Effects of intravenously administered yohimbine on antinociceptive, cardiorespiratory, and postural changes induced by epidural administration of detomidine hydrochloride solution to healthy mares.

This research explores the impact of intravenously administered yohimbine on the antinociceptive, cardiorespiratory, and postural changes in mares that have been administered detomidine hydrochloride epidurally. The study found that yohimbine effectively antagonizes most detomidine-induced effects except for respiratory rate depression.

Research Methodology

• Eight healthy mares were part of this randomized, crossover study.
• Detomidine hydrochloride, a sedative, was administered epidurally to each horse. The dosage, 0.06 mg/kg of body weight, corresponded to the weight of each mare.
• After 61 minutes, the mares were then dosed with either yohimbine (0.05 mg/kg; test) or sterile saline solution (0.9% NaCl; control). The substances were administered intravenously.
• A minimum period of 2 weeks separated the treatments to avoid any interaction.
• Perineal analgesia was determined by the lack of sensory perception to electrical stimulation of perineal dermatomes and needle-prick stimulation of coccygeal to 15th thoracic dermatomes.
• Several physiological factors including arterial pH, PaCO2, PaO2, heart and respiratory rates, rectal temperature, arterial blood pressure, cardiac output, sweating and urination were measured and observesments were made for changes.

Results and Implications

• Yohimbine notably reduced the detomidine-induced effects of perineal analgesia, head ptosis (drooping), changes in pelvic limb position, and sweating and diuresis (increased or excessive fluid elimination).
• The drug also antagonized the detomidine-induced decreases in heart rate and cardiac output, but it did not influence the detomidine-induced decrease in respiratory rate.
• In conclusion, yohimbine can effectively counteract most effects of epidurally administered detomidine with the exception of bradypnea (abnormally slow breathing).
• This indicates that detomidine may affect the respiratory rate by other means aside from the stimulation of alpha2-adrenoceptors, or that yohimbine possesses respiratory depressant effects.
• As a clinical application, yohimbine could serve as an effective alpha2-adrenoceptor antagonist in all cases excluding respiratory depression when detomidine is administered epidurally to mares.