Influence of detomidine and xylazine on spleen dimensions and on splenic response to epinephrine infusion in healthy adult horses.

To compare the changes in splenic length and thickness and in packed cell volume (PCV) following detomidine or xylazine administration and subsequent epinephrine infusion. Spleen relaxation occurs following xylazine or detomidine administration and interferes with subsequent splenic contractile response to epinephrine. Randomized non-blinded crossover experimental study. 6 healthy adult mares. The mares received an intravenous (IV) epinephrine infusion (1 μg kg(-1 ) minute(-1) over 5 minutes) one hour after IV administration of detomidine (0.01 mg kg(-1) ), xylazine (0.5 mg kg(-1) ) or no drug (control), with a withdrawal period of at least 7 days between experiments. The splenic length measured in two different axes, the splenic thickness, and the PCV were measured prior to sedation (T0), 30 minutes later, and at 5-minute intervals from the start of the epinephrine infusion (T1) until T1 + 40 minutes. Changes from base-line and between treatments were compared using a two-way anova for repeated measures. Significance was set at p < 0.05. Splenic length was significantly increased and PCV was significantly decreased after detomidine administration compared to baseline. Epinephrine infusion resulted in a significant decrease in splenic length and thickness, and a significant increase in PCV, irrespective of prior treatment with detomidine or xylazine. Detomidine administration was followed by a sonographically detectable increase of splenic length. Neither detomidine nor xylazine interfered with the ability of the spleen to contract following subsequent administration of an epinephrine infusion given one hour later. Previous sedation with alpha-2 agonists does not preclude the efficiency of epinephrine as a medical treatment of left dorsal displacement of the large colon, but further investigations are required with other drug doses and different time intervals between administrations.