B. Willms

Normalization of fasting hyperglycaemia by exogenous glucagon-like peptide 1 (7-36 amide) in type 2 (non-insulin-dependent) diabetic patients.

SummaryGlucagon-like peptide 1 (GLP-1) (7-36 amide) is a physiological incretin hormone that is released after nutrient intake from the lower gut and stimulates insulin secretion at elevated plasma glucose concentrations. Previous work has shown that even in Type 2 (non-insulin-dependent) diabetic patients GLP-1 (7-36 amide) retains much of its insulinotropic action. However, it is not known whether the magnitude of this response is sufficient to normalize plasma glucose in Type 2 diabetic patients with poor metabolic control. Therefore, in 10 Type 2 diabetic patients with unsatisfactory metabolic control (HbAlc 11.6±1.7%) on diet and sulphonylurea therapy (in some patients supplemented by metformin or acarbose), 1.2 pmol ×kg−1×min−1 GLP-1 (7-36 amide) or placebo was infused intravenously in the fasting state (plasma glucose 13.1±0.6 mmol/l). In all patients, insulin (by 17.4±4.7 nmol ×1−1×min; p=0.0157) and C-peptide (by 228.0±39.1 nmol×1−1×min; p=0.0019) increased significantly over basal levels, glucagon was reduced (by -1418±308 pmol ×1−1×min) and plasma glucose reached normal fasting concentrations (4.9±0.3 mmol/l) within 4 h of GLP-1 (7-36 amide) administration, but not with placebo. When normal fasting plasma glucose concentrations were reached insulin returned towards basal levels and plasma glucose concentrations remained stable despite the ongoing infusion of GLP-1 (7-36 amide). Therefore, exogenous GLP-1 (7-36 amide) is an effective means of normalizing fasting plasma glucose concentrations in poorly-controlled Type 2 diabetic patients. The glucose-dependence of insulinotropic actions of GLP-1 (7-36 amide) appears to be retained in such patients.

Both Subcutaneously and Intravenously Administered Glucagon-Like Peptide I Are Rapidly Degraded From the NH2-Terminus in Type II Diabetic Patients and in Healthy Subjects

To fate of exogenous glucagon-like peptide I (GLP-I)(7–36) amide was studied in nondiabetic and type II diabetic subjects using a combination of high-pressure liquid chromatography (HPLC), specific radioimmunoassays (RIAs), and a sensitive enzyme-linked immunosorbent assay (ELISA), whereby intact biologically active GLP-I and its metabolites could be determined. After GLP-I administration, the intact peptide could be measured using an NH2-terminally directed RIA or ELISA,while the difference in concentration between these assays and a COOH-terminal–specific RIA allowed determination of NH2-terminally truncated metabolites. Subcutaneous GLP-I was rapidlydegraded in a time-dependent manner, forming a metabolite, which co-eluted on HPLC with GLP-I(9–36) amide and had the same immunoreactive profile. Thirty minutes after subcutaneous GLP-I administration to diabetic patients (n = 8), the metabolite accounted for 88.5 ± 1.9% of the increase in plasma immunoreactivity determined by the COOH-terminal RIA, which was higher than the levels measured in healthy subjects (78.4 ± 3.2%; n = 8; P < 0.05). Intravenously infused GLP-I was also extensively degraded, but no significant differences were seen between the two groups. Intact GLP-I accounted for only 19.9 ± 3.4% of the increase in immunoreactivity measured with the COOH-terminal RIA in normal subjects (n = 8), and 25.0 ± 4.8% of the increase in diabetic subjects (n = 8), the remainder being the NH2-terminally truncated metabolite.

Glucagonostatic Actions and Reduction of Fasting Hyperglycemia by Exogenous Glucagon-Like Peptide I(7–36) amide in type I diabetic patients

