atropine. The blood lactate response was reduced and the rise in free fatty acids was delayed in both groups of sympathectomized subjects, in whom the normal rises of plasma cyclic AMP and noradrenaline were absent. The plasma pancreatic glucagon response was appropriate to the prevailing blood glucose concentrations in all three groups. The cortisol response was impaired and the pattern of ACTH secretion was abnormal in sympathectomized subjects given atropine. Growth hormone levels were higher in both sympathectomized groups. Blood glucose homeostasis was impaired during combined adrenergic denervation and cholinergic blockade. Glucagon secretion was activated independently of vagal control. In the sympathectomized group given atropine, the rise in plasma cortisol was blunted despite a greater degree of hypoglycaemia. A blockade of central cholinergic receptors producing impaired activation of ACTH secretion at hypothalamic level may explain, at least in part, this delayed restoration of normoglycaemia.

[Glucagon, growth hormone, and cortisol response to insulin-induced hypoglycemia in insulin-dependent diabetics (IDD) without autonomic neuropathy (author's transl)]

Insulin-induced hypoglycemias are a sign of non-sufficient counterregulation, in which different contra-insulinary hormones participate. The aim of the study was to investigate, whether there exists a difference between IDD and non-diabetics regarding secretion of glucagon, cortisol, and growth hormone during an insulin-induced hypoglycemia and further on pointing out, expecially, the importance of glucagon. Insulin-induced hypoglycemias are counterregulated in non-diabetics, not in IDD. The missing glucagon secretion during insulin-induced hypoglycemia in IDD seems to be independent from an autonomic neuropathy. Only after high doses of exogenous glucagon can one see a counterregulating increase of glucose. The STH secretion is similar in non-diabetics and IDD during an insulin-induced hypoglycemia and has evidently only a secondary effect in hypoglycemic counterregulation. The STH secretion may be the expression of a diencephal-triggered stress situation. The cortisol secretion is the same in both groups. The gluconeogenetic effect of cortisol is not sufficient to accomplish a fast compensation of hypoglycemia. This does not exclude long-term effects. When inhibiting the secretion of insulin and different contra-insulinary hormones with somatostatin, one is able to demonstrate that glucagon alone is a sufficiently counterregulatory hormone in insulin-induced hypoglycemias.

Beta blockade and diabetes mellitus: effect of oxprenolol and metoprolol on the metabolic, cardiovascular, and hormonal response to insulin-induced hypoglycemia in normal subjects

In a double-blind randomized study, the effect of the acute administration of a single oral dose of oxprenolol, a nonselective beta-blocker, and of metoprolol, a beta 1 selective blocker, on insulin-induced hypoglycemia was tested in seven normal subjects. Neither of the drugs potentiated the hypoglycemic effect of insulin. The recovery from hypoglycemia was delayed by both blocking agents only in the late phases of the experimental observation. This effect could not be accounted for by suppression of release of the counterregulatory hormones glucagon or cortisol, but may be mediated by the inhibition of NEFA and gluconeogenic-substrate release in response to hypoglycemia. Both drugs blocked the hypoglycemia-induced tachycardia. Only oxprenolol raised diastolic blood pressure during hypoglycemia. Symptoms of hypoglycemia were not masked by either blocking agent, and sweating was enhanced and prolonged by both drugs. Thus, no clear-cut differences in the glycemic response to insulin-induced hypoglycemia were found between metoprolol and oxprenolol, but the drugs differed in their influence upon the blood pressure response to insulin-induced hypoglycemia.

The effect of different diets and of insulin on the hormonal response to prolonged exercise

The importance of carbohydrate availability during exercise for metabolism and plasma hormone levels was studied. Seven healthy men ran on a treadmill at 70% of individual maximal oxygen uptake having eaten a diet low (F) or high (CH) in carbohydrate through 4 days. At exhaustion the subjects were encouraged to continue to run while glucose infusion increased plasma glucose to preexercise levels. Forearm venous blood, biopsies from vastus muscle and expiratory gas were analyzed. Time to exhaustion was longer in CH- (106 +/- 5 min (S.E.)) than in F-expts. (64 +/- 6). During exercise, overall carbohydrate combustion rate, muscular glycogen depletion and glucose and lactate concentrations, carbohydrate metabolites in plasma, and estimated rate of hepatic glucose production were higher, fat metabolites lower, and the decrease in plasma glucose slower in CH- than in F-expts. Plasma norepinephrine increased and insulin decreased similarly in CH- and F-expts., whereas the increase in glucagon, epinephrine, growth hormone and cortisol was enhanced in F-expts. Glucose infusion eliminated hypoglycemic symptoms but did not substantially increase performance time. During the infusion epinephrine decreased markedly and glucagon even to preexercise levels. Infusion of insulin (to 436% of preexercise concentration) in addition to glucose in F-expts. did not change the plasma levels of the other hormones more than infusion of glucose only but reduced fat metabolites in plasma. At exhaustion muscular glycogen depletion was slow, and the glucose gradient between plasma and sarcoplasma as well as the muscular glucose 6-phosphate concentration had decreased.

CONCLUSIONS

The preceding diet modifies the energy depots, the state of which (as regards size, receptors and enzymes) is of prime importance for metabolism during prolonged exercise. Plentiful carbohydrate stores favor both glucose oxidation and lactate production. During exercise norepinephrine increases and insulin decreases independent of plasma glucose changes whereas receptors sensitive to glucose privation but not to acute changes in insulin levels enhance the exercise-induced secretion of glucagon, epinephrine, growth hormone and cortisol. Abolition of cerebral hypoglycemia does not inevitably increase performance time, because elimination of the hypoglycemia may not abolish muscular energy lack.

Differential effect of isoproterenol on acute glucagon and insulin release in man

In man, the infusion of arginine or isoproterenol elevates immunoreactive glucagon and insulin levels. Since arginine administered as a pulse stimulates the acute secretion of both hormones, and an insulin rise is observed after the bolus injection of isoproterenol, these findings probably represent a direct effect of arginine and isoproterenol on islet cells. To determine if there is an acute alpha-cell response to isoproterenol, we have administered this beta-adrenergic agonist as a bolus to healthy volunteers. Arginine administered as a pulse elicited both insulin and glucagon responses whereas pulses of isoproterenol, at half maximal and maximal insulin-stimulating doses, had little effect on glucagon levels. This relative insensitivity of the alpha cells to stimulation by isoproterenol suggests that endogenous beta-adrenergic tone may have a stronger influence on insulin than on glucagon secretion. Furthermore, these findings raise the possibility that beta-adrenergic regulation of plasma glucagon levels in vivo occurs by an indirect mechanism rather than a direct effect on the alpha cells.

Plasma glucagon levels in haemorrhagic shock

Eleven healthy dogs were subjected to haemorrhagic shock for 90 min. after which shed blood was reinfused. Detailed studies were made of cardiopulmonary function. Samples of blood were taken at frequent intervals for the measurement of glucagon, insulin and glucose. Three dogs had samples taken for catecholamine levels. The glucagon level rose during haemorrhagic shock but there was no relationship between this rise and the change in cardiorespiratory measurement, but there was a relationship between the plasma glucagon level, the blood glucose and the catecholamine level. It is suggested that the release of glucagon in haemorrhagic shock is mediated by sympathetic stimulation of the alpha cell and that the rise in glucagon is in part responsible for the hyperglycaemia which is found in shock.