The effect of adrenergic blockade on the glucagon responses to starvation and hypoglycemia in man

Direct effects of catecholamines on hepatic glucose production in conscious dog are due to glycogenolysis

The effects of catecholamines (CATS) infused into the hepatic portal vein were studied in ten 18-h-fasted conscious dogs. Glucose production (GP) and gluconeogenesis (GNG) were assessed using tracer ([3H]glucose, [14C]alanine) and arteriovenous difference techniques. Each experiment consisted of a 100-min equilibration, a 40-min basal, and two 90-min test periods. A pancreatic clamp (somatostatin + basal portal insulin and glucagon) was used to fix insulin and glucagon at basal levels. Propranolol (1 microgram.kg-1.min-1) and phentolamine (2 micrograms.kg-1.min-1) were infused intraportally during both test periods of the blockade group while a carrier solution was infused in the control group. Norepinephrine (NE; 100 ng.kg-1.min-1) and epinephrine (Epi; 40 ng.kg-1.min-1) were infused intraportally during the second test period of both protocols. Portal NE (70 +/- 46 to 8,404 +/- 674 and 162 +/- 57 to 6,530 +/- 624 pg/ml, respectively) and portal Epi (21 +/- 11 to 3,587 +/- 309 and 29 +/- 6 to 2,989 +/- 406 pg/ml, respectively) rose in the control and adrenergic blockade groups, respectively. The increases in arterial NE and Epi were modest in both groups. Intraportal infusion of CATS increased GP from 2.1 +/- 0.2 to 6.2 +/- 1.0 mg.kg-1.min-1 in the control group but did not change it (2.7 +/- 0.4 to 2.7 +/- 0.3 mg.kg-1.min-1) in the blockade group. Portal CATS had no effect on GNG in the presence or absence of adrenergic blockade (GNG rose from 0.7 +/- 0.2 to 0.9 +/- 0.2 and 0.8 +/- 0.2 to 1.0 +/- 0.2 mg.kg-1.min-1 in the control and blockade groups, respectively). In conclusion, portal infusion of catecholamines significantly augmented GP by selectively stimulating glycogenolysis. The increase in hepatic GP could be completely inhibited by intraportal adrenergic blockade.

Effects of hyperinsulinemia on the subsequent hormonal response to hypoglycemia in conscious dogs

The aim of this study was to determine if differing periods of prior hyperinsulinemic nonhypoglycemia can modify the subsequent counterregulatory response to hypoglycemia. Experiments were carried out on 19 normal 18-h fasted conscious dogs. Insulin was infused intraportally at 8 mU.kg-1.min-1 for 3 h on two occasions and 3.5 h on a third separate occasion. This resulted in similar steady-state arterial insulin levels during each protocol (4,370 +/- 433 pmol/l). Each animal was maintained at a similar plasma glucose nadir (2.8 +/- 0.6 mmol/l) for 2 or 2.5h, depending on the protocol. In protocol I (n = 7) plasma glucose was allowed to fall to the desired hypoglycemic plateau by 30 min. In a second group of dogs (protocol II, n = 5) there was a 30-min period of euglycemic hyperinsulinemia followed by a 30-min fall (similar to protocol I) in plasma glucose. In a third group of dogs (protocol III, n = 7), there was an initial 15-min period of euglycemic hyperinsulinemia followed by a 45-min fall in plasma glucose. Differing periods of euglycemic hyperinsulinemia had distinct effects on subsequent counterregulation. During the final 2 h of hypoglycemia the incremental area under the curve (AUC) for glucagon was significantly greater in protocol I vs. II (3.0 +/- 1.0, -0.5 +/- 0.2 micrograms.l-1.min-1, P < 0.02, respectively). Conversely, catecholamine levels were increased in protocol II (30 min prior hyperinsulinemic euglycemia) compared with protocol I (epinephrine 1,448 +/- 268, 855 +/- 119 nmol.l-1.min-1; norepinephrine 244 +/- 30, 166 +/- 23 nmol.l-1.min-1, respectively, P < 0.05). During protocol III, glucagon and catecholamine levels were intermediate between protocols I (no euglycemic hyperinsulinemia) and II (30 min euglycemic hyperinsulinemia).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Preserved insulin secretion and insulin independence in recipients of islet autografts

BACKGROUND

Transplantation of pancreatic islets, rather than whole pancreas, has been introduced as a treatment for diabetes mellitus. We studied five patients ranging in age from 12 to 37 years who had severe chronic pancreatitis for which they underwent total pancreatectomy followed by isolation and hepatic transplantation of their own islets.

METHODS

All patients had remained insulin-independent for 1 to 7 1/2 years after transplantation. The numbers of islets transplanted ranged from 110,000 to 412,000. Islet function was assessed by measuring the plasma insulin responses to intravenous glucose and arginine and the plasma glucagon responses to hypoglycemia and arginine. In one patient, islet function was studied during catheterization of the hepatic vein, portal vein, and splenic artery and by analysis of a liver-biopsy specimen.

