Endogenous endothelins mediate increased distal tubule acidification induced by dietary acid in rats.

Abstract

We examined if endogenous endothelins mediate the decreased HCO 3

Endothelin-Induced Increased Nitric Oxide Mediates Augmented Distal Nephron Acidification as a Result of Dietary Protein

“…Increased intake of dietary protein that is composed of acidproducing amino acids such as casein increases metabolic acid production and leads to increased renal acid excretion (18) that is mediated by augmented distal nephron acidification (1,2,19 (24). Our previous investigations as to the mechanism(s) for HiPro-induced augmented distal nephron acidification revealed augmented distal nephron H ϩ secretion that is due to endothelin-stimulated increased Na ϩ /H ϩ exchange and increased H ϩ -ATPase activity (1,2), the latter as a result of endothelin-stimulated increased aldosterone activity (2).…”

“…[ET-1] in urine was measured using a RIA kit (Peninsula Laboratories, Inc., Belmont, CA) after disposable column extraction (Sep-Pak C18, Milford, MA) preconditioned with methanol, H 2 O, and acetic acid as described (15) and as done previously (16).…”

Increased Endothelin Activity Mediates Augmented Distal Nephron Acidification Induced by Dietary Protein

“…Each reaction contained 2 l of cDNA from the conventional PCR, 3 mM MgCl 2 , 0.5 mM of each primer, and 1ϫ of FastