Acetyl-salicylic acid impairs insulin-mediated glucose utilization and reduces insulin clearance in healthy and non-insulin-dependent diabetic man

Summary The effect of acetyl-salicylic acid (ASA, 3 g per day for 3 days) on glucose utilization and insulin secretion was studied in healthy volunteers and Type 2 diabetic patients using the hyperglycaemic and euglycaemic insulin clamp technique. When in healthy subjects arterial plasma glucose was acutely raised and maintained at +7 mmol/l above fasting level, the plasma insulin response was enhanced by ASA (70±7 vs. 52±7mU/l), whereas the plasma C-peptide response was identical. Despite higher insulin concentrations, glucose utilization was not significantly altered (control, 61±7; ASA, 65±6mol·kg^–1·min^–1) indicating impairment of tissue sensitivity to insulin by ASA. Inhibition of prostaglandin synthesis was not likely to be involved in the effect of ASA, since insulin response and glucose utilization were unchanged following treatment with indomethacin. In the euglycaemic insulin (1 mU·kg^–1·min^–1) clamp studies, glucose utilization was unaltered by ASA despite higher insulin concentrations achieved during constant insulin infusion (103±4vs. 89±4mU/l). In Type 2 diabetic patients, fasting hyperglycaemia (10.6 ±1.1 mmol/l) and hepatic glucose production (15±2 mol·kg^–1·min^–1) fell upon ASA treatment (8.6±0.7 mmol/l; 13±1 mol·kg^–1· min^–1). During the hyperglycaemic clamp study, the plasma response of insulin, but not of C-peptide, was enhanced by ASA, whereas tissue sensitivity to insulin was reduced by 30 percent. It is concluded that in healthy and Type 2 diabetic man, ASA impairs tissue sensitivity to the action of insulin. This effect is counterbalanced by an augmented plasma insulin response to glucose, which results from a reduced insulin clearance rate. In Type 2 diabetic patients, the reduction in hepatic glucose production may be responsible for the amelioration of hyperglycaemia following ASA treatment.     

Sulphonylurea therapy doubles B-cell response to glucose in Type 2 diabetic patients

Summary The effect of sulphonylurea therapy for 3 weeks on glucose-stimulated insulin secretion and insulin resistance was studied in Type 2 diabetic patients. The fasting plasma insulin and C-peptide concentrations on diet alone were compared with each subject's fasting concentrations on sulphonylurea treatment at a lower fasting plasma glucose and at the original diet-alone glycaemic level obtained by the hyperglycaemic clamp technique. At this isoglycaemic level (mean 11 mmol/l), plasma insulin levels increased from 6.9 mU/l on diet alone to 12.1 mU/l on sulphonylurea treatment (p<0.01). The subjects were also studied by the hyperglycaemic clamp technique at mean glycaemic levels of 13 mmol/l before and after sulphonylurea treatment; the incremental insulin response was similarly enhanced from 7.6±3.5 to 13.7±6.9 mU/l (p<0.02) respectively. Sulphonylureas appear to reduce glycaemia by enhancing B-cell function two-fold. In the patients studied this was from approximately 21% to 37% of a normal response. Insulin resistance assessed by the same hyperglycaemic clamps as endogenous plasma insulin concentrations divided by glucose infusion rates was unchanged by sulphonylurea therapy (mean 4.37 compared to 4.40 mU. 1^–1·mg^–1·kg·min on diet alone).     

Counterregulation in Type 2 (non-insulin-dependent) diabetes mellitus. Normal endocrine and glycaemic responses,up to ten years after diagnosis

Summary We have examined hormonal and metabolic responses to insulin-induced hypoglycaemia in 10 Type 2 (non-insulin-dependent) diabetic patients treated with tablets and 10 age, sex and weight matched control subjects. Diabetic patients were under 110% ideal body weight, had no autonomie neuropathy and were well controlled (HbA₁, 7.1±0.2%). After the diabetic patients were kept euglycaemic by an overnight insulin infusion, hypoglycaemia was induced in both groups by intravenous insulin at 30 mU·m^–2·min^–1 for 60 min and counterregulatory responses measured for 150 min. There were no significant differences between diabetic patients and control subjects in the rate of fall (3.3±0.3 vs 4.0±0.3 mmol·1^–1·h^–1), nadir (2.4±0.2 vs 2.3±0.1 mmol/l) and rate of recovery (0.027±0.002 vs 0.030±0.003 mmol·1^–1·min^–1) of blood glucose. Increments of glucagon (60.5±5.7 vs 70±9.2 ng/l) and adrenaline (1.22±0.31 vs 1.45±0.31 nmol/l) were similar in both groups. When tested using this model, patients with Type 2 diabetes, without microvascular complications and taking oral hypoglycaemic agents show no impairment of the endocrine response and blood glucose recovery following hypoglycaemia.     

