Role of glucagon suppression on gluconeogenesis during insulin treatment of the conscious diabetic dog

Summary In seven insulin-deficient (<3 mU/l) pancreatectomised dogs, the direct and glucagon-related indirect effects of intraportal insulin infusion (350 U/kg-min; 12±1 mU/l) on glucose production were determined. Insulin was infused for 300 min during which time the plasma glucagon concentration was allowed to fall (314±94 to 180±63 ng/l) for 150 min before being replaced by an infusion intraportally at 2.6ng/kg-min (323±61 ng/l) for the remaining 150 min. Glucose production and gluconeogenesis were determined using arterio-venous difference and tracer techniques. Insulin infusion shut off net hepatic glucose output and caused the plasma glucose, blood glycerol and plasma non-esterified fatty acid levels to fall. It caused the hepatic fractional extraction of alanine (0.41 ±0.10 to 0.21±0.06) and lactate (0.32 ±0.09 to 0.04 ±0.03) to fall which increased their concentrations. When glucagon was replaced, all of these changes were fully or partly reversed with the exception of the changes in glycerol and nonesterified fatty acids. Indeed, 70% of the fall in hepatic glucose production and virtually 100% of the changes in lactate and alanine metabolism produced by basal insulin infusion were mediated by a fall in glucagon. However, the fall in hepatic uptake of glycerol was unaffected by changes in glucagon and thus gluconeogenesis from this substrate was inhibited by insulin per se probably as a result of reduced lipolysis. The latter effect of insulin may explain the incomplete restoration of hepatic glucose production when hyperglucagonaemia was re-established during insulin infusion.     

Very low density lipoprotein metabolism in non-ketotic diabetes mellitus: Effect of dietary restriction

Summary We have measured the turnover of very low density lipoprotein (VLDL) triglyceride as well as plasma glucose, insulin and non-esterified fatty acid levels in nine mildly obese non-ketotic, insulinopenic diabetic subjects before and during an energy restricted diet. During the baseline period, subjects were hypertriglyceridaemic, hyperglycaemic and insulinopenic. During dietary restriction (mean weight loss: 2.3±0.4 kg) plasma triglyceride fell from 8.4±3.0 to 3.4±0.89 mmol/l (mean±SEM; p<0.05), and plasma glucose fell from 13.9 ±1.7 to 9.8±1.4 mmol/l (p<0.01). Neither fasting plasma insulin nor the insulin response to an oral glucose load changed. Plasma non-esterified fatty acid concentrations remained constant as well. During the baseline period, the transport rate of VLDL-triglyceride in the diabetic subjects was more than twice that in an age-weighted matched control group (27.4±2.9 versus 12.1±0.8 mg/kg ideal body weight per h). The fractional catabolic rates were similar in the two groups (0.20±0.05 versus 0.21±0.02/h). During energy restriction of the diabetic subjects, the VLDL-triglyceride transport rate fell to 17.4±2.9 mg/kg ideal body weight per h (p<0.05 versus baseline) while the fractional catabolic rate remained constant at 0.21±0.06/h (NS versus baseline). These data indicate that the major abnormality in triglyceride metabolism in these non-ketotic, insulinopenic diabetic patients was over-production of VLDL-triglyceride.     

Immunoneutralization of endogenous glucagon with monoclonal glucagon antibody normalizes hyperglycaemia in moderately streptozotocin-diabetic rats

