Reflex sympathetic effects on liver vascular space and liver perfusion in dogs

The effects of sympathetic fiber activation on liver vascular volume and on the perfusion of the liver were ascertained in dogs by use of the multiple indicator-dilution technique. Portal vein-hepatic vein dilution patterns were obtained following injection of a mixture containing 51Cr-labeled red blood cells (a vascular reference), 14C-labeled sucrose (an interstitial reference), and 3H-labeled water (a cellular reference). Liver vascular, interstitial, and cellular water spaces were measured from the dilution data under control conditions and following activation of the sympathetic system by bilateral occlusion of carotid arteries. Carotid occlusion significantly increased plasma norepinephrine values without changing plasma epinephrine concentration, indicating that the resulting reflex sympathetic activation was selective for peripheral fibers. Although average blood flow did not change, liver vascular volume decreased by 40% during the sympathetic activation, and sucrose interstitial space and accessible cellular water space were unchanged. These findings indicate that there were no areas of no flow in the liver during the sympathetic activation, despite the observed large diminution in vascular blood content.