Erythrocyte sodium-lithium countertransport activity and total body insulin-mediated glucose disposal in normoalbuminuric normotensive Type 1 (insulin-dependent) diabetic patients

Summary Insulin resistance in Type 1 (insulin-dependent) diabetes mellitus may be associated with raised erythrocyte sodium-lithium countertransport activity in patients with hypertension, or nephropathy, or both. However, in these circumstances it is difficult to separate the impact of hypertension, hyperlipidaemia and nephropathy on erythrocyte sodium-lithium countertransport from that of insulin resistance. We have therefore examined the relationship between insulin-mediated glucose disposal and erythrocyte sodiumlithium countertransport in 41 normotensive (mean blood pressure 120/74 mm Hg), normoalbuminuric (mean albumin excretion 6.2 g/min), normolipidaemic (mean serum cholesterol 4.3 mmol/l and mean serum triglycerides 1.0 mmol/l) Type 1 diabetic patients. Erythrocyte sodium-lithium countertransport was on average 0.31 mmol Li · h^–1 · l erythrocytes ^–1 (range 0.07–0.69). Nine patients had values above 0.40 mmol Li · h^–1 erythrocytes^–1 (0.51±0.10 mmol Li · h^–1 · l erythrocytes^–1). The patients with high erythrocyte sodium-lithium countertransport were matched for age, sex, BMI, HbA₁ and duration of diabetes, with nine patients with normal erythrocyte sodium-lithium countertransport. Insulin-mediated glucose disposal was evaluated during the last hour of a euglycaemic clamp (insulin 0.015 U · kg^–1 · h^–1; blood glucose clamped at 7.0 mmol/l). The free insulin levels were comparable between the patients with high and normal erythrocyte sodium-lithium countertransport (37.2±14.7 mU/l and 34.7±17.2 mU/l respectively). Insulin-mediated glucose disposal was on average 3.1±1.5 (range 0.8–6.8) mg · kg^–1 · min^–1. Erythrocyte sodium-lithium countertransport did not correlate with insulin-mediated glucose disposal in all 41 cases (r _s=–0.14), but when the matched groups were compared, patients with raised erythrocyte sodium-lithium countertransport had lower insulin-mediated glucose disposal rates compared to those with normal erythrocyte sodium-lithium countertransport (2.7±1.1 vs 3.9±1.3 mg · kg^–1 · min^–1; p=0.044). In these 18 patients a significant inverse relationship was found between erythrocyte sodium-lithium countertransport and insulin-mediated glucose disposal (r _s=–0.62; p=0.003). Raised erythrocyte sodium-lithium countertransport appears to be associated with insulin insensitivity in Type 1 diabetes, even in the absence of hyperlipidaemia, hypertension and nephropathy.     

In vivo insulin action and muscle glycogen synthase activity in Type 2 (non-insulin-dependent) diabetes mellitus: effects of diet treatment

