The effect of phenformin on amino acid-induced insulin secretion in diabetics

Twenty-one patients with mild maturity-onset diabetes were given introduodenal infusions of an amino acid mixture (0.5 g amino acids per kg body weight). In 9 other patients L-arginine was infused intravenously in a constant dose of 25 g. Alpha-amino nitrogen, blood glucose and plasma insulin levels were assayed under control conditions and after three days of treatment with phenformin, 150 mg daily, plus the same 150 mg dose 60 min before the second loading. Intraduodenal infusion of the amino acid mixture provoked a greater increase in plasma insulin than intravenous infusion of L-arginine, this increase being significantly inhibited by phenformin only in the first case. Since no evident influence of phenformin on the intestinal absorption of amino acids could be demonstrated, this effect may be explained by a local action on the intestinal wall exposed to high concentrations of the drug, resulting in the inhibition of the insulin secretion stimulating activity of the gut.     

Alterations of plasma immunoreactive glucagon-like peptide-1 behavior in non-insulin-dependent diabetics

The basal level of plasma immunoreactive glucagon-like peptide-1 (IR GLP-1) was significantly elevated in non-insulin-dependent diabetics (NIDD), and this elevation of IR GLP-1 was mainly due to an increase in the large component of IR GLP-1, corresponding to the pancreatic form. During the oral glucose-tolerance test (OGTT), the total plasma IR GLP-1 decreased in normal subjects but increased significantly in diabetic patients. Chromatographic analysis showed that IR GLP-1 consisted of several different molecular forms. OGTT caused a decrease in the pancreatic form but increased the intestinal form in normal subject, resulting into a net decrease in total plasma IR GLP-1. Whereas in NIDD the increase in the intestinal form was more prominent and the suppression of the pancreatic form was practically abolished to result in a net increase of total plasma IR GLP-1. This observation is consistent with the fact that in normal subjects the total change in IR GLP-1 was significantly correlated with both the total change of gut glucagon as well as that of pancreatic glucagon, but in diabetics the total change of GLP-1 only correlated to that of gut glucagon. The impaired suppression of pancreatic GLP-1 and enhanced release of intestinal GLP-1 could have some physiological importance in NIDD.     

A method for measuring the release of gut glucagon-like immunoreactivity from rat jejunum „In Vitro“

Summary A convenient method for measuring the release of gut glucagon-like immunoreactivity (G-LI) from rat jejunal pieces incubated in vitro is described. The method utilises Trasylol, EDTA, and excessive glucagon antibody to prevent GLI breakdown. There was satisfactory recovery of added pancreatic glucagon to the incubates, and a highly significant release of GLI was recorded when high glucose concentrations (5–40 g%) were incubated with the pieces.

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Methode zur Bestimmung der Freisetzung von glucagon-ähnlicher immunologischer Aktivität des Darmes aus dem Jejunum der Ratte in vitro.

Zusammenfassung Es wird eine brauchbare Methode zur Bestimmung der Freisetzung von glucagonähnlicher immunologischer Aktivität (GLI) des Darmes beschrieben. Die Methode benutzt Trasylol, EDTA und einen Überschuß von Glucagonantikörpern, um den Abbau von GLI zu verhindern. Die Rückgewinnung von zugefügtem Pankreasglucagon aus den Inkubaten war zufriedenstellend und eine hoch signifikante Freisetzung von GLI wurde beobachtet, wenn hohe Glucosekonzentrationen (5–40%) mit den Darmstücken inkubiert wurden.

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Méthode de mesure de la libération de la substance intestinale douée de l'immunoréactivité du glucagon (glucagon-like) à partir du jéjunum de rat in vitro

Résumé Les auteurs décrivent une méthode commode pour mesurer la libération de la substance intestinale immunologiquement glucagon-like (GLI) à partir de fragments de jéjunum de rat, incubés in vitro. La méthode utilise du trasylol, de l'EDTA et un excès d'anticorps anti-glucagon pour empêcher la dégradation du GLI. Il y avait une récupération satisfaisante du glucagon pancréatique ajouté aux incubats, et une libération de GLI hautement significative a été enregistrée lorsque de fortes de concentrations de glucose (5– 40 g%) étaient mises à incuber avec les fragments.

