Effect of Hepatic Portal Injection of Ouabain on the Hepato-Sympathoadrenal Reflex

Abstract

The purpose of the present investigation was to evaluate the effects of an intraportal injection of ouabain (2 mg/kg), an inhibitor of the sodium-potassium pump, on plasma catecholamine response in unrestrained normally fed rats with and without an intact hepatic vagus nerve. Three groups of rats were submitted to two injection conditions each. Hepatic vagotomized (HV) rats were randomly injected with ouabain or saline (0.9%) in the portal vein. Sham-operated rats were either injected with ouabain or saline in the portal or jugular vein. Ouabain or saline were injected at 0 min and again at 20 min. Plasma catecholamines were measured before the first injection and 15 min after each injection. Blood glucose concentrations were significantly ( p < 0.01) increased by the ouabain injection as compared with basal values and saline-injected groups. The hyperglycemic effect of ouabain was not affected by the hepatic vagotomy or the site of infusion. The injection of ouabain, either into the portal or the jugular vein and either after HV or the sham operation, resulted in a significant ( p < 0.01) increase in epinephrine levels as compared with saline-infused rats. Plasma norepinephrine levels were significantly ( p < 0.05) increased after the second intraportal injection of ouabain in both HV and sham-operated groups. However, the injection of ouabain into the jugular vein did not change the plasma norepinephrine levels. The latter observation indicates a specific action of ouabain in the liver on the sympathetic activity.