Summary Insulin resistant glucose metabolism is a key element in the pathogenesis of Type 2 (non-insulin-dependent) diabetes mellitus. Insulin resistance may be of both primary (genetic) and secondary (metabolic) origin. Before and after diet-induced improvement of glycaemic control seven obese patients with newly-diagnosed Type 2 diabetes were studied with the euglycaemic clamp technique in combination with indirect calorimetry and forearm glucose balance. Muscle biopsies were obtained in the basal state and again after 3 h of hyperinsulinaemia (200 mU/l) for studies of insulin receptor and glycogen synthase activities. Similar studies were performed in seven matched control subjects. Insulin-stimulated glucose utilization improved from 110±11 to 183±23 mg·m^–2·min^–1 (p<0.03); control subjects: 219+23 mg·m^–2·min^–1 (p=NS, vs post-diet Type 2 diabetes). Nonoxidative glucose disposal increased from 74±17 to 138+19 mg·m^–2·min^–1 (p<0.03), control subjects: 159±22 mg· m^–2·m^–1 (p=NS, vs post-diet Type 2 diabetic patients). Forearm blood glucose uptake during hyperinsulinaemia increased from 1.58±0.54 to 3.35±0.23 mol·l^–1·min^–1 (p<0.05), control subjects: 2.99±0.86 mol·l^–1·min^–1 (p=NS, vs post-diet Type 2 diabetes). After diet therapy the increase in insulin sensitivity correlated with reductions in fasting plasma glucose levels (r=0.97, p<0.001), reductions in serum fructosamine (r=0.77, p<0.05), and weight loss (r=0.78, p<0.05). Values of muscle glycogen synthase sensitivity to glucose 6-phosphate (A_0.5 for glucose 6-phosphate) were similar in the basal state. However, insulin stimulation of glycogen synthase was more pronounced after diet treatment (A_0.5: 0.43±0.06 (before) vs 0.30±0.04 mmol/l (after); p<0.03; control subjects: 0.22±0.03 mmol/l). Muscle insulin receptor binding and kinase activity were similar before and after diet treatment and comparable to values in the control group. The data suggest that impaired insulin stimulation of in vivo glucose turn-over and muscle glycogen synthase activity tend to be restored during successful diet treatment of patients with Type 2 diabetes.     

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.     

Hepatic and peripheral insulin resistance: A common feature of Type 2 (non-insulin-dependent) and Type 1 (insulin-dependent) diabetes mellitus

Summary Hepatic glucose production (³H-glucose technique) and insulin-mediated glucose uptake (insulin clamp technique) were measured in 38 Type 2 (non-insulin-dependent) and 11 Type 1 (insulin-dependent) diabetic patients. Fasting plasma glucose concentration was 8.3 ± 0.5 mmol/l in the former, and 9.6 ± 1.3 mmol/1 in the latter group; the respective fasting plasma insulin levels were 19 ± 2 mU/l (p < 0.005 versus 13 ± 1 mU/l in 33 age-matched control subjects), and 9 ± 1 mU/l (p < 0.01 versus 14 ± 1 mU/l in 36 younger control subjects). In the fasting state, hepatic glucose production was slightly increased (15%, 0.1 > p > 0.05) in the Type 2 diabetic patients and markedly elevated (65%, p < 0.001) in the Type 1 patients compared with their respective control groups. In both groups of diabetic subjects, the rates of hepatic glucose production were inappropriately high for the prevailing plasma glucose and insulin levels, indicating the presence of hepatic resistance to insulin. Basal plasma glucose clearance was also significantly reduced in both the Type 2 (34%) and the Type 1 (14%) diabetic subjects. The fasting plasma glucose concentration correlated directly with hepatic glucose production, and inversely with plasma glucose clearance. During the insulin clamp, plasma insulin was maintained at approximately 100 mU/l in all groups, while plasma glucose was maintained constant at the respective fasting levels. Total glucose uptake was reduced in both the Type 2 (4.57 ± 0.31 versus 6.39 ± 0.25 mg · min^–1 · kg^–1 in the control subjects, p < 0.01) and the Type 1 (4.77 ± 0.48 versus 7.03 ± 0.22 mg · min^–1 · kg^–1, p < 0.01) diabetic patients. Insulin-stimulated glucose clearance was reduced to a similar extent in Type 2 (54%) and Type 1 (61%) diabetic subjects, and correlated directly with fasting glucose clearance. These results show that insulin resistance is a common feature of both types of diabetes and can be demonstrated in the basal as well as the insulin-stimlated state. Both hepatic and peripheral resistance to the action of insulin contribute to diabetic hyperglycaemia.     

