Effects of glucagon-like peptide 1 (7–36 amide) on whole-body protein metabolism in healthy man

The incretin glucagon-like peptide 1 (GLP-1) shows glucose-dependent insulinotropic activity and may exert anabolic effects. Whole-body protein metabolism was assessed by measuring [1-¹³C]-leucine kinetics in 13 healthy volunteers during hyperglycaemic clamping with or without pancreatic clamping (somatostatin infusion) in order to differentiate between insulin-mediated and direct GLP-1 effects. During intact pancreatic secretion leucine flux and leucine oxidation rate as parameters of whole-body protein breakdown decreased markedly after 180 min of synthetic GLP-1 infusion (GLP-1 vs. placebo: P < 0.003). Indirect calorimetry showed an increase in energy expenditure and CO₂ production during GLP-1 administration (P < 0.0005). Plasma insulin increased after 3 h of GLP-1 infusion to 1486 ± 145 pmol L^?1 vs. 185 ± 12 pmol L^?1 for saline (P < 0.0001). When plasma insulin levels were kept constant (GLP-1 vs. saline, NS) during pancreatic clamping, GLP-1 effects on both protein metabolism and energy expenditure were abolished. Thus, GLP-1 infusion in man exerts protein anticatabolic and thermic effects, which are mediated by GLP-1-induced stimulation of insulin secretion.     

Effect of glucagon-like peptide 1 (7-36 amide) on insulin-mediated glucose uptake in patients with type 1 diabetes

OBJECTIVE: To examine the insulinomimetic insulin-independent effects of glucagon-like peptide (GLP)-1 on glucose uptake in type 1 diabetic patients. RESEARCH DESIGN AND METHODS: We used the hyperinsulinemic-euglycemic clamp (480 pmol. m(-2) x min(-1)) in paired randomized studies of six women and five men with type 1 diabetes. In the course of one of the paired studies, the subjects also received GLP-1 at a dose of 1.5 pmol. kg(-1) x min(-1). The patients were 41 +/- 3 years old with a BMI of 25 +/- 1 kg/m(2). The mean duration of diabetes was 23 +/- 3 years. RESULTS: Plasma glucose was allowed to fall from a fasting level of approximately 11 mmol/l to 5.3 mmol/l in each study and thereafter was held stable at that level. Plasma insulin levels during both studies were approximately 900 pmol/l. Plasma C-peptide levels did not change during the studies. In the GLP-1 study, plasma total GLP-1 levels were elevated from the fasting level of 31 +/- 3 to 150 +/- 17 pmol/l. Plasma glucagon levels fell from the fasting levels of approximately 14 pmol/l to 9 pmol/l during both paired studies. Hepatic glucose production was suppressed during the glucose clamps in all studies. Glucose uptake was not different between the two studies ( approximately 40 micromol. kg(-1) x min(-1)). CONCLUSIONS: GLP-1 does not augment insulin-mediated glucose uptake in lean type 1 diabetic patients.     

Internalization of glucagon-like peptide-1(7–36)amide in rat insulinoma cells

Glucagon-like peptide-1(7-36)amide [GLP-1(7-36)amide] is supposed to be an important physiologic incretin. Recently, high affinity receptors for GLP-1(7-36)amide have been demonstrated on rat insulinoma-derived RINm5F cells. The present study examined the internalization and degradation of the GLP-1-receptor complex. Internalization of the peptide was time- and temperature-dependent. At 37 degrees C binding and internalization was rapid. At 60 min 35% of 125I-labeled GLP-1(7-36)amide was internalized. Incubation in the presence of increasing concentrations of non-labeled GLP-1(7-36)amide resulted in a decrease of internalization of 125I-labeled peptide indicating that this process is saturable. Incubation in the presence of 0.2 mM chloroquine, an inhibitor of intracellular hormone degradation, resulted in intracellular accumulation of 125I-GLP-1(7-36)amide. HPLC-supported analysis of cell content after internalization of 125I-GLP-1(7-36)amide during a 60-min incubation period at 37 degrees C revealed an elution profile showing two maxima of radioactivity: one represented intact labeled GLP-1(7-36)amide, the other an intracellular degradation product of the peptide. Chloroquine caused a 5-fold increase of the peak representing intact 125I-GLP-1(7-36)amide thus demonstrating inhibition of degradation of labelled peptide. Furthermore, a 4-fold increase of the other peak occurred possibly mirroring a delay of release of degradation products by chloroquine. It was excluded that chloroquine is able to interfere with GLP-1(7-36)amide-binding to its receptor.     