RESULTS

After transplantation, the mean (+/- SD) fasting plasma glucose concentration was 122 +/- 47 mg per deciliter (6.8 +/- 2.6 mmol per liter) and the hemoglobin A1c concentration was 6.0 +/- 0.8 percent in the five patients. The values were most abnormal--214 mg per deciliter (11.9 mmol per liter) and 7.3 percent, respectively--in the patient who received only 110,000 islets. The acute plasma insulin responses to glucose and to arginine in the five patients were 23 +/- 13 and 26 +/- 10 microU per milliliter (168 +/- 94 and 184 +/- 70 pmol per liter), respectively, as compared with 58 +/- 6 and 37 +/- 8 microU per milliliter (416 +/- 44 and 267 +/- 61 pmol per liter) in the normal subjects. The peak plasma glucagon responses to insulin and arginine were 21 +/- 4 and 65 +/- 36 pg per milliliter, respectively, as compared with 125 +/- 28 and 156 +/- 99 pg per milliliter in the normal subjects. All five patients had plasma epinephrine but not pancreatic polypeptide responses to hypoglycemia. The results of the hepatic-vein catheterization in one patient indicated that the transplanted islets released insulin and glucagon in response to arginine. Immunoperoxidase staining of this patient's liver-biopsy specimen showed that the islets contained insulin, glucagon, and somatostatin but not pancreatic polypeptide.

CONCLUSIONS

Intrahepatic transplantation of as few as 265,000 islets can result in the release of insulin and glucagon at appropriate times and in prolonged periods of insulin independence.

Hypoglycemia in pediatric renal allograft recipients

Symptomatic hypoglycemia developed 5 to 45 months after transplantation in nine children who had renal transplants before 6 years of age. During hypoglycemia, serum glucose levels ranged from 14 to 39 mg/dl (0.8 to 2.1 mmol/L). Hypoglycemic episodes occurred between 1.7 and 7.5 years of age. Six patients had generalized seizures; the remaining three had diaphoresis with stupor or lethargy. None of the children had serious infections, diabetes, congenital defects of glucose metabolism, or a history of treatment with insulin or oral hypoglycemic agents. Six patients had hypoglycemic symptoms after a prolonged fast, and at least four had ketosis. Eight of the nine patients were receiving propranolol when hypoglycemia occurred. No differences in the daily prednisone dose, the number of transplant rejection episodes, or the frequency of treatment with medications other than propranolol were noted between hypoglycemic patients and 56 normoglycemic age-matched renal transplant recipients. All hypoglycemic patients were subsequently treated with frequent feedings and discontinuation of propranolol. No further hypoglycemic episodes have occurred in eight of nine patients. Symptomatic hypoglycemia should be recognized as a potentially devastating complication of pediatric renal transplantation.

Alpha-adrenergic system in the modulation of pancreatic A and B cell function in normal rats

The role of the alpha-adrenergic system in the control of pancreatic A and B cell function was investigated in an isolated perfused rat pancreas model. Two experimental procedures were performed. In the first one we evaluated the effects of two distinct concentrations (10(-8) M and 10(-7) M) of five adrenergic substances, with varying degrees of potency on the alpha-adrenergic presynaptic receptor, on insulin (IRI) and glucagon (IRG) release induced by arginine (20 mM) plus glucose (6.6 mM). In the second procedure we studied the effects of the two alpha-blocking agents yohimbine (alpha 2-blocker) and prazosin (alpha 1-blocker) at 10(-7) M on epinephrine-modulated IRI and IRG response to the same combined metabolic stimulus. The inhibitory activity on basal and metabolically induced IRI secretion of the agonists was superimposable on their potency on the presynaptic alpha 2-adrenergic receptors. Similarly, the alpha 1-blocking agent prazosin was less effective than the alpha 2-blocker yohimbine in counteracting the inhibitory effects of epinephrine on basal and arginine plus glucose-induced insulin release. The alpha-cell activity was clearly stimulated by epinephrine, whereas selective alpha-adrenergic drugs showed no significant action on IRG secretion. Both alpha-blockers were ineffective on basal IRG release, while they had some potentiating effect on the epinephrine-induced glucagon release in basal state and during the metabolic stimulus, without a significant difference between the two drugs. We conclude that, at least in the isolated perfused rat pancreas, alpha 2-adrenergic receptors are involved in the inhibition of IRI release induced by catecholamines. On the contrary, the alpha-adrenergic system does not seem to play an essential role in the regulation of IRG secretion; the potentiation of the epinephrine-induced stimulation of A cell function by the alpha-adrenergic blockade could be accounted for by a greater availability of the catecholamine at the beta-receptor binding sites.

Beta-adrenergic contribution to glucagon-induced glucose production and insulin secretion in uremia

Spontaneous or propranolol-induced hypoglycemia can occur in uremic humans. We studied glucose kinetics (using [3-3H]glucose) in five uremic humans 24 h after hemodialysis and in seven normal controls. The effect of glucagon infusion at rates of 3, 6, 12, and 18 ng X kg-1 X min-1 at 60-min intervals was compared with either saline or beta-adrenergic blockade (propranolol infusion). In uremics, plasma glucose increased by 20-25% and by 40-50% at the 3 and 6 ng X kg-1 X min-1 glucagon doses, respectively, with no further increases at higher infusion rates. Glucose production increased transiently and in tandem with glucose uptake at each glucagon increment (P less than 0.0001). During beta-adrenergic blockade, the effect of glucagon in stimulating glucose production was blunted by 14-24% at the 6-18 ng X kg-1 X min-1 doses (P less than 0.05). During saline infusion, plasma insulin concentrations increased progressively to peak levels fourfold above basal at the 18 ng X kg-1 X min-1 dose. This increase in plasma insulin was virtually abolished by concomitant beta-adrenergic blockade (P = 0.0002). In contrast to uremic subjects, normal controls exhibited lesser degrees of hyperglycemia and hyperinsulinemia at all glucagon infusion rates. Propranolol infusion had no effect on the increments in glucose production and uptake nor on the plasma insulin response. These results suggest that in uremic humans propranolol independently reduces the hepatic response to glucagon and the insulin secretory response to hyperglycemia and/or hyperglucagonemia. These observations provide a possible mechanism for the adrenergic regulation of glucose homeostasis in uremia.

Receptor binding and adenylate cyclase activities of glucagon analogues modified in the N-terminal region

In this study, we determined the ability of four N-terminally modified derivatives of glucagon, [3-Me-His1,Arg12]-, [Phe1,Arg12]-, [D-Ala4,Arg12]-, and [D-Phe4]glucagon, to compete with 125I-glucagon for binding sites specific for glucagon in hepatic plasma membranes and to activate the hepatic adenylate cyclase system, the second step involved in producing many of the physiological effects of glucagon. Relative to the native hormone, [3-Me-His1,Arg12]glucagon binds approximately twofold greater to hepatic plasma membranes but is fivefold less potent in the adenylate cyclase assay. [Phe1,Arg12]glucagon binds threefold weaker and is also approximately fivefold less potent in adenylate cyclase activity. In addition, both analogues are partial agonists with respect to adenylate cyclase. These results support the critical role of the N-terminal histidine residue in eliciting maximal transduction of the hormonal message. [D-Ala4,Arg12]glucagon and [D-Phe4]glucagon, analogues designed to examine the possible importance of a beta-bend conformation in the N-terminal region of glucagon for binding and biological activities, have binding potencies relative to glucagon of 31% and 69%, respectively. [D-Ala4,Arg12]glucagon is a partial agonist in the adenylate cyclase assay system having a fourfold reduction in potency, while the [D-Phe4] derivative is a full agonist essentially equipotent with the native hormone. These results do not necessarily support the role of an N-terminal beta-bend in glucagon receptor recognition. With respect to in vivo glycogenolysis activities, all of the analogues have previously been reported to be full agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of alpha and beta adrenergic blockade on hepatic glucose balance before and after oral glucose. Role of insulin and glucagon

In conscious dogs, phentolamine infusion significantly increased fasting portal vein insulin, glucagon, and decreased net hepatic glucose output and plasma glucose. Propranolol significantly decreased portal vein insulin, portal flow, and increased hepatic glucose production and plasma glucose. Phentolamine, propranolol, and combined blockade reduced glucose absorption after oral glucose. alpha, beta, and combined blockade abolished the augmented fractional hepatic insulin extraction after oral glucose. Despite different absolute amounts of glucose absorbed and different amounts of insulin reaching the liver, the percent of the absorbed glucose retained by the liver was similar for control and with alpha- or beta blockade, but markedly decreased with combined blockade. Our conclusions are: (a) phentolamine and propranolol effects on basal hepatic glucose production may predominantly reflect their action on insulin and glucagon secretion; (b) after oral glucose, alpha- and beta-blockers separately or combined decrease glucose release into the portal system; (c) net hepatic glucose uptake is predominantly determined by hyperglycemia but can be modulated by insulin and glucagon; (d) direct correlation does not exist between hepatic delivery and uptake of insulin and net hepatic glucose uptake; (e) alterations in oral glucose tolerance due to adrenergic blockers, beyond their effects on glucose absorption, can be, to a large extent, mediated by their effects on insulin and glucagon secretion reflecting both hepatic and peripheral glucose metabolism.

Effect of clonidine on glucose, insulin and glucagon responses to a protein meal in type 2 diabetics

The authors investigated the effects of clonidine (alpha-2 stimulating agent) on blood glucose, insulin and glucagon levels in order to assess the alpha-adrenergic regulation of endocrine pancreatic secretion. Ten hypertensive female subjects affected with type 2 diabetes were studied; each subject was given a protein meal (boiled beef 200 g); blood samples were taken at -30, 0, 30, 60, 90 and 120 min; after this test each subject was treated for 4 days with clonidine (0.150 mg, 3 times/day per os); at the 5th day the protein meal was repeated under the same conditions except for the added administration of clonidine. Plasma glucose, insulin and glucagon were estimated. The administration of a protein meal caused a significant increase of blood glucose (peak at 60 min), insulin (peak at 90 min) and glucagon (peak at 90 min) levels; the association of clonidine caused an increase of blood glucose (single values and total areas) without changes of insulin and glucagon levels, when compared to those obtained before clonidine treatment. In conclusion, the association of clonidine to a protein meal caused impaired glucose tolerance presumably due to a direct glycogenolytic effect, occurring in the liver on account of an alpha-2 receptor stimulation, insulin and glucagon not being involved in this phenomenon.

Beta-blockers and glucose control

Literature on the effects of beta-blockers on blood glucose is reviewed. Data are presented regarding the adrenergic influences on glucose regulation and the effects of beta-blockade during hypo- and hyperglycemia in normal and diabetic individuals. beta-adrenergic stimulation enhances insulin and glucagon secretion, as well as glycogenolysis, gluconeogenesis, and lipolysis. alpha-adrenergic stimulation inhibits insulin secretion and may inhibit glucagon secretion and enhance liver glycogenolysis. In nondiabetics, beta-blockers represent minimal risk of affecting glucose control. In insulin-dependent diabetics, beta-blockers can prolong, enhance, or alter the symptoms of hypoglycemia, while hyperglycemia appears to be the major risk in noninsulin-dependent diabetics. beta-blockers can potentially increase blood glucose concentrations and antagonize the action of oral hypoglycemic drugs.

Opiate modulation of glucose turnover in dogs

We examined the effect of opiate infusion and of opiate blockage on glucose turnover in the basal state, using isotope dilution techniques in trained conscious dogs (n = 5). After a primed-continuous infusion of 3-3H glucose to steady state specific activity (90 minutes), infusion of one of the following was given: D-met2 pro5 enkephalinamide (DMPE), a potent morphine-like opiate, 0.5 mus g/kg/min; naloxone, an opiate antagonist, 1.25 mg followed by 10 mus g/min; or saline control. Infusion of DMPE led to a fall in glucose from 92 +/- 3 to 87 +/- 3 mg/dL by 60 minutes (P less than 0.05), associated with a rise in glucose utilization (Rd) from 3.0 +/- 0.4 to 3.9 +/- 0.6 mg/kg/min by 30 minutes (P less than 0.05); a transient rise in glucose production (Ra; from 3.2 +/- 0.4 to 4.3 +/- 0.4 mg/kg/min; P less than 0.05). Changes in counterregulatory hormones did not account for these findings; insulin was unchanged during all infusions; glucagon showed small late rises at 75 minutes during both DMPE and naloxone infusion; cortisol rose by 30 and 15 minutes, respectively, of DMPE and naloxone infusion; epinephrine rose transiently after 5 minutes of naloxone but was unchanged during DMPE, and norepinephrine was unchanged throughout. Saline infusion had no effects on any of these indices. We conclude that a potent opiate with morphine-like effects (DMPE) can lower glucose in dogs by enhancing peripheral glucose utilization independently of hormonal changes.

Adrenergically mediated intrapancreatic control of the glucagon response to glucopenia in the isolated rat pancreas

Alpha adrenergic blockade with phentolamine (10 microM) reduces the glucagon response to severe glucopenia (from 150 to 25 mg/dl) to 22% of the control values in the isolated perfused rat pancreas. Propranolol (10 microM) had no significant effect. Neither alpha nor beta adrenergic blockade reduced the magnitude of glucopenic suppression of insulin secretion, but phentolamine increased insulin levels before and during glucopenia. The pattern of somatostatin secretion in these experiments resembled that of insulin. Depletion of norepinephrine from sympathetic nerve endings by pretreatment with 6-hydroxydopamine lowered the pancreatic norepinephrine content to less than 20% of control values and reduced the glucagon response to glucopenia to 69% of the controls. Combined alpha and beta adrenergic blockade during less severe glucopenia (from 120 to 60 mg/dl) reduced the glucagon response to 21% of controls. However, slight glucopenia (from 100 to 80 mg/dl), which elicited only 11% increase in glucagon in the control experiments, was not altered significantly by combined alpha and beta adrenergic blockade. Morphologic studies of adrenergic nerve terminals labeled with [3H]norepinephrine revealed associations with alpha cells. It is concluded that in the isolated rat pancreas adrenergic mediation accounts for most of the glucagon but not insulin response to glucopenia. It is controlled within the pancreas itself, possibly through a direct enhancement by glucopenia of norepinephrine release from nerve endings.

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.

Effect of sodium salicylate on hormonal responses to hypoglycaemia in type II diabetics

Prostaglandins and prostaglandin synthesis inhibitors are known to influence the secretion of a number of hormones. More specifically, sodium salicylate is known to increase insulin secretion in Type II diabetics in response to a glucose stimulus. To challenge the hypothesis that prostaglandins may be instrumental in a generalized defect of glucose recognition in Type II diabetics, the effect of sodium salicylate on the hormonal counter-regulatory response to insulin-induced hypoglycaemia was examined. Before salicylate treatment, seven Type II diabetics had brisk increases (mean +/- SEM) in circulating adrenaline (time 0 = 50 +/- 7 pg/ml; peak = 1630 +/- 330 pg/ml), noradrenaline (time 0 = 260 +/- 46 pg/ml; peak = 770 +/- 140 pg/ml), glucagon (time 0 = 38 +/- 6 pg/ml; peak = 75 +/- 10 pg/ml) and pancreatic polypeptide (time 0 = 149 +/- 30 pg/ml; peak = 1170 +/- 180 pg/ml) in response to insulin-induced hypoglycaemia. In contrast to previous studies in normal subjects, treatment with sodium salicylate failed to augment hypoglycaemia-induced secretion of adrenaline, noradrenaline or pancreatic polypeptide in Type II diabetics. The glucagon response to hypoglycaemia was augmented by sodium salicylate when the data were expressed as the incremental area under the glucagon vs. time curve, but not when peak response was used for analysis. These results are inconsistent with a prostaglandin-related generalized defect in glucose recognition in Type II diabetics and suggest that augmentation of hormone secretion in these patients by sodium salicylate may be specific for glucose-induced insulin secretion.

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.

Improved but not normalized glucose counter-regulation during glucagon infusion in Type 1 (insulin-dependent) diabetes

Glucose counter-regulation during insulin-induced hypoglycaemia was studied in Type 1 diabetic patients without evidence of autonomic neuropathy and compared with that of a non-diabetic control group. The glucose recovery rate following hypoglycaemia was delayed in the diabetic compared with the control subjects and this was most pronounced for the initial, rapid phase of glucose increase (glucose increase in 15 min, control: 1.1 +/- 0.1 versus 0.4 +/- 0.1 mmol/l; p less than 0.01). The release of glucagon during hypoglycaemia was blunted in the diabetic patients (maximal plasma levels, control: 148 +/- 25 versus 70 +/- 10 pg/ml; p less than 0.01). The adrenaline levels were also lower compared with the control subjects (maximal plasma levels, control: 7.23 +/- 1.21 versus 3.27 +/- 0.87 nmol/l; p less than 0.05). To evaluate the importance of the blunted glucagon response for the delayed glucose compensation, glucagon was infused during the hypoglycaemia. Overall glucose recovery rate was improved but did not return to normal. Consequently impaired glucagon release in the diabetic patients cannot alone explain impaired glucoregulation; the lower adrenaline levels and/or an effect of the previous glucose levels per se on hepatic glucose production are probably also of importance.

Decreased plasma epinephrine concentrations after glucose ingestion in humans

Plasma levels of norepinephrine (NE), epinephrine (E), immunoreactive insulin (IRI), and glucose were measured in six healthy volunteers after glucose consumption and in six volunteers after a water solution. Ingestion of the glucose (100 g) solution significantly decreased E levels from 46.7 +/- 8.0 to 20.8 +/- 1.9 pg/mL (P less than 0.01). Three hours after the glucose ingestion, plasma E levels nearly returned to basal values. Plasma IRI and glucose levels peaked at 45 minutes after glucose consumption (P less than 0.01), then declined toward basal values. Plasma NE levels were unaffected by glucose consumption. There were no changes in glucose, IRI, NE, or E levels in the control group. These results suggest that E behaves as a counter-regulatory hormone to insulin under stimulation by glucose.

Opiates modulate insulin action in vivo in dogs

To investigate the influence of opiates on insulin action in vivo, we induced mild physiological hyperinsulinaemia (15-20 mU/l) in five trained conscious dogs in the absence or presence of ongoing infusion with the opiate agonist D-met2-pro5-enkephalinamide (DMPE, 0.5 micrograms X kg-1 X min-1), or the opiate antagonist naloxone (1.25 mg followed by 1 microgram X kg-1 X min-1). The effects on glucose production and glucose utilization were measured by isotope dilution using 3-3H-glucose. Glucose fell similarly over 30 min in response to insulin in controls (0.021 +/- 0.003 mmol X l-1 X min-1), and both the DMPE and naloxone studies (0.016 +/- 0.002 mmol X l-1 X min-1 and 0.017 +/- 0.003 mmol X l-1 X min-1, respectively). In control dogs, insulin lowered glucose by transiently suppressing production by 0.028 +/- 0.006 mmol X kg-1 X min-1 at 20-30 min without changing utilization. In contrast, in both the DMPE and naloxone studies insulin lowered glucose by markedly raising utilization at 20 min by 0.094 +/- 0.017 and 0.139 +/- 0.022 mmol X kg-1 X min-1, respectively. Furthermore, insulin failed to suppress production in both DMPE and naloxone studies and, as plasma glucose fell, production rose in both treatment groups at 20 min by 0.045 +/- 0.012 and 0.089 +/- 0.022 mmol X kg-1 X min-1 respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of exogenous glucagon on gastric acid secretion, mucosal blood flow, and stress ulcers in the rat: dose-response results under non-stress conditions and immobilization stress

In non-stressed rats and rats stressed by immobilization, gastric secretion (acid, pepsin), mucosal blood flow (MBF), stress ulcers as well as glucose, insulin, and glucagon in blood were studied during 8 h, with and without additional infusion of exogenous glucagon (0.2, 1.4, 9.8 micrograms/kg/h). Metabolic clearance of glucagon and the disappearance half-time of exogenous glucagon from blood do not differ during zero stress and stress, a fact that favors the assumption of hypersecretion of glucagon as the cause of stress hyperglucagonemia. During stress alone acid secretion (volume, acidity) and MBF are lower than during zero stress; pepsin remains unchanged. Under zero stress condition additionally administered glucagon inhibits pepsin and MBF, but not acid secretion, in a dose-dependent manner. The ulcer index increased without changing the severity of ulcers. During stress the intermediate and highest glucagon doses stimulate MBF and pepsin secretion, other variables remaining unchanged. It is concluded that glucagon effects on functions of the gastric mucosa in the rat vary fundamentally, depending upon the environmental conditions.

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.

Beta-adrenoceptor-blocking drugs: current status and the significance of partial agonist activity

There is some evidence that partial agonism is an important property of beta-blocking drugs, and this property may be exploited to produce a new range of positive inotropic drugs. With the established beta-adrenoceptor-blocking drugs, the level of partial agonist activity is weak and the dose-response curve for this property is shallow. However, its absence appears to increase the likelihood of inducing bronchospasm and bradycardia, and drugs that lack intrinsic sympathomimetic activity appear more likely to be associated with rebound cardiac arrhythmias on cessation of treatment. The idea of a small level of hormone activity--in this case, catecholamine activity--being necessary to maintain normal cardiac and perhaps bronchial function is not new. Minimal doses of steroids are essential to maintaining the inotropic action of cardiac muscle. There is now enough accumulated evidence to suggest that a minimal degree of beta-adrenoceptor stimulation is also important for normal bronchial and cardiac function, and its absence increases the incidence of bradycardia and the risks of bronchospasm and rebound arrhythmias.

Dietary components that regulate serum somatomedin-C concentrations in humans

Dietary components responsible for the regulation of somatomedin-C in humans were assessed in five adult volunteers of normal weight who were fasted for 5 d on three occasions, then refed three diets of differing composition. The serum somatomedin-C decreased from a mean prefasting value of 1.85 +/- 0.39 U/ml (+/- 1 SD) to 0.67 +/- 0.16 U/ml at the end of fasting (P less than 0.005). After refeeding for 5 d with a normal diet, the mean serum somatomedin-C increased to 1.26 +/- 0.20 U/ml. A protein-deficient (32% of control), isocaloric diet resulted in a significantly smaller increase, to a mean value of 0.90 +/- 0.24 U/ml (P less than 0.05). A diet deficient in both protein and energy led to a further fall 0.31 +/- 0.06 U/ml. The changes in somatomedin-C during fasting and refeeding correlated significantly with mean daily nitrogen balance (r = 0.90). We conclude that both protein and energy intake are regulators of serum somatomedin-C concentrations in adult humans, and energy intake may be of greater importance. The correlation between changes in somatomedin-C and nitrogen balance suggests that the former are directly related to changes in protein synthesis and may be helpful in assessing the response to nutritional therapy.

Evidence for a therapeutic effect of dl-propranolol in benign and malignant insulinoma: report of three cases

Two patients suffering from benign and one patient suffering from malignant insulinoma experienced frequent incapacitating hypoglycemic attacks which did not respond to treatment with streptozotocin, diazoxide and/or diphenylhydantoin. Dl-propranolol, in dosages ranging from 30-240 mg/day, successfully abolished the symptoms of hypoglycemia, prevented recurrent hypoglycemic attacks, and normalized blood glucose levels concomitant with a reduction in pulse rate to 60/min. The main mechanism of the drug's effect seems to be the suppression of insulin release. However, other mechanisms may be involved such as increased peripheral insulin resistance. No side effects of treatment with dl-propranolol were noted. In patients suffering from insulinoma who are refractory to other forms of treatment, and for those who need symptomatic relief before surgery, dl-propranolol may play an important therapeutic role.

Pancreatic endocrine function after total gastrectomy and truncal vagotomy

Oral and intravenous glucose tolerance tests were performed in four groups: (1) preoperative patients, (2) patients with interposition reconstruction after total gastrectomy, (3) patients with Roux-Y reconstruction after total gastrectomy, and (4) patients with intrathoracic replacement after esophagectomy. We obtained the following results: (1) Hyperglucagonemia in response to orally administered glucose occurred after truncal vagotomy and occurred in the presence and absence of gastric tissue. (2) compared wtih the preoperative study, all postoperative groups demonstrated glucose intolerance. (3) The glucose intolerance was due to increased glucagon, insulinopenia, and possibly nutritional factors. (4) The insulin response to intravenous glucose suggests an impairment in the first phase of insulin secretion in the surgically treated group, demonstrating a role for the vagus in insulin secretion. (5) The glucose tolerance curve shows that the interposition operation is superior the the Roux-Y operation.

The failure of aminophylline to modulate glucagon release in man

There are conflicting results regarding the impact of cyclic AMP on pancreatic glucagon release. The effect of aminophylline, a phosphodiesterase inhibitor, on glucagon secretion was studied in four non-obese, non-diabetic, healthy young male volunteers. The subjects received separate infusions of: 1) aminophylline; 2) aminophylline and propranolol; 3) arginine; 4) aminophylline and arginine; 5) insulin; 6) aminophylline and insulin; and 7) aminophylline and isoproterenol. Aminophylline not only failed to alter glucagon levels but also did not affect the glucagon responses observed after arginine and insulin-induced hypoglycemia. The concurrent infusion of isoproterenol and aminophylline also failed to cause a glucagon response. Although glucagon release has been evoked by cyclic AMP in some in vitro system, administration of aminophylline to human subjects does not enhance secretion. These results indirectly suggest that cyclic AMP is of little importance in the control of glucagon secretion in man, though the effects of aminophylline at the cellular level may be complex.

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.

Hormonal and substrate responses during recovery from hypoglycaemia in man during beta 1-selective and non-selective beta-adrenergic blockade

Recovery from acute hypoglycaemia induced by the injection of insulin has been examined in six human subjects under control conditions, under non-selective beta blockade (propranolol) and under selective beta 1 blockade (metoprolol). The normal blood glucose recovery was biphasic with an initial rapid and a slower subsequent phase of recovery. The early recovery mechanism was unaffected by either form of beta blockade, but with propranolol the late phase of recovery was significantly prolonged. Rises in blood lactate and plasma free fatty acids following hypoglycaemia were markedly reduced by propranolol but to a much lesser degree with metoprolol. The counterregulatory hormonal responses of glucagon, cortisol and growth hormone were augmented appropriately for the prolonged hypoglycaemia associated with propranolol. Non-selective beta adrenergic blockade with propranolol is associated with an impairment of the late phase of blood glucose recovery from hypoglycaemia. The possible mechanisms of this impairment are discussed.

Effects of vagotomy and gastrectomy on pancreatic glucagon release

The effects of gastrectomy and vagotomy on pancreatic glucagon release were investigated clinically. The study included 20 men and eight women, who ranged in age from 28 to 69 years, and who were divided into the following four groups: 1) patients with gastroduodenal ulcers treated with partial gastrectomy, by the Billroth I method, whose hepatic branch was preserved (n = 7). 2) Patients with gastroduodenal ulcers treated with partial gastrectomy, by the Billroth II method, whose hepatic branch was preserved (n = 7). 3) Patients with gastric carcinoma treated with subtotal gastrectomy, by the Billroth I method. In these cases lymphadenectomy required section of the hepatic branch (n = 7). 4) Patients with gastric carcinoma treated with subtotal gastrectomy, by the Billroth II method. In these cases lymphadenectomy required section of the hepatic branch (n = 7). Oral glucose tolerance tests were performed in 10 patients, before operation, and in 28 gastrectomized and vagotomized patients. In the preoperative patients and in the first group, oral glucose (50g) suppressed pancreatic glucagon release, but in the other groups pancreatic glucagon levels were markedly increased.

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.

Adrenergic influence on glucocounterregulation in man

To investigate the adrenergic role in glucocounterregulatory mechanisms, single-blind randomised studies were performed in 7 normal males during severe insulin-induced hypoglycaemia with or without adrenergic blockade. Intravenous phentolamine administration (5 mg stat and 0.5 mg/min) did not interfere with the restoration of euglycaemia from hypoglycaemia. However, recovery of blood glucose in the presence of propranolol (3 mg/3 min and 0.8 mg/min) was retarded when compared with control studies (mean plasma glucose levels +/- SEM , 50 +/- 6 mg/dl versus 66 +/- 4 mg/dl at 120 min after insulin administration) despite appropriate glucagon, epinephrine, cortisol, and growth hormone responses. Plasma norepinephrine response was unaffected by propranolol but augmented threefold by phentolamine. Increases in plasma lactate, pyruvate and non-esterified fatty acids were blunted with propranolol while rebound non-esterified fatty acid was observed with phentolamine infusion. These data suggest that complete recovery of blood glucose from sever hypoglycaemia requires full sympathetic nervous system activity despite the integrity of other counterregulatory mechanisms.

Prostaglandin synthesis inhibitors reverse alpha-adrenergic inhibition of acute insulin response to glucose

Prostaglandin E (PGE) has several effects on glucose homoeostasis and insulin secretion. The same events can be induced by alpha-adrenergic stimulation, which is known to stimulate PGE synthesis. To evaluate the hypothesis that PGE may be one intracellular mediator for certain alpha-adrenergic events, we examined the effects of a known PG synthesis inhibitor Sodium salicylate (SS) (40 mg/min iv) on the alpha-adrenergic effects of epinephrine (Epi) at two doses (3 and 6 micrograms/min) in normal male subjects. The lower dose of epinephrine diminished the acute insulin response (AIR) after a 20-g intravenous glucose pulse (control, 463 +/- 149; epinephrine, 97 +/- 38% of basal insulin, mean +/- SE, n = 6, P < 0.02); SS markedly augmented the AIR during epinephrine towards control values (339 +/- 137%; P < 0.02). In 12 subjects, the higher dose of Epi abolished the AIR. When similar studies were performed during a SS infusion, the AIR was partially restored (96 /+- 27% of basal insulin, n = 12, P < 0.01). Similarly, partial reversal of this alpha-adrenergic effect of Epi was observed with indomethacin, another inhibitor of PG synthesis. At both doses of Epi, SS augmented the glucose disappearance rate (KG) after the glucose pulse (P < 0.001). Sodium salicylate also increased basal glucagon levels (P < 0.05). In contrast, SS did not affect the glycemic response, the suppression of basal insulin levels, or the hemodynamic responses induced by adrenergic stimulation. We conclude that two prostaglandin synthesis inhibitors partially reverse the alpha-adrenergic inhibition of the AIR to glucose caused by Epi, without affecting other adrenergic events. The data are compatible with a role for prostaglandins in alpha-adrenergic events selectively in the pancreatic islet.

[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.

Comparison of glucagon responses to 2-deoxy-D-glucose and hypoglycemia in man

2-Deoxy-D-glucose (2DG), by competitive inhibition of glucose utilization, produces a state of intracellular glucopenia with resultant activation of both the sympathetic and parasympathetic branches of the autonomic nervous system. We have investigated the relationship between the activation of the autonomic nervous system caused by this drug and glucagon secretion. Subjects experienced symptoms identical to those observed during true hypoglycemia and demonstrated a marked rise in both gastric acid secretion and urinary epinephrine excretion. Mean immunoreactive glucagon (IRG) levels rose only slightly post-2DG (maximal mean increment, 18 pg/ml). Insulin-induced hypoglycemia, although eliciting a similar increase in urinary epinephrine excretion, was followed by a severalfold increase in IRG. Thus, although hypoglycemia and 2DG induced similar discharge of the autonomic nervous system, the glucagon response to hypoglycemia was much greater. These observations provide strong evidence that marked increases in sympathetic and parasympathetic discharge in man are weak alpha-cell stimuli and further support the hypothesis that the rise in IRG that occurs during hypoglycemia is not mediated primarily via the autonomic nervous system.

