Effect of thiamylal on the response to carotid occlusion and mild hemorrhage in rabbits.

The effects of anesthesia (thiamylal, 30 mg/kg) on steady-state mean arterial pressure responses to bilateral carotid occlusion (BCO) and rapid 8% hemorrhage were studied in 11 rabbits chronically instrumented with an arterial pressure catheter and balloon occluders on the common carotid arteries. The BCO was repeated in the conscious and anesthetized states both before and after transecting the aortic nerves (AN). With the AN intact, the BCO response was an increase in mean systemic arterial pressure of 23.6 +/- 2.1 (SE) mmHg in the conscious state and 24.7 +/- 1.2 in the anesthetized state. With the AN cut (AN) BCO response was 46.2 +/- 1.7 mmHg in conscious state and 45.7 +/- 2.6 in anesthetized state. There was no significant difference in BCO response between conscious and anesthetized states, whether the AN was present or absent. The hemorrhage experiment was repeated on separate days under various conditions, including carotid sinus reflex elimination (CS). With AN intact the posthemorrhage fall in mean arterial pressure (delta MAPh) was 3.2 +/- 0.6 mmHg in the conscious state. Under anesthesia, delta MAPh was 3.4 +/- 0.6 mmHg in the AN intact condition, 7.3 +/- 0.9 in AN, and 34.5 +/- 6.8 in (AN + CS). There was no significant difference in delta MAP between the conscious and anesthetized states under the intact AN condition. We conclude that, in the rabbit, thiamylal anesthesia has little effect on the BCO response and the restoration of arterial pressure after a mild hemorrhage.