Failure to establish islet amyloid polypeptide (amylin) as a circulating beta cell inhibiting hormone in man

Summary The presence of islet amyloid polypeptide in amyloid within pancreatic islet cells in Type 2 (non-insulin-dependent) diabetes, and its reported inhibition of glucose uptake by skeletal muscle in vitro, has prompted speculation concerning its role in the pathogenesis of diabetes. We investigated the effect of infused synthetic amidated human islet amyloid polypeptide (mol. wt. 3904, confirmed by mass spectroscopy) on intravenous glucose tolerance. Seven healthy, non-obese volunteers (age±SD, 27±4 years) were infused over 50 min with normal (0.9%) saline or islet amyloid polypeptide at 50 pmol·kg^–1·min^–1. After 20 min, a bolus of 0.5 g/kg glucose was given within 1 min and blood sampling continued for up to 60 min. Circulating concentrations of islet amyloid polypeptide reached at steady state were 1130±90 pmol/l. The calculated half-life was 11.8±0.9 min, metabolic clearance rate 5.7±0.6 ml·kg^–1·min^–1 and apparent distribution space therefore 94±12 ml/kg. However, islet amyloid polypeptide was found to have no effect on the peak value reached, or the total area under the curve for plasma glucose, insulin or glucagon following intravenous glucose. This study suggests circulating islet amyloid polypeptide may not be an important influence on intravenous glucose tolerance in man.     

Decreased hepatic glucagon responses in Type 1 (insulin-dependent) diabetes mellitus

Summary The effect of glucagon infusion on hepatic glucose production during euglycaemia was evaluated in seven Type 1 (insulin-dependent) diabetic patients and in ten control subjects. In the diabetic subjects normoglycaemia was maintained during the night preceding the study by a variable intravenous insulin and glucose infusion. During the study endogenous insulin secretion was suppressed by somatostatin (450 g/h) and replaced by insulin infusion (0.15 mU·kg^–1·min^–1). ³H-glucose was infused for isotopic determination of glucose turnover. Plasma glucose was clamped at 5 mmol/1 for 2 h 30 min and glucagon (1.5 ng· kg^–1·min^–1) was then infused for the following 3 h. Hepatic glucose production and glucose utilisation were measured during the first, second and third hour of the glucagon infusion. Basal hepatic glucose production (just prior to glucagon infusion) was similar in diabetic (1.2±0.3 mg·kg^–1·min^–1) and control (1.6±0.1 mg·kg^–1·min^–1) subjects. In diabetic patients hepatic glucose production rose slowly to 2.1±0.5 mg·kg^–1·min^–1 during the first hours of glucagon infusion and stabilized at this level (2.4±0.5 mg·kg^–1·min^–1) in the third hour. In control subjects hepatic glucose production increased sharply to higher levels than in the diabetic subjects (3.4±0.3 mg·kg^–1·min^–1) during the first and second hour of glucagon infusion (p<0.05) and then gradually fell (2.9±0.4 mg·kg^–1·min^–1) during the third hour. In conclusion, when stimulated with glucagon at a physiologic plasma concentration diabetic patients had 1) an overall reduced hepatic glucose production response and 2) an abnormal sluggish response pattern. These abnormalities may imply inappropriate counter-regulation following a hypoglycaemic episode.     

How does glucose regulate the human pancreatic A cell in vivo?

