Cation Shifts and Blood Pressure Regulation in the Dog

Abstract

Dynamic transfers of sodium, potassium and water into and out of the extracellular space were studied in 13 dogs during induced changes in blood pressure. The inulin space, measured after a 2-hour equilibration period in the bilaterally nephrectomized animal, served as reference standard for the extracellular fluid. Infusions of norepinephrine, Pitressin and angiotonin were used as pressor, Isuprel and carbachol as depressor agents. In all instances, sodium, with variable amounts of water, moved out of the extracellular space during a rise in blood pressure and reversed during a fall. In general, potassium, in lesser bulk, moved inversely to sodium although it was more variable in degree and, in the case of angiotonin, did not change at all. These results accord with the theory that blood pressure regulation depends, inter alia, on the sodium transfer mechanisms.