What is the mechanism of localization for Tc mertiatide (MAG-3)?

• A. Filtration
• B. Reabsorption
• C. Secretion
• D. Diffusion

Answer: (C)

The mechanism of localization for Tc mertiatide (MAG-3) is secretion. MAG-3 is a radiopharmaceutical used in renal imaging that is specifically designed to evaluate kidney function and perfusion. When administered, MAG-3 is handled by the kidneys similarly to endogenous substances like para-aminohippuric acid (PAH). It is secreted by the renal tubular cells, particularly in the proximal tubules. This secretion process allows MAG-3 to be concentrated in the renal system, reflecting renal blood flow and tubular function.

In contrast, the other potential mechanisms listed—filtration, reabsorption, and diffusion—do not apply to how Tc mertiatide operates within the kidneys. Filtration refers to the process where substances are filtered from the blood into the urine at the glomerulus, which is not the primary action for MAG-3. Reabsorption would involve substances being reabsorbed back into the bloodstream after filtration, which relates to filtration but again does not characterize MAG-3's behavior. Diffusion involves passive movement across cell membranes and does not adequately describe the active transport mechanisms utilized by MAG-3 within the nephron. Therefore, secretion is the accurate mechanism of localization for Tc mertiatide in renal imaging