The Importance of the Spleen in Blood Volume Shifts of the Systemic Vascular Bed Caused by the Carotid Sinus Baroreceptor Reflex in the Dog

To quantify the relative importance of the spleen in the carotid sinus baroreceptor reflex control of total blood volume, we studied the reflex control of systemic vascular capacity before and after removal of the spleen in 18 sodium pentobarbital-anesthetized dogs. Venous return was diverted into a reservoir while cardiac output and venous pressure were maintained constant. Intrasinus pressure was either raised or lowered between 50 and 200 mm Hg, and this mobilized blood into or out of the reservoir. Two sets of experiments were performedone in which the spleen was acutely removed and the other in which a snare ocoluder was placed around the spleen. In the first series with the spleen intact, the volume shift amounted to 8.42 ml/kg and after splenectomy the volume shift was attenuated to 5.17 ml/kg. The average difference in these responses amounted to 2.69 ml/kg. In the second series of experiments in which we repeatedly measured volume shifts with spleen intact and spleen removed, the volume shift amounted to 10.57 ml/kg with spleen intact and 8.20 ml/kg with spleen removed. The average difference amounted to 2.37 ml/kg. There was a significant increase in total systemic vascular compliance for all dogs tested in both sets of experiments from 2.15 ± 0.08 to 2.41 ± 0.12 ml/nun Hg per kg when intrasinus pressure was increased from SO to 200 mm Hg before spleen removal. After spleen removal, the compliance still increased significantly from 2.17 ± 0.12 to 2.47 ml/mm Hg per kg when intrasinus pressure was increased from 50 to 200 mm Hg. However, total systemic vascular compliance before and after spleen removal at the same intrasinus pressure showed no significant differences. We conclude that, although the spleen contributes singificantly to the blood volume mobilization, it is not the major contributor to total systemic blood volume shifts caused by carotid sinus baroreceptor reflex in dogs.