Activation of the
polyol pathway under hyperglycemic conditions is proposed to contribute to the development of
diabetic nephropathy. The mechanisms by which this activation may lead to functional and structural changes within the kidney are yet to be definitively established. We have examined in vitro the steps linking increased
polyol pathway activity resulting from
hyperglycemia to
prostaglandin production. Following the demonstration of increased
prostaglandin E (
PGE) levels in glomeruli from diabetic rats (14.9 +/- 2.5 v 59.1 +/- 19.4 ng
PGE/mg
protein), a specific inhibitor of
aldose reductase,
HOE-843, was used in vitro to analyze the response to
hyperglycemia of the steps preceding
prostaglandin production. In explants of glomeruli from control animals, increasing the
glucose concentration in vitro from 5.6 mmol/L to 25 mmol/L resulted in a significant increase in the flux of
glucose through the pentose phosphate pathway ([PPP] 1.29 +/- 0.08 v 2.00 +/- 0.11 nmol/h), de novo
diacylglycerol synthesis (2.2 +/- 0.1 v 3.1 +/- 0.2 micromol/mg
protein), membrane protein kinase C (PKC) activity (18.7 +/- 0.5 v 24.3 +/- 0.75 pmol/microg
protein), and in vitro
phospholipase A2 (PLA2) activity (2.18 +/- 0.46 v 3.83 +/- 1.07 nmol
arachidonic acid hydrolyzed/min/mg cytosolic
protein). For all parameters measured, the increase resulting from the increased
glucose concentration could be prevented by in vitro addition of
HOE-843 for 24 hours before measurement. These findings provide evidence to suggest a mechanism linking increased
polyol pathway activity and an increase in PLA2 activity to increased
prostaglandin production, which is observed in diabetes of recent onset and may ultimately lead to changes associated with the development of
diabetic nephropathy.