Summary To investigate the mechanism whereby changes in plasma glucose level alter human pancreatic A-cell activity in vivo, A-cell activity was determined during manipulation of plasma glucose and pancreatic B-cell activity by insulin and glucose infusions. A-cell activity (the acute immunoreactive glucagon response to intravenous arginine, 0–10 min) rose from 482±125 to 968±191 pg · ml^-1 · 10 min^-1 (mean±SEM) when the plasma C-peptide level (a measure of B-cell activity) was suppressed from 2164±365 to 872±162 pg/ml by an insulin infusion at euglycaemia (employing the glucose clamp technique) in six normal subjects. Raising plasma glucose to 6.7 mmol/l during the same insulin infusion returned mean C-peptide (2688±581 pg/ml) and the acute glucagon response to arginine (447±146 pg · ml^-1 · 10 min^-1) close to basal levels. Individual changes in the acute glucagon response to arginine followed the C-peptide changes. The mean change in the acute glucagon response to arginine per unit change in plasma glucose (-191±36) was similar to that seen when plasma glucose was raised to twice basal levels in six different subjects without an insulin infusion (-159±45). This suggests that, when plasma glucose is raised to about twice basal level in vivo, the major factor in suppressing A-cell activity is the concurrent change in B-cell activity rather than direct effects of glucose or circulating insulin on the A cell.     

Hepatic glucose production during intraperitoneal and intravenous closed-loop insulin regulation of blood glucose in Type 1 (insulin-dependent) diabetic patients

Summary Intraperitoneal infusion of insulin should be more physiological than intravenous insulin since part of the insulin is directed toward the portal vein, which allows the liver to retain its major role in glucose homeostasis. The regulation of hepatic glucose production during the intraperitoneal and intravenous infusions of insulin were compared in eight Type 1 (insulin-dependent), C-peptide-deficient diabetic patients. Primed, continuous infusions of [6,6-²H] glucose were given in the postabsorptive state and during continuous infusion of unlabelled glucose at 1.5 and 4 mg/kg· min, while normoglycaemia was maintained by closed-loop intraperitoneal and intravenous insulin delivery. During all three periods, plasma glucose concentrations remained near normal (variations 3.8–6.1%). The insulin infusion rates required for normal plasma glucose concentrations were essentially the same for the intravenous and intraperitoneal routes in all cases, although the variations were greater with intraperitoneal insulin. Plasma free-insulin levels were only slightly, non-significantly lower with intraperitoneal infusion than with intravenous infusion. Hepatic glucose production was significantly lower with intraperitoneal insulin during all three conditions: basal: 1.71±0.14, i.p. vs 2.37±0.26 mg/kg · min, i.v.; 1.5 mg/kg · min glucose infusion: 0.49±0.23, i.p. vs 0.88±0.18 mg/kg · min, i.v.; 4 mg/kg · min glucose infusion: 0.31±0.10, i.p. vs 0.56±0.12 mg/kg · min, i.v. These results, obtained with steady-state conditions for plasma glucose, isotopic plasma glucose enrichments and unlabelled glucose infusion rates, suggest that better control of hepatic glucose production leading to normoglycaemia was achieved with the intraperitoneal infusion.     

Importance of glucagon in the control of futile cycling as studied in alloxan-diabetic dogs

Summary In order to determine the role of glucagon in futile or substrate cycling in diabetes, we measured tracer determined glucose kinetics during a combined infusion of 2-³H-glucose (total glucose production) and 6-³H-glucose (glucose production) in six alloxan-diabetic dogs. The animals received either a 420 min infusion of (1) somatostatin alone (0.3 g·kg^–1· min^–1), (2) somatostatin with insulin replacement (100 U·kg^–1min^–1) or (3) glucagon (6 ng·kg^–1· min^–1) together with somatostatin and transient insulin replacement. When somatostatin was given alone, plasma glucagon (p<0.004) and insulin (p<0.0001) were suppressed. Glucose production and disappearance and plasma glucose concentrations fell (p<0.0001), but the metabolic clearance of glucose did not change significantly. In the basal state, futile cycling comprised 29±4%, 33±4% and 33±3% of total glucose production in the three goups of studies, which is high compared to normal dogs. The absolute rate of futile cycling fell slightly but significantly from 10.0±1.7 to 8.3±1.7 mol·kg·^–1min^–1 (p<0.0008). When insulin replacement was given during somatostatin infusion to correct for the small somatostatin-induced insulin suppression, there were similar changes in plasma glucagon, glucose concentrations and glucose kinetics as seen during the infusion of somatostatin alone. Futile cycling decreased to a slightly greater extent from 12.8±2.8 to 9.5±1.7mol·kg^–1·min.^–1 (p<0.02). When glucagon was infused together with somatostatin and insulin replacement, plasma glucagon (p<0.0002) increased and plasma glucose levels rose (p<0.001) due to a transient increase in glucose production. Metabolic clearance of glucose did not change significantly. There was a marked increase in futile cycling from 12.2±1.7 to 21.7±1.7mol· kg^–1·min^–1 (p<0.0001) in response to exogenous glucagon excess. There was a slight (p<0.01) drop in free fatty acid levels with somatostatin. Free fatty acid levels nearly doubled (p<0.025) with the infusion of glucagon together with somatostatin. In conclusion, (a) futile cycling was increased in alloxan-diabetic dogs; (b) glucagon suppression can suppress futile cycling only if total insulin deficiency is prevented; and (3) hyperglucagonaemia increases futile cycling, and this effect is more pronounced during insulin deficiency.     