Contribution of glucose/glucose 6-phosphate cycle activity to insulin resistance in Type 2 (non-insulin-dependent) diabetes mellitus

Summary It has been suggested that increased glucose/glucose 6-phosphate substrate cycling impairs net hepatic glucose uptake in Type 2 (non-insulin-dependent) diabetes mellitus and contributes to hyperglycaemia. To investigate glucose/glucose 6-phosphate cycle activity and insulin action in Type 2 diabetes we studied eight patients and eight healthy control subjects, using the euglycaemic glucose clamp and isotope dilution techniques with purified [2-³H]- and [6-³H] glucose tracers, in the post-absorptive state and eight patients and five healthy control subjects during consecutive insulin infusions at rates of 0.4 and 2.0 mU·kg^–1·min^–1. [2-³H]glucose and [6-³H]glucose radioactivity in plasma samples were determined using selective enzymatic detritiation, allowing calculation of glucose turnover rates for each isotope, the difference being glucose/glucose 6-phosphate cycling. Endogenous glucose production ([6-³H]glucose) was greater in diabetic than control subjects in the post-absorptive state (15.6±1.5 vs 11.3±0.4 mol·kg^–1·min^–1, p<0.05) and during the 0.4 mU insulin infusion (10.1±1.3 vs 5.2±0.3 mol·kg^–1·min^–1, p<0.01) indicating hepatic insulin resistance. Glucose/glucose 6-phosphate cycling was significantly greater in diabetic than in control subjects in the post-absorptive state (2.6±0.4 vs 1.6±0.2 mol·kg^–1·min^–1, p<0.05) but not during the 0.4 mU insulin infusion (2.0±0.4 vs 2.0±0.3 mol·kg^–1·min^–1). During the 2.0 mU insulin infusion endogenous glucose production was suppressed to a similar degree in both groups (2.6±0.5 vs 3.4±0.7 mol · kg^–1·min^–1) but glucose disappearance was lower in the diabetic subjects (30.8±2.0 vs 52.4±4.6 mol·kg^–1·min^–1, p<0.01). During the 2.0 mU insulin infusion glucose/glucose 6-phosphate cycling was greater in the diabetic subjects (3.8±0.7 vs 0.8±0.6 mol·kg^–1·min^–1, p<0.05). In conclusion, both hepatic and peripheral insulin action are impaired in Type 2 diabetes. Increased glucose/glucose 6-phosphate cycling is seen in the post-absorptive state and also during marked hyperinsulinaemia, when insulin resistance is predominantly due to reduced peripheral tissue glucose uptake.     

Partial recovery of insulin secretion and action after combined insulin-sulfonylurea treatment in Type 2 (non-insulin-dependent) diabetic patients with secondary failure to oral agents

Summary Metabolic control, insulin secretion and insulin action were evaluated in seven Type 2 (non-insulin-dependent) diabetic patients with secondary failure to oral antidiabetic agents before and after two months of combined therapy with supper-time insulin (Ultratard: 0.4 U/kg body weight/day) plus premeal glibenclamide (15 mg/day). Metabolic control was assessed by 24 h plasma glucose, NEFA, and substrate (lactate, alanine, glycerol, ketone bodies) profile. Insulin secretion was evaluated by glucagon stimulation of C-peptide secretion, hyperglycaemic clamp (+7 mmol/l) and 24 h free-insulin and C-peptide profiles. The repeat studies, after two months of combined therapy, were performed at least 72 h after supper-time insulin withdrawal. Combining insulin and sulfonylurea agents resulted in a reduction in fasting plasma glucose (12.9±7 vs 10.4±1.2 mmol/l; p<0.05) and hepaic glucose production (13.9±1.1 vs 11.1±1.1 mol·kgc-min^–1; p<0.05). Mean 24 h plasma glucose was also lower (13.7±1.2 vs 11.1±1.4 mmol/l; p<0.05). Decrements in fasting plasma glucose and mean 24 h profile were correlated (r=0.90; p<0.01). HbA_1c also improved (11.8±0.8 vs 8.9±0.5%; p<0.05). Twenty-four hour profile for NEFA, glycerol, and ketone bodies was lower after teatment, while no difference occurred in the blood lactate and alanine profile. Insulin secretion in response to glucagon (C-peptide =+0.53±0.07 vs +0.43±0.07 pmol/ml) and hyperglycaemia (freeinsulin = 13.1±2.0 vs 12.3±2.2 mU/l) did not change. On the contrary, mean 24 h plasma freeinsulin (13.2±2.6 vs 17.5±2.2 mU/l; p<0.01) and C-peptide (0.76±0.10 vs 0.98±0.13 pmol/l; p<0.02) as well as the area under the curve (19.1±4.1 vs 23.6±3.1 U/24 h;p<0.01 and 1.16±0.14 vs 1.38±0.18 mol/24 h; p<0.02 respectively) were significantly increased. The ratio between glucose infusion (M) and plasma insulin concentration (I) during the hyperglycaemic clamp studies (M/I, an index of insulin sensitivity), was not statistically different (1.40±0.25 vs 1.81±0.40 mol·kg^–1· min^–1/mU·l^–1). These data suggest that, in Type 2 diabetic patients with secondary failure to oral antidiabetic agents, the combination of supper-time longacting insulin and premeal sulfonylurea agents can improve metabolic control. This positive effect is possibly mediated through an increased secretion of insulin in response to physiologic stimuli.     

