Beta endorphin modulation of the glucoregulatory effects of repeated epinephrine infusion in alloxan-diabetic and normal dogs

Summary When repeated epinephrine infusions are given to normal dogs as a partial stress model, there is exaggerated hyperglycaemia, associated with reduced plasma insulin levels and markedly decreased glucose clearance. In the present study, we have examined the hormonal and metabolic responses to two successive 60-min epinephrine (0.1 g-kg^–1·min^–1) infusions with or without concomitant infusion of beta endorphin (0.3 g·kg^–1·min^–1) in 6 alloxan-diabetic dogs. These studies have been compared to similar studies in 5 normal dogs.In the diabetic dogs, plasma glucose rose from 12.3±2.2 to 16.2±2.4 mmol/l (p<0.001) in response to the first epinephrine infusion and rose further to 18.1±2.5 mmol/l (p<0.001) during the second epinephrine infusion. The increases in plasma glucagon and glucose production were comparable with both infusions, but considerably greater than previously observed in normal dogs.In normal dogs, beta endorphin diminished the insulin response to the first epinephrine infusion (p<0.02), and abolished this response to the second (p<0.05). In addition beta endorphin also diminished the glucagon response to the second epinephrine infusion (p<0.01) and greatly potentiated epinephrine-induced suppression of glucose metabolic clearance during both infusions (p<0.001). However, beta endorphin did not appreciably alter the hyperglycaemic response to epinephrine due to a concomitant attenuation of the epinephrine-induced increase in hepatic glucose production.In contrast to normal dogs, beta endorphin did not modulate the effects of either the first or second epinephrine infusion on glucose kinetics in diabetic dogs. Also, beta endorphin failed to inhibit glucagon or insulin secretion in response to epinephrine in the diabetic animals. Since the alloxan-diabetic and normal dogs respond differently to the combined infusion of beta endorphin and epinephrine we conclude that the effects of beta endorphin observed in the normal dogs are dependent upon intact pancreatic endocrine function.     

Glucoregulatory function of glucagon in hypo-, eu- and hyperthyroid miniature pigs

Summary The glucoregulatory function of glucagon was investigated in hypo-, eu- and hyperthyroid miniature pigs. Infusion glucagon, (3 ng x kg body weight⁻¹ · min⁻¹) transiently increased blood glucose (p<0.01) and hepatic glucose production (p<0.01) in euthyroidism, but was without effect in hyperthyroidism. Infusing glucagon plus somatostatin (2 ng x kg body weight⁻¹ · min⁻¹ and 0.2 μg x kg body weight⁻¹ · min⁻¹) transiently increased blood glucose (Δ 3.0 to 4.3 mmol/l) and hepatic glucose production (Δ 3.3 to 7.7 umol x kg body weight⁻¹ · min⁻¹) in all thyroid states, the effect was less pronounced in hyperthyroid pigs. By contrast, hypoglucagonaemia (74 to 107 pg/ml) at basal insulin (28 to 35 μU/ml) provoked hypoglycaemia (1.4 to 2.2 mmol/l) and a fall in glucose production (Δ 4.7 to 8.3 umol x kg body weight⁻¹ · min⁻¹), which was independent of the thyroid state; the effect was most pronounced in hyperthyroidism (p<0.01). Hepatic glycogen content, arterial gluconeogenic precursor concentrations as well as the glycaemic response (Δ 0.60 mmol/l) to alanine infusion (23 umol x kg body weight⁻¹ · min⁻¹) were all unaffected by hyperthyroidism. We conclude that moderate experimental hyperthyroidism reduces glucagon action due to reduced glycogen mobilisation. This may in part result from increased insulin sensitivity.     

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.     

Production and metabolic clearance of glucose under basal conditions in Type II (non-insulin-dependent) diabetes mellitus