Summary The role of glucagon in diabetic hyperglycaemia has been a matter of controversy because of difficulties in the production of selective glucagon deficiency. We developed a high-capacity (40 nmol/ ml), high-affinity (0.6·10¹¹ l/mol) monoclonal glucagon antibody (Glu-mAb) and gave i.v. injections (4 ml/kg) to rats in order to study the effect of selective glucagon deficiency on blood glucose. Controls received a mAb against trinitrophenyl. Glu-mAb completely abolished the hyperglycaemic effect of 2.86 nmol/kg glucagon in normal rats (p<0.05, n=6). In moderately hyperglycaemic rats injected with streptozotocin as neonates (N-STZ), Glu-mAb abolished a postprandial increase in blood glucose (from 11.2±0.7 mmol/l to 17.3±1.8 mmol/l in controls vs 10.5±0.9 mmol/l to 9.3±1.0 mmol/l; cross-over: n=6, p<0.05). No significant effect of Glu-mAb treatment was observed in more hyperglycaemic N-STZ rats (cross-over, n=4) and in severely hyperglycaemic rats injected with STZ as adults (n=6), but after insulin treatment of the latter, at doses partially restoring blood glucose levels (12.7±4.3 mmol/l), Glu-mAb administration almost normalized blood glucose (maximal difference: 6.0±3.8 mmol/l; cross-over: n=5, p<0.05). In conclusion, our results provide strong additional evidence for the hypothesis that glucagon is involved in the pathogenesis of diabetes. The hormone plays an important role in the development of STZ-diabetic hyperglycaemia, but glucagon neutralization only leads to normoglycaemia in the presence of insulin.Abbreviations A-STZ rats Adult streptozotocin injected rats - AUC area under the curve - BW body weight - Con-mAb monoclonal control antibody - Glu-mAb monoclonal anti-glucagon antibody - K_a constant of association - NIDDM non-insulin-dependent diabetes mellitus - N-STZ rats neonatal streptozotocin-injected rats - OGTT oral glucose tolerance test - STZ streptozotocin     

Effects of recombinant human insulin-like growth factor I and insulin on counterregulation during acute plasma glucose decrements in normal and Type 2 (non-insulin-dependent) diabetic subjects

Summary Insulin-like growth factor I (65 μg/kg) or insulin (0.1 IU/kg) were injected i.v. on two separate occasions in random order in normal and in Type 2 (non-insulin-dependent) diabetic subjects. Insulin-like growth factor I and insulin injection resulted in identical decrements of plasma glucose concentrations after 30 min but in delayed recovery after insulin-like growth factor I as compared to insulin in both groups (p<0.05 insulin-like growth factor I vs insulin). Counterregulatory increases in plasma glucagon, adrenaline, cortisol and growth hormone concentrations after hypoglycaemia (1.9±0.2 mmol/l) in normal subjects were blunted after insulin-like growth factor I administration compared to insulin (p<0.05). Plasma glucose in Type 2 diabetic subjects did not reach hypoglycaemic levels but the acute glucose decrease to 4.5±0.8 mmol/l was associated with significantly lower responses of plasma glucagon and adrenaline but higher cortisol levels after insulin-like growth factor I compared to insulin (p<0.003). Plasma concentrations of non-esterified fatty acids and leucine decreased similarly after insulin-like growth factor I and insulin in both groups. The present results demonstrate that insulin-like growth factor I is capable of mimicking the acute effects of insulin on metabolic substrates (plasma glucose, non-esterified fatty acids, leucine). The decreases of plasma glucose were similar after both peptides in normal and in diabetic subjects who were presumably insulin resistant. Counterregulatory hormone responses to plasma glucose decrements differed, however, between insulin-like growth factor I and insulin and in the diabetic and the control subjects. After insulin-like growth factor I the increases in adrenaline, cortisol, growth hormone and glucagon were blunted in normal subjects despite slightly lower plasma glucose concentrations.     

Contrasting metabolic effects of continuous and pulsatile growth hormone administration in young adults with Type 1 (insulin-dependent) diabetes mellitus