OBJECTIVE Glucagon-like peptide I(7–36) amide (GLP-1) is a physiological incretin hormone that, in slightly supraphysiological doses, stimulates insulin secretion, lowers glucagon concentrations, and thereby normalizes elevated fasting plasma glucose concentrations in type II diabetic patients. It is not known whether GLP-1 has effects also in fasting type I diabetic patients. RESEARCH DESIGN AND METHODS In 11 type I diabetic patients (HbA1c 9.1 ± 2.1%; normal, 4.2–6.3%), fasting hyperglycemia was provoked by halving their usual evening NPH insulin dose. In random order on two occasions, 1.2 pmol · kg−1 · min−1 GLP-1 or placebo was infused intravenously in the morning (plasma glucose 13.7 ± 0.9 mmol/l; plasma insulin 26 ± 4 pmol/l). Glucose (glucose oxidase method), insulin, C-peptide, glucagon, GLP-1, cortisol, growth hormone (immunoassays), triglycerides, cholesterol, and nonesterified fatty acids (enzymatic tests) were measured. RESULTS Glucagon was reduced from ∼8 to 4 pmol/l, and plasma glucose was lowered from 13.4 ± 1.0 to 10.0 ± 1.2 mmol/l with GLP-1 administration (plasma concentrations ∼100 pmol, P < 0.0001), but not with placebo (14.2 ± 0.7 to 13.2 ± 1.0). Transiently, C-peptide was stimulated from basal 0.09 ± 0.02 to 0.19 ± 0.06 nmol/l by GLP-1 (P < 0.0001), but not by placebo (0.07 ± 0.02 to 0.07 ± 0.02). There was no significant effect on nonesterified fatty acids (P = 0.34), triglycerides (P = 0.57), cholesterol (P = 0.64), cortisol (P = 0.40), or growth hormone (P = 0.53). CONCLUSIONS Therefore, exogenous GLP-1 is able to lower fasting glycemia also in type I diabetic patients, mainly by reducing glucagon concentrations. However, this alone is not sufficient to normalize fasting plasma glucose concentrations, as was previously observed in type II diabetic patients, in whom insulin secretion (C-peptide response) was stimulated 20-fold.

Effects of subcutaneous glucagon-like peptide 1 (GLP-1 [7–36 amide]) in patients with NIDDM

Summary Intravenous glucagon-like peptide (GLP)-1 [7–36 amide] can normalize plasma glucose in non-insulin-dependent diabetic (NIDDM) patients. Since this is no form for routine therapeutic administration, effects of subcutaneous GLP-1 at a high dose (1.5 nmol/kg body weight) were examined. Three groups of 8, 9 and 7 patients (61 ± 7, 61 ± 9, 50 ± 11 years; BMI 29.5 ± 2.5, 26.1 ± 2.3, 28.0 ± 4.2 kg/m2; HbA1 c 11.3 ± 1.5, 9.9 ± 1.0, 10.6 ± 0.7 %) were examined: after a single subcutaneous injection of 1.5 nmol/kg GLP [7–36 amide]; after repeated subcutaneous injections (0 and 120 min) in fasting patients; after a single, subcutaneous injection 30 min before a liquid test meal (amino acids 8 %, and sucrose 50 g in 400 ml), all compared with a placebo. Glucose (glucose oxidase), insulin, C-peptide, GLP-1 and glucagon (specific immunoassays) were measured. Gastric emptying was assessed with the indicator-dilution method and phenol red. Repeated measures ANOVA was used for statistical analysis. GLP-1 injection led to a short-lived increment in GLP-1 concentrations (peak at 30–60 min, then return to basal levels after 90–120 min). Each GLP-1 injection stimulated insulin (insulin, C-peptide, p < 0.0001, respectively) and inhibited glucagon secretion (p < 0.0001). In fasting patients the repeated administration of GLP-1 normalized plasma glucose (5.8 ± 0.4 mmol/l after 240 min vs 8.2 ± 0.7 mmol/l after a single dose, p = 0.0065). With the meal, subcutaneous GLP-1 led to a complete cessation of gastric emptying for 30–45 min (p < 0.0001 statistically different from placebo) followed by emptying at a normal rate. As a consequence, integrated incremental glucose responses were reduced by 40 % (p = 0.051). In conclusion, subcutaneous GLP-1 [7–36 amide] has similar effects in NIDDM patients as an intravenous infusion. Preparations with retarded release of GLP-1 would appear more suitable for therapeutic purposes because elevation of GLP-1 concentrations for 4 rather than 2 h (repeated doses) normalized fasting plasma glucose better. In the short term, there appears to be no tachyphylaxis, since insulin stimulation and glucagon suppression were similar upon repeated administrations of GLP-1 [7–36 amide]. It may be easier to influence fasting hyperglycaemia by GLP-1 than to reduce meal-related increments in glycaemia. [Diabetologia (1996) 39: 1546–1553]

Gastric inhibitory polypeptide (GIP) and insulin in obesity: increased response to stimulation and defective feedback control of serum levels.

