MODULE SUPPLEMENT: ENDOCRINE SYSTEM
Aldosterone

In addition to glucocorticoids, the adrenal glands produce Aldosterone which is intimately related to renal sodium regulation and fluid and electrolyte balance. Aldosterone levels decrease with age and its release in older adults is less responsive to upright posture or decreased sodium intake than in younger adults. These changes are outlined below:

• Plasma Renin activity: Decreased
• Measured aldosterone levels: Decreased
• Aldosterone release in response to low levels of sodium and postural challenge: Decreased
• Aldosterone release in response to ACTH stimulation: No apparent significant change

The major reason for the decrease in aldosterone is a decrease in the conversion of active renin to renin which thus decreases the activity of the renin-angiotensin-aldosterone system. The clinical implications of these changes are discussed in greater detail in the module on renal changes with age (see Changes in Renal Homeostatic Controls--Note: This link will open in a new browser window which you can close to return here). However, in summary, aldosterone promotes the retention of sodium in exchange for potassium and hydrogen. Thus, with lower levels of aldosterone, older adults are predisposed to losing sodium and hyponatremia.