Redistribution of cardiac output during grooming of the rat

Changes in blood flow in the carotid, superior mesenteric, or renal artery or terminal aorta during grooming were measured in the conscious rat with a chronically implanted electromagnetic flow probe. Arterial pressure was measured simultaneously with an indwelling catheter. During grooming, carotid flow almost doubled and arterial pressure rose slightly, while hindquarter (terminal aortic) flow decreased by an average of about 20%. Superior mesenteric flow decreased occasionally and renal flow remained almost unchanged. Heart rate increased by an average of about 10%. An increase in carotid flow during grooming was similarly observed after cervical sympathectomy. After ganglion blockade with hexamethonium, grooming did not decrease hindquarter flow any more. These findings suggest that during grooming a substantial amount of blood flow is switched from the hindquarters to the carotid areas, to achieve a redistribution of cardiac output largely by excitation of the respective regional sympathetic and parasympathetic fibers and that sympathetic vasoconstrictor fibers supplying different vascular areas are controlled by separate pathways from separate neuron groups.