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

Summary 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 28mU/m² per min plus 16 ±3.8mU/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.     

Differential effects of insulin therapy on hepatic and peripheral insulin sensitivity in Type 2 (non-insulin-dependent) diabetes

Summary Hepatic glucose production and metabolic clearance rate of glucose were measured using (3-³H) glucose at steady state, basally and during two sequential 2 h insulin (25 and 40mU · kg^–1 · h^–1)/glucose(2 and 3mg · kg^–1 · min^–1) infusion periods. Eight diabetic subjects were studied before and after 1 week of twice daily insulin therapy; six control subjects matched for age, weight and degree of obesity were also studied. In the diabetic patients, pre-treatment hepatic glucose production was 20.0 ± 2.2, 9.9 ± 2.9, and 1.4 ± 0.8 mol · kg^–1 · min^–1 respectively (± SEM) for each of the three periods, and fell significantly with treatment to 12.8 ± 1.7,4.0 ± 1.5 and 1.9 ± 1.0 mol · kg^–1 · min^–1. Hepatic glucose production in normal subjects was 13.2 ± 0.6, 2.2 ± 0.8 and < 1 mol · kg^–1 · min^–1. The pre-treatment metabolic clearance rate in all diabetic studies with insulin levels 30 mU/l was 1.10 ± 0.14 ml · kg^–1 · min^–1 and remained virtually unchanged following insulin therapy; this was significantly lower than in the control subjects (6.83 ± 1.02, p < 0.001). Basal non-esterified fatty acid levels were higher (p < 0.02) in the pre-treated diabetic patients compared to post-treated diabetic patients and control subjects. Non-esterified fatty acids in each group fell to similar levels during the insulin infusions, but the rate of fall was slower in the pre-treated diabetic patients. Insulin receptor binding to erythrocytes was normal in the diabetic subjects and unchanged by treatment. Therefore, following insulin treatment of uncontrolled Type 2 (non-insulin-dependent) diabetes, the initially increased basal hepatic glucose production, and decreased hepatic sensitivity, return towards normal. However, the glucose clearance remains low, despite good diabetic control, and appears to be a major factor in the continuing glucose intolerance. As insulin receptor binding is normal, the defect of glucose clearance in Type 2 diabetes appears compatible with a post-receptor defect of glucose metabolism.     

Impaired insulin action in newly diagnosed type 1 (insulin-dependent) diabetes mellitus

Summary Hepatic and peripheral insulin sensitivity were investigated in five newly diagnosed Type 1 (insulin-dependent) diabetic subjects before and after 1 week of twice daily insulin therapy. Eight weight-matched control subjects were also studied. Hepatic glucose production and glucose utilization were measured basally and during two sequential 2-h insulin (25 and 40 mU· kg^–1· h^–1)/glucose infusion periods. In the untreated hyperglycaemic diabetic patients hepatic glucose production was 16.3±2.6, 8.1±1.1 and 3.6±2.8|mol· kg^–1· min^–1 respectively for each of the three periods (mean±SEM), and fell with treatment to 12.5±1.4, 0.5±0.5 and 0.5±0.5 mol· kg^–1· min^–1. Hepatic glucose production for normal subjects was 13.4±0.7, 2.3±0.8 and <0.1 mol-kg^–1· min^–1. Glucose utilization was 12.7±1.4,18.2±0.7 and 22.1±3.4mol· kg^–1· min^–1 before treatment in the diabetic subjects, and 11.8±1.7, 20.9±3.3 and 30.1±3.6 after treatment. These values compare with those in the euglycaemic control subjects (13.4±0.7, 18.7±1.6 and 36.3±2.7 mol · kg^–1· min^–1). The pre-treatment metabolic clearance rate of glucose in all diabetic studies with insulin levels >30mU/l was 2.6 ±0.4 and rose to 3.9 ±0.5 ml· kg^–1· min^–1 following insulin therapy. This was significantly lower than in the control subjects (6.7±0.8 ml· kg^–1 · min^–1; p<0.005). Basal nonesterified fatty acid levels were high in the untreated, but normal in the treated diabetic subjects, and fell in response to insulin infusion. Basal -hydroxybutyrate levels were high in both diabetic groups, but also fell in response to insulin infusion. Erythrocyte insulin receptor binding was normal in the untreated diabetic subjects, and was not changed by treatment. Therefore, treatment of newly diagnosed Type 1 diabetic subjects with insulin reverses the hepatic insensitivity to insulin. In contrast, treatment only partially improves peripheral glucose disposal. Since erythrocyte insulin receptor binding is normal, it is likely that a post-receptor defect in peripheral glucose metabolism exists in Type 1 diabetic patients despite insulin therapy and good diabetic control for a period of 1 week.     

