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Cation and water shifts in response to pressor agents in the conscious dog Warren, James Darcy


The hallmark of essential hypertension is a persistent elevation of blood pressure. Certain changes are associated with the state of hypertension including a derangement of water and electrolytes. Recent work indicates the upset in sodium and water may be causally related to the hypertension. Transitary, acute hypertension may be produced by means of drugs. The drug induced blood pressure rise is accompanied by a disturbance in water and electrolytes. Further work is required to clarify the relationship between shifts in electrolytes and agents that may increase blood pressure (pressor agents). In order to carry out the programme of research on pressor agents it was necessary to review the fundamental tool, namely the accurate measurement of shifts in water. This review led to a refinement in the technique of measuring water by infusing inulin continuously. With nephrectomized animals the inulin dilution technique is a satisfactory method to measure the extracellular space. An equally accurate index of the extracellular space can be provided with an inulin infusion which maintains the extracellular inulin concentration at a constant level. In the present study the cation and water shifts between cells and the extracellular space associated with two dissimilar pressor agents were observed, using trained, conscious dogs. The pressor agents used were norepinephrine, elaborated by the adrenal medulla and pitressin, elaborated by the posterior pituitary gland. Norepinephrine had no effect, in our hands, on sodium, potassium or water movement. Pitressin had distinct effects, with rapid depression of the extracellular volume and the extracellular sodium concentration, and elevation of the extracellular potassium concentration. The changes caused by pitressin were associated with a pressor response.

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