Diabetes attenuates the minimum anaesthetic concentration (MAC) and MAC-blocking adrenergic response reducing actions of clonidine in rats

Background: It is well known that clonidine, an alpha (2) agonist, reduces anaesthetic requirement and attenuates haemodynamic responses against noxio us stimuli. However, the diabetic state is known to affect several function s of alpha (2) adrenoceptors. We investigated the effects of streptozotocin (STZ)-induced diabetes mellitus (DM) on these beneficial actions of clonid ine in halothane-anaesthetized rats. Methods: The rats were randomly assigned to one of three groups: diabetes ( n = 24, induced by 50 mg(.)kg(-1) IV STZ), diabetes treated with insulin (n = 24), or control (n = 24). We evaluated the effects of clonidine on minim um anaesthetic concentration (MAC) and minimum concentration of halothane n eeded to suppress cardiovascular responses evoked by a noxious stimulus (MA C-blocking adrenergic responses: MAC-BAR) in each group. MAC and MAC-BAR of halothane were determined by the tail clamp method. MAC-BAR was defined as the MAC which attenuated haemodynamic responses within 10% following the t ail clamp. Results: The diabetic state decreased MAC of halothane by approximately 10% , while MAC-BAR of halothane had been little affected. In the diabetes grou p, MAC reducing action of clonidine (30 and 100 mug(.)kg(-1), IV) was compl etely abolished and MAC-BAR reducing action of clonidine was partially redu ced (30 but not 100 mug(.)kg(-1), IV). Insulin treatment preserved these ac tions of clonidine. Conclusion: It is suggested that the diabetic state attenuates the benefici al actions of clonidine and that insulin treatment of diabetes preserves th ese actions of clonidine.