Aims/hypothesis: The pathogenesis of fasting hyperglycaemia in Type II (non-insulin-dependent) diabetes mellitus has yet to be clarified. Rates of glucose production (R _a), utilization and metabolic clearance rate were therefore measured during an extended fast, in control subjects and in Type II diabetic patients. Methods: Nine subjects with newly-diagnosed or diet-treated diabetes and seven control subjects matched for age and weight (BMI 36.0 ± 2.4 and 35.3 ± 3.1 kg/m² respectively) underwent an overnight fast followed by a 10-h unprimed infusion of [6-³H]glucose. Plasma tracer concentrations were fitted by a single-compartment model. Results: The metabolic clearance rate was near-constant [61.7 + 2.4 ml/(min-m²)] in diabetic patients and [75.5 ± 3.3 ml/(min-m²)] in control subjects (p < 0.05). It was correlated to the glucose concentrations both at t = 0 (r = –0.752, p = 0.0008) and t = 10 h (r = –0.675, p = 0.004). The calculated volume of distribution was 17.3 ± 1.4 l (18.2 % weight, diabetes), 19.6 ± 2.4 l (18.4 % weight, control). Glycaemia fell from 10.7 ± 0.8 mmol/l to 6.5 ± 0.3 mmol/l by 10 h (p < 0.05) in diabetes and from 5.6 ± 0.6 to 4.8 ± 0.1 mmol/l in control subjects (p < 0.05). The rate of glucose production decreased in parallel, from 563 ± 33 to 363 ± 23 μmol/(min-m²) (p < 0.05) in diabetes from 419 ± 20 to 347 ± 32 μmol/(min-m²) in control subjects. Initial R _a was higher in diabetic patients than in control subjects (p < 0.05) and was highly correlated to glycaemia (r = 0.836, p = 0.0001). By 10 h, R _a had converged in diabetic patients and control subjects and all correlation with glycaemia was lost (r = 0.0017, p = 0.95). Conclusions/interpretation: In relatively early diabetes, the more “labile” portion of fasting hyperglycaemia, which subsequently decreased, was closely related to the simultaneously decreasing R _a. The 25 % increase in glucose concentrations which persisted as stabilized R _a, resulted from about a 20 % lower metabolic clearance rate. [Diabetologia (2001) 44: 983–991] Received: 28 February 2001 and in revised form: 17 April 2001     

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.     

The relationship between peripheral glucose utilisation and insulin sensitivity in the regulation of hepatic glucose production: studies in normal and alloxan-diabetic dogs

BACKGROUND: Hepatic glucose overproduction (HGP) of diabetes could be primary or could occur in response to the metabolic needs of peripheral (skeletal muscle (SkM)) tissues. This question was tested in normal and diabetic dogs. METHODS: HGP, SkM glucose uptake (Rd(tissue)), metabolic clearance of glucose (MCRg) and glycolytic flux (GF(exog)), and SkM biopsies were measured in the same dogs before and after alloxan-induced diabetes. Normal dogs were exposed to (1) an extended 20-h fast, (2) low- and high-dose glucose infusions (GINF) at basal insulinaemia, and chronic diabetic dogs were exposed to (3) hyperglycaemia, (4) phlorizin-induced normoglycaemia, and (5) poor and good diabetic control. RESULTS: (1) Prolonged fast: HGP, Rd(tissue), and GF(exog) fell in parallel (p < 0.05). (2) Low-dose GINF: plasma glucose, insulin, Rd(tissue), MCRg, and GF(exog) were unchanged, but HGP fell by approximately 40%, paralleling the supplemental GINF. (3) High-dose GINF at basal insulin: plasma glucose doubled and synchronous changes in HGP, Rd(tissue), MCRg, and GF(exog) occurred; IC(glucose), G6P, and glycogen were unchanged. (4) Hyperglycaemic diabetes: HGP was raised (p < 0.05), matching urinary glucose loss (UGL) and decreased MCR(g), and maintaining normal basal Rd(tissue) and GF(exog). SkM IC(glucose) was increased and glycogen decreased (both p < 0.05). (5) Phlorizin-induced normoglycaemia in diabetic dogs: HGP rose, matching the increased UGL, while maintaining normal Rd(tissue) and GF(exog). Intramuscular substrates normalised. (6) Whole body and SkM metabolism normalised with correction of the insulin resistance and good diabetic control. CONCLUSION: HGP reflects whether SkM is in a state of relative glucose 'excess' or absolute/relative glucose 'deprivation'.     

