Influence of general anesthetics on baroreflex control of circulation

1. The effects of sodium pentobarbital and alpha-chloralose anesthesia on the baroreflex control of circulation were studied in groups of 7 to 11 rats. The tests were performed in conscious undisturbed rats and repeated after anesthesia. 2. Pentobarbital (15 min) depressed the initial peak of the pressor response produced by carotid occlusion by 68% (15 +/- 1 vs 47 +/- 3 mmHg) and the maintained response by 52% (13 +/- 1 vs 27 +/- 4). Depression by chloralose was 48% (26 +/- 5 vs 50 +/- 3) and 21% (19 +/- 2 vs 24 +/- 3), respectively. The inhibition progressively declined at 30, 60, 90 and 120 min after pentobarbital but was unchanged up to 120 min after chloralose. 3. The baroreflex sensitivity index for bradycardic responses (phenylephrine injection) diminished by 50% after pentobarbital (-1.1 +/- 0.3 vs -2.2 +/- 0.3 beats/min per mmHg) and remained unaltered after chloralose. 4. The baroreflex sensitivity index for tachycardic responses (nitroprusside injection) was depressed by 61% after pentobarbital (-1.5 +/- 0.5 vs -3.8 +/- 0.5 beats/min per mmHg) and 35% after chloralose (-2.5 +/- 0.2 vs -3.9 +/- 0.5). 5. In general the depression of reflex control of circulation was more severe after pentobarbital than after chloralose anesthesia, while the resting control arterial pressure was not affected by either. The inhibition of the baroreflex tachycardic responses was more intense than that of the bradycardic responses and represented a better index of the depression exerted on the pressure responses to carotid occlusion.