Altered tail-skin temperature responsiveness in streptozotocin-induced diabetic rats

We evaluated the tail-skin temperature response to administration of several doses of isoproterenol in streptozotocin-induced diabetic rats after 48 h and after 4 weeks of diabetes. Blood glucose concentrations were significantly increased over controls 48 hours after administration of streptozotocin (65 mg/kg, i.v.) and remained elevated to a similar degree in the 4-week group. Basal rectal temperature and tail-skin temperature (TST) were not different between controls and the diabetic groups and were not affected by administration of saline. However, administration of isoproterenol (25 micrograms/kg, s.c.) caused a significant rise in TST in the control group, but not in the rats diabetic for 4 weeks. A similar but exaggerated response was observed in the controls after subcutaneous administration of 40 micrograms/kg and 100 micrograms/kg of isoproterenol. The TST response in the 4-week diabetic rats still remained negligible with the two higher doses of isoproterenol. When the data were summarized as area under the TST curve, a dose-dependent increase was observed in the control groups and a significant absence of response was observed in the 4-week group. The rats studied 48 h after streptozotocin injection had a similar TST response to the control group after administration of 40 micrograms/kg of isoproterenol. Colonic temperatures did not significantly change between the two groups in any of the studies, although the colonic temperatures tended to rise in the control groups following administration of isoproterenol. We conclude from this study that the absence of a tail-skin temperature response in rats diabetic for 4 weeks results from either a reduced beta-adrenergic receptor mediated response or an altered neural thermoregulatory reflex response, or both. These changes are probably not due to streptozotocin treatment or increases in blood glucose.