Failure of nocturnal changes in growth hormone to alter carbohydrate tolerance the following morning

Summary To determine whether the increases in growth hormone that occur during sleep alter carbohydrate tolerance the following morning, two groups of volunteers were studied on two occasions. In one group saline alone was injected and infused (i. e. no octreotide) on one occasion and on the other octreotide was injected at 23.00 hours to inhibit endogenous growth hormone secretion followed by saline infusion to create a state of relative nocturnal growth hormone deficiency. In the other group the octreotide injection was followed on one occasion by a constant growth hormone infusion designed to maintain growth hormone concentrations at “basal” levels throughout the night whereas on the other it was followed by a constant infusion plus two supplemental growth hormone infusions given at midnight and 02.30 hours to mimic the normal nocturnal rise in growth hormone. The next morning, subjects were fed a radiolabelled mixed meal. The differences in the nocturnal growth hormone concentrations had no effect on the glucose, insulin, C-peptide and glucagon concentrations following breakfast ingestion nor did they alter postprandial rates of glucose production, disappearance or substrate oxidation. Thus, the normal nocturnal rise in growth hormone does not appear to be an important regulator of carbohydrate tolerance the following morning. [Diabetologia (1998) 41: 1064–1072] Received: 15 January 1998 and in revised form: 27 April 1998     

Assessment of glucose turnover rates in euglycaemic clamp studies using primed-constant [3-3H]-glucose infusion and labelled or unlabelled glucose infusates.

Underestimation of glucose turnover rates has been a problem in clamp studies using primed-constant [3-3H]-glucose infusion technique. Due to slow mixing in interstitial compartments concealed specific activity gradients may arise between plasma and interstitial compartments during intravenous unlabelled glucose infusion. Such specific activity gradients, however, can be prevented if plasma specific activity is maintained constant. Two euglycaemic clamp studies (insulin infusion 40 mU m-2 min-1) were performed in six lean normal subjects. Using conventional unlabelled glucose infusates plasma specific activity declined by 74%, tracer determined glucose appearance was smaller than actual glucose infusion rates (317 +/- 11 vs 366 +/- 15 mg m-2 min-1, p < 0.001), and erroneous negative values were calculated for glucose production (- 49 +/- 7 mg m-2 min-1). Average underestimation during the first 2 h correlated with glucose infusion rates (r = 0.88, p < 0.02). In contrast, when plasma specific activity was maintained constant, using appropriately labelled glucose infusates, tracer determined glucose appearance and glucose infusion rates were similar (385 +/- 16 vs 385 +/- 17 mg m-2 min-1), and negative errors for glucose production were avoided. In conclusion, using unlabelled glucose infusates, as in previous studies, suppression of glucose production is overestimated and stimulation of glucose utilization is underestimated. As errors were greater with larger glucose infusions, the mistakes may have been greatest in insulin sensitive control subjects, and smaller in insulin resistant subjects. Therefore, re-evaluation of hepatic insulin sensitivity seems appropriate in diabetes, obesity, and other insulin resistant states.     

Heterogeneity of plasma glucagon immunoreactivity in normal, depancreatized, and alloxan-diabetic dogs.

Filtration of basal plasma from normal, alloxan-diabetic, and depancreatized dogs on Bio Gel P-10 yielded four glucagon-immunoreactive fractions. One of them appeared in the true glycagon area with the glucagon-125I (3500 mol vt). Of the other three, one appeared in the void volume (greater than 20000 mol wt), another just before the insulin-125I (congruent to 9000 mol wt), and the last one close to the salt peak (less than 2000 mol wt). The increase of total plasma glucagon immunoreactivity observed in depancreatized and alloxan diabetic dogs was mainly due to an increase in the 3500 and 9000 molecular-weight fractions. Arginine infusion in depancreatized dogs caused an increase in the 3500 molecular-weight fraction. Somatostatin or insulin infusion in depancreatized and alloxan-diabetic dogs resulted in disappearance of the 3500 molecular-weight fraction.     

The effects of carbohydrate-enriched meals on glucose turnover and metabolic clearance rates of glucose in Type 2 diabetic patients