Effects of islet amyloid polypeptide on hepatic insulin resistance and glucose production in the isolated perfused rat liver

Summary The impact of (pancreatic) islet amyloid polypeptide on glucose metabolism and insulin sensitivity was examined in isolated rat livers perfused in a non-recirculating system. Continuous infusion of 10^–7mol/l islet amyloid polypeptide affected neither basal nor glucagon (10^–9 mol/l)-stimulated glucose output by livers from fed rats, but it did increase the hepatic cyclic AMP release within 44 min (7.91±12.07 vs control: 0.07±0.03 pmol·100 g body weight^–1). The effect of the peptide on the ability of insulin to inhibit glucagon-induced hepatic glycogenolysis was measured in three experimental groups (n = 6). As expected glucagon (7×10^–11 mol/l) increased integral hepatic glucose release within 84 min (763.4±161.7 vs –25.7±73.2 mol · 100 g body weight^–1 in the control group, p<0.001), while insulin (100 mU/l) decreased the glucagon-stimulated glucose production (395.2±180.0 mol·100 g body weight^–1, p<0.01). Simultaneous infusion of 10^–7 mol/l islet amyloid polypeptide however, was not able to reverse insulin-dependent inhibition of glucagon-stimulated hepatic glucose output (370.0±102.5 mol·100 g body weight^–1, NS) or to enhance lactate-induced gluconeogenesis of livers from 24 h fasted rats (n = 8). The glucose production stimulated by 10^–9 mol/l glucagon was slightly greater in islet amyloid polypeptide-pre-treated livers than in a control group without addition of islet amyloid polypeptide (5 min: 3.60±3.36 vs 1.67±1.28 mol·min^–1·100 g body weight^–1). These results suggest that islet amyloid polypeptide neither directly affects hepatic glycogenolysis nor causes insulin resistance to hormone-sensitive glucose production, but may increase the size of the hepatic glycogen pool by enhancing gluconeogenesis.     

Transient insulin resistance following infusion of adrenaline in Type 1 (insulin-dependent) diabetes mellitus

Summary Insulin resistance was assessed after an intravenous infusion of adrenaline (50 ng·kg^–1·min^–1) or saline (control study) given between 08.00 and 08.30 hours in nine patients with Type 1 (insulin-dependent) diabetes mellitus. The blood glucose level during a somatostatin (100g/h)-insulin (0.4mU·kg^–1·min^–1)-glucose (4.5 mg·kg^–1·-min^–1)-infusion-test performed between 1030 and 14.30 hours served as an indicator of the total body insulin resistance. Blood glucose was maintained around 7 mmol/l between 08.00 and 10.30 hours by a constant infusion of regular insulin (0.57 mU·kg^–1· min^–1) and a variable infusion of a 20% glucose solution. The infusion of adrenaline raised plasma adrenaline to 2.7±0.3 nmol/l (mean±SEM) at the end of the infusion; thereafter it returned to its basal level within 30 min. The plasma levels of free insulin, glucagon, cortisol and growth hormone were similar in the adrenaline and the control studies from 08.00 to 14.30 hours. In comparison with the control study the infusion of adrenaline decreased the need for intravenous glucose significantly over the initial 2 h. Furthermore, during the somatostatin-insulin-glucose infusion test the blood glucose rose significantly (p<0.05) over the initial 2h; thereafter no significant differences between the two studies were seen. It is concluded that a short term infusion of adrenaline, resembling the adrenergic hormone response to hypoglycaemia, induces a diabetogenic effect which subsides within 6 h after omission of the adrenaline infusion.     