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     

The course and determinants of insulin action in Type 1 (insulin-dependent) diabetes mellitus

Summary The course and determinants of insulin action were investigated in 8 newly diagnosed Type 1 (insulin-dependent) diabetic patients, who were studied every 3 months for one year, and in three groups of 8 patients each with 5, 10 and 20 years diabetes, studied once. Fifteen healthy subjects matched for age, sex and body weight served as control subjects. Dose-response curves were constructed using sequential euglycaemic (5.0 mmol/l) clamps (insulin infusion rates: 0.5, 1.0, 2.0 and 5.0 mU·kg^–1·min^–1 in periods of 2h). After 1/2 month of insulin treatment, insulin responsiveness was normal, but sensitivity was decreased (ED₅₀ 70±7 mU/l (SEM) vs 54±4mU/l in control subjects, p<0.05). After 6 months, insulin sensitivity was improved (ED₅₀ 57±4 mU/l, p<0.01 vs 1/2 month and not significant (NS) vs control subjects); but after 9 and 12 months, it was reduced again, similarly to 0.5 month. Insulin responsiveness remained normal at all time-points. In the three groups of patients with longstanding diabetes, impaired insulin sensitivity with normal responsiveness was noted also (ED₅₀ 73±9 mU/l, p<0.02 vs control subjects). At 6, 9 and 12 months, glycaemic control (HbA₁) and insulin dose were inverse correlates for insulin action; in patients with longstanding disease, this was noted for HbA₁ and body weight, in control subjects for body weight. In conclusion, decreased insulin sensitivity re-develops in Type 1 diabetes within the first year following an initial improvement. Presumably, hyperglycaemia plays a role in the pathogenesis of this recurrence.     

Insulin resistance in Type 2 (non-insulin-dependent) diabetic patients with hypertriglyceridaemia

Summary Hypertriglyceridaemia, which is frequently seen in Type 2 (non-insulin-dependent) diabetes mellitus, is associated with insulin resistance. The connection between hypertriglyceridaemia and insulin resistance is not clear, but could be due to substrate competition between glucose and lipids. To address this question we measured glucose and lipid metabolism in 39 Type 2 diabetic patients with hypertriglyceridaemia, i. e. mean fasting serum triglyceride level equal to or above 2 mmol/l (age 59±1 years, BMI 27.4±0.5 kg/m², HbA_1c8.0±0.2%, serum triglycerides 3.2±0.2 mmol/l) and 41 Type 2 diabetic patients with normotriglyceridaemia, i. e. mean fasting serum triglyceride level below 2 mmol/l (age 58±1 years, BMI 27.0±0.7 kg/m², HbA_1c7.8±0.2 %, serum triglycerides 1.4±0.1 mmol/l). Insulin sensitivity was assessed using a 340 pmol·(m²)^–1· min^–1 euglycaemic insulin clamp. Substrate oxidation rates were measured with indirect calorimetry and hepatic glucose production was estimated using a primed (25 Ci)-constant (0.25 Ci/min) infusion of [3-³H]-glucose. Suppression of lipid oxidation by insulin was impaired in patients with hypertriglyceridaemia vs patients with normal triglyceride levels (3.5±0.2 vs 3.0±0.2mol·kg^–1· min^–1; p<0.05). Stimulation of glucose disposal by insulin was reduced in hypertriglyceridaemic vs normotriglyceridaemic patients (27.0±1.3 vs 31.9±1.6 mol·kg^–1·min^–1; p<0.05) primarily due to impaired glucose storage (9.8±1.0 vs 14.6±1.4mol·kg^–1·min^–1; p<0.01). In contrast, insulinstimulated glucose oxidation was similar in patients with hypertriglyceridaemia and in patients with normal triglyceride concentrations (16.9±0.8 vs 17.2±0.7mol·kg^–1·min^–1). Hepatic glucose production in the basal state and during the clamp did not differ between the two groups. We conclude therefore that oxidative substrate competition between glucose and lipids does not explain insulin resistance associated with hypertriglyceridaemia in Type 2 diabetes. The question remains whether the reduced nonoxidative glucose disposal observed in the patients with hypertriglyceridaemia is genetically determined or a consequence of increased lipid oxidation.     