Summary The addition of fructose to natural meals elicits lower serum glucose and immunoreactive insulin responses when compared with that of sucrose and starch meals. Differences in rates of splanchnic glucose appearance and peripheral glucose disposal may be partly responsible. To evaluate the role of both parameters after different carbohydrate-enriched meals, we measured the arterialized venous blood glucose, immunoreactive insulin and gastric inhibitory polypeptide concentrations in seven Type 2 diabetic patients after ingestion of isocaloric test meals. Measurements were made in a random manner on three separate occasions. Fructose, sucrose, and bread supplementation constituted 68% of the total carbohydrate content of each meal. Rates of total glucose appearance, glucose utilization and metabolic clearance rates of glucose were determined by the D³-H-3glucose prime-continuous infusion technique. The mean fasting glucose levels were similar in the three groups. Mean peak glucose concentrations and integrated incremental areas were significantly lower (p < 0.02) after the fructose-enriched meals compared with that of either sucrose or bread. The basal arterialized venous blood glucose levels were similar in all three groups. The mean incremental integrated arterialized venous blood glucose area was significantly lower in the fructose group when compared with the sucrose (p < 0.05) and bread (p < 0.02) groups. The mean fasting gastric inhibitory polypeptide levels were similar in the three groups. However, the mean incremental integrated gastric inhibitory polypeptide areas were significantly lower in the fructose group compared with the sucrose and bread groups (p < 0.01 and p < 0.05 respectively). Basal hepatic glucose outputs were not significantly different in the three groups. After each test meal ingestion, the rate of total glucose appearance was lowest for the fructose group, intermediate for the bread group and highest for the sucrose group. However, the metabolic clearance rate did not change from the baseline despite variable arterialized venous blood glucose responses after each test meal. We conclude that the differences in glycaemic responses after carbohydrate-enriched meals cannot be ascribed solely to differences in peripheral glucose disposal in Type 2 diabetic patients. Rather, the rates of total splanchnic glucose output appear to determine the ultimate glycaemic responses after different carbohydrate-enriched meals in Type 2 diabetic patients.     

On the determination of basal glucose production rate in patients with Type 2 (non-insulin-dependent) diabetes mellitus using primed-continuous 3-3H-glucose infusion

Summary Using primed-continuous 3-³H-glucose infusion, basal glucose production rate has been reported to be 140% higher than normal or almost normal in hyperglycaemic patients with Type 2 (non-insulin-dependent) diabetes mellitus. To determine whether these markedly different results could be due to the mode of priming: fixed or adjusted, or the mode of calculation: steady state or non-steady state equations, we studied 11 patients with Type 2 diabetes (fasting plasma glucose 8–20 mmol/l). For 6 h 3-³H-glucose (0.40 Ci/min) was infused preceded by a priming dose of 40 Ci (fixed priming), or 40 Ci · plasma glucose (mmol/l)·5^–1 (adjusted priming). In diabetic patients the plasma glucose concentration was not constant but declined 0.52±0.07 mmol·l^–1· h^–1. Furthermore, the rate of fall was correlated to the fasting plasma glucose concentration (r=0.90, p<0.01). Thus, the fasting state was not a steady state condition. Using adjusted priming a constant tracer steady state level was obtained within 60 min. In contrast, using fixed priming tracer steady state was not reached within 6 h. The initial tracer level was far below, and increased in time towards the steady state level observed after adjusted priming. Consequently, using Steele's equations after fixed priming, glucose production rates calculated after 90–120 min were overestimated in proportion to fasting hyperglycaemia. In conclusion: The fasting state in patients with Type 2 diabetes is not a steady state condition. Adjusted priming seems most appropriate in Type 2 diabetes. By estimating glucose production 2 h after fixed priming or assuming steady state conditions, most previous studies may have overestimated basal glucose production in Type 2 diabetes in proportion to fasting hyperglycaemia.     

Plasma clearance of transferrin in control and hypotransferrinaemic mice: implications for regulation of transferrin turnover

Summary. Kinetic studies were performed to determine the clearance of iodinated transferrin in hypotransferrinaemic mice, as compared to normal animals. Clearance of i.v. (and i.p.) administered radiolabelled protein in homozygous (hpx/hpx) mice was significantly faster than in heterozygous (hpx/+) and wild-type control (+/+) groups. A comparable t_1/2 value for transferrin clearance in hpx/hpx mice was derived from a study in which immunoassay was performed on serum samples obtained at various times post-injection with normal mouse serum, indicating that the clearance of ¹²⁵I reflected true clearance of transferrin protein. The clearance rate in the hpx/+ group was significantly slower than in +/+ mice. Calculation of transferring synthesis rates in these two groups suggested that transferrin levels do not regulate transferrin synthesis rates, but may affect degradation; this observation is consistent with the fact that transferrin levels in hpx/+ mice are > 50% of the values in +/+ mice, and indicates a partial compensation for reduced synthesis. The rapid clearance in hpx/hpx mice is an additional factor in determining the low levels of circulating transferrin in these synthesis-impaired mutants.     