Normalization of hepatic glucose regulation despite systemic insulin delivery. Studies in patients with pancreatic transplantation for Type 1 (insulin-dependent) diabetes mellitus

Summary With current surgical techniques for pancreatic transplantation, the graft is anastomosed to the iliac vessels, resulting in delivery of insulin to the systemic circulation rather than to the portal vein as in healthy man. The possible influence of the altered route of insulin delivery on the regulation of splanchnic glucose metabolism was studied in four patients with Type 1 (insulin-dependent) diabetes mellitus at 6–19 months after combined pancreatic and kidney transplantation. Four non-diabetic, age-matched renal transplant recipients and two groups of age-matched healthy subjects served as controls. The studies were carried out in the basal state and during two rates of intravenous glucose infusion (2 and 4 mg · kg^–1 · min–1). Fasting arterial glucose and splanchnic glucose output was similar in all groups. Basal hyperinsulinaemia was present in pancreatic graft recipients compared to healthy subjects. During low rate intravenous glucose infusion splanchnic glucose output decreased to a similar extent in all groups. With the higher glucose infusion rate (4 mg · kg^–1 · min^–1) a net glucose uptake was observed which was similar in all three groups. Peripheral glucose uptake was unchanged at the lower glucose infusion rate but increased by 45–55% at the higher rate. It is concluded that despite systemic insulin delivery from a heterotopic pancreatic graft, hepatic glucose metabolism appears normal both in the post-absorptive state and in response to glucose-stimulated endogenous insulin secretion. Portal insulin delivery is thus not necessary for normal hepatic glucose metabolism in the Type 1 diabetic patient.     

The effect of intraportal and peripheral infusions of glucagon on insulin and glucose concentrations and glucose tolerance in normal man

Summary The effect of peripheral and intraportal infusions of 0.86 pmol/kg · min^–1 of glucagon on plasma glucose, plasma insulin, and glucose tolerance was examined in four normal subjects. Peripheral glucagon concentrations increased by 60–90 pmol/l during intraportal and 70–180 pmol/l during peripheral infusions. The infusions caused increases in plasma glucose levels of approximately 1 mmol/l, and in plasma insulin levels of 75–100%, regardless of route of administration. Intravenous glucose tolerance tests carried out during the glucagon infusions showed that glucose tolerance remained within the normal range and was uninfluenced by the route of administration.     

Basal and 24-h C-peptide and insulin secretion rate in normal man

Summary An understanding of the metabolic abnormalities rising from inappropriate insulin delivery in diabetic patients demands a knowledge of 24-h and basal insulin secretion rates in normal man. We have used biosynthetic human C-peptide to determine its kinetic parameters in 10 normal subjects and applied these to measurements of plasma concentrations in the same subjects to determine pancreatic secretion rate. Metabolic clearance rate measured by stepped primed infusion of biosynthetic human C-peptide at rates of 10, 19 and 26nmol/h was 4.7±0.7 (±SD) ml·kg^–1·min^–1, and was independent of infusion rate. Fractional clearance (T_1/2, 26±3 min) and distribution volume (0.178±0.039 l/kg) were calculated from the decline in concentration after cessation of the highest rate infusion. Basal insulin secretion calculated from the C-peptide metabolic clearance rate and plasma concentrations for the period 02.00 to 07.00 hours was 1.3±0.4U/h. Over 24h total insulin secretion on a standard high carbohydrate diet was 63±15 U, calculated from the area under the C-peptide concentration curve. Basal insulin secretion, therefore, accounted for 50±8% of total insulin secretion. Although only 5.6±1.1% of C-peptide was detected in 24-h urine collections, urinary C-peptide excretion was significantly related to 24-h C-peptide secretion (r=0.74,p<0.02).     

