Effect of xylazine and detomidine on urine production in horses deprived of food and water

Abstract

Alpha-2 agonists cause transient dose-related increase in urine flow in normal horses. Although important clinically, effects of these drugs in dehydrated animals are not known. The purpose of this study was to describe the influence of xylazine (XYL) and detomidine (DET) on urine flow in mares deprived of food and water for 24 hours. Six clinically normal mares [12.5 ± 3.3 (mean ± SE) years] weighing 471 ± 23 kg were each studied four times; each study was separated by at least 7 days. The morning following fasting, the urinary bladder was catheterized (Foley) and emptied. Urine was then collected for 2 hours and a composite urine sample along with a sample of jugular venous blood provided baseline values. Shortly after emptying the bladder, saline, 0.5 or 1.0 mg kg−1 XYL or 0.03 mg kg−1 DET was injected IV (treatment randomly assigned) and urine and blood samples obtained over the next 2 hours. Data were analyzed by RM anova followed by Dunnett's test for pairwise comparisons p < 0.05; indicated by (S). Pretreatment urine flow was 0.30 ± 0.03 mL kg−1 hour−1, urine specific gravity (SG) was 1.032 ± 0.001, packed cell volume (PCV) was 37.8 ± 1.0%, and total plasma solids (TP) was 6.85 ± 0.12 g dL−1; values for four treatment periods within a grouping did not differ. At 1 hour post-treatment, urine flow (mL kg−1 hour−1) was 0.31 ± 0.04, 1.09 ± 0.48, 2.33 ± 0.89(S), and 2.14 ± 0.58 (S) for saline, 0.5 XYL, 1.0 XYL and DET, respectively. By 2 hours, urine flow was at or returning to baseline with all treatments except DET where a further increase was noted (8.28 ± 0.92(S)). A time related decrease in urine specific gravity (e.g. 1.010–1.021 at 1 hour post-treatment) was associated with the increase in urine flow but PCV and TP did not change significantly with time or treatment. These data indicate that XYL and DET cause an important time-related, transient increase in urine flow despite food and water deprivation. Consequently, severity of dehydration accompanying inadequate water intake during periods of normal or excessive fluid losses may be exacerbated by concurrent administration of alpha-2 agonists in horses.