Arteriolar nitric oxide concentration is decreased during hyperglycemia-induced βII PKC activation

beta II protein kinase C (beta PKC) is activated during acute and chronic hyperglycemia and may alter endothelial cell function. We determined whether blockade of bPKC protected in vivo endothelial formation of NO, as measured with NO-sensitive microelectrodes in the rat intestinal vasculature. NaCl hyperosmolarity, a specific endothelial stimulus to increase NO formation, caused similar to 20% arteriolar vasodilation and similar to 30% increase in NO concentration ([ NO]). After topical 300 mg/dl hyperglycemia for 45 min, both responses were all but abolished. In comparison, pretreatment with LY-333531, a specific bPKC inhibitor, maintained vasodilation and [NO] responses to NaCl hyperosmolarity after hyperglycemia. The bPKC inhibitor alone had no significant effects on resting diameter or [NO] or their responses to NaCl hyperosmolarity. In separate rats, after topical hyperglycemia had suppressed dilation to ACh, LY-333531 restored similar to 70% of the dilatory response. These data demonstrated that activation of bPKC during acute hyperglycemia depressed in vivo endothelial formation of NO at rest and during stimulation. This abnormality can be minimized by inhibition of bPKC before hyperglycemia and can be substantially reversed by PKC inhibition after hyperglycemia-induced abnormalities have occurred.