The effects of glucose-dependent insulinotropic polypeptide infused at physiological concentrations in normal subjects and Type 2 (non-insulin-dependent) diabetic patients on glucose tolerance and B-cell secretion

Summary The effects of porcine glucose-dependent insulinotropic polypeptide given by continuous intravenous infusion in normal subjects (n=6) and Type 2 (non-insulin-dependent) diabetic patients (n=6) have been investigated. The subjects were studied on 2 separate days after overnight fasts. On each day 25 g of glucose was infused from 0–30 min plus an infusion of either porcine glucose-dependent insulinotropic polypeptide (0.75 pmol·kg^–1·min^–1) or control solution. During the glucose-dependent insulinotropic polypeptide infusion plasma glucose values were reduced in normal subjects from 30–60 min (p<0.01) and in Type 2 diabetic patients at 45 and 60 min (p<0.05). In the normal subjects insulin concentrations were greater from 10–35 min (p<0.01) following glucose-dependent insulinotropic polypeptide infusion and peak values were increased by 123%. In the Type 2 diabetic patients following glucose-dependent insulinotropic polypeptide infusion insulin levels were increased from 4–40 min (p<0.01) but peak values were only increased by 27%. In the normal subjects C-peptide values were greater from 25–45 min (p<0.01) following glucose-dependent insulinotropic polypeptide infusion and peak C-peptide levels were increased by 82%. In the Type 2 diabetic patients following the glucose-dependent insulinotropic polypeptide infusion C-peptide levels were increased from 6–55 min (p<0.01) and peak values were increased by 20%. Plasma glucose-dependent insulinotropic polypeptide levels were within the physiological post prandial range during the glucose-dependent insulinotropic polypeptide infusion. Glucose-dependent insulinotropic polypeptide is insulinotropic in normal subjects and Type 2 diabetic patients at physiological concentrations and results in improved glucose tolerance. This insulinotropic effect is less marked in the diabetic patients and may represent insensitivity of the B cell to glucose-dependent insulinotropic polypeptide.     

Effect of dexamethasone on insulin sensitivity,islet amyloid polypeptide and insulin secretion in humans

Summary The response of islet amyloid polypeptide and insulin and their molar ratios were investigated in eight healthy volunteers before and after treatment with dexamethasone by oral and frequently-sampled intravenous glucose tolerance tests. Following dexamethasone treatment the insulin sensitivity index decreased significantly from 6.5±1.3 to 4.1±1.0 (U·ml^–1·min^–1, p<0.05. The area under the curve representing above-basal levels of insulin during oral glucose tolerance test increased significantly following dexamethasone treatment from 48132±9736 to 82230±14846 pmol·l^–1·3 h^–1, p<0.05, the area under the curve of islet amyloid polypeptide increased from 1308±183 to 2448±501 pmol·l^–1·3h^–1, p<0.05. The overall insulin/islet amyloid polypeptide molar ratios calculated from the area under the curve during the 3-h period of the oral glucose tolerance test was not significantly different before and after dexamethasone treatment (42±5 vs 40±4). During the oral glucose tolerance test the insulin/islet amyloid polypeptide ratio increased significantly from baseline to 30 min (p<0.05), then declined towards initial values before and after dexamethasone treatment. In conclusion, dexamethasone induced a significant decrease in insulin sensivity and a significant increase in insulin secretion during the oral glucose tolerance test. However, in contrast to previous animal experiments we did not find a change in the insulin/islet amyloid polypeptide ratio before and after dexamethasone treatment.     

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.     