Summary Plasma growth hormone profiles in adolescents with Type 1 (insulin-dependent) diabetes mellitus are characterized by both increases in pulse amplitude and higher baseline concentrations. To determine which of these abnormalities adversely affect metabolic control, we studied six young adults overnight on three occasions. On each night somatostatin (50–100 g·m^2–1·h^–1) and glucagon (1ng· kg^–1·min^–1) were infused continuously and 18mU/kg of growth hormone was given as either: three discrete pulses of 6 mU·kg^–1· h^–1 at 180-min intervals or a 12-h infusion (1.5 mU·kg^–1· h^–1) or buffer solution only on a control night. Euglycaemia was maintained by an insulin-varying clamp. Blood samples were taken every 15 min for glucose and growth hormone and every hour for intermediate metabolites and non-esterified fatty acids. Comparable normoglycaemic conditions were achieved on all three nights. Growth hormone levels achieved (mean±SEM) on study nights were: 32.8±2.2 mU/l (peak level during growth hormone pulses); 9.8± 0.8 mU/l (continuous growth hormone) and 1.1±0.3 mU/l (control level). Pulsatile growth hormone administration led to an increase in insulin requirements (mean±SEM: 0.17±0.03 vs control 0.09±0.01 mU·kg^–1· min^–1, p < 0.05) whereas insulin requirements following continuous growth hormone administration were unchanged. Cross-correlation confirmed an increase in insulin requirements occurring 135 min after a growth hormone pulse (r=0.21, p < 0.001). Growth hormone administration (continuous and pulsatile) led to a significant increase in B-hydroxybutyrate levels compared to the control night: 0.21±0.01 mmol/l (mean±SEM), 0.29±0.01 mmol/l, 0.08±0.01 mmol/l (p< 0.001) during the night with pulsatile growth hormone, continuous growth hormone and control respectively. Mean plasma non-esterified fatty acids were also increased following growth hormone administration: 0.94±0.04 mmol/l (mean±SEM), 1.09±0.07 mmol/l, 0.61±0.05 mmol/l (p<0.003), during the night with pulsatile growth hormone, continuous growth hormone and control respectively. It appears that the pulsatile and baseline growth hormone signals have contrasting metabolic effects in young adults with Type 1 diabetes mellitus.     

Modulation of hepatic glucose production by non-esterified fatty acids in Type 2 (non-insulin-dependent) diabetes mellitus

Summary To study the effect of changes in plasma non-esterified fatty acid concentration on suppression of hepatic glucose production by insulin eight Type 2 (non-insulin-dependent) diabetic patients participated in three euglycaemic, hyperinsulinaemic (108pmol · m^2–1 · min^–1) clamp studies combined with indirect calorimetry and infusion of [3-³H]-glucose and [1-¹⁴C]palmitate; (1) a control experiment with infusion of NaCl 154 mmol/l, (2) heparin was infused together with insulin, and (3) an antilipolytic agent, Acipimox, was administered at the beginning of the experiment. Six healthy volunteers participated in the control experiment. Plasma non-esterified fatty acid concentrations during the insulin clamp were in diabetic patients: (1) 151±36 mol/1, (2) 949±178 mol/l, and (3) 65±9 mol/l; in healthy control subjects 93±13 mol/l. Non-esterified fatty acid transport rate, oxidation and non-oxidative metabolism were significantly higher during the heparin than during the Acipimox experiment (p<0.001). Suppression of hepatic glucose production by insulin was impaired in the diabetic compared to control subjects (255±42 vs 51±29 mol/min, p<0.01). Infusion of heparin did not affect the suppression of hepatic glucose production by insulin (231±49 mol/min), whereas Acipimox significantly enhanced the suppression (21±53 mol/min, p<0.001 vs 154 mmol/l NaCl experiment). We conclude that insulin-mediated suppression of hepatic glucose production is not affected by increased non-esterified fatty acid availability. In contrast, decreased non-esterified fatty acid availability enhances the suppression of hepatic glucose production by insulin.     

Increased glucose carbon recycling in severely insulin deficient Type 1 (insulin-dependent) diabetic subjects

Summary Six Type 1 (insulin-dependent) diabetic subjects were studied in order to determine the contribution of recycling of glucose carbon to the overproduction of glucose which is characteristic of the fasting hyperglycaemia produced by insulin withdrawal. The subjects were studied on two occasions, once after an overnight insulin infusion and once following 24 h of insulin withdrawal. The difference in turnover rates of 1-¹⁴C-glucose and 3-³H-glucose was used as a measure of glucose recycling. Insulin withdrawal caused a marked metabolic derangement with a rise in non-esterified fatty acids from 0.69±0.23 to 1.11±0.21 mmol/l (mean±SEM, p<0.05), total ketones from 0.27±0.06 to 2.06±0.51 mmol/l (p<0.01), cortisol from 341±43 to 479±31 nmol/l (p<0.05) and growth hormone from 1.1±0.3 to 19+5-mu/l (p<0.05). Glucose turnover rose from 13.8±2.3 mol·kg^–1·min^–1 at a glucose of 6.9±0.7 mmol/l in the insulin infused study to 25.8±4.4 mol·kg^–1·min^–1 (p<0.05) at a glucose of 16.4±0.7 mmol/l in the insulin withdrawn study. Recycling also rose from 3.0±0.4 mol· kg^–1·min^–1 to 9.4±2.2 mol·kg^–1·min^–1 (p<0.05) when insulin withdrawn, accounting for 23±3% and 36±3% of glucose turnover, respectively. We conclude that in the severely insulin deficient Type 1 diabetic subject recycling of glucose carbon is a major contributor to the excess glucose production.     

