Cationic Shifts and Blood Pressure Regulation

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Abstract
The effects of Pitressin and norepinephrine on movements of sodium, potassium, and water into and out of the intracellular compartment were measured in bilaterally nephrectomized rats using inulin as a measure of extracellular fluid volume. Observations were made from 0.5 to 7 min. following injection of the test substances. Pitressin causes a movement of sodium and water into cells and the extrusion of potassium during the pressor plase of its action. These effects were observed at 0.75 and 1.5 min. after the injection of 30 or 60 mU. The reverse movements were observed during the subsequent return of the blood pressure towards normal. A secondary shift of sodium into cells was observed at 5 min. Norepinephrine caused similar shifts in sodium, water, and potassium in relation to its blood pressure effects. These were more rapid in onset than those induced by Pitressin. Our operational theory is that the regulation of the blood pressure depends, inter alia, on the "sodium transfer systems" broadly defined, which govern the rate of entrance and extrusion of sodium, water and potassium in smooth muscle cells.