Enhanced in vivo sensitivity of vanadyl-treated diabetic rats to insulin.

Vanadium has been reported to have insulin-like properties and has recently been demonstrated to be beneficial in the treatment of diabetic animals. In the present study, concentration dependence of the therapeutic effects of vanadium and the nature of interaction under in vivo conditions between vanadium and insulin were examined in streptozotocin-diabetic rats. During a 2-week period, blood glucose levels in all treated animals were decreased. At higher concentrations of vanadyl this decrease was greater and more rapid, and remained consistently lower for the entire treatment period. Daily intake of vanadyl, however, reached a similar steady state in all groups. Acute administration of submaximal doses of insulin, which had minimal effects in untreated diabetic rats, lowered blood glucose concentrations in vanadyl-treated and vanadyl-withdrawn animals to control levels. Chronic treatment of streptozotocin-diabetic rats with submaximal levels of vanadyl and insulin, ineffective alone, also produced significant decreases in blood glucose levels when used in combination. Finally, the insulin dosage required to maintain a nonglycosuric state in spontaneously diabetic (BB) rats was reduced in the presence of vanadyl. These studies indicate that chronic oral vanadyl treatment (a) produces a concentration-related lowering of blood glucose in diabetic rats, (b) potentiates the in vivo glucose lowering effects of acute and chronic administrations of insulin in streptozotocin-diabetic rats, and (c) substitutes for, or potentiates, the effects of chronic insulin therapy in spontaneously diabetic BB rats.