Effects of vatinoxan on cardiorespiratory function and gastrointestinal motility during constant-rate medetomidine infusion in standing horses

Background Medetomidine suppresses cardiovascular function and reduces gastrointestinal motility in horses mainly through peripheral alpha(2)-adrenoceptors. Vatinoxan, a peripheral alpha(2)-antagonist, has been shown experimentally to alleviate the adverse effects of some alpha(2)-agonists in horses. However, vatinoxan has not been investigated during constant-rate infusion (CRI) of medetomidine in standing horses. Objectives To evaluate effects of vatinoxan on cardiovascular function, gastrointestinal motility and on sedation level during CRI of medetomidine. Study design Experimental, randomised, blinded, cross-over study. Methods Six healthy horses were given medetomidine hydrochloride, 7 mu g/kg i.v., without (MED) and with (MED+V) vatinoxan hydrochloride, 140 mu g/kg i.v., followed by CRI of medetomidine at 3.5 mu g/kg/h for 60 min. Cardiorespiratory variables were recorded and borborygmi and sedation levels were scored for 120 min. Plasma drug concentrations were measured. The data were analysed using repeated measures ANCOVA and paired t-tests as appropriate. Results Initially heart rate (HR) was significantly lower and mean arterial blood pressure (MAP) significantly higher with MED compared with MED+V. For example at 10 min HR (mean +/- s.d.) was 26 +/- 2 and 31 +/- 5 beats/minute (P = 0.04) and MAP 129 +/- 15 and 103 +/- 13 mmHg (PPeer reviewe