Atropine and glycopyrrolate significantly raise the heart rate of Sonoran Desert toads (Incilius alvarius).

OBJECTIVE

To evaluate the effects of atropine and glycopyrrolate on the heart rate (HR) of Sonoran Desert toads (Incilius alvarius).

METHODS

In part 1, toads received 0.1 mg/kg atropine IM, 0.025 mg/kg glycopyrrolate IM, 0.05 mg/kg glycopyrrolate IM, saline, or negative control in a randomized crossover study. Heart rate was monitored at baseline and 1, 3, 5, 10, 15, 20, 25, 30, 40, 50, and 60 minutes. In part 2, toads received 10 mg/kg alfaxalone IM followed by 0.05 mg/kg glycopyrrolate or saline. Heart rate was monitored at baseline and 1, 3, 5, 10, 15, 20, 25, 30, 40, 50, 60, 80, 100, and 120 minutes.

RESULTS

In part 1 (n = 19), all 3 anticholinergic protocols significantly increased the HR between 3 and 15 minutes versus both controls. Atropine significantly increased the HR versus saline between 3 and 30 minutes. Both glycopyrrolate doses significantly increased the HR versus saline at 60 minutes. In part 2 (n = 10), glycopyrrolate significantly increased the HR versus saline at 10 minutes (mean HR difference 6.8 beats/min, SE of the difference 1.467 [95% CI, 1.024 to 12.58]).

CONCLUSIONS

Atropine and glycopyrrolate significantly increased the HR in conscious toads, with glycopyrrolate having longer efficacy. The effective period of glycopyrrolate was briefer in alfaxalone-sedated toads.

CLINICAL RELEVANCE: Performing safe, effective anesthesia can be challenging in amphibians given their unique physiology. Anticholinergic drugs are commonly used in veterinary medicine to address anesthesia-induced bradycardia. Additional studies are indicated to further evaluate the clinical efficacy of anticholinergics in amphibians.