Influence of yohimbine and tolazoline on the cardiovascular, respiratory, and sedative effects of xylazine in the horse

Abstract

To determine the effects of yohimbine and tolazoline on the cardiovascular, respiratory and sedative effects of xylazine, four horses were sedated with xylazine and treated with either yohimbine, tolazoline or saline. Xylazine was administered as an intravenous (i.v.) bolus (1.0 mg/kg) followed by a continuous infusion at the rate of 12 micrograms/kg/min. Heart rate, respiratory rate, mean arterial pressure, arterial blood gases, and the chin-to-floor distance were recorded throughout the experiment. After 60 min, either yohimbine or tolazoline was administered i.v. in incremental doses until reversal of sedation (defined as the return of the chin-to-floor distance to baseline values) was achieved. A control group in which a saline bolus was administered instead of an antagonist drug was included for comparison. The average dose of yohimbine administered was 0.12 +/- 0.02 (SEM) mg/kg. While the average dose of tolazoline was 7.5 +/- 1.1 mg/kg. Both tolazoline and yohimbine antagonized the ventricular bradycardia and A-V conduction disturbances observed with xylazine administration. No change in mean arterial pressure was observed with xylazine or yohimbine administration, but tolazoline caused persistent mild systemic hypertension. There were no clinically significant changes in respiratory rate or arterial blood gas values with administration of either xylazine, yohimbine or tolazoline. The chin-to-floor distance decreased significantly with xylazine administration and increased significantly with administration of either yohimbine or tolazoline. In conclusion, both yohimbine and tolazoline successfully antagonized the cardiovascular and CNS depression associated with xylazine administration.

Pharmacokinetics and pharmacodynamics of three intravenous doses of yohimbine in the horse

“…The variation in response between individual horses witnessed here as well as in the DiMaio Knych et al. (2010) has been demonstrated previously (Kollias‐Baker et al. , 1993).…”

“…, 1987). In horses, yohimbine has effectively reversed xylazine‐induced sedation, bradycardia and atrioventricular conduction disturbances (Kollias‐Baker et al. , 1993).…”

Determination of xylazine and its metabolites by GC–MS in equine urine for doping analysis

“…It is also used or abused in horses because of its calming effect. The drug has also anaesthetic and muscle relaxing properties and the extent of these effects may vary in intensity depending on the administrating dose [1,2]. It produces a profound hypertensive response within 15 s after injection.…”

Efeitos hemogasométricos da xilazina e da romifidina em cabras tratadas por ioimbina

“…A redução da pressão parcial de oxigênio (paO 2 ) e o aumento na pressão parcial de dióxido de carbono no sangue arterial (paCO 2 ) foram avaliados após a administração de xilazina a eqüinos (Kollias-Baker et al, 1993) e caprinos (Stegmann, 1999). Os valores médios de paCO 2 superior a 45mmHg e de pH menor que 7,5, após a administração de xilazina, caracterizaram a presença de hipoventilação e acidose respiratória (Haskins, 1983).…”