SummaryTo investigate the possibility that an abnormality of the entero-insular axis is responsible for the hyperinsulinaemia of obesity, serum immunoreactive gastric inhibitory polypeptide (IR-GIP) and insulin (IRI) were measured after the ingestion of a liquid mixed test meal, glucose or fat, in normal weight and obese subjects. The latter were divided into a group with normal oral glucose tolerance (nOGT) and a group with pathological glucose tolerance (pOGT). Fasting levels of IR-GIP were significantly elevated in the obese group with pOGT. After the mixed meal the overweight subjects showed a significantly greater response of IR-GIP than the controls, with highest levels in the pOGT group. Simultaneously, the IRI response was significantly greater in the obese subjects than in the controls. The increases of IR-GIP and IRI after an oral load of 100 g glucose were normal in the obese subjects, but showed a significantly greater integrated response in the obese patients with pOGT. The ingestion of 100 g fat induced no IRI release but a significantly greater release of IR-GIP in the obese subjects, irrespective of their glucose tolerance. It is concluded that fat is a stronger releaser of IR-GIP than glucose. The effect of a combined load of glucose (30 g) and fat (100 g) was also compared in obese and normal weight subjects with the effect of either alone. Fat but not glucose released significantly more IR-GIP in obese subjects. In normal weight controls, but not in obese subjects, the IR-GIP release after fat plus glucose became significantly smaller than after fat alone. Since only the combined ingestion of glucose and fat and not fat alone releases insulin it is suggested that endogenous insulin inhibits GIP release and that this feedback control between insulin and GIP is defective in patients with obesity.

Inhibition of Gastric Inhibitory Polypeptide (GIP) Release by Insulin and Glucose in Juvenile Diabetes

The effect of glucose and insulin on fat- and glucose-induced gastric inhibitory polypeptide (GIP) release has been studied in insulin-dependent juvenile-type diabetics. Blood glucose and serum immunoreactive GIP (IR-GIP) were measured after an oral load of 100 g glucose or 100 g fat was given and during an infusion of one of the following: saline, glucose, glucose plus insulin, or insulin. The infusion of insulin alone (in the presence of elevated glucose levels) or together with glucose significantly suppressed the IR-GIP rise after fat ingestion, but it did not alter the GIP response to oral glucose. Intravenous infusion of glucose had a slight but significant inhibitory effect on fat-stimulated increase of IR-GIP, which cannot be related to endogenous insulin release in these insulin-deficient diabetics. It is suggested that an insulin-mediated increase of glucose utilization in the GIP cell interferes only with increased GIP secretion stimulated by the utilization of fatty acids but not of glucose. This could explain the existence of a negative feedback control between insulin and GIP secretion for fat but not for glucose-induced GIP release.

Alteration of bile acid metabolism and vitamin-B12-absorption in diabetics on biguanides

SummarySince vitamin B12malabsorption has been described in diabetics on biguanides and inhibition of bile acid absorption found in rat ileum the effect of treatment with different biguanides (phenformin, buformin, metformin) on bile acid metabolism and vitamin B12 absorption was assessed in maturity onset diabetics. Biguanides did not alter faecal weight or faecal fat excretion, but they decreased faecal bile acid excretion. All biguanides tested increased deconjugation of glycocholic acid, as determined by a simple breath test technique. Vitamin B12 malabsorption was most prominent in patients on metformin. Discontinuation of biguanide treatment, or administration of antibiotics, normalized or improved the increased deconjugation of bile acids and the Schilling test. Decreased faecal bile acid excretion, positive14C-glycocholate breath tests, pathological Schilling tests and the reversal of pathological tests by antibiotic treatment suggest that small intestinal bacterial overgrowth, leading to binding of the intrinsic-factor-vitamin B12-complex to bacteria, is responsible for the previously observed pathological Schilling tests in diabetics on biguanides. Bile acid malabsorption, possibly responsible for the cholesterol-lowering effect of biguanides, does not occur in diabetics on biguanides. Whether qualitative changes in small intestinal bile acid composition might affect cholesterol metabolism remains to be determined.

