Effect of acute hemorrhage on carotid occlusion response in the cat

¹ Department of Pharmacology, University of California Medical Center, Los Angeles, California

The relationship between carotid occlusion response and mean arterial pressure, after small successive hemorrhages, was investigated in the cat anesthetized with -chloralose. Carotid occlusion response decreased as arterial pressure fell to a level of about 130 mm Hg, but below this level, carotid occlusion response increased. This increase was found to be due to carotid chemoreceptor activity, as it disappeared when the animal breathed oxygen immediately prior to and during the occlusion and was absent in animals after carotid chemoreceptor inactivation. This increase was not present in animals anesthetized with sodium pentobarbital. As this increase was also present in the unanesthetized animal, pentobarbital in anesthetic doses must block the effect of carotid chemoreceptor activity, probably by a central action. In 20% of the animals the carotid occlusion response increased after the first few hemorrhages by an amount equal to the fall in arterial pressure. This increase was not due to chemoreceptor activity, but was probably due to a ceiling phenomenon.