MODIFICATION OF CARDIOPULMONARY AND INTESTINAL MOTILITY EFFECTS OF XYLAZINE WITH GLYCOPYRROLATE IN HORSES

Xylazine (XYL) administration in horses is accompanied by significant cardiovascular depression characterized by a 25-35 % decrease in cardi ac output (GO) which is likely to compromise tissue oxygen delivery (D O2), and usually vagally mediated bradycardia is an important cause of this reduced cardiovascular performance. To examine the possible bene fit of preventing the bradycardiac response, 6 healthy horses were tre ated with intravenous (IV) saline (SAL) or 2.5 mu g/kg glycopyrrolate (GLY) in a blinded, randomized, crossover trial. Fifteen minutes later , 1 mg/kg XYL was administered IV and systolic, diastolic and mean blo od pressures (SEP, DBP, and MBP, respectively), central venous pressur e (CVP), mean pulmonary artery pressure, heart rate (HR), CO, and arte rial and mixed venous blood gases were measured at the following times : baseline, 2, 5, and 10 min post-SAL or GLY; and 2, 5, 10, 15, 30, 45 and 60 min post-XYL. Determination of cardiac index (CI), stroke inde x (SI), left ventricular work, systemic vascular resistance (SVR), DO, , oxygen uptake, and oxygen extraction ratio were made at the same tim e. Gastrointestinal (GI) motility was evaluated by four-quadrant auscu ltation for 24 h post-XYL. Statistical analysis of continuous variable s was carried out using ANOVA for repeated measures and Wilcoxon's ran k-sum test for nonparametric data. In GLY treated horses, HR, SEP, MBP , DBP, CI, DO2 and mixed venous oxygen tension were significantly high er up to 30 min after XYL (P less than or equal to 0.02) while CVP and SI were significantly lower 2 and 5 min post-XYL, respectively. In bo th groups, GI motility as assessed by auscultation was virtually aboli shed for an hour, with a non-significant tendency for the decrease in motility to last longer in the GLY/XYL group. None of the treated hors es developed abdominal discomfort. No significant difference was obser ved in the other variables. The study shows that 2.5 mu g/kg GLY preme dication reduces the cardiovascular depression caused by 1 mg/kg XYL, without adversely affecting GI motility.