THE EFFECT OF DETOMIDINE AND ITS ANTAGONISM WITH TOLAZOLINE ON STRESS-RELATED HORMONES, METABOLITES, PHYSIOLOGICAL-RESPONSES, AND BEHAVIOR IN AWAKE PONIES

Six ponies were used to investigate the effect of tolazoline antagonis m of detomidine on physiological responses, behavior, epinephrine, nor epinephrine, cortisol, glucose, and free fatty acids in awake ponies. Each pony had a catheter inserted into a jugular vein 1 hour before be ginning the study. Awake ponies were administered detomidine (0.04 mg/ kg intravenously [IV]) followed 20 minutes later by either tolazoline (4.0 mg/kg IV) or saline. Blood samples were drawn from the catheter 5 minutes before detomidine administration (baseline), 5 minutes after detomidine administration, 20 minutes after detomidine administration which was immediately before the administration of tolazoline or salin e (time [T] = 0), and at 5, 30, and 60 minutes after injections of tol azoline or saline (T = 5, 30, and 60 minutes, respectively). Compared with heart rate at T = 0, tolazoline antagonism increased heart rate 4 5% at 5 minutes. There was no difference in heart rate between treatme nts at 30 minutes. Blood pressure remained stable after tolazoline, wh ile it decreased over time after saline. Compared with concentrations at T = 0, tolazoline antagonism of detomidine in awake ponies resulted in a 55% increase in cortisol at 30 minutes and a 52% increase in glu cose at 5 minutes. The change in free fatty acids was different for to lazoline and saline over time. Free fatty acids decreased after detomi dine administration. Free fatty acids did not change after saline admi nistration. After tolazoline administration, free fatty acids increase d transiently. Tolazoline tended to decrease sedation and analgesia at 15 and 60 minutes postantagonism. Antagonism of detomidine-induced ph ysiological and behavioral effects with tolazoline in awake ponies tha t were not experiencing pain appears to precipitate a stress response as measured by cortisol, glucose, and free fatty acids. If antagonism of an alpha-agonist is contemplated, the potential effect on hormones and metabolites should be considered. (C) Copyright 1997 by The Americ an College of Veterinary Surgeons