ACE-inhibition increases hepatic and extrahepatic sensitivity to insulin in patients with Type 2 (non-insulin-dependent) diabetes mellitus and arterial hypertension

Summary To assess the effects of ACE-inhibition on insulin action in Type 2 (non-insulin-dependent) diabetes mellitus associated with essential hypertension, 12 patients with Type 2 diabetes (on diet and oral hypoglycaemic agents) and arterial hypertension were examined on two occasions, in a single blind, cross-over study, after two days of treatment with either captopril or a placebo. The study consisted of a euglycaemic-hyperinsulinaemic clamp (two sequential steps of insulin infusion at the rates of 0.25 mU·kg^–1·min^–1 and 1 mU·kg^–1·min^–1, 2 h each step), combined with an infusion of 3-³H-glucose to measure the rate of hepatic glucose production and that of peripheral glucose utilization. The results show that blood pressure was lower after captopril (sitting, systolic 148±5 mmHg, diastolic 89±2 mm Hg) compared to placebo (155±6 and 94±2 mm Hg) (p<0.05). Captopril treatment resulted in a more suppressed hepatic glucose production (2.7±0.4 vs 4.94±0.55 mol·kg^–1·min^–1), and a lower plasma non-esterified fatty acid concentration (0.143±0.05 vs 0.200±0.05 mmol/l) (captopril vs placebo, p<0.05) at the end of the first step of insulin infusion (estimated portal plasma insulin concentration 305±28 pmol/l); and in a greater glucose utilization (36.5±5.1 vs 28±3.6mol·kg^–1·min^–1, p<0.001) at the end of the second step of insulin infusion (arterial plasma insulin concentration of 604±33 pmol/l). We conclude that captopril improved insulin sensitivity in Type 2 diabetes associated with hypertension at the level of the liver and extrahepatic tissues, primarily muscle and adipose tissue. Thus, in contrast to other antihypertensive drugs such as diuretics and beta-blockers which may have a detrimental effect on insulin action, ACE-inhibitors appear to improve insulin action in Type 2 diabetes and essential hypertension, at least on a short-term basis.     

Effect of insulin on renal sodium handling in hyperinsulinaemic Type 2 (non-insulin-dependent) diabetic patients with peripheral insulin resistance

