Renin secretion is stimulated by all EXCEPT:

# Renin secretion is stimulated by all EXCEPT:

A. Cardiac failure

B. Low Na+ in proximal tubule

C. Sympathetic stimulation

D. High Na+ in proximal tubule

The correct answer is D. High Na+ in proximal tubule.

Explanation: Renin secretion, primarily by the juxtaglomerular cells in the kidneys, is stimulated by factors that signal a need to increase blood pressure or sodium retention. These include:

A. Cardiac failure: Reduced cardiac output lowers renal perfusion, stimulating renin release to activate the renin-angiotensin-aldosterone system (RAAS) to restore blood pressure.

B. Low Na+ in proximal tubule: Detected by the macula densa, low sodium levels signal reduced filtrate delivery, triggering renin secretion to promote sodium reabsorption and increase blood volume.

C. Sympathetic stimulation: Activation of the sympathetic nervous system, via beta-adrenergic receptors, directly stimulates renin release to address stress or low blood pressure.

D. High Na+ in proximal tubule, however, does not stimulate renin secretion. High sodium levels in the proximal tubule (or at the macula densa in the distal tubule) typically indicate adequate or excessive sodium delivery, suppressing renin release as there is no need to activate RAAS.