[Biochemical, histochemical, histological and functional studies on the effect of phenformin on small intestine mucosa in rat and in man]

Inhibition of ethanol absorption by butyl-biguanide in rat gastrointestinal tract in vivo

The effect of 1-butyl-biguanide and glibenclamide on the ethanol absorption in the rat gastrointestinal tract has been investigated. Oral administration of biguanide (100 mg/kg) inhibited the appearance of ethanol in the blood following oral ethanol loading. Glibenclamide (10 mg/kg) did not induce any alteration in the blood alcohol concentration as compared with the control's level. Oral biguanide pretreatment did not induce any change in the blood alcohol concentration when ethanol was given i.v. We conclude that 1-butyl-biguanide does exert an inhibitory effect on the absorption of ethyl alcohol in vivo in the rat.

Quantitative study of mucosal structure, enzyme activities and phenylalanine accumulation in jejunal biopsies of patients with early and late onset diabetes

A study of the three-dimensional structure of the upper jejunal mucosa in diabetics has been carried out. The structural findings were related to 14C-L-phenylalanine uptake in vitro, sucrase activity in mucosal homogenates, and the enzyme content of the absorptive cells as measured cytophotometrically. A low grade mucosal transformation of the sprue-type was found, which was associated with decreased sucrase activity, and with no reduction in phenylalanine accumulation. On the other hand the specific activities of alkaline phosphatase, non-specific esterase, and succinic dehydrogenase in the surface cells remained unchanged.

Oxidation of an exogenous glucose load using naturally labelled 13C-glucose. Effect of butylbiguanide therapy in obese mildly diabetic subjects

The effect of a 14 day-administration of butylbiguanide was investigated in a group of 10 obese patients with mild-to-moderate glucose intolerance. Glucose tolerance was significantly improved, while fasting blood glucose and plasma levels of free fatty acids, insulin and glucagon remained unchanged. The estimation of the amount of the oral glucose load oxidized into CO2 was performed by means of a recently described procedure using "naturally labelled 13C-glucose" as tracer. The curves depicting the oxidation of the exogenous glucose load were similar in shape and magnitude before and after administration of the biguanide; in the latter case, however, slightly higher rates of oxidation of exogenous glucose were recorded during the 2nd, 3rd and 4th hours of the test. These data do not provide evidence that the biguanide-induced improvement in glucose tolerance in patients with mild-to-moderate glucose intolerance is associated with any inhibiting or delaying effect of this type of drug on intestinal absorption (and subsequent oxidation) of the exogenous glucose load. On the contrary, a slight, but statistically significant, increase in the oxidation of exogenous glucose has been observed after butylbiguanide.

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

Since 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, positive 14C-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.

Transitory blindness during ethanol and phenethylbiguanide induced lactic acidosis in a subject with diabetes mellitus. A case report

Transitory blindness is described in a diabetic patient with typical ethanol- and phenethylbiguanide induced lactic acidosis. The blindness developed in the course of 8 hours, but the vision returned during treatment with iv bicarbonate, insulin and glucose. The condition is discussed in relation to a presumed inhibition of the oxidative metabolism in the retina.

Oral versus intravenous administration of butylbiguanide: effect on oral glucose tolerance in normal humans

1. The effect of oral and intravenous administration of butylbiguanide on the oral glucose tolerance test was investigated in 12 normal human volunteers. Orally administered butylbiguanide lowered the oral glucose tolerance curve and the corresponding serum insulin values, whereas intravenously injected butylbiguanide had no effect. 2. The lactate/pyruvate ratio determined 180 min. after glucose ingestion increased after oral butylbiguanide administration. No effect was observed after intravenous administration. 3. The decrease in serum phosphate levels observed after oral glucose loading was not influenced by butylbiguanide administered by either route. In addition, no effect of this drug was observed on fasting levels of glucose, insulin, phosphate, bicarbonate, lactate and pyruvate. 4. These results are compatible with recent observations that biguanides inhibit active transport mechanisms in the intestine. In addition, the effect of biguanides on blood levels of glucose metabolites is discussed with respect to their known action on oxidative phosphorylation.

Inhibition of bile salt absorption by blood-sugar lowering biguanides

The effect of blood sugar lowering biguanides (phenethyl-, butyl- and dimethylbiguanide) upon jejunal and ileal transport of bile salts (tauro- and glycocholate) was tested in rat small intestine by an in vitro technique. Giguanides inhibited active transport of bile salts in the ileum, but did not affect diffusional absorption of bile salts in the jejunum. The inhibitory effect was time-dependent and not reversible under in vitro incubation conditions, suggesting that biguanides must enter intestinal mucosal cells in order to exert their inhibitory action on active transport of glucose analogues, amino acids, calcium and bile salts. Since biguanides achieve high tissue concentrations in the small intestine even after parenteral administration, inhibition of ileal bile salt reabsorption by biguanides could possibly explain the lipid- and cholesterol-lowering effect of these oral antidiabetic drugs.