Relation of Na+, K(+)-ATPase to delayed motor nerve conduction velocity: effect of aldose reductase inhibitor, ADN-138, on Na+, K(+)-ATPase activity

The role of sorbitol, myo-inositol, and Na+, K(+)-adenosine triphosphatase (ATPase) activity on motor nerve conduction velocity (MNCV) in streptozotocin (STZ)-diabetic rats was studied. Reduction of MNCV and Na+, K(+)-ATPase in caudal nerves appeared after 3 weeks of diabetes, and at this time treatment with aldose reductase inhibitor (ARI), ADN-138 and 1% myo-inositol supplement was begun. One percent myo-inositol supplement for 3 weeks resulted in a significant increase in myo-inositol levels in diabetic nerves, but left MNCV and sorbitol levels unchanged. In contrast, treatment with ADN-138 for 3 weeks reduced sorbitol levels in diabetic nerves and resulted in significant increases in MNCV and Na+, K(+)-ATPase in the nerves. Since ADN-138 did not restore myo-inositol levels, the increase in Na+, K(+)-ATPase levels by ADN-138 treatment was independent of myo-inositol levels. Also, nerve Na+ levels in ADN-138-treated rats were reduced and the ratio of K+ to Na+ was raised, while 1% myo-inositol supplement did not affect them. These results suggest that treatment with ADN-138 elevates MNCV through a series of processes: ARI----reduction of sorbitol level----increase in Na+, K(+)-ATPase activity----correction of K+, Na+ imbalance----increase in MNCV.