Effect of acute acidosis and alkalosis on leucine kinetics in man

Summary. The effects of acute pH changes on whole body leucine kinetics (1-¹³C-leucine infusion technique) were determined in normal subjects. Plasma insulin, glucagon, and growth hormone concentrations were kept constant by somatostatin and replacement infusions of the three hormones. When acidosis was produced by ingestion of NH4CI (4 mmol kg^-1 p. os; n = 8) arterialized pH decreased within 3 h from 7.39±0.01 to 7.31 ±0.01 (P<0.001) and leucine plasma appearance increased by 0.13 ±0.04 μmol kg^-1 min^-1 (P<0.02); in contrast, when alkalosis was produced by intravenous infusion of 4 mmol kg^-1 NaHCO₃ (n= 1, pH 7.47 ±0.01), leucine plasma appearance decreased by -0.09 ± 0.04 (xmol kg^-1 min^-1 (P<0.01 vs. acidosis). Whole body leucine flux also increased during acidosis compared to alkalosis (P<0.05), suggesting an increase in whole body protein breakdown during acidosis. Apparent leucine oxidation increased during acidosis compared to alkalosis (P=0.05). Net forearm leucine exchange remained unaffected by acute pH changes. Plasma FFA concentrations decreased during acidosis by -107 ±67 μmol l^-1 (P<0.05) and plasma glucose increased by 1.90±0.25 mmol l^-1 (P<0.02); in contrast, alkalosis resulted in an increase in plasma FFA by 83 ± 40 (μmol 1^-1 (P<0.02; P<0.01 vs. acidosis), suggesting an increase in lipolysis; plasma glucose decreased compared to acidosis (P<0.01). The data demonstrate that acute metabolic acidosis and alkalosis, as they occur in clinical conditions, influence protein breakdown, and in the opposite direction, lipolysis.     

Inhibition of carbohydrate-mediated glucagon-like peptide-1 (7-36)amide secretion by circulating non-esterified fatty acids

Two studies were performed to assess the entero-insular axis in simple obesity and the possible effect of variations in the level of circulating non-esterified fatty acids (NEFA) on one of the components of the entero-insular axis, glucagon-like peptide-1 [(7-36) amide]. In the first study, we compared the entero-pancreatic hormone response to oral carbohydrate in obese and lean women. Obese subjects demonstrated hyperinsulinaemia and impaired glucose tolerance but this was not associated with an increased secretion of either glucose-dependent insulinotropic polypeptide or glucagon-like peptide-1 (GLP-1). These findings therefore provide no support for the hypothesis that overactivity of the entero-insular axis contributes to the hyperinsulinaemia seen in obesity. Indeed, the plasma GLP-1 response to carbohydrate was markedly attenuated in obese subjects, confirming previous observations. In the second study, in which carbohydrate-stimulated GLP-1 responses were again evaluated in obese and lean women, circulating NEFA levels were modulated using either heparin (to increase serum NEFA) or acipimox (to reduce serum NEFA). Treatment with acipimox resulted in complete suppression of NEFA levels and in a markedly higher GLP-1 response than the response to carbohydrate alone or to carbohydrate plus heparin. We suggest that higher fasting and postprandial NEFA levels in obesity may tonically inhibit nutrient-mediated GLP-1 secretion, and that this results in attenuation of the GLP-1 response to carbohydrate. However, although serum NEFA levels post-acipimox were similarly suppressed in both lean and obese subjects, the GLP-1 response was again significantly lower in obese subjects, suggesting the possibility of an intrinsic defect of GLP-1 secretion in obesity. The reduction of GLP-1 levels in obesity may be important both in relation to its insulinotropic effect and to its postulated role as a satiety factor.     

