Blockades of ATP-sensitive potassium channels and L-type calcium channels improve analgesic effect of morphine in alloxan-induced diabetic mice

In the present study interactions between analgesic effect of morphine with blockade of ATP-sensitive potassium channels and L-type calcium channels were investigated in alloxan-induced diabetic mice. A hot plate test was used to assess analgesic effect of drugs in adult male NMRI mice. All drugs were injected through an intraperitoneal route. A diabetic mouse model was established by injections of alloxan for three consecutive days. Seventy-two hours after the final injection, mice with a blood glucose level higher than 11.1mmol/l were considered as diabetic. The results showed that morphine at doses of 10 and 15mg/kg induced analgesia in both non-diabetic and diabetic mice, but the analgesic effect of morphine at dose of 7.5mg/kg was decreased in diabetic mice. Injections of an ATP-sensitive potassium channel blocker, glibenclamide (4, 8, 12, 20mg/kg) had no effect in non-diabetic mice, while at doses of 12 and 20mg/kg induced analgesia in diabetic mice. Blockade of L-type calcium channels with nimodipine at different doses (2.5, 5, 10 and 20mg/kg) was ineffective in non-diabetic mice, but at dose of 20mg/kg induced analgesia in diabetic mice. Co-administrations of glibenclamide (20mg/kg) or nimodipine (20mg/kg) along with different doses of morphine (5, 7.5 and 10mg/kg) improved the analgesic effect of the later drug in diabetic mice. According to the present results, it is possible that diabetes via affecting the potassium and calcium channels in the pain pathways may alter processing of pain in the peripheral and central nervous system.