     

Metabolic abnormalities during combined sulphonylurea and phenformin therapy in maturity-onset diabetics

Summary Twelve hour metabolic rhythms have been determined in two groups of subjects during combined therapy with a sulphonylurea and phenformin 50 mg twice daily. Subjects with clinical evidence of complications of diabetes showed greater abnormalities in concentrations of blood intermediary metabolites than a group of subjects without complications despite similar mean blood glucose concentrations in the two groups (7.6 mmol/l with complications; 7.3 mmol/l without complications). Mean blood lactate (1.93 mmol/l v 1.39 mmol/l), alanine (0.56 mmol/1 v 0.43 mmol/l), total blood ketone bodies (0.20 mmol/l v 0.14 mmol/l) and several other intermediary metabolites and their ratios were significantly higher in the group with diabetic complications. It is suggested that the differences between the two groups may arise from impaired disposal of phenformin leading to higher blood concentrations in the group with diabetic complications, despite normal liver function tests and plasma creatinine concentration. It is probable that this accumulation of phenformin results in more pronounced effect upon blood glucose and other intermediary metabolites. Thus, the metabolic abnormalities previously reported in patients treated by phenformin alone are also present during combined sulphonylurea and phenformin therapy, and in the presence of diabetic microangiopathy these abnormalities are accentuated.     

Characterization of phenformin and metabolites in plasma.

A colorimetric assay of biguanides was adapted for small volumes of plasma and its specificity was improved. This method is based on the reaction of guanidine groups with alpha-naphtol-diacetyl. Interference of endogenous guanidine derivatives and of the water-soluble metabolites of phenformin can be excluded by the extraction procedure. Counting of plasma fractions from 14C-phenformin-injected rats and thin-layer chromatography, before and after treatment with beta-glucuronidase, were also performed: the results suggest that after adequate extraction of plasma, the colorimetric assay measures specifically the biologically active phenformin. Results of this assay in plasma from biguanide-induced lactic acidotic patients and rats are given and compared with controls : results are consistent with the hypothesis of an accumulation of biologically active biguanide in such cases.     

Immunocytochemical and ultrastructural characterization of coexistence of pancreatic polypeptide and glucagon-like immunoreactivity in the pancreatic endocrine cells of Sparus auratus L. (Teleostei)

Coexistence of pancreatic polypeptide (PP)- and glucagon-like immunoreactivity was demonstrated in the pancreatic endocrine cells of the teleost fish Sparus auratus. An immunofluorescence double-staining method revealed coexistence of glucagon- and PP-like immunoreactivity in endocrine cells of small and intermediate islets. In contrast to small islets, the intermediate ones also contained a variable number of glucagon-immunoreactive cells next to cells having both immunoreactivities. Coexistence of both immunoreactivities could not be observed in endocrine cells of the principal islet, whereas many cells containing glucagon and a few cells containing PP immunoreactivity were found. By an immunogold double-staining method the precise ultrastructural location of each immunoreactivity could be demonstrated. Again, cells containing glucagon- and/or PP-like immunoreactivity were found. Although, only two different types of granules were observed, four distinct cell types could be distinguished. Based on this granule morphology two cell types showing coexistence were found: one cell type, only present in the small islets, showing a different distribution of glucagon and PP immunoreactivity within the granules (predominantly in the center and periphery, respectively) and another cell type with larger granule cores, present in small as well as intermediate islets, having a mixed distribution of both immunoreactivities.     

Effect of phenformin on substrate metabolism of working muscle in maturity onset diabetics