A 6-hour nocturnal interruption of a continuous subcutaneous insulin infusion: 1. Metabolic and hormonal consequences and scheme for a prompt return to adequate control

Summary Interruption of a continuous subcutaneous insulin infusion, most often due to technical problems occurring during the night, is a not uncommon event whose metabolic consequences have received relatively little attention until now. We have therefore investigated the changes in blood glucose, plasma non-esterified fatty acids, 3-hydroxybutyrate, glucagon and free insulin in eight C-peptide negative Type 1 diabetic patients whose pumps were deliberately stopped between 23.00 h and 05.00 h. A control test with the pump functioning normally was carried out in each patient and the studies were randomized. Considering the values at 23.00 h as reference, interruption of the insulin infusion resulted in (1) a rapid decrease in plasma free insulin significant after 1 h and reaching a nadir of 6±2 mU/l after 6 h; (2) a rise in blood glucose which was significant at hour 3 and reached 17.4±1.9 mmol/l at hour 6; (3) a moderate increase in plasma non-esterified fatty acids which remained in the range of 700–800 mol/l; (4) an early and linear rise in plasma 3-hydroxybutyrate, significant after 1 h and averaging 1290±140 mol/l after 6 h; (5) a late increase (hour 5) in plasma glucagon. The second aim of our study was to provide for the patient a precise scheme of insulin supplements administered via the pump and based on blood glucose monitoring (Dextrostix — Glucometer) and semi-quantitative evaluation of ketonuria (Acetest). Resetting the pump at its basal rate at 05.00h and giving insulin supplements (2–8 U) at 06.45 h (with the usual breakfast dose) and again at 10.00 h have proved efficacious in restoring satisfactory metabolic control by noon the day after starting the experiment. These results form practical recommendations to patients undergoing this type of accident.     

Exogenous hyperglucagonaemia in insulin controlled diabetic rats increases urea excretion and nitrogen loss from organs

Summary In order to study the effect of hyperglucagonaemia on nitrogen metabolism in diabetes, zinc protamin glucagon 60 g was injected subcutaneously 3 times daily for 4 weeks into streptozotocindiabetic rats (n=5), adequately treated with long acting insulin. This raised the plasma concentration of glucagon to 725±125 (mean±SEM), which is not different from that found in portal blood of uncontrolled diabetic rats: 400±75 ng/l. The controls were 5 diabetic rats treated with insulin alone and 5 non-diabetic rats.Compared with control rats the nitrogen balance was reduced (p<0.05) and the nitrogen contents of carcass, heart, intestines, and kidneys were reduced by 15–30% (p<0.05) in the glucagon treated rats. The hepatic capacity of urea synthesis and the alanine elimination rate were determined in the 3 above-mentioned groups, and confirmed in 3 identical groups followed for only 2 weeks; and in addition in a group of glucagon treated diabetic rats, where the long acting glucagon was substituted by neutral insulin the last two days before investigation. The capacity of urea-N synthesis and the alanine elimination rate were, respectively, in control rats: 9.6±0.8 and 5.9±0.3 mol/(min 100 g body weight), in insulin treated diabetic rats: 8.5±0.7 and 5.4±0.6 mol/(min 100g body weight), in glucagon treated rats: 6.3±0.4 (lower than controls, p<0.05) and 10.4±0.4 (higher than controls, p<0.05) (mol/(min 100 g body weight), and in glucagon treated rats given neutral insulin: 20.7±1.6 and 10.9±0.3 mol/(min 100 g body weight) (both higher than controls, p<0.05). Hyperglucagonaemia in itself leads to loss of nitrogen from organs, probably by an increased hepatic conversion of amino-nitrogen to urea-nitrogen, as evidenced by the increased urea excretion. This proceeds despite an insulin induced decrease in the capacity of urea synthesis and may thus rather be attributed to changes in the affinity of urea synthesis for amino-nitrogen.     