Biological potency of neurotensin metabolites in vivo: Importance of alcohol ''fixation'' of blood

Neurotensin (NT), a 13-amino acid peptide, is released from the ileum following a meal. It is metabolized principally by the kidney and in the circulation to N-terminal fragments and apparently rapidly degraded C-terminal fragments. The present study was designed to compare the biological activity (plasma pancreatic polypeptide response) and the clearance kinetics of NT(1-13), the N-terminal fragment NT(1-11) and the C-terminal fragment NT(8-13). To measure accurately the circulating concentrations of short-lived NT fragments in the circulation, a method was devised of collecting blood directly into alcohol ('alcohol fixation'). The alcohol fixation procedure prevented the post-collection losses of the C-terminal fragment NT(8-13) and established that, based on blood levels achieved, NT(8-13) had 70% of the pancreatic polypeptide stimulating potency of NT(1-13). Nevertheless, the metabolic clearance rate of NT(8-13) was about sevenfold higher than the intact molecule, NT(1-13), suggesting that circulating C-terminal fragments have a minor physiological role. When the N-terminal fragment NT(1-11) was infused, there was no sustained effect on pancreatic polypeptide secretion although it was cleared at a rate similar to that of NT(1-13). It is concluded that the use of alcohol fixation prevents post-collection losses of NT fragments and enables true biological potencies of short-lived fragments to be assessed. The biological activity of NT resides in the C-terminus which, once split from the protective N-terminus, is rapidly degraded in the circulation. The remaining intact but inactive N-terminus is relatively stable.     

In vivo insulin resistance during pregnancy in the rat

Summary The glucose disappearance rate measured after IV glucose injection (1 g/kg body wt) remained unchanged between 12 and 21 day of gestation in the rat. In contrast, insulin secretion in response to IV glucose was markedly increased on day 19 and 21 of pregnancy, suggesting resistance to endogenous insulin. Glucose kinetics (glucose production, utilization and clearance) in response to various doses of IV insulin have been studied in anaesthetised postabsorbtive 19 day pregnant and virgin rats using 6-³H glucose. With the supramaximal dose of insulin (4 U/kg body wt) no differences in glucose kinetics were found between pregnant and virgin rats. In contrast, with the two lower doses of insulin (0.15 and 0.05 U/kg body wt) glucose production was inhibited by 36±3% and 13±2% (Mean±SEM) respectively in virgin rats, but was not decreased in pregnant rats. When the effect of insulin on glucose clearance was expressed as % of the maximal effect obtained with 4 U/kg body weight, the rise in glucose clearance in response to the two lower doses of insulin (0.15 and 0.05 U/kg body wt) was lower in pregnant (57.5±6 and 27.4±4%) than in virgin rats (73.3±6 and 42.2±7%). These results suggest that a decreased sensitivity to insulin appears in late pregnancy in the rat and could involve both liver and skeletal muscle.     

Subcutaneous versus intraperitoneal administration of insulin on post-prandial hyperglycaemia and glucose turnover in alloxan diabetic dogs

Summary The effects of subcutaneous and intraperitoneal insulin delivery by a closed-loop insulin infusion device on post-prandial hyperglycaemia and rates of glucose appearance and disappearance were compared in alloxan diabetic dogs. No differences in basal or post-prandial values or patterns of response were observed between the two routes of insulin delivery. In addition, the amounts of insulin infused and the plasma insulin concentrations achieved were not different for the two routes of insulin administration. These studies demonstrate that in the dog there appears to be no difference in the pattern of disposal of glucose from a mixed meal when insulin was administered intraperitoneally or subcutaneously at the rates of insulin infusion used in these experiments. Key words: Subcutaneous insulin, intraperitoneal insulin, glucose turnover, diabetic dogs.     

Some peculiarities of the glucoregulatory response to glucose infusion in the rat

Summary The glucoregulatory response to the i.v. infusion of different doses of glucose and glucose plus insulin was studied in anesthetized rats by using the primed constant infusion of glucose-2-³H. Infusion of glucose at the rate of 10 mg/kg/min induced a rise of about 100% in blood glucose, while the hepatic release of glucose showed only a small and transient decrease. A proportional increase of glycemia and glucose utilization (Rd) was observed without any appreciable change in the metabolic clearance rate (MCR) of glucose; a two-fold increase in plasma insulin was recorded at all times. In the group of rats receiving 20 mg/kg/min of glucose, changes in the above parameters were slightly greater; MCR showed a moderate increment in spite of the six-fold rise of plasma insulin. Finally, the infusion of large doses of insulin together with 20 mg/kg/min of glucose resulted in complete cessation of glucose release by the liver and in a remarkable increase of Rd and MCR. These results suggest a poor adaptability of the glucoregulatory system of the rat in response to glucose infusion as compared to other mammalian species.     