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.

Propranolol and blood glucose: simultaneous measurements over a wide range of doses and the effect of propranolol on the glucose tolerance test

No correlation was found between blood glucose and simultaneous measurements of plasma propranolol concentration in patients with schizophrenia, on a daily dose of 80 mg to 1800 mg of propranolol as an adjunct to phenothiazine medication. The Glucose Tolerance Test (GTT) in ten patients on propranolol and phenothiazines did not differ significantly from those of a matched control group on phenothiazine alone. Two patients with mild diabetes showed no significant change in their GTT after stopping propranolol. These observations accord with the view that relatively high doses of propranolol as an adjunct to phenothiazine medication in schizophrenia are safe from the standpoint of glucose metabolism. This does not apply to the insulin dependent diabetic who is in danger of severe hypoglycaemia when glycogenolysis is blocked by propranolol.

Role of glucagon, catecholamines, and growth hormone in human glucose counterregulation. Effects of somatostatin and combined alpha- and beta-adrenergic blockade on plasma glucose recovery and glucose flux rates after insulin-induced hypoglycemia

To further characterize mechanisms of glucose counterregulation in man, the effects of pharmacologically inducd deficiencies of glucagon, growth hormone, and catecholamines (alone and in combination) on recovery of plasma glucose from insulin-induced hypoglycemia and attendant changes in isotopically ([3-(3)H]glucose) determined glucose fluxes were studied in 13 normal subjects. In control studies, recovery of plasma glucose from hypoglycemia was primarily due to a compensatory increase in glucose production; the temporal relationship of glucagon, epinephrine, cortisol, and growth hormone responses with the compensatory increase in glucose appearance was compatible with potential participation of all these hormones in acute glucose counterregulation. Infusion of somatostatin (combined deficiency of glucagon and growth hormone) accentuated insulin-induced hypoglycemia (plasma glucose nadir: 36+/-2 ng/dl during infusion of somatostatin vs. 47+/-2 mg/dl in control studies, P < 0.01) and impaired restoration of normoglycemia (plasma glucose at min 90: 73+/-3 mg/dl at end of somatostatin infusion vs. 92+/-3 mg/dl in control studies, P<0.01). This impaired recovery of plasma glucose was due to blunting of the compensatory increase in glucose appearance since glucose disappearance was not augmented, and was attributable to suppression of glucagon secretion rather than growth hormone secretion since these effects of somatostatin were not observed during simultaneous infusion of somatostatin and glucagon whereas infusion of growth hormone along with somatostatin did not prevent the effect of somatostatin. The attenuated recovery of plasma glucose from hypoglycemia observed during somatostatin-induced glucagon deficiency was associated with plasma epinephrine levels twice those observed in control studies. Infusion of phentolamine plus propranolol (combined alpha-and beta-adrenergic blockade) had no effect on plasma glucose or glucose fluxes after insulin administration. However, infusion of somatostatin along with both phentolamine and propranolol further impaired recovery of plasma glucose from hypoglycemia compared to that observed with somatostatin alone (plasma glucose at end of infusions: 52+/-6 mg/dl for somatostatin-phentolamine-propranolol vs. 72+/-5 mg/dl for somatostatin alone, P < 0.01); this was due to further suppression of the compensatory increase in glucose appearance (maximal values: 1.93+/-0.41 mg/kg per min for somatostatin-phentolamine-propranolol vs. 2.86+/-0.32 mg/kg per min for somatostatin alone, P < 0.05). These results indicate that in man (a) restoration of normoglycemia after insulin-induced hypoglycemia is primarily due to a compensatory increase in glucose production; (b) intact glucagon secretion, but not growth hormone secretion, is necessary for normal glucose counterregulation, and (c) adrenergic mechanisms do not normally play an essential role in this process but become critical to recovery from hypoglycemia when glucagon secretion is impaired.

Reduction of plasma triglyceride concentration by acute stress in man

Three different forms of stress all resulted in acute reduction of plasma triglyceride concentrations. Pyrogen reactions in two hypertriglyceridemic men resulted in the lowering of very-low-density lipoprotein (VLDL) triglyceride levels by 93% and 73% due to decreased secretion of this lipoprotein into plasma. More modest reductions in plasma triglycerides were observed after 2-deoxyglucose-induced intracellular glucopenia and insulin-induced hypoglycemia. With hypoglycemia, the lowering of plasma triglyceride concentration correlated significantly with the stimulation of urinary epinephrine output (r = 0.86) but with neither the urinary norepinephrine response nor with the increase in plasma immunoreactive glucagon levels. To further test whether these changes in plasma triglyceride levels were mediated via the sympathetic nervous system, hypoglycemia was evoked by insulin in subjects with traumatic spinal cord transactions. Two such subjects, who demonstrated sympathetic stimulation in response to hypoglycemia, had evidence of reduced VLDL secretion into plasma, while in two who had no evidence of an adrenergic response. VLDL secretion was not inhibited. Thus, acute lowering of plasma triglyceride concentrations by certain forms of stress appears to be mediated via the sympathetic nervous system.