Which of the following statements regarding aldosterone are true?

a. Its secretion is directly related to the serum potassium concentration

b. Angiotensin II is a more potent regulatory factor than ACTH

d. Secondary hyperaldosteronism occurs with renal artery stenosis

Aldosterone secretion is controlled by changes in the afferent arteriolar pressure in the renal cortex as well as by changes in sodium content in the renal tubule. These changes are sensed by the juxtaglomerular apparatus and by the macula densa and act through the renin angiotensin system. At least two other factors influence aldosterone secretion. Aldosterone secretion is directly related to the serum potassium concentration. An increase in serum potassium directly stimulates aldosterone production, whereas a decrease in serum potassium has the opposite effect. Because of its early point of action in the steroidogenic pathway, ACTH also increases secretion of aldosterone, although it is much less potent in this regard than in its stimulation of cortisol. The stimulatory effects of potassium and ACTH on aldosterone secretion can be overcome by angiotensin II stimulation.

Primary hyperaldosteronism is characterized by mineralocorticoid hypersecretion which promotes a positive sodium balance and hypokalemia. About 80% of patients with primary hyperaldosteronism have serum potassium levels of 3.5 mEq/L or less. Causes of secondary hyperaldosteronism are related to increased renin secretion. These include renal artery stenosis, congestive heart failure and renal salt-wasting.