Summary The effect of biguanides on substrate metabolism of muscle was studied by measurement of arterial and deep venous concentrations of glucose, lactate pyruvate and oxygen and of forearm blood flow in 6 maturity onset diabetics before and after five days of oral phenformin (150mg/day).At rest, substrate balances and forearm blood flow obtained before and after treatment with phenformin did not differ significantly. During work, before treatment, a considerable muscular release of glucose (–6.64 ± 2.87 mol/100g · min), lactate and pyruvate developed, which decreased continuously during recovery. Treatment with phenformin revealed a significant net utilisation of glucose during work (1.66 ± 1.87) and recovery (1.62 ± 0.34). An almost identical quantity of lactate and pyruvate continued to be produced during work as before. However, during recovery, lactate release was increased (untreated: –1.42 ± 0.67, treated: –2.96 ± 1.08) while pyruvate release was reduced. Accordingly, while before treatment increased deep venous L/P ratio slowly normalized during recovery (12.7 ± 2.3) it persisted after phenformin (29.7 ± 9.5). Adaptation of muscular oxygen uptake during recovery occurred within 3 minutes before treatment (8.2 ± 0.3), but not even within 5 minutes after treatment (10.8 ± 0.5). Thus phenformin enhances muscle glucose uptake and lactate release. This peripheral effect may be of clinical importance, since an eightfold increase of muscle lactate and pyruvate release was found in one case of fatal, phenformin-induced lactic acidosis.     

Comparative effects of phenformin,metformin and glibenclamide on metabolic rhythms in maturity-onset diabetics

Summary Twelve hour metabolic rhythms have been performed on six maturity-onset diabetic subjects during successive periods of therapy with phenformin, metformin, and glibenclamide. Moderate control of blood glucose concentration was achieved with phenformin and metformin, the lowest concentrations being found with glibenclamide. Mean blood lactate concentration was grossly elevated during phenformin therapy, moderately elevated with metformin and normal during glibenclamide treatment. Similar patterns were found for the lactate/pyruvate ratio, alanine, glycerol and ketone bodies. Serum triglyceride concentrations were significantly higher during phenformin treatment than with the other two regimes. Serum insulin concentration was higher on glibenclamide than with either biguanide. Most of these effects of the biguanides could be accounted for by an inhibitory effect on hepatic gluconeogenesis. It is concluded that the use of biguanides as hypoglycaemic agents in diabetes is associated with the production of multiple metabolic abnormalities.     

The effect of portal diversion upon function of the reticuloendothelial system and upon plasma fibronectin levels

A previous publication suggested that for 9 weeks after portal diversion in dogs, there were no changes in reticuloendothelial function assessed by measurement of t1/2 or phagocytic index of reticuloendothelial test lipid emulsion. The present study was conducted in rats over 18 weeks. It was observed that the phagocytic index decreased and the t1/2 lengthened at 18 weeks after either portacaval shunt or portacaval transposition and that plasma levels of fibronectin were elevated four- or five-fold after either form of diversion, whilst only being elevated two-fold after sham operation. There was an increase in portacaval shunt rats in liver tissue distribution of administered lipid emulsion when tested between 6 and 12 weeks post-operatively which then returned towards normal. The activity in portacaval transposition and sham-operated rats was unaltered. These studies suggest that the delay in clearance of administered particles in portacaval shunt and portacaval transposition rats is related to the portal diversion rather than to altered blood flow and thus the finding is of relevance in patients with cirrhosis who also have significant portacaval shunting.     

Insulin and glucagon-like immunoreactivity in the river lamprey (Lampetra fluviatilis).

Recently it has been established that the islet tissue of the river lamprey secretes insulin. These studies were aimed at determining serum levels of insulin-like immunoreactivity after isletectomy, glucose loading, and adrenaline treatment of adult river lampreys. Comparison of human insulin standard curves with lamprey islet tissue dilution curves indicates that the two curves have significantly different slopes. Although quantification of insulin in lamprey serum was therefore not possible, differences between control and experimental groups can be tested for by hierarchical analysis of variance. The insulin concentration in the serum of totally isletectomized animals is significantly lower than that of sham-operated controls. Two hours after a single injection (100 mg) of glucose there was no significant difference in insulin concentration as compared with saline-injected controls, but 8 and 24 hr after such injection insulin levels were significantly elevated. After long-term glucose loading (100 mg of glucose twice daily for 12 days) serum levels of insulin were significantly elevated. Insulin levels in adrenaline-treated animals (0.1 mg twice daily for 3 days) were significantly lower than in saline-injected controls. Glucagon-like immunoreactivity was found in both extracts of the intestine and the cranial islet tissue. These studies indicate the significant role of insulin in the control of carbohydrate metabolism in the river lamprey during the fasting stage of its life cycle.     

