Effects of circulating catecholamines on hepatic blood volume in anesthetized cats

Arterial and portal norepinephrine and epinephrine levels, and hepatic blood volumes were measured in cats anesthetized with pentobarbital sodium to determine the basal levels after surgery and adrenalectomy in comparison with levels during intravenous infusions of norepinephrine and epinephrine that produced hepatic venoconstriction. In addition, the hypothesis that norepinephrine released into portal blood during mesenteric nerve stimulation might produce hepatic venous responses was tested. No epinephrine was detected in any plasma samples except during intravenous epinephrine infusions. Surgery did not increase, and adrenalectomy did not decrease, the basal norepinephrine levels measured after anesthesia (0.8 +/- 0.1 ng/ml). These basal levels were below the minimal levels required to produce hepatic venous responses. Equal plasma levels of norepinephrine and epinephrine produced similar hepatic venous responses and maximal responses required increases in plasma levels of 100 times the basal levels. Stimulation of mesenteric nerves at 2 Hz produced no change in portal norepinephrine levels, whereas at 8 Hz it produced a doubling of these levels. No significant changes in hepatic volume occurred. It is concluded that although basal levels of circulating catecholamines may reflect overall sympathetic nervous activity, they are not high enough to produce hepatic venous responses. Sympathetic control of the hepatic venous bed is mediated through the hepatic innervation, and circulating catecholamines play at most a minor role.