Objective: Ketamine, an intravenous anesthetic agent, can modulate vascular tone. Nitric oxide (NO), constitutively produced in endothelial cells, contributes to vasoregulation. In this study, we attempted to evaluate the effects of ketamine on NO biosynthesis in human umbilical vein endothelial cells and its possible mechanism.
Design: Controlled laboratory study
Settings: Research laboratory in a universal hospital.
Subjects: Human umbilical vein endothelial cells prepared from human umbilical cord veins were exposed to 1, 10, 100, and 1000 microM ketamine for 1, 6, and 24 hrs.
Measurements and main results: Exposure to 1, 10, and 100 microM ketamine for 1, 6, and 24 hrs was not cytotoxic to human umbilical vein endothelial cells. However, ketamine at 1000 microM significantly caused cell apoptosis. A therapeutic concentration of ketamine (100 microM) time-dependently reduced the levels of nitrite in human umbilical vein endothelial cells. Immunoblot analysis revealed that ketamine time-dependently decreased endothelial NO synthase protein production in human umbilical vein endothelial cells. Results of an assay by reverse-transcription polymerase chain reaction showed that ketamine significantly inhibited levels of endothelial NO synthase messenger RNA. Ketamine time-dependently reduced bradykinin-enhanced intracellular calcium concentrations. Analysis by confocal microscopy further demonstrated the suppressive effects of ketamine on bradykinin-induced calcium mobilization.
Conclusions: A clinically relevant concentration of ketamine can reduce NO biosynthesis. The suppressive mechanisms occur not only by pretranslational inhibition of eNOS expression but also by a posttranslational decrease in endothelial NO synthase activity due to a reduction in intracellular calcium levels.