The effect of shellfish in the diet upon the plasma lipid levels in humans

In order to document any hypercholesterolemic effects from the ingestion of shellfish, 6 normal men were given two diets containing different shellfish, each preceded by a low cholesterol baseline diet. Diet I contained 449 mg cholesterol per day from lobster, crab, and shrimp. Diet II contained clam, oyster, and scallop and provided 447 mg of sterols of which cholesterol constituted only 40 percent. The other sterols are uniquely characteristic of these shellfish (i.e. brassicasterol, 24-methylene cholesterol, etc.). In a second study, 2 normal men and 1 type II hypercholesterolemic woman were fed the baseline diet and shellfish diet II to provide 623 mg of sterols per day. The plasma cholesterol of the 6 subjects averaged 184 ± 35 mg/dl during baseline diet, 192 ± 35 mg/dl in shellfish diet I (p < 0.05) and 182 ± 24 mg/dl during shellfish diet II. In the second study, the plasma cholesterol of the 2 normal men did not change. The cholesterol of the hypercholesterolemic woman increased from 311 mg/dl (baseline) to 352 during the shellfish diet (p < 0.05). Plasma triglyceride levels remained unchanged. Our data indicated that large quantities of lobster, crab, and shrimp were only mildly hypercholesterolemic in normals, but less so than other cholesterol-containing foods. Clams, oysters, and scallops were not hypercholesterolemic in normal subjects but were in a hypercholesterolemic patient.     

Diurnal profile of pancreatic exocrine secretion and plasma levels of gut hormones (cholecystokinin and pancreatic polypeptide)

We examined diurnal changes of pancreatic exocrine secretion and plasma levels of cholecystokinin (CCK) and human pancreatic polypeptide (hPP) in men with postoperative transient external pancreatic drainage (3 with pancreatico-jejunostomy: PJ, and 5 with pancreato-duodenectomy:PD). Plasma CCK levels increased and the pancreatic exocrine secretion showed a corresponding increase after meals in both groups. In the PJ group hPP levels increased after meals and there was a significant correlation between the plasma levels of CCK and hPP. In the PD group the plasma hPP levels were not detectable throughout the study and there was a better correlation between the exocrine secretion and the plasma CCK levels than in the PJ group. Plasma CCK levels showed rhythmic changes associated with pancreatic exocrine secretion, with no significant changes in plasma glucose and insulin in the night (24:00-07:00). These results suggested that (1) the resection of the pancreatic head which is rich in hPP contents led to a complete loss of anti-CCK effects on CCK, and that (2) fluctuation in plasma CCK levels, in the fasting state, might initiate pancreatic exocrine secretion.     

Elevated plasma levels of glucagon-like peptide-1 after oral glucose ingestion in patients with pancreatic diabetes

OBJECTIVE: The purpose of the present study was to evaluate plasma glucagon-like peptide-1 (GLP-1) responses after oral glucose ingestion in patients with chronic pancreatitis and to clarify how GLP-1 secretion relates to pancreatic diabetes. METHODS: An oral glucose tolerance test (OGTT) was performed in 17 patients with chronic pancreatitis. Plasma glucose, immunoreactive insulin (IRI), C-peptide, glucagon, and GLP-1 levels at each time point during OGTT were measured. The diagnosis of chronic pancreatitis was made by the findings of endoscopic retrograde pancreatography (ERP): evident dilation of the main pancreatic duct with or without pancreatolithiasis. RESULTS: The patients were divided into three groups according to the World Health Organization classification of diabetes based on plasma glucose levels after OGTT. The groups were: normal (three patients), impaired glucose tolerant (IGT) (six patients), and diabetic (DM) (eight patients). In the DM group, IRI and C-peptide response levels after oral glucose ingestion were significantly reduced as compared with those of the normal and IGT groups. No significant glucagon responses to oral glucose ingestion were found in the three groups. In contrast, plasma GLP-1 levels were significantly elevated after oral glucose ingestion in the DM groups as compared with normal and IGT groups. CONCLUSIONS: The present study affords evidence that plasma GLP-1 levels become elevated with development of pancreatic diabetes, although the precise mechanism of this elevation remains undetermined.