Tubuloglomerular feedback (TGF) is a mechanism by which increased NaCl delivery to the macula densa DECREASES GFR. The mediator released by macula densa cells that constricts the afferent arteriole is:

• A Angiotensin II
• B Renin
• C Prostaglandin E2
• D Adenosine (via A1 receptors on the afferent arteriole) ✓

Explanation

When NaCl delivery to the macula densa is increased (high GFR or excess NaCl intake), macula densa cells increase ATP release, which is converted to adenosine in the juxtaglomerular interstitium. Adenosine acts on A1 receptors on the afferent arteriole smooth muscle, causing vasoconstriction and reducing GFR — a negative feedback loop. Renin is suppressed by the same macula densa signal (reduced renin release reduces angiotensin II, which dilates the afferent arteriole). Prostaglandins oppose TGF-mediated constriction.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.