Adrenergic influence on glucocounterregulation in man

Summary 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 severe hypoglycaemia requires full sympathetic nervous system activity despite the integrity of other counterregulatory mechanisms.     

Regulatory effect of glucagon on its own receptor concentrations and target-cell sensitivity in the rat

Summary To evaluate the role of glucagon on its hepatocyte receptor concentrations, groups of rats were injected with a long-acting glucagon preparation (20 [G-20], 40 [G-40] or 60 [G-60] g/100 g body weight) every 8 h for 4 days. Glucagon receptors in liver plasma membranes of treated animals were decreased in number (control = 1.66±0.20 ng/0.5 mg protein versus G-20=1.24±0.26, G-40=1.03±0.26, G-60 =0.70±0.03 ng/0.5 mg protein; p<0.05, < 0.001, < 0.001, respectively), but they were indistinguishable from receptors of control rats by other criteria including affinity and kinetics of association. Degradation of both glucagon and receptor sites did not account for differences observed in binding. Similar results were obtained with isolated hepatocytes. In relation to controls, isolated hepatocytes of treated rats had a reduced number of receptors (control = 0.70±0.05 versus G-40=0.47±0.04 ng/10⁶ cells; p< 0.02) proportionate to the decreased glucagon-stimulated production of cyclic AMP and glucose. Four to eight hours exposure of cultured hepatocytes of nontreated rats to 4 × 10^-8 mol/l glucagon produced a decreased binding of ¹²⁵I-glucagon to its receptor (p<0.05). In contrast, hormone exposure for shorter periods of time (0–2 h) was without effect. These results suggest (1) an inverse relationship between circulating glucagon levels and hepatocyte glucagon receptor concentration, and (2) a direct relation between receptor number and target-cell response.     

Hormonal responses to insulin infusion in diabetes mellitus

Summary Twenty diabetic patients and fourteen normal volunteers received infusion of 2.4 U neutral porcine insulin/h until either the blood glucose level was stable, or until hypoglycaemia occurred. As previously reported [1] in the normal group the blood glucose stabilised at 2.8±0.1 mmol/l without any hypoglycaemic symptoms. There was an increase in blood levels of glucagon, cortisol and growth hormone as the blood glucose level fell, the mean peak increments being 167±33 pg/ml, 400±71 nmol/l and 29±7 mU/l, respectively. In ten of the diabetic subjects (Group A) the blood glucose level stabilised at 3.6±0.2 mmol/l during the insulin infusion, with peak increments in plasma glucagon (110±24pg/ml), cortisol (411±71 nmol/l) and growth hormone (22±6 mU/l), not significantly different from those in the normal subjects. These rises in hormone levels occurred during the last hour of infusion after normoglycaemia was reached and maintained. The ten remaining diabetics (Group B) developed symptoms of hypoglycaemia during the infusion. The peak increments in plasma glucagon (19±7 pg/ml), cortisol (183±36 nmol/l) and growth hormone (6±2 mU/l) in this latter group were significantly less than those in the other diabetic group or the normals. The absence of counter-regulatory hormonal responses in the Group B diabetics was related to the development of hypoglycaemia and may be the result of a dysfunction of hypothalamic gluco-regulatory centres.     

Absence of exercise-induced hypoglycaemia in Type I (insulin-dependent) diabetic patients during maintenance of normoglycaemia by short-term,open-loop insulin infusion

