THE UPTAKE OF NORADRENALINE BY TISSUES AFTER THE CONTINUOUS INFUSION TO RABBIT

Abstract

The uptake of norepinephrine by tissues was assayed biochemically in the unanesthetized rabbit which had received the continuous infusion of norepinephrine. The infusion of 0.5 [mu]g/kg/min of norepinephrine increased the norepinephrine content in the brain stem, atria, spleen, and of epinphrine in the adrenal glands. The only tissue which did not increase the content of norepinephrine was the brain cortex. The increase in the amine content reached a plateau by the infusion for 30 minutes in the adrenals and by the infusion for 1 hour in the brain stem and the atria. In the spleen the amine content continued to increase until a tendency to decline was observed by the infusion for 3 hours. Two hours after the termination of the infusion of 2 [mu]g/kg/min of norepinephrine the increased amine content in the brain stem, atria and ventricles showed a tendency to decrease to the control level, but the content in the brain cortex and the adrenals remained to increase with 3 hours after the infusion. The increased amine content in the spleen declined below the control level 1 hour after the infusion, but then the content of the amine re-increased for next 2 hours. These results indicate that the tissues take up the infused norepinephrine considerably until the storage sites of it are saturated. The delayed increased of norepinephrine content in the spleen suggests that the spleen may serve to regulate the concentration of the circulating amine, while the very slight fluctuations in the uptake and recovery of the amine in the adrenals may indicate the slow exchange of adrenal catecholamine between the extracellular sites and the storage granules.