Rabbit carotid sinus reflex under pentobarbital, urethan, and chloralose anesthesia

To determine the effects of different anesthesias on the performance of the arterial baro-reflex, the open-loop characteristic of the carotid sinus reflex was analyzed in 24 rabbits under anesthesia with pentobarbital (30 mg/kg), urethan (800 mg/kg), alpha-chloralose (80 mg/kg), or a mixture of alpha-chloralose (40 mg/kg) and urethan (0.4 g/kg). For each rabbit and anesthesia, mean systemic arterial pressure and heart rate were measured as carotid sinus pressure was changed in 10-mmHg steps between 40 and 150 mmHg. This set of measurements was repeated four times at 1-h intervals. A logistic function curve was fitted to the carotid sinus pressure-arterial pressure relationship. The parameters of this curve were then analyzed to delineate the specific effects of the anesthesias on the relationship. The main finding was that the response range and the slope parameters under alpha-chloralose anesthesia were significantly smaller than those obtained under the other anesthesias. Propylene glycol, used as the solvent for chloralose, did not affect the reflex control of arterial pressure or heart rate. The reflex under chloralose-urethan anesthesia showed characteristics similar to those under urethan anesthesia. We conclude that although alpha-chloralose has traditionally been used in the dog to obtain strong reflex responses, it weakens the reflex control of arterial pressure in the rabbit.