Summary To assess the risk and possible mechanisms of hypoglycaemia during moderate exercise in Type I (insulin-dependent) diabetic patients receiving constant insulin infusion, five insulin-dependent male diabetic patients were exercised 18 h after their last meal and 30 h after their last injection of intermediate acting insulin. Intravenous insulin was initially delivered via a closed-loop infusion system programmed to lower mean blood glucose from 11.3 ± 1.8 to 4.8 ± 0.4 mmol/l over approximately 3.5 h. Blood glucose was then maintained at this level for 4 h. At this time, the closed-loop infusion was discontinued and replaced by an open-loop system. The average amount of insulin infused per min during the 4 h normoglycaemic closed-loop period was calculated and this amount was infused at a constant rate during both a 30 min period of exercise on a bicycle ergometer (approximately 65% maximum oxygen uptake) and a 30 min rest period which followed. Five nondiabetic males served as control subjects. Despite significantly higher free insulin concentrations (p < 0.05) and identical preexercise blood glucose concentrations, blood glucose rose during exercise only in the diabetic group (0.5 ± 0.2 mmol/l; p < 0.01). Changes in the serum concentrations of lactate, glycerol, glucagon, cortisol, non-esterified fatty acids and growth hormone were similar in the two groups and did not account for the increment of blood glucose in the diabetic patients. Beta-hydroxybutyrate concentrations were, however, higher in the diabetic patients at the onset of exercise (p < 0.01) and decreased significantly more than the control subjects during exercise. We conclude that exercise under these conditions in diabetic patients is not attended by hypoglycaemia.     

Effects of calcium and calcitonin on circulating levels of glucagon and glucose in diabetes mellitus

Summary The effects of Ca²⁺ and calcitonin infusions on circulating glucagon, glucose, C-peptide, Ca²⁺, and calcitonin were investigated in hyperglucagonaemic insulin-dependent diabetics. In 14 insulin-deprived diabetics and 12 healthy volunteers 2 h infusions of saline (0.154 mol/l), Ca²⁺ (0.375 mmol/kg body weight), and calcitonin (4.5 IU/kg body weight) were performed. There were no significant changes during saline infusion. In the diabetics, Ca²⁺ infusions induced a rise of plasma Ca²⁺ up to 3.2±0.1 mmol/l and a fall of circulating glucagon (-26.4±5.7%; p<0.001) and glucose (-23.3 ±3.6%; p<0.05). Plasma calcitonin rose to twice basal values (p<0.025). During calcitonin infusions plasma Ca²⁺ decreased slightly to 2.1±0.2 mmol/l; a fall was found in both glucose (— 24.4±4.0%; p<0.05) and circulating glucagon (-22.5±4.3%; p<0.001). Two groups of 6 healthy volunteers were subjected to saline and Ca²⁺, or to Ca²⁺ and calcitonin infusions. Both Ca²⁺ and calcitonin infusions induced a fall of serum insulin (— 30.1±6.6%; p< 0.05). Calcitonin depressed circulating glucagon by-18.6±4.4% (p<0.025), whereas during Ca²⁺ infusions glucagon decreased only by -6.5±1.9% (p>0.1). We conclude from our results that an increase of circulating calcitonin induced by Ca²⁺ infusions or by exogenous calcitonin administration appears to depress elevated circulating glucagon and glucose in insulin-dependent diabetics.     

Reinterpretation of the effect of haloperidol and ethanol on insulin secretion

Summary We were unable to confirm the report of haloperidol induced dose-dependent inhibition of insulin and glucagon release from the isolated canine pancreas. The possibility that the inhibition was caused by ethanol, previously used as the solvent for haloperidol, was tested. Infusion of ethanol at increasing concentrations (15.8 to 252 mmol/l) caused a progressive inhibition of insulin (-17±1 to -69 ±2%) and glucagon (-13±3 to -67±3%) secretion, using a perfusate containing 200 mg/dl glucose and 2.65 mmol/l calcium. Haloperidol (5 to 20 mol/l) dissolved in ethanol (252 mmol/l) did not augment the inhibitory effects of ethanol. At a low calcium concentration (1.3 mmol/l) ethanol further inhibited insulin secretion (-83 ± 2%) with no additional inhibition by 20 mol/l haloperidol (-80±3%). At a high calcium concentration (8.8 mmol/l) the inhibitory effect of ethanol on insulin or glucagon secretions was diminished and variable. This strongly suggests that the inhibition of insulin and glucagon secretion previously attributed to haloperidol was caused by the ethanol solvent.     

