UBC Theses and Dissertations
The role of vasopressin in the diuretic response to left atrial distension Mason, James Melvin
The concept that the renal excretion of water and electrolytes is partly governed by the volume in some fluid compartment of the body is one which has received some experimental verification. Attempts to define a mechanism sensitive to changes in some fluid compartment of the body have provided support both for and against the theory that stimulation of sensory nerve endings in the intrathoracic circulation sets up afferent impulses in the vagus nerves which diminish the release of antidiuretic hormone from the neurohypophysis and so cause diuresis. Evidence which supports the theory comes from experiments in which atrial distension has been associated with a reduction of antidiuretic activity in the circulating blood. Evidence which does not support the theory comes from experiments in which the diuretic response to left atrial distension has been demonstrated during infusion of vasopressin at rates adequate to completely inhibit water diuresis in conscious dogs (0.025 m-u./kg./min.). A series of experiments has been carried out in an attempt to define the role of antidiuretic hormone in the diuretic response to left atrial distension. In one series, experiments were designed to test the effects of different doses of vasopressin upon the diuretic response to left atrial distension. The results of this series showed that the diuretic response to left atrial distension was composed of an increase in solute excretion and an increase in water excretion. At a rate of infusion of vasopressin of 0.4 m-u./kg./min. or above the increase in water excretion was abolished while the increase in solute excretion was unaffected. In another series, experiments were designed to test the renal response to large changes in vasopressin concentration. The concentrations of vasopressin used (0.4 m-u./kg./min. and 0.04 m-u./kg./min.) completely inhibited water diuresis in conscious dogs. The results of this series indicated that in the hydrated anaesthetized dog, a change from the high concentration of vasopressin to the lower concentration may cause a transient dilute diuresis. These results support the view that a decrease in the circulating concentration of antidiuretic hormone is one mechanism which may produce a diuretic response to left atrial distension. The results will be reported in a condensed form (Mason and Ledsome, 1971; Ledsome and Mason, 1971).
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