Reabsorption of betaine in Henle's loops of rat kidney in vivo

Abstract

This study was designed 1) to localize and 2) to characterize betaine reabsorption from the tubular lumen in rat kidney in vivo, and 3) to test whether reabsorption is modulated by the diuretic state. [(14)C]betaine (+ [(3)H]inulin) was microperfused through the proximal convoluted tubule (PCT) and microinfused into late proximal (LP) and early distal (ED) tubules, long loops of Henle (LLH), and vasa recta of the rat in vivo et situ, and the fractional recovery of the (14)C label was determined end proximally (PCT) and in the final urine, respectively. [(14)C]betaine was not reabsorbed during ED microinfusion, whereas fractional reabsorption during LP microinfusion was 82% at 0.06 mM betaine and decreased gradually to 4.8% at 60 mM. L-Proline had lower Michaelis-Menten constant (K(m)) and sarcosine a higher K(m) than betaine. Chronic, but not acute, diuresis inhibited betaine reabsorption in Henle's loops. Fractional [(14)C]betaine reabsorption in PCT was much smaller than that during LP microinfusion. [(14)C]betaine (7.28 mM) microinfused 1) into LLH was reabsorbed to 30% and 2) into vasa recta appeared in the ipsilateral urine to a much higher extent than contralaterally. In both cases, no saturation was detected at 70 mM. We conclude that betaine is reabsorbed by mediated transport from descending limbs of short Henle's loops by a proline-preferring carrier in a diuresis-modulated manner. In the deep medulla, bidirectional blood/urine betaine transport exists.

Biodistribution and Radiation Dosimetry of Deuterium-Substituted 18F-Fluoromethyl-[1, 2-2H4]Choline in Healthy Volunteers

“…2) suggest incomplete tubular reabsorption of the parent tracer, similar to that seen with 18 F-FCH (9). This is in contrast to the efficient tubular reabsorption of the nature-identical 11 C-betaine (37).…”

[18F]Fluoromethyl-[1,2-2H4]-Choline: A Novel Radiotracer for Imaging Choline Metabolism in Tumors by Positron Emission Tomography

“…Urine levels of choline analogues result largely from unmetabolized parent radiotracer (data not shown), as betaine analogues are efficiently reabsorbed in the kidney tubules (44,45). Due to their ionization properties, oxidation intermediates (such as aldehyde) are unlikely to be reabsorbed efficiently within the kidney tubules and could contribute to urinary radioactivity (45). It was a concern that the high stability of D4-FCH, and hence higher levels of parent radiotracer in plasma, will lead to high levels of radioactivity in the urine.…”

High sodium chloride intake decreases betaine-homocysteineS-methyltransferase expression in guinea pig liver and kidney

“…They had free access to tap water and standard chow during a 5-day acclimation period, after which the animals weighed an average of 401 g and were randomized into two treatment groups (n ϭ 5). The experimental treatments were free access to either tap water (control) or NaCl (500 mM)-containing tap water, similar to hyperosmotic protocols used for rats (1,22). Water consumption was recorded daily.…”