Relative roles of insulin and hypoglycaemia on induction of neuroendocrine responses to,symptoms of,and deterioration of cognitive function in hypoglycaemia in male and female humans

Summary To assess the relative roles of insulin and hypoglycaemia on induction of neuroendocrine responses, symptoms and deterioration of cognitive function (12 cognitive tests) during progressive decreases in plasma glucose, and to quantitate glycaemic thresholds, 22 normal, non-diabetic subjects (11 males, 11 females) were studied on four occasions: prolonged fast (n=8, saline euglycaemia study, SA-EU), stepped hypoglycaemia (plasma glucose plateaus of 4.3, 3.7, 3 and 2.3 mmol/l) or euglycaemia during insulin infusion at 1 and 2 mU·kg^–1·min^–1 (n=22, high-insulin hypoglycaemia and euglycaemia studies, HI-INS-HYPO and HI-INS-EU, respectively), and stepped hypoglycaemia during infusion of insulin at 0.35 mU· kg^–1·min^–1 (n=9, low-insulin hypoglycaemia study, LO-INS-HYPO). Insulin per se (SA-EU vs HI-INS-EU), suppressed plasma glucagon (20%) and pancreatic polypeptide (30%), whereas it increased plasma noradrenaline (R10%, p<0.05). Hypoglycaemia per se (HI-INS-HYPO vs HI-INS-EU) induced responses of counterregulatory hormones (CR-HORM), symptoms and deteriorated cognitive function. With the exception of suppression of endogenous insulin secretion, which had the lowest glycaemic threshold of 4.44±0.06 mmol/l, pancreatic polypeptide, glucagon, growth hormone, adrenaline and cortisol had similar glycaemic thresholds (3.8-3.6 mmol/l); noradrenaline (3.1±0.0 mmol/l), autonomic (3.05±0.06 mmol/l) and neuroglycopenic (3.05±0.05 mmol/l) symptoms had higher thresholds. All 12 tests of cognitive function deteriorated at a glycaemic threshold of 2.45±0.06 mmol/l, but 7 out of 12 tests were already abnormal at a glycaemic threshold of 2.89±0.06 mmol/l. Although all CR-HORM had a similar glycaemic threshold, the lag time of response (the time required for a given parameter to increase) of glucagon (15±1 min) and growth hormone (14±3 min) was shorter than adrenaline (19±3 min) and cortisol (39±4 min) (p<0.05). With the exception of glucagon (which was suppressed) and noradrenaline (which was stimulated), insulin per se (HI-INS-HYPO vs LO-INS-HYPO) did not affect the responses of CR-HORM, and did not influence the symptoms or the cognitve function during hypoglycaemia. Despite lower responses of glucagon, adrenaline and growth hormone (but not thresholds) in females than males, females were less insulin sensitive than males during stepped hypoglycaemia.     

Divergent effect of glucagon antibodies on arginine and glucose-stimulated insulin secretion in the rat

Summary The effects of glucose and arginine on insulin secretion in the presence of glucagon antibodies were investigated in rats in vivo. In contrast to controls, animals given glucagon antibodies showed an inhibition of arginine-stimulated (p < 0.001), but not glucose-stimulated, insulin secretion. That these effects were not due to incomplete neutralisation of endogenous glucagon is evidenced by the presence of large antibody excess throughout the duration of the experiments. Both the glucagonotropic effect of arginine (319 ± 60ng/l, p < 0.01) and the insulinotropic effect of exogenous glucagon (8.3 ± 0.8 g/l, p < 0.001) were demonstrable under our experimental conditions in the absence of exogenous glucagon antibodies. These observations suggest that different mechanisms are involved in the stimulation of insulin release by arginine and by glucose, and that glucagon may play an important physiological role in the mediation and regulation of insulin secretion by secretogogues, such as arginine.     

