THE ROLE OF CIRCULATING FLUID VOLUME AND RELATED PHYSIOLOGICAL PARAMETERS IN THE CONTROL OF ALDOSTERONE SECRETION.

Summary In an investigation of the role of circulating fluid volume in the control of aldosterone secretion in sodium deficient sheep with cervical adrenal autotransplants, measurements of adrenal secretion of cortisol, corticosterone and aldosterone, I 131 gamma globulin space, plasma sodium and potassium concentrations and adrenal blood flow were made under the following circumstances:‐ A. When the estimated sodium deficit was replaced by the intravenous infusion of sodium solution (i) as 4M ‐NaCl, (ii) as isotonic Ringer type solution, B. When plasma volume was increased without substantial alteration of sodium status by the intravenous infusion of plasma volume expanders, using (i) 25% sheep albumin and (ii) 6% dextran in normal saline. These procedures produced concurrent variation in other parameters of known importance in aldosterone control, including plasma sodium and potassium concentrations, and therefore the relationship between plasma volume and aldosterone secretion rate was assesed by a system of multivariate analysis. Plasma volume was found to be inversely related to aldosterone secretion rate both during established sodium deficiency and during the subsequent intravenous infusion in 6% dextran in normal saline, but no such relationship could be established for the experiments in groups A or B (i). Even in the expertmental groups where the relationship was significant, the derived regression equations indicated that any causal roll of plasma volume in the regulation of aldosterone secretion was relatively minor. Results from experiments of the types A and B above did not suggest the existence of a simple relationship between aldosterone secretion and the observed changes in systolic, diastolic mean arterial or pulse pressures.