Pathogenesis
Aldosterone enhances exchange of sodium for potassium in the kidney, so increased aldosteronism will lead to hypernatremia (elevated sodium level) and hypokalemia (low blood potassium). Once the potassium has been significantly reduced by aldosterone, a sodium/hydrogen pump in the nephron becomes more active, leading to increased excretion of hydrogen ions and further exacerbating the elevated sodium level resulting in a further increase in hypernatremia. The hydrogen ions exchanged for sodium are generated by carbonic anhydrase in the renal tubule epithelium, causing increased production of bicarbonate. The increased bicarbonate and the excreted hydrogen combine to generate a metabolic alkalosis.
The high pH of the blood makes calcium less available to the tissues and causes symptoms of hypocalcemia (low calcium levels).
The sodium retention leads to plasma volume expansion and elevated blood pressure. The increased blood pressure will lead to an increased glomerular filtration rate and cause a decrease in renin release from the granular cells of the juxtaglomerular apparatus in the kidney. If a patient is thought to suffer from primary hyperaldosteronism, the aldosterone:renin activity ratio is used to assess this. The decreased renin levels and in turn the reactive down-regulation of angiotensin II are thought to be unable to down-regulate the constitutively formed aldosterone, thus leading to an elevated ratio (lending the assay to be a clinical tool for diagnostic purposes).
Aside from hypertension, other manifesting problems include myalgias, weakness, and chronic headaches. The muscle cramps are due to neuron hyperexcitability seen in the setting of hypocalcemia, muscle weakness secondary to hypoexcitability of skeletal muscles in the setting of low blood potassium (hypokalemia), and headaches which are thought to be due to both electrolyte imbalance (hypokalemia) and hypertension.
Secondary hyperaldosteronism is often related to decreased cardiac output, which is associated with elevated renin levels.
Read more about this topic: Conn's Syndrome