Insulin-Like Effects on Liver Golgi Membrane Preparations of Bis(Oxalato)Oxovanadate(IV) Complex Ion, a New Vanadate Compound

Recent studies have shown the insulin-like effect of vanadyl sulphate or sodium ortho (or meta-)vanadate administered orally to rats. Toxicity of these drugs and reluctance by the animals to drink the solutions and take food, concerning the amelioration of some diabetes syndrome discussed in 1994 by Domingo et al. (1), McNeill et al. (2) and Wiliams and Malabu (3), prompted us to investigate a new vanadate complex: disodium bis(oxalato)oxovanadate (IV), Na2[VO(OX)2]H2O. The main object of the experiment was to study whether this complex administered as 3 mmol/l solution in 0.5% NaCl during 7 days could act on the subcellular level and influence the activity of liver Golgi membrane galactosyltransferase activity. Free blood sugar level was lowered (but was still higher than in the control group) in diabetic rats after seven days of vanadate action and was accompanied by lowered, however not statistically significant, serum triglyceride levels. The yields of isolated Golgi-rich membrane fractions were about half of the level in diabetic groups (untreated and treated with vanadium) compared with the control groups. Purity of these membrane fractions, expressed as nmol Gal transferred per mg of proteins and per h, was the same in four groups investigated and showed the possibility to compare them. Activity of galactosyltransferase calculated in nmol Gal transferred per 1 g of liver and per 1 h or per whole liver in the same time (as a possibility of glycosylation of the secretory and membrane glycoproteins) was lower in both diabetic groups. However, after vanadium treatment (D+V group), the activity was higher than in untreated diabetic rats (D group) in three of five investigated animals. Vanadyl-oxalate complex did not normalize in a statistically significant manner the enzyme activity which was significantly lower in diabetes than in control. This is similar to insulin influence on the galactosyltransferase activity reported previously by Kaczmarski et al. in 1981 (4) and Kordowiak et al. in 1981 (5).