Summary The sodium retaining effect of insulin was studied in ten Type 2 (non-insulin-dependent) diabetic patients (mean age 56 (43–73) years, mean body mass index 29.5 (24.2–33.7) kg/m²) and eight age-matched control subjects (mean age 57 (43–68) years, mean body mass index 23.4 (20.8–26.6) kg/m²). The renal clearances of ^99mTc-DTPA, lithium, sodium and potassium were measured over a basal period of 90 min. Then insulin was infused at a rate of 40 mU·mirr^–1·m^–2. After an equilibration period of 90 min, the clearance measurements were repeated during a new 90 min period. Blood glucose was clamped at the basal level (diabetic patients: 9.9±3.5, control subjects: 5.3±0.5 mmol/l) by a variable glucose infusion. Basal plasma insulin concentration was elevated in the diabetic patients (0.12±0.05 vs 0.05±0.02 pmol/ml, p<0.01). Insulin infusion resulted in comparable absolute increments in plasma insulin concentrations in the diabetic group and in the control group (0.44±0.13 vs 0.36±0.07 pmol/ml, NS). The metabolic clearance rate of glucose during the last 30 min of insulin infusion was lower in the diabetic patients (155±62 vs 320±69 ml·min^–1·m², p<0.01), reflecting peripheral insulin resistance. The decline in sodium clearance during insulin infusion was similar in diabetic subjects (1.8±1.1 vs 0.7±0.4 ml·min^–1·1.73 m^–2, p< 0.01) and in control subjects (1.7±0.3 vs 0.8±0.3 ml · min^–1 · 1.73 m^–2, p<0.01). The glomerular filtration rate and lithium clearance was unchanged, consequently calculated distal tubular fractional sodium reabsorption increased (diabetic patients: 92.9±4.1 vs 97.1±1.5, p<0.01, control subjects: 93.1±1.1 vs 96.5±0.6%, p< 0.01). Estimated extracellular fluid volume was 10% higher in the diabetic subjects (16.3±2.1 vs 14.8±2.01·1.73 m^–2, NS). In conclusion, the sodium retaining effect of insulin is preserved in Type 2 diabetic patients with peripheral insulin resistance. Insulin may contribute to sodium and fluid retention and thus to the increased frequency of hypertension in hyperinsulinaemic Type 2 diabetic patients.     

Loss of regular oscillatory insulin secretion in islet cell antibody positive non-diabetic subjects

Summary Basal insulin secretion was compared in nine islet-cell antibody positive, non-diabetic first-degree relatives of children with Type 1 (insulin-dependent) diabetes mellitus and nine normal control subjects matched for age, sex and weight. Acute insulin responses to a 25 g intravenous glucose tolerance test were similar in the two groups (243 (198–229) vs 329 (285–380) mU·l^–1·10min^–1, mean (±SE), p=0.25). Fasting plasma insulin was assayed in venous samples taken at one min intervals for 2 h. Time series analysis was used to demonstrate oscillatory patterns in plasma insulin. Autocorrelation showed that regular oscillatory activity was generally absent in the islet-cell antibody positive group, whereas a regular 13 min cycle was shown in control subjects (p< 0.0001). Fourier transformation did, however, show a 13 min spectral peak in the islet-cell antibody positive group, consistent with intermittent pulsatility. We conclude that overall oscillatory patters of basal insulin secretion are altered in islet-cell antibody positive subjects even when the acute insulin response is within the normal range.     

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.     

Predominant role of reduced beta-cell sensitivity to glucose over insulin resistance in impaired glucose tolerance

Aims/hypothesis Impaired glucose tolerance (IGT) is an insulin-resistant state and a risk factor for Type 2 diabetes. The relative roles of insulin resistance and insulin deficiency in IGT have been disputed.Methods In 40 IGT subjects and 63 sex-, age-, and weight-matched controls with normal glucose tolerance (NGT), we measured (i) indices of insulin sensitivity of fasting glucose production (by tracer glucose) and glucose disposal (M value on a 240 pmol·min^–1·m^–2 insulin clamp) and (ii) indices of beta-cell function (glucose sensitivity, rate sensitivity, and potentiation) derived from model analysis (Am J Physiol 283:E1159–E1166, 2002) of the insulin secretory response (by C-peptide deconvolution) to oral glucose.Results In comparison with NGT, IGT were modestly insulin resistant (M=29±2 vs 35±2 µmol·min^–1·kg_FFM^–1, p=0.01); insulin sensitivity of glucose production also was reduced, in approximate proportion to M. Despite higher baseline insulin secretion rates, IGT was characterized by a 50% reduction in glucose sensitivity [53 (36) vs 102 (123) pmol·min^–1·m^–2·mM^–1, median (interquartile range), p=0.001] and impaired potentiation [1.6 (0.8) vs 2.0 (1.5) units, p<0.04] of insulin release, whereas rate sensitivity [1.15 (1.15) vs 1.38 (1.28) nmol·m^–2·mM^–1] was not significantly reduced. Glucose sensitivity made the single largest contribution (~50%) to the observed variability of glucose tolerance.Conclusion/interpretation In IGT the defect in glucose sensitivity of insulin release quantitatively predominates over insulin resistance in the genesis of the reduced tolerance to oral glucose.