The cardiorespiratory effects of intrathecal xylazine in the conscious rabbit
1990
Nolan, A. M. | ERHARDT, W.
The α2 agonist xylazine produced a dose‐dependent decrease in mean arterial blood pressure in conscious rabbits when injected intrathecally (i.t.) through a cannula previously implanted under general anaesthesia. Intrathecal administration of 200 and 400 μg of xylazine produced a significant reduction in arterial blood pressure from control values (maximum depressions of 25% and 33%, respectively). There was little effect on cardiac output and arterial carbon‐dioxide tension and no effect on respiratory rate, arterial oxygen tension and pulse rate. Intrathecal injection of 100 μl of 0.9% saline had no effect. Intravenous (i.v.) tolazoline (0.5 mg/kg) abolished xylazine‐induced hypotension (200 μg) in four rabbits. Contrast radiography revealed that 100 μl of solution injected i.t. in anaesthetized rabbits spread distally over eight vertebral spaces. There was little rostral spread. It was concluded that xylazine‐induced hypotension following i.t. injection was due to local activation of α2 adrenoceptors present in the thoracic spinal cord. It is postulated that spinal α2 adrenoceptors may play an important role in the hypotension recorded in animals after parenteral injection of xylazine.
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