The control of aldosterone secretion

Abstract

The elucidation of complex clinical conditio involving disorder of aldosterone secretion re quires identification by animal experiment of th main mechanisms 'which control aldosteron secretion. The introductory section of this pape is concerned with the methodological basis o such animal experiments. The principle o approach adopted in the authors' laboratory ha been that of step by step surgical preparation o an animal so that the function of anatomicall deep seated, and otherwise inaccessible, struc tures can be studied in the conscious confiden animal. It is important that the process o measurement of a physiological function shoul not itself introduce uncontrolled or undesire variables. The baseline levels are found in th conscious confident animal. A sheep w-ith permanent unilateral parotid fistula and w-ith th left adrenal gland transplanted to a combine carotid artery-jugular vein skin loop in the nec represents a Xvery satisfactory preparation for experiments on aldosterone control. Using the Kliman and Peterson double isotope derivative assay for steroids, it is possible to have an accuratel record, at frequent intervals, of adrenal secretion rates without sampling causing significant blood loss, and concurrent measurement of parotid salivary Na- 'K- ratio gives a continuous record of peripheral blood aldosterone concentration w-hich, because of the short half-life of aldosterone, rapidly reflects changes of adrenal secretion rate. Difficulties in the interpretation of acute experiments involving surgical proceduresi under anaesthesia are discussed. The criteria for! categorization of an extract which is active uponl an effector organ as a hormone are considered. Some of the principal chemical and biological methods for measuring aldosterone are described! in the second section of the paper. In the third section, effects of variation of Na- and body fluid balance on aldosterone secretion are discussed. This includes a summary of experiments in this laboratory demonstrating that local concurrent reduction of Na - and increase of the K- concentrations in adrenal arterial blood causes increased aldosterone secretion. Some aspects of the evidence that there is a humoral agent other than ACTH Nwhich stimulates aldosterone secretion- discussed also. The final section of the paper binly concerned with experiments on the nce of the central nervous system on aldosecretion. Decerebration experiments in authors' laboratory indicate central nervous hence on aldosterone secretion and suggest an ant localization in the midbrain, but the its emphasize the difficulties of interpretation expriments involving acute nervous ablations. val experimental study of pinealectomized s did not provide evidence of this structure a role in the adrenal response to changes Na+ balance. Copyright © 2011 The Fellowship of Postgraduate Medicine.