Altered thermoregulatory responses to clonidine in streptozotocin-diabetic rats

1. The effects of streptozotocin (STZ) treatment on alpha 2-adrenoceptor regulation of body temperature were studied by monitoring the response of colonic temperature to administration of clonidine. 2. A dose-dependent fall in colonic temperature occurred in control rats given clonidine challenge (0.05-2.0 mg kg-1, s.c.); this response was inhibited by prior administration of either yohimbine or idazoxan (2 mg kg-1, s.c.) but not by the peripherally-acting alpha 2-adrenoceptor antagonist L-659,066 (10 mg kg-1, s.c.). 3. In rats treated with STZ (65 mg kg-1, i.v.) administration of clonidine elicited a dose-independent hyperthermia (circa 1 degree C.); this effect was unaltered by prior administration of yohimbine or idazoxan. 4. Naloxone (5 mg kg-1, s.c.) elicited a small fall in temperature (< 1 degree C.) in both control and STZ-treated rats; naloxone pretreatment did not alter the temperature response to clonidine in either group. 5. Nicotinic acid (10 mg kg-1, s.c.) caused a similar small elevation in temperature in both groups. 6. Administration of replacement insulin to STZ-treated rats maintained weight gain and low blood glucose while the thermoregulatory response to clonidine slowly reverted to normal. 7. These results show that altered central temperature control is an element of the generalised abnormality of alpha 2-receptor function induced by STZ.