Automated feedback control of subcutaneous glucose concentration in diabetic dogs

Summary The subcutaneous tissue is generally considered as a potential site for the monitoring of intracorporal glucose concentration by means of implanted sensors. We studied the suitability of using the resulting signal from the interstitial glucose concentration as an input in a feedback-controlled system for insulin administration. Miniaturized glucose electrodes (amperometric glucose oxidase sensors for the measurement of hydrogen peroxide) were implanted in insulin-dependent diabetic dogs. The output of these sensors was fed into the controller of a bedside-type artificial B cell. Insulin was infused by the device intravenously on the basis of a proportional-differential algorithm. The glucose patterns were compared to identical experiments where feedback control was accomplished on the basis of paracorporal blood glucose measurement using the same algorithm. Normoglycaemia was restored and maintained in both sets of experiments and oral glucose loads were well compensated for. It is concluded that the apparent subcutaneous glucose concentration is appropriate as an input signal for an artificial B cell.     

Atypical antipsychotic drugs induce derangements in glucose homeostasis by acutely increasing glucagon secretion and hepatic glucose output in the rat

Aims/hypothesis  Use of the second-generation antipsychotic drugs (SGAs) results in the development of obesity and a type 2 diabetes-like syndrome. We hypothesised that, in addition to the insulin resistance associated with the obesity, the SGAs might have acute effects on glucose metabolism that could contribute to the derangements in glucose metabolism. Methods  We investigated the effects of therapeutically relevant levels of three different antipsychotic medications (haloperidol, quetiapine and clozapine) on glucose tolerance, measures of insulin resistance and hepatic glucose production, and on insulin and glucagon secretion in rats. Results  We found that these drugs induce impaired glucose tolerance in rats that is associated with increased insulin secretion (clozapine>quetiapine>haloperidol) but is independent of weight gain. However, Akt/protein kinase B activation is normal, and at these levels of drug there was no effect on insulin action in fat cells or soleus muscle, and no effect on insulin sensitivity as evaluated by insulin tolerance tests. We show that clozapine induces increased glucose levels following pyruvate and glycerol challenges, indicating an increase in hepatic glucose output (HGO). Increased HGO would in turn increase insulin release and would explain the apparent phenotype mimicking insulin resistance. We provide evidence that this effect could at least in part be mediated by a stimulation of glucagon secretion. Conclusions/interpretation  Our findings indicate that SGAs can cause acute derangements in glucose metabolism that are not caused by a direct induction of insulin resistance but act via an increase in glucagon secretion and thus stimulation of hepatic glucose production. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Demonstration of a relatively hepatoselective effect of covalent insulin dimers on glucose metabolism in dogs

Summary Insulin analogues with relatively greater effect on hepatic glucose production than peripheral glucose disposal could offer a more physiological approach to the treatment of diabetes mellitus. The fact that proinsulin exhibits this property to a minor degree may suggest that analogues with increased molecular size may be less able than insulin to obtain access to peripheral receptor sites. Covalent insulin dimers have previously been shown to possess lower hypoglycaemic potencies than predicted by their in vivo receptor binding affinities. Reduced rates of diffusion to peripheral target tissues-might be an explanation for the lower in vivo potency compared to insulin. To test the relative hepatic and peripheral effects of covalent insulin dimers, glucose clamp procedures with D-[3-³H] glucose tracer infusions were used in anaesthetised greyhounds to establish dose-response curves for rates of hepatic glucose production and glucose disposal with insulin, N^B1, N^{B 1},-suberoyl-insulin dimer, and N^B29, N^{B 29},-suberoyl-insulin dimer. With N^B1, N^{B 1},-suberoyl-insulin dimer molar potencies relative to insulin were 68%, (34–133) (mean and 95% fiducial limits), for inhibition of hepatic glucose production and 14.7%, (10.3–20.9) for glucose disposal. With N^B29,N^{B 29},-suberoyl-insulin dimer potencies were 75%, (31–184) and 2.5%, (1.5–4.3), for inhibition of hepatic glucose production and for glucose disposal, respectively. The demonstration that both dimers exhibit a significantly greater effect on glucose production than on glucose disposal supports the suggestion that analogues with increased molecular size may exhibit reduced ability to gain access to peripheral target cells.Abbreviations B1-B 1D N^B1,N^{B 1},-suberoyl-insulin dimer - B29-B 29D N^B29,N^{B 29},-suberoyl-insulin dimer - Ra hepatic glucose production rate - Rd peripheral glucose disposal rate - M_r relative molecular weight - MCR metabolic clearance rate - ANOVA analysis of variance