Sandostatin,a new analogue of somatostatin,reduces the metabolic changes induced by the nocturnal interruption of continuous subcutaneous insulin infusion in Type 1 (insulin-dependent) diabetic patients

Summary With the aim of assessing a new somatostatin analogue to prevent the metabolic changes induced by a 6-h nocturnal arrest of an insulin pump, nine C-peptide negative Type 1 (insulin-dependent) diabetic patients were submitted blindly to two interruptions (from 23.00 to 05.00 hours) of their continuous s.c. insulin infusion, once after a single s.c. injection at 23.00 hours of 50 g SMS 201-995 (Sandostatin, Sandoz) and once after 0.9% NaCl. Plasma SMS 201-995 levels peaked at 24.00 hours and then declined with an elimination half-life averaging 144±15 min. Plasma glucagon and growth hormone levels were significantly reduced after SMS 201-995 whereas the progressive fall in plasma-free insulin levels from 23.00 to 05.00 hours was unaffected. In the control test, blood glucose levels tended to decrease slightly from 23.00 to 02.00 hours and then increased markedly from 02.00 to 05.00 hours (+5.3±1.5mmol/l) while after SMS 201-995 they decreased significantly from 23.00 to 02.00 hours (–2.6±0.5 mmol/l), resulting in values below 3 mmol/l in seven subjects, but showed a secondary increase until 05.00 hours (+3.5±1.5 mmol vs 23.00h; p<0.05 vs 0.9% NaCl). While the rises in plasma non-esterified fatty acid and glycerol levels were not reduced by SMS 201-995, the increase in plasma 3-hydroxybutyrate levels, although similar from 23.00 to 02.00 hours, was significantly reduced from 02.00 to 05.00 hours (+77±20 vs+124±31 mol·l^–1·h^–1 p<0.005). Thus, SMS 201-995 significantly reduced the metabolic alterations due to a 6-h nocturnal interruption of a continuous s.c. insulin infusion but at the cost of a rather high risk of early hypoglycaemia.     

Effect of glucagon antibodies on plasma glucose,insulin and somatostatin in the fasting and fed rat

Summary A potent high-titre glucagon antibody pool was used to induce a state of acute glucagon deficiency in order to investigate the importance of glucagon in maintaining euglycaemia in the fed and fasted anaesthetised rat. Binding characteristics of the antiserum and evidence of its neutralisation of the biological effects of exogenous glucagon are described. The amount of antibody administered was capable of neutralising up to 12 times the total content of glucagon (approximately 1nmol) in the rat pancreas. The hyperglycaemic response to 1.43 nmol exogenous glucagon was significantly inhibited in the rat by glucagon antibodies given intravenously or intraperitoneally (p < 0.001). However, no changes in plasma glucose occurred in rats fasted 16 h (4.35±0.1 mmol/l or 24 h (4.0±0.05 mmol/l) after antibody administration. The same dose of glucagon antibodies produced no change in plasma glucose (6.1±0.2 mmol/l), immunoreactive insulin (1.85±0.05 g/l) or immunoreactive somatostatin (110±30 ng/l) in rats after antibody administration. Antibody excess, equivalent to a binding capacity for glucagon of 40 nmol/l in the plasma of recipient animals, was demonstrable at all times after passive immunisation. The absence of any affect on glucose concentrations following immunoneutralisation of glucagon suggests that glucagon secretion may not be a major factor in the maintenance of euglycaemia in the rat.     

Influence of glucagon on plasma levels of potassium in man

Summary To investigate the role played by glucagon in the regulation of plasma potassium, we have examined the behaviour of this ion during four 2 h infusions of saline, glucagon (200 ng/min), cyclic somatostatin (priming dose of 50 g followed by 5.8 g/min) and somatostatin plus glucagon in 6 normal volunteers. Glucagon alone produced no change in potassium, despite an increase in insulin. Somatostatin, in addition to depressing insulin, produced a slight but significant (p < 0.01) increase in potassium ( max: 0.2–0.8 mmol/l: mean ± SEM, 0.4±0.1). Infusion of somatostatin together with glucagon suppressed the glucagon-induced increase in insulin and greatly augmented the increase in blood glucose. Potassium rose significantly more (p < 0.02) than after somatostatin alone ( max: 0.5–1.3 mmol/l; mean 0.9±0.1), indicating that hyperkalaemia results from hyperglucagonaemia in the absence of insulin. Evidence is presented that this last phenomenon is not mediated by hyperglycaemia or by a reduction in aldosterone secretion. It is suggested that low blood insulin and increased glucagon could be one of the mechanisms that underlie or magnify the hyperkalaemia observed in cases of serious stress or decompensated diabetes.