COMPARISON OF THE EFFECTS OF VARIOUS VANADIUM SALTS ON GLUCOSE-HOMEOSTASIS IN STREPTOZOTOCIN-DIABETIC RATS

Oral administration of vanadium salts to severely diabetic rats leads to a spectacular decrease of plasma glucose levels in spite of the ins ulin deficiency of the animals. The insulin-like properties of vanadiu m have been attributed to the cationic form, vanadyl, into which the a nionic form, vanadate, is reduced within cells. This has led to the su ggestion that vanadyl is the form of choice for the treatment. In this study, rats made insulin-deficient and diabetic with streptozotocin w ere treated with three salts of vanadium: sodium orthovanadate, sodium metavanadate and vanadylsulfate. The salts were added to the drinking water, in concentrations that led to ingestion of the same amount of vanadium element by the three groups of rats (similar to 8 mg/kg per d ay). The initial, transient, loss of weight that affected the treated rats was slightly smaller in the vanadyl-treated group than in the van adate-treated groups. However, during steady-state treatment, the thre e groups exhibited a similar food intake (lower than in controls) and growth rate (higher than in controls). The decreases in plasma glucose levels, in urinary volume and in glucosuria, and the improvement of t he tolerance to an oral glucose load were similar regardless of the ty pe of vanadium salt. Withdrawal of the treatment after 14 weeks was fo llowed by a rapid increase in plasma glucose levels which, however, re mained clearly lower than in controls for at least 4 weeks, whereas pl asma insulin levels increased only transiently. A smaller glucosuria a nd a slightly better tolerance to oral glucose than in controls were s till observed in the previously treated rats. In conclusion, when simi lar amounts of vanadium are ingested in the form of vanadyl, orthovana date or metavanadate by insuIin-deficient diabetic rats, similar benef icial and adverse effects are observed. Interestingly, a partial impro vement of glucose homeostasis persists after withdrawal of the treatme nt.