Background: Patients receiving oral hypoglycemic agents for diabetes mellitus are at increased risk of cardiovascular mortality. Oral hypoglycemic agents are inhibitors of the ATP-sensitive potassium (KATP) channel. Ischemic preconditioning is mediated by KATP channel activation. We therefore hypothesized that myocardium from patients taking long-term oral hypoglycemic agents would be resistant to the protection by ischemic preconditioning.
Methods and results: Isolated human right atrial trabeculae were suspended in an organ bath at 37 degrees C, with field stimulation at 1 Hz. Control trabeculae were then subjected to 45 minutes of simulated ischemia (hypoxic, glucose-free buffer with pacing at 3 Hz) and 120 minutes of reperfusion. Ischemic preconditioned (IPC) trabeculae from patients without oral hypoglycemic therapy and from patients taking insulin (Ins+IPC) were given 5 minutes of simulated ischemia before this injury. Trabeculae (Oral Hypo+IPC) were obtained from patients taking long-term oral hypoglycemic agents and were also exposed to 5 minutes of simulated ischemia before this injury. Developed force (DF) was recorded. Recovery of DF relative to preischemic values was 28 +/- 4% in control trabeculae, whereas IPC trabeculae showed 52 +/- 5% recovery (P < .05 versus control). In patients receiving long-term oral hypoglycemic agents (Oral Hypo+IPC), recovery of DF was 27 +/- 3%, but in trabeculae from insulin-treated patients (Ins+IPC), it was 45 +/- 6%.
Conclusions: Human myocardium from patients without long-term exposure to oral hypoglycemic agents is functionally protected by preconditioning. Long-term oral hypoglycemic intake blocks the protection by preconditioning. These data suggest that ischemic preconditioning in human myocardium relies on KATP channels, and long-term inhibition of KATP channels with oral hypoglycemic agents may explain the excess cardiovascular mortality in these patients.