What is the primary hormone that increases in response to renal artery stenosis in a young female?

• A. Renin
• B. Aldosterone
• C. Angiotensin II
• D. Antidiuretic hormone

Answer: (C)

In the context of renal artery stenosis, the primary hormone that increases is renin. Renal artery stenosis leads to a decreased blood flow to the affected kidney, which triggers a compensatory response. The juxtaglomerular cells in the kidney detect this reduction in perfusion pressure and respond by secreting renin.

Renin is an enzyme that catalyzes the conversion of angiotensinogen, produced by the liver, into angiotensin I. This is then converted into angiotensin II by the action of angiotensin-converting enzyme (ACE) primarily in the lungs. Angiotensin II has several effects, including vasoconstriction and stimulation of aldosterone release from the adrenal cortex, which promotes sodium and water retention.

Thus, while angiotensin II is critical for the physiological response to renal artery stenosis, it is the increased level of renin that signifies the primary hormonal change in response to renal artery stenosis. Consequently, renin acts as the initiator of the renin-angiotensin-aldosterone system, ultimately leading to secondary changes in other hormones, including aldosterone and angiotensin II.