Altered thermoregulatory responses to clonidine in streptozotocin-diabetic rats

1 The effects of streptozotocin (STZ) treatment on α₂-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 α₂-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°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°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 α₂ receptor function induced by STZ.