Gastric inhibitory polypeptide (GIP) and insulin in obesity: II. Reversal of increased response to stimulation by starvation or food restriction

SummaryThe response of serum immunoreactive gastric inhibitory polypeptide (IR-GIP) and immunoreactive insulin (IRI) to a liquid mixed test meal, glucose or fat has been examined in obese subjects before and after starvation or reduced caloric intake (800 calories). Basal serum levels of IR-GIP increased significantly during starvation of obese persons and remained elevated over the whole starvation period while basal serum IRI levels decreased. The exaggerated IR-GIP response of obese subjects with normal or pathological glucose tolerance to a test meal and of obese subjects with glucose intolerance to 100 g glucose ingestion decreased significantly after starvation or food restriction. Simultaneously, the serum IRI response decreased. The exaggerated IR-GIP response of obese subjects to oral triglycerides which did not affect serum IRI or glucose levels was also significantly decreased after food restriction. The IR-GIP response of obese subjects to a test meal was already reduced after 5 days of food restriction together with an improved glucose tolerance. At this stage the IRI response was unchanged. After weight reduction in obese subjects there was a significant decrease of the IRI response to oral but not to intravenous glucose, while the glucose response decreased irrespectively of the mode of glucose administration. The IR-GIP response decreased only after oral glucose. The data are compatible with the hypothesis that the exaggerated IR-GIP response of obese subjects to oral glucose or fat load is secondary to the increased food intake and that changes in IRI response to oral glucose are related to changes in IR-GIP response.

The redox state of NAD+/NADH systems in guinea pig liver during increased fatty acid oxidation

Abstract As fatty acids fail to stimulate gluconeogenesis in guinea pig livers6,7, changes in the redox state of the substrate pairs lactate/pyruvate, 3-hydroxybutyrate/acetoacetate, glutamate/(α-oxoglutarate)(NH4+) and α-glycerophosphate/dihydroxy-acetone phosphate as well as changes in the ATP/ADP ratio were studied in guinea pig livers during increased oxidation of fatty acids in vivo and during liver perfusion. the following results were obtained: 1. 1. Under normal conditions the redox state of the lactate/pyruvate system is more negative, that of the 3-hydroxybutyrate/acetoacetate system more positive in guinea pig liver (in vivo and during isolated perfusion) than in rat liver. The redox state of the α-glycerophosphate/dihydroxyacetone phosphate system is about the same as in rat liver. 2. 2. During increased oxidation of fatty acids, the redox state of the lactate/ pyruvate system in isolated perfused guinea pig livers becomes more negative, whereas the redox state of the 3-hydroxybutyrate/acetoacetate system shows a slight increase only during prolonged fatty acid oxidation. In vivo, fat feeding for 3 days leads to an increase in the lactate/pyruvate ration, to a dramatic increase in the α-glycerophosphate/dihydroxyacetone phosphate ration, and to a doubling of the 3-hydroxybutyrate/acetoacetate ratio. 3. 3. The ATP/ADP ratio in the guinea pig liver is not altered by an increased oxidation of fatty acids. 4. 4. Data are presented which make it unlikely that the activity of 3-hydroxybutyrate dihydrogenase (EC 1.1.1.30) is insufficient to establish the 3-hydroxybutyrate/acetoacetate equilibrium under the experimental condition used. 5. 5. Under normal conditions the redox state of the 3-hydroxybutyrate dehydrogenase system and that of the glutamate dehydrogenase (EC 1.4.1.3) system are in equilibrium in rat and guinea pig liver. Under certain experimental conditions a disequilibrium is observed as well in guinea pig as in rat liver. It is suggested that this results from different compartmentation of some fo the substrates of these redox systems.

EFFECT OF EXOGENOUS INSULIN ON FASTING SERUM LEVELS OF GASTRIC INHIBITORY POLYPEPTIDE (GIP) IN JUVENILE DIABETES

The effect of insulin on fasting levels of immunoreactive gastric inhibitory polypeptide (IR‐GIP) has been examined in insulin‐dependent, juvenile‐type diabetics who were well‐controlled with two doses of an intermediate insulin. After withdrawal of the evening insulin injection the fasting blood glucose and serum IR‐GIP levels were elevated and decreased significantly following intravenous insulin towards normal values. There was a significant positive correlation between levels of blood glucose and serum IR‐GIP before and during insulin application. It is suggested that fasting serum GIP levels increase in case of insulin deficiency because basal GIP secretion is suppressed by normal insulin levels.