Glucose-dependency of the insulin stimulatory effect of glucagon-like peptide-1 (7–36) amide on the rat pancreas

The glucose-dependent action of GLP-1 (7–36) amide (GLP-1) on insulin secretion was studied in isolated islets and in the perfused rat pancreas. In islet experiments in the presence of non-stimulatory glucose levels (<3 mmol/1) a GLP-1 concentration of 10 nmol/1 increased insulin secretion by 83%. However, higher GLP-1 concentrations (25 and 100 nmol/l) could not further enhance this effect (85 and 83%, respectively). The onset of the stimulatory action of a supramaximal GLP-1-load (25 nmol/l) was at a glucose level of 3 mmol/l. In the perfused pancreas, 25 nmol/l GLP-1 induced a strong insulin release at 5 mmol/l glucose, but under basal glucose (2.8 mmol/l) only a slight enhancement of insulin secretion occurred during the late phase (30 to 54 min) of perfusion (P<0.05). In conclusion, a slight but not dose-dependent stimulation of insulin secretion by supramaximal GLP-1 loads under basal glucose levels was found. The necessary GLP-1 concentrations to achieve this in vitro effect are beyond physiological or postprandial levels.     

Comparison of the effect of GIP and GLP-1 (7–36amide) on insulin release from rat pancreatic islets

After ingestion of glucose both GIP (gastric inhibitory polypeptide, glucose-dependent insulinotropic polypeptide) and GLP-1(7-36amide) (glucagon-like polypeptide-1, 7-36amide) may play a physiological role in augmenting insulin release. Their insulinotropic effect was compared in isolated rat islets after 24-h maintenance in tissue culture (11 mmol l-1 glucose). Ten islets per vial were then incubated in Krebs-Ringer-Hepes buffer for 30 min; insulin was measured radioimmunologically. Both hormones were always compared in the same experiment. At 16.7 mmol l-1 glucose both GIP and GLP-1(7-36amide) 2 x 10(-10) mol l-1 significantly increased insulin release; 10(-10) mol l-1 of either hormone had no significant effect. The response at 10(-9) and 10(-8) mol l-1 was similar for both; at 4 x 10(-10) mol l-1 GLP-1(7-36amide), however, was clearly more effective than GIP. At low glucose (2.8 or 5.0 mol l-1) no significant differences were found. A concentration of 10(-8) mol l-1 of both hormones was slightly stimulatory. At 8.3 mmol l-1 glucose, 10(-9) mol l-1 GLP-1(7-36amide) was 60% more effective than GIP (4.8 +/- 0.4 vs. 3.0 +/- 0.4, n = 13, P less than 0.005), the response to 10(-8) mol l-1 was similar. These data show comparable effects of high concentrations of GIP and GLP-1(7-36amide) on glucose-induced insulin release; at presumably physiological concentrations, however, GLP-1(7-36amide) was clearly more effective. The combination of the two peptides was not more than additive, suggesting that they act via the same final mechanism.     

Hyperglycaemia but not hyperinsulinaemia prevents the secretion of glucagon-like peptide-1 (7-36 amide) stimulated by fat ingestion.

The effect of insulin and glucose on fat-induced gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (7-36 amide) (GLP-1 (7-36 amide)) was studied in five healthy subjects during continuous glucose infusion (Protocol 1) and during hyperinsulinaemic euglycaemic blood glucose clamp (Protocol 2). In Protocol 1, 50 g fat was orally ingested and glucose was infused at a rate of 0.7 g/kg/h for 2 h continuously from the time of fat ingestion. Either glucose infusion alone or fat ingestion alone was carried out in the same subjects as the control. The release of GIP and GLP-1 (7-36 amide) was suppressed in the hyperglycaemic hyperinsulinaemic state. In protocol 2, 50 g of fat was ingested and insulin was infused at a rate of 0.1 U/kg/h with an artificial pancreas system to obtain the normoglycaemic hyperinsulinaemic state. The release of GIP was significantly suppressed in the normoglycaemic hyperinsulinaemic state as well as in the hyperglycaemic hyperinsulinaemic state. However, the release of GLP-1 (7-36 amide) was suppressed in the hyperglycaemic hyperinsulinaemic state but not in the euglycaemic hyperinsulinaemic state. Thus, it is concluded that insulin inhibits fat-induced GIP, but not GLP-1 (7-36 amide), secretion and that glucose is likely to inhibit GLP-1 (7-36 amide) secretion.     

Preserved incretin activity of glucagon-like peptide 1 [7-36 amide] but not of synthetic human gastric inhibitory polypeptide in patients with type-2 diabetes mellitus.

