Effect of intermittent high glucose on synthesis of nitric oxide in human umbilical vein endothelial cells and its mechanism.

Objective: To compare the effect of intermittent and constant high glucose media on the synthesis of vascular relaxing factor nitric oxide (NO) in cultured human umbilical vein endothelial cells (HUVECs), and to investigate its mechanism.
Methods: HUVECs were exposed to 5.5 mmol/L glucose (normal control), 20 mmol/L glucose (constant high glucose), and 5.5 mmol/L alternating with 20 mmol/L glucose (intermittent high glucose) for 7 days. The NO level was measured using Griess Reaction in cell culture supernatants; the expressions of PI3K, PKB and eNOS mRNA and protein were measured with RT-PCR or Western blot.
Results: NO level in the intermittent high glucose group was significantly lower than that in the constant high glucose group (P<0.05). The expression of PI3K, PKB, and eNOS in the intermittent high glucose group was significantly lower than that in the constant high glucose group (P<0.05).
Conclusion: Intermittent high glucose could be more deleterious to endothelial cells than constant high glucose, and may lead to decrease synthesis of NO by inhibiting PI3K/PKB/eNOS pathway activation.