Pain threshold in diabetic rats: effects of good versus poor diabetic control.

Pain threshold was assessed via tail flick latency in streptozotocin diabetic rats following a 1-month period of either good or poor diabetic control. Additionally, tail flick latencies were determined under test conditions of euglycemia (60-120 mg/dl) and hyperglycemia (greater than 250 mg/dl) for both groups of diabetic rats. Conditions of hyperglycemia resulted in a significant decrease in tail flick latency in diabetic animals maintained in good as well as poor diabetic control. However, tail flick latencies for animals in the good but not in the poor diabetic control group increased when animals were euglycemic at the time of testing. Animals in the poor diabetic control group continued to have reduced tail flick latencies even after acute normalization of blood glucose levels. These results suggest that chronic states of hyperglycemia that attend prolonged periods of poor diabetic management may lead to persistent alterations in pain threshold. In contrast, the reduced pain threshold of rats maintained in good diabetic control was reversed by a normalization of blood glucose levels. These findings provide evidence for two patterns of hyperalgesia in diabetic rats: (1) a readily reversible form in well-maintained diabetic rats that is altered by reducing circulating blood glucose levels to control values and (2) a more persistent form found in poorly controlled diabetic rats that does not respond to acute normalization of blood glucose.