Characterization of the insulin-antagonistic effect of growth hormone in man

Summary The insulin-antagonistic effect of growth hormone was characterized by infusing the hormone at three different infusion rates (6, 12 or 24 mU·kg^–1·min^–1) for one h in 11 healthy subjects. The insulin effect was measured with the euglycaemic clamp technique combined with D-(3-³H)-glucose infusion to evaluate glucose production and utilization. A control study with NaCl (154 mmol·l^–1) infusion was also performed. The insulin levels during the clamps were similar in all studies (36±0.2 mU·l^–1). Peak growth hormone levels were reached at 60 min (growth hormone 6mU·kg^–1·h^–1: 31±5; growth hormone 12 mU·kg^–1·h^–1: 52±4 and growth hormone 24 mU·kg^–1·h^–1: 102±8mU·l^–1). The insulin-antagonistic effect of growth hormone started after 2 h, was maximal after 4–5 h (39% inhibition of glucose infusion rate between control and growth hormone 24 mU·kg^–1·h^–1) and lasted for 6–7 h after peak levels. The resistance was due to a less pronounced insulin effect both to inhibit glucose production and to stimulate glucose utilization. Growth hormone infusion of 12 mU·kg^–1·h^–1 induced a similar insulin-antagonistic effect as the higher infusion rate whereas 6 mU·kg^–1·h^–1 induced a smaller response with a duration of 1 h between 3–4 h after peak levels of growth hormone. The present study demonstrates that growth hormone levels similar to those frequently seen in Type 1 (insulin-dependent) diabetic patients during poor metabolic control or hypoglycaemia, have pronounced insulin-antagonistic effects. The effects starts after about 2–3 h, is maximal after 4–5 h and lasts for about 6–7 h. Both duration and inhibitory effect of growth hormone are related to the plasma levels, where a maximal effect is seen at about 50 mU·l^–1 or higher.     

Normal insulin sensitivity during the phase of glucose intolerance but insulin resistance at the onset of diabetes in the spontaneously diabetic BB rat

Summary In diabetes-prone BB rats, 30 to 50% of animals undergo autoimmune destruction of the pancreatic B-cells leading to a short period of glucose intolerance, followed by an abrupt onset of diabetes. We have examined whether the glucose intolerance period and the onset of diabetes are associated with changes in insulin sensitivity, using the euglycaemic hyperinsulinaemic clamp coupled with [3-³H] glucose infusion. Glucose intolerant rats were detected by a transient glycosuria one hour after an oral glucose load performed every four days. Insulin sensitivity studied in these rats the day following their detection was normal. Other diabetes-prone BB rats were tested daily and studied on the first day of glycosuria. In the basal state, glucose production was increased in diabetic rats (11.3±1.1 vs 7.1±0.8mg·min^–1·kg^–1, p<0.05). Tissue glucose utilization was similar in diabetic and control rats (8.3±0.5 vs 7.1±0.8mg·min^–1·kg^–1) despite a three fold higher glycaemia in the diabetic rats. During the hyperinsulinaemic clamps, glycaemia was clamped at 6.1–6.6 mmol/l in diabetic and control rats. A decreased insulin sensitivity was observed in diabetic rats at submaximal (200 U/ml) and maximal (1500 U/ml) insulin concentrations for both inhibition of hepatic glucose production and stimulation of glucose utilization. No autoantibodies against insulin could be detected in the plasma of diabetic rats. Plasma concentrations of glucagon, catecholamines, ketone bodies and fatty acids were similar in control and diabetic rats during the clamp studies. Our results suggest that the decrease of basal insulin concentration is responsible for the insulin resistance in the diabetic BB rat at onset of diabetes, either directly or through the increased glycaemia.     

