Effect of hyperglycemia on the efficacy of morphine analgesia in rats.

The effect exerted by hyperglycemia on the analgesic potential of morphine was studied in female Wistar rats with the hotplate device and the formalin test. Hyperglycemia induced by an intraperitoneal (ip) injection of alloxan (40mg/Kg) significantly (p < 0.05) reduced the potency of morphine in the two tests employed. While morphine caused an inhibition of 48.64% (44.83 +/- 3.69s vs 30.16 +/- 4.12s) in the pain sensitivity of control non-diabetic animals using the hotplate device, an inhibition of only 36.25% (31.50 +/- 2.28s Vs 23.12 +/- 1.80s) was recorded in the pain sensitivity of the diabetic group using the same method. In the formalin test, morphine inhibited the pain sensitivity by 35.23% (1.93 +/- 0.17 Vs 1.25 +/- 0.21) in the control non diabetic group and by 25.93% (2.16 +/- 0.09 Vs 160 +/- 0.15) in the diabetic group. From these data, it is hypothesized that the hyperglycemic state is responsible for selectively affecting the potency of morphine. These results, if found to be true in man, may have clinical implications for the use of morphine in diabetic subjects.