The Effect Of Acute Experimental Hyperglycaemia On Pain Sensitivity Of Rats

It has been shown that hyperglycaemia had an influence on pain threshold (Davis et al, 1956; Lee et al, 1990; Kolta et al, 1996; Chen&Pan, 2002). Most of previous studies focused on the relationship between diabetic hyperglycaemia and pain threshold, however, little attention has been paid on the effect of non-diabetic hyperglycaemia on pain sensitivity. To investigate the influence of non-diabetic hyperglycaemia on pain sensitivity, we established an acute experimental hyperglycaemia model under non-diabetic hyperglycaemia state and observed whether acute hyperglycaemia could induce the change of pain sensitivity in rats. We further estimated the change of pain sensitivity under peripheral tissue injury in rats. It has been shown that peripheral tissue injury"could induce persistent spontaneous pain, thermal hyperalgesia and mechanicalhyperalgesia, the present study was to investigate the effect of acute hyperglycaemia on the above three pain syndromes, respectively.Method:1. Establishment of acute experimental hyperglycaemia rats model.STZ group: 10 adult male Sprague-Dawley rats were intraperitoneally injected STZ (50mg/Kg). After STZ injection, glucose level elevated rapidly and maintained at 9mmol/L on the second day. On the llth day, glucose level reached to 15mmol/L, which is due to the relationship between STZ-induced hyperglycaemia and the impair of pancreatic P cell. Blood gloucose level of saline group maintained at 4mmol/L during this period.2. The quantitative measurement of thermal hyperalgesia.Paw withdrawal thermal latency (PWTL) was used to reflect thermal pain sensitivity.3. The quantitative measurement of mechanical hyperalgesia.Paw withdrawal mechanical threshold (PWMT) was used to reflect mechanical pain sensitivity.4. The measurement of spontaneous pain.Bee venom induced persistent spontaneous nociception was used to reflect spinal cord mediated nociceptive flexor reflect.Blood glucose, PWTL and PWMT were measured by same experimenter at same time under same condition.Result:1. The influence of acute experimental hyperglycaemia on painsensitivity of rats1.1 The influence of acute experimental hyperglycaemia on basal thermal pain threshold.Basal PWMT didn't change with the elevation of glucose. Both experimental group and saline group didn't display any change.1.2 The influence of acute experimental hyperglycaemia on basal mechanical pain threshold.Basal PWMT tended to decrease with the elevation of glucose. After intraperitoneal injection of STZ (50mg/Kg), the basal PWMT remarkably decreased, changing from 12.98 2.19g to 2.71 0.52g on the 4th day and returning to basal level on the 9th day. At the end of the experiment, the 12th day, the PWMT in the STZ group reached to 15.18 3.09g. The PWMT of saline group didn't display any change.2. The influence of acute experimental hyperglycaemia on inflammatory pain2.1 Persistent spontaneous nociceptionSubcutaneous injection of bee venom could induce peripheral tissue inflammation and persistent spontaneous flinch reflexes. The number of flinch of the 1st hour was recorded. The number of flinch increased with the elevation of the glucose in both STZ group and saline group.2.2 Paw withdrawal thermal latencyThe PWTL of injected hindpaw and uninjected hindpaw were measured at 3, 6, 9, 24, 48, 72 h time point after bee venom injection. It was found that thermal hyperalgesia could be induced in both STZ group and saline group. The decrease of PWTL in the two groups did not display significant difference under the inflammatory state.2.3 Paw withdrawal mechanical thresholdThe PWMT of injected hindpaw and uninjected hindpaw were also measured at 3, 6, 9, 24, 48, 72 h time point after bee venom injection. Mechanical hyperalgesia were also induced in both STZ group and saline group. The time course of the mechanical hyperalgesia in STZ group displayed significant prolongation. Under the inflammatory state, the PWMT of STZ group markedly decreased compa...