Determination and kinetic analysis of non-insulin mediated glucose uptake in Type 1 (insulin-dependent) diabetes mellitus

Summary In man, total glucose uptake is the sum of insulin mediated glucose uptake and non-insulin mediated glucose uptake. The latter pathway has not been examined in Type 1 (insulin-dependent) diabetes mellitus. In order to assess non-insulin mediated glucose uptake in Type 1 diabetes, we measured steady-state rates of glucose uptake during glucose clamps at 5.27, 9.71 and 12.5 mmol/l using low (0.25 mU· kg^–1·min^–1), intermediate (0.75 mU·kg^–1·min^–1) and high (1.50 mU·kg^–1·min^–1) insulin infusion rates in 10 subjects with Type 1 diabetes. For insulin infusion rates of 0.25, 0.75 and 1.50 mU·kg^–1·min^–1 as plasma glucose rose from 5.27 to 9.71 mmol/l, total glucose uptake increased by 35, 43 and 52 percent respectively (p<0.05 for each insulin infusion rate). For all three insulin infusion rates, there was no significant increase in total glucose uptake as plasma glucose increased from 9.71 to 12.5 mmol/l. At each glycaemic level, glucose uptake correlated significantly with plasma free insulin (r=0.81, p<0.01 at 5.71 mmol/l; r=0.84, p<0.01 at 9.71 mmol/l; r=0.73, p<0.02 at 12.5 mmol/l). Linear regression analysis to a point corresponding to plasma free insulin equalling zero, yielded values for non-insulin mediated glucose uptake (mmol·kg^–1·min^–1) of 0.11,0.14,0.18 at plasma glucose of 5.27, 9.7 and 12.5 mmol/l respectively. Thus, increasing plasma glucose concentrations were associated with increasing rates of non-insulin mediated glucose uptake. For each insulin infusion rate used, the percent of total glucose uptake accounted for by non-insulin mediated glucose uptake remained independent of plasma glucose concentration, but decreased as insulin infusion rate increased. During the insulin infusion at 0.25 mU·kg^–1·min^–1, this percentage ranged from 83.7 to 91.4%. Analysis of glucose uptake data derived for theoretical plasma insulin levels of 0, 40, 80 and 160 U/ml yielded linear Eadie-Hofstee plots (r=– 0.83 to – 0.99), suggesting that insulin increased Vmax but did not alter Km. Hence, in these subjects with Type 1 diabetes, glucose uptake, both insulin mediated and non-insulin mediated can be described by Michaelis-Menten kinetics. Comparison of values obtained for Vmax and Km in the present studies of Type 1 diabetes with those obtained from non-diabetic subjects indicates that non-insulin dependent glucose uptake in Type 1 diabetes is quantitatively similar to that of non-diabetic subjects.     

Peripheral and hepatic insulin sensitivity in subjects with impaired glucose tolerance

Summary Recent evidence suggests that the post-prandial hyperglycaemia in impaired glucose tolerance is primarily due to impaired suppression of basal hepatic glucose output. This in turn appears to be secondary to decreased first phase insulin secretion, although decreased hepatic insulin sensitivity, which is a feature of non-insulin-dependent diabetes mellitus, might also play a role. Eight mildly overweight subjects with impaired glucose tolerance and eight closely matched control subjects with normal glucose tolerance underwent an intravenous glucose tolerance test to assess first phase insulin secretion. Insulin sensitivity was examined by a 150-min hyperinsulinaemic-euglycaemic clamp. Somatostatin was infused from 150 min to suppress endogenous insulin secretion, and glucagon and insulin were replaced by constant infusion. Glucose with added dideuterated glucose (labelled infusion technique) was infused to maintain euglycaemia. First phase insulin secretion ( 0–10 min insulin area ÷ 0–10 min glucose area) was significantly decreased in the subjects with impaired glucose tolerance (median [range]: 1.2 [0.2–19.4] vs 9.1 [2.6–14.5] mU·mmol^–1; p<0.01). During the clamp, circulating insulin (93±8 [mean±SEM] and 81±10 mU·l^–1) and glucagon (54±4 and 44±6 ng·l^–1) levels were comparable. Total glucose disposal was decreased in subjects with impaired glucose tolerance (2.78±0.27 vs 4.47±0.53 mg·kg^–1·min^–1; p<0.02), and was primarily due to decreased non-oxidative glucose disposal. However, hepatic glucose output rates were comparable during the clamp (0.38±0.10 and 0.30±0.18 mg·kg^–1·min^–1). Therefore, the main defects in subjects with impaired glucose tolerance are decreased first phase insulin secretion and peripheral non-oxidative glucose disposal, but hepatic glucose output shows normal responsiveness to insulin.Abbreviations FPIS First phase insulin secretion - PG plasma glucose - NIDDM non-insulin-dependent diabetes mellitus - IGT impaired glucose tolerance - HGO hepatic glucose output - IVGTT intravenous glucose tolerance test - OGTT oral glucose tolerance test     

