To elucidate the molecular mechanisms underlying the development of diabeti
c neuropathy, we isolated the Schwann cells from the sciatic nerves of adul
t rats and characterized the polyol pathway activity. Despite the presence
of aldose reductase (AR) activity, no accumulation of sorbitol was observed
in the cells cultured under 30 mM glucose conditions. Increased levels of
sorbitol were detected in the medium conditioned by these cells. SNK-860 (f
idarestat), an inhibitor of AR, decreased the sorbitol levels at 10(-6) M,
while addition of SDI-158, an inhibitor of sorbitol dehydrogenase, did not
affect the level in the cells grown in high glucose, These observations sug
gested that sorbitol produced by AR in the isolated Schwann cells may be pr
edominantly excreted. In contrast, a significant increase in sorbitol level
was observed in cells cultured under hyperosmotic conditions with 30 mM gl
ucose. A significant correlation was observed between sorbitol level and AR
activity (r = 0.998), The increase was suppressed by addition of SNK-860,
while SDI-158 augmented sorbitol accumulation in a dose-dependent manner. T
hese results suggested that the isolated Schwann cells may not accumulate s
orbitol unless the activity of AR is augmented by some as yet undetermined
mechanism under high glucose conditions, such as the hyperosmotic stress in
duced in this study. (C) 1999 Wiley-Liss, Inc.