In type-2 diabetes, the overall incretin effect is reduced. The present investigation was designed to compare insulinotropic actions of exogenous incretin hormones (gastric inhibitory peptide [GIP] and glucagon-like peptide 1 [GLP-1] [7-36 amide]) in nine type-2 diabetic patients (fasting plasma glucose 7.8 mmol/liter; hemoglobin A1c 6.3 +/- 0.6%) and in nine age- and weight-matched normal subjects. Synthetic human GIP (0.8 and 2.4 pmol/kg.min over 1 h each), GLP-1 [7-36 amide] (0.4 and 1.2 pmol/kg.min over 1 h each), and placebo were administered under hyperglycemic clamp conditions (8.75 mmol/liter) in separate experiments. Plasma GIP and GLP-1 [7-36 amide] concentrations (radioimmunoassay) were comparable to those after oral glucose with the low, and clearly supraphysiological with the high infusion rates. Both GIP and GLP-1 [7-36 amide] dose-dependently augmented insulin secretion (insulin, C-peptide) in both groups (P < 0.05). With GIP, the maximum effect in type-2 diabetic patients was significantly lower (by 54%; P < 0.05) than in normal subjects. With GLP-1 [7-36 amide] type-2 diabetic patients reached 71% of the increments in C-peptide of normal subjects (difference not significant). Glucagon was lowered during hyperglycemic clamps in normal subjects, but not in type-2 diabetic patients, and further by GLP-1 [7-36 amide] in both groups (P < 0.05), but not by GIP. In conclusion, in mild type-2 diabetes, GLP-1 [7-36 amide], in contrast to GIP, retains much of its insulinotropic activity. It also lowers glucagon concentrations.     

Effects of infused glucose on glycogen metabolism in healthy humans

SUMMARY. In order to determine whether or not hepatic glycogen breakdown contributes to systemic glucose flux during glucose infusion, net carbohydrate oxidation (indirect calorimetry) and the total rate of glucose appearance (6,6^-2H-glucose) were measured in six healthy women during infusion of U^-13C labelled glucose (22 μmol/kg/min). Glucose infusion completely suppressed endogenous glucose production and increased net carbohydrate oxidation from 10.9±l.6 to 18.9±l.0 μmol/kg/min. To differentiate between the oxidation of endogenous (i.e. glycogen) and of exogenous carbohydrates, the ¹³CO₂ production was measured and the oxidation of exogenous ¹³C labelled carbohydrate was calculated. For this purpose, the specific recovery factor in breath of ¹³CO₂ issued from oxidation of uniformly labelled glucose was determined during infusions of equimolar amounts of ¹³C bicarbonate, 1-¹³C acetate and 2-¹³C acetate. The average recovery was 53.9±l.5%. The oxidation of exogenous carbohydrate was 20.9±0.74μmol/kg/min. This value was slightly higher than net carbohydrate oxidation, indicating that no oxidation of endogenous, unlabelled carbohydrate, and, hence, no utilization of hepatic glycogen took place. These results indicate that (i) estimation of glucose oxidation from indirect calorimetry and tracer technology give concordant results when an appropriate factor of ¹³CO₂ recovery in breath is used, and (ii) utilization of previously formed glycogen is inhibited during hyperglycaemia and hyperinsulinaemia.     

Effects of glucagon-like peptide-1-(7-36)-amide on pancreatic islet and intestinal blood perfusion in Wistar rats and diabetic GK rats

The aim of the present study was to evaluate the effects of GLP-1 [glucagon-like peptide-1-(7-36)-amide] on total pancreatic, islet and intestinal blood perfusion in spontaneously hyperglycaemic GK rats and normal Wistar rats using a microsphere technique. GK rats had hyperglycaemia and increased pancreatic and islet blood flow. Blood glucose concentrations were not affected when measured shortly (8 min) after GLP-1 administration in either GK or Wistar rats. GLP-1 had no effects on baseline pancreatic or islet blood flow in Wistar rats, but did prevent the blood flow increase normally seen following glucose administration to these animals. In GK rats, administration of GLP-1 decreased both pancreatic and islet blood flow. Glucose administration to the GK rats decreased pancreatic and islet blood flow. This decrease was not affected by pre-treatment with GLP-1. We conclude that administration of GLP-1 leads to a decrease in the augmented blood flow seen in islets of diabetic GK rats. The GLP-1-induced action on islet blood perfusion may modulate output of islet hormones and contribute to the antidiabetogenic effects of the drug in Type 2 diabetes (non-insulin-dependent diabetes).     

Intravenous and subcutaneous administration of a long-acting somatostatin analogue: effects on glucose metabolism and splanchnic haemodynamics in healthy subjects

The effect of SMS 201-995, a long-acting somatostatin analogue, on splanchnic blood flow and glucose metabolism, was investigated in five groups of healthy subjects. Groups A (n = 4), B (n = 5), C (n = 5) and D (n = 5) were studied before, during and after a 60-min intravenous infusion of SMS (1.7, 0.8, 0.2 and 0.1 micrograms min-1, respectively). Group E (n = 6) was investigated before and for 6 h after a subcutaneous injection of 25 micrograms of SMS. The splanchnic blood flow decreased by 20-25% in all groups in response to SMS and remained low during the entire observation periods. Arterial concentrations of glucose showed a 15-20% decline during SMS infusion in Groups A and B (P less than 0.05-0.01) and a less pronounced decrease in the other groups. Fifteen minutes after the end of infusion the glucose levels started to rise and in group A, the levels were significantly higher than basal (+25%, P less than 0.05-0.01) at 90-180 min after the end of infusion. The net splanchnic glucose production, determined in groups A and B, decreased by 65-75% in response to SMS infusion. Towards the end and immediately after the infusions, however, the net glucose output increased, but decreased again at 30-60 min after the end of infusion. Arterial, insulin and glucagon concentrations decreased significantly during infusion in all groups. This decline was more pronounced for insulin (50%) than for glucagon (20-25%) and insulin concentrations remained low for a longer period after the end of infusions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of the new somatostatin analogue (BIM 23014) on blood glucose homeostasis in normal men

Changes in blood glucose homeostasis induced by the new somatostatin analogue BIM 23014 (BIM) were studied. Eight normal men (study 1) received either vehicle or 1000, 2000 and 3000 micrograms BIM as a 24 h s.c. infusion. Blood glucose, plasma insulin, C-peptide, glucagon and growth hormone (GH) were measured before treatment and then hourly for 24 h. In five normal men (study 2) an oral glucose tolerance test (OGTT) was performed during vehicle infusion and then on days 1 and 7 of a continuous s.c. infusion of 2000 micrograms BIM daily for 7 days. The same biological parameters as in study 1 were measured before OGTT and then twice-hourly for 5 h. Dose-dependent and transient glucose intolerance was observed in the first half of study 1. Except for glucagon, BIM significantly (P < 0.01) reduced plasma insulin, C-peptide and GH levels. In study 2 BIM infusion induced glucose intolerance and a drop in plasma insulin and C-peptide on day 1 which disappeared on day 7 of infusion. Higher on day 7 than on day 1, plasma GH secretion was significantly (P < 0.01) reduced throughout BIM infusion. In contrast plasma glucagon levels were not modified at any time. Side-effects were abdominal cramps and diarrhoea which were observed in most subjects when increasing BIM daily dose. In conclusion, BIM infusion induced transient changes in glucose homeostasis and insulin secretion in normal men. By contrast, plasma GH levels remained reduced throughout the treatment. BIM appears to be a useful tool to selectively inhibit GH secretion.     

Effect of metformin on glucagon-like peptide 1 (GLP-1) and leptin levels in obese nondiabetic subjects

OBJECTIVE: To evaluate the effects of metformin on glucagon-like peptide 1 (GLP-1) and leptin levels. RESEARCH DESIGN AND METHODS: A total of 10 obese nondiabetic male patients were studied before and after a 14-day treatment with 2,550 mg/day metformin and were compared with 10 untreated obese control subjects. On days 0 and 15, leptin and GLP-1(7-36)amide/(7-37) levels were assessed before and after an oral glucose load during a euglycemic hyperinsulinemic clamp to avoid the interference of variations of insulinemia and glycemia on GLP-1 and leptin secretion. The effects of metformin on GLP-1(7-36)amide degradation in human plasma and in a buffer solution containing dipeptidyl peptidase IV (DPP-IV) were also studied. RESULTS: Leptin levels were not affected by the oral glucose load, and they were not modified after metformin treatment. Metformin induced a significant (P < 0.05) increase of GLP-1(7-36)amide/(7-37) at 30 and 60 min after the oral glucose load (63.8 +/- 29.0 vs. 50.3 +/- 15.6 pmol/l and 75.8 +/- 35.4 vs. 46.9 +/- 20.0 pmol/l, respectively), without affecting baseline GLP-1 levels. No variations of GLP-1 levels were observed in the control group. In pooled human plasma, metformin (0.1-0.5 microg/ml) significantly inhibited degradation of GLP-1(7-36)amide after a 30-min incubation at 37 degrees C; similar results were obtained in a buffer solution containing DPP-IV. CONCLUSIONS: Metformin significantly increases GLP-1 levels after an oral glucose load in obese nondiabetic subjects; this effect could be due to an inhibition of GLP-1 degradation.     

Effects of islet-activating protein (IAP) on blood glucose and plasma insulin in healthy volunteers (phase 1 studies)

Islet-activating protein (IAP) is a new active substance purified from the culture medium of Bordetella pertussis. The active protein possesses a molecular weight of 77,000 and an isoelectric point of pH 7.8. The nature of IAP-action is characterized by enhancement of insulin secretory response to glucose and other stimulants. A single injection of IAP into spontaneous diabetes rats resulted in normalization of their glucose intolerance over a period of a month. Acute and chronic animal toxicity tests showed that LD50 of IAP was 127 micrograms/kg in mice and 144 micrograms/kg in rats. After these animal experiments, phase 1 studies were designed and undertaken to establish dosage, duration of action and other factors. IAP of 0.5 micrograms/kg or 1.0 micrograms/kg did not bring about any serious toxic or adverse effects in five volunteers. On the 4th day of a single injection of IAP, insulin secretory response was proved to be enhanced. Follow-up studies showed that the IAP-action continued over a month or at most two months. Two features of IAP, i.e., the enhancement of insulin secretory response and the long duration of the action, was confirmed in healthy persons as well as in animals. As expected, IAP has a strong antigenic reaction resulting in formation of IgG antibody and possibly IgE antibody. The antigenicity of IAP causes some hindrance to clinical usefulness. For avoidance of anaphylactic reaction, IAP should be given repeatedly with care. The problem concerning antigen-antibody reaction should be overcome as soon as possible before the clinical use of IAP as a medicament.     

左旋四氢帕马汀在大鼠急性全脑缺血再灌注时对能量代谢内皮素—1及一氧化氮的影响

目的：了解左旋四氢帕马汀（L-THP)在大鼠急性全脑缺血再灌注损伤中对一氧化氮（NO）、内皮素－1（ET－1）、三磷酸腺苷（ATP）及乳酸的影响,探讨L－THP对脑缺血再灌注损伤的保护作用。方法：采用Pulsinelli方法建立大鼠急性全脑缺血再灌注损伤模型,观察L－THP在再灌注期间对NO、ET－1及能量代谢的影响。结果：L－THP可抑制再灌注早期NO、ET－1及乳酸的过量产生,提高ATP含量。结论L－THP可以通过对NO、ET－1及能量代谢的影响对大脑起保护作用。     

Effects of lysine infusion on the renal metabolism of aprotinin (Trasylol) in man.

1. Aprotinin (Trasylol) is a cationic 6500 Da polypeptide that inhibits proteolytic enzymes, and when labelled with 99mTc it is a reproducible marker for the renal tubular turnover of small filtered proteins in man. Lysine potently inhibits tubular peptide uptake, and may thus depress the uptake and metabolism of aprotinin. This was investigated in 14 glomerulonephritic patients with normal renal function and variable proteinuria and in one healthy subject. 2. 99mTc-labelled aprotinin was given intravenously alone, and again 3 days later, immediately after the intravenous administration of 3-6 g of lysine, followed by an infusion over 1 h of 0.3-1.9 g of lysine/kg in individual patients. Activity over kidneys and in urine was measured over 24 h and chromatography was used to separate the undegraded peptide from free isotope. 3. At the low dosage of lysine (< 0.8 g/kg) given to six patients, kidney activity (representing tubular uptake) was unchanged, but early urine samples contained some undegraded aprotinin. Urinary excretion of free isotope, representing tubular metabolism, fell from 1.6 +/- 0.2% of dose/h with no lysine to 0.9 +/- 0.1% of dose/h in the 24 h after lysine, suggesting suppression of tubular aprotinin degradation. Corrected fractional degradation was calculated from the mean urinary excretion of free isotope over a given interval, determined by chromatography, divided by the mean cumulative kidney counts over this same interval, and this also fell after lysine from 0.06 +/- 0.006 to 0.03 +/- 0.006 h-1 (P < 0.005) between 3.75 and 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)     

A new hypoglycemic agent, JTT-608, evokes protein kinase A-mediated Ca(2+) signaling in rat islet beta-cells: strict regulation by glucose, link to insulin release, and cooperation with glucagon-like peptide-1(7-36)amide and pituitary adenylate cyclase-activating polypeptide

A new nonsulfonylurea oral hypoglycemic agent, JTT-608, has been reported to stimulate insulin release at elevated, but not low, glucose concentrations and consequently not to induce hypoglycemia in rats. Accordingly, this drug is potentially a safer antidiabetic agent than sulfonylureas. To explore the mechanisms underlying this glucose-dependent insulinotropism, the present study investigated the effects of JTT-608 on cytosolic free Ca(2+) concentration ([Ca(2+)](i)) and protein kinase A (PKA) activity in rat islet beta-cells by microfluorometry using, respectively, fura-2 and a fluorescence PKA substrate, DR II. In the presence of glucose at normal and elevated concentrations (5.0-16.7 mM) JTT-608 (30-1000 microM) concentration dependently increased [Ca(2+)](i) in up to 88% of single beta-cells, whereas at lower glucose concentrations (2.8 and 4.2 mM) it had little effect. The [Ca(2+)](i) responses were inhibited under Ca(2+)-free conditions and by nitrendipine, an L-type Ca(2+) channel blocker. JTT-608 rapidly activated PKA and a PKA inhibitor, H89, inhibited [Ca(2+)](i) responses to JTT-608. JTT-608 also stimulated insulin release from rat islets in a glucose- and Ca(2+)-dependent manner. The glucose-unresponsive beta-cells, which failed to respond to 8.3 mM glucose with increases in [Ca(2+)](i), were frequently recruited to [Ca(2+)](i) increases by JTT-608. JTT-608 also induced oscillations of [Ca(2+)](i). Glucagon-like peptide-1(7-36)amide (GLP-1), pituitary adenylate cyclase-activating polypeptide (PACAP), and acetylcholine (ACh) enhanced the action of JTT-608 on [Ca(2+)](i). In conclusion, JTT-608 evokes PKA-mediated Ca(2+) influx and Ca(2+) signaling in rat islet beta-cells in a glucose-regulated manner, which may account for its glucose-dependent insulinotropism. JTT-608 and neurohormones may cooperatively activate islet beta-cells under physiological conditions.     

Effects of dopexamine in comparison with fenoterol on carbohydrate,fat and protein metabolism in healthy volunteers

Objective In critically ill patients adrenergic agonists are used to treat haemodynamic disorders. Their metabolic actions should be considered in controlling metabolic homeostasis. Dopexamine has assumed effects on carbohydrate, fat and protein metabolism. The aim of this study was to define its metabolic actions and compare these with those of fenoterol by using a stable isotope dilution technique.Design Prospective, randomized experimental study.Setting Experimental section of a university anaesthesiology department.Participants Twenty-seven healthy male volunteers in three groups with nine participants each.Interventions Participants received a 4-h infusion of dopexamine (2.25 µg/kg per min), fenoterol (at least 0.025 µg/kg per min) or saline.Measurements and results Before and every 80 min during drug infusion, we measured endogenous glucose production and the plasma appearance rates for leucine and urea. In addition, we measured plasma concentrations of glucose, lactate, free fatty acids (FFAs), noradrenaline, adrenaline, insulin, glucagon and potassium. Endogenous glucose production did not differ among the groups. Glucose plasma concentration and glucose clearance remained constant during the dopexamine infusion. Fenoterol increased glucose plasma concentration and decreased glucose clearance. Lactate, FFAs, insulin and noradrenaline plasma concentrations were increased and the rate of leucine appearance was decreased by both drugs. The rate of urea appearance did not differ from the control group.Conclusions Dopexamine has no or only weak effects on carbohydrate metabolism, its effects on fat and protein metabolism are comparable to those of fenoterol. This metabolic profile may be advantageous in increasing cardiac output in patients with impaired glucose tolerance.