Pancreatic procolipase activation peptide-enterostatin-inhibits pancreatic enzyme secretion in the pig.

Pancreatic procolipase, a protein cofactor for lipase, is activated by trypsin, with a simultaneous formation of colipase and a pentapeptide with the sequence Val-Pro-Asp-Pro-Arg (VPDPR). This peptide was found to significantly inhibit pancreatic protein secretion after intraduodenal infusion in pigs (2 mg/kg/h). The inhibition, amounting to 60%, occurred under base-line conditions as well as after stimulation with cholecystokinin (CCK)/secretin (1 U of each peptide/h/kg body wt). In contrast, intravenous infusion of VPDPR (0.2 mg/h/kg) did not affect pancreatic secretion. There was no significant change in the plasma levels of pancreatic polypeptide, insulin, glucagon, or glucose following intraduodenal infusion of VPDPR. It is concluded that the procolipase activation peptide might have an inhibitory function in pancreatic enzyme secretion mediated indirectly through a gut action. Therefore, the lipolytic enzymes of pancreas may also take part in the feed-back regulation of the pancreatic function. We suggest the name enterostatin for this novel regulatory peptide.     

Possible mechanism by which somatostatin-induced glucagon suppression improves glucose tolerance during insulinopaenia in man

Summary The present study examines the question of whether lowering the basal plasma glucagon concentration alters the response of the liver to an intravenous glucose load under conditions where insulin is present at near-basal concentrations. Acute hyperglycaemia of 220–240 mg/dl was induced by peripheral venous glucose infusion in two groups of normal men who had undergone hepatic vein catheterization. Somatostatin (0.9 mg/h) was infused in both groups together with an infusion of insulin (0.15 mU/kg/min) to maintain arterial insulin levels at 7–12 U/ml. Glucagon (1.5 ng/kg/min) was infused in one group resulting in a rise in plasma glucagon levels from 148±37 to 228±25 pg/ml, thus mimicking basal portal glucagon concentrations, whereas in the second group glucagon was not replaced, resulting in a fall in circulating glucagon levels from 132±21 to 74±15 pg/ml. In the glucagon-deprived group, net splanchnic glucose production (NSGP) fell from 143±31 to –72.5±39 mg/ min (p<0.01), indicating that net splanchnic glucose uptake had occurred. By contrast, NSGP did not change significantly (137±20 vs 151±60 mg/min) in the group in which both insulin and glucagon were replaced during hyperglycaemia. These data thus suggest that during hyperglycaemia, when the insulin concentration is fixed at basal levels, glucagon may play an important role in determining whether or not the liver diminishes its output of glucose and stores glucose in response to a glucose load.     

Intravenous insulin has no effect on myocardial contractility or heart rate in healthy subjects

Summary To evaluate the acute effects of intravenous insulin on myocardial contractility and heart rate, echocardiography was performed in 12 healthy subjects and continuous heart rate recording in 11 healthy subjects before and during eugly-caemic insulin and glucose infusion. The rate of insulin infusion was 0.5–1.0 mU·kg^–1·min^–1. Serum insulin concentration was increased from 14.1±5.5 (mean±SD) to a plateau level of 91.3±22.8 mU/l. Left ventricular end-diastolic diameter, ejection phase indices and the heart rate remained at basal levels during the intervention. Thus moderate hyperinsulinaemia, induced by euglycaemic insulin and glucose infusion, has no inotropic or chronotropic effects in healthy supine subjects.