Felodipine potentiates morphine analgesia in control and streptozotocin diabetic female rats.

Tolerance to morphine analgesia was seen in diabetes. Calcium channel blockers potentiate opioid analgesia while calcium agonists antagonize. Therefore, the present study using thermal pain threshold was taken up to find out, whether felodipine, altered morphine analgesia in experimental diabetes. From the end of 6th week of streptozotocin-diabetes, felodipine was administered po for 2 week to half of the control and diabetic female rats. Morphine analgesia was recorded 1 hr after the first (acute effect) and last dose (chronic effect) of felodipine. Significant elevation of pain threshold was seen in the first 6 weeks in diabetic rats compared to controls. No tolerance was seen to morphine (2 mg/kg, sc) analgesia in diabetic rats. In both control and diabetic rats acute administration of felodipine produced significant analgesia while both acute and chronic administration of felodipine produced significant potentiation of morphine analgesia in control diabetic rats. The results suggest that prior felodipine may enhance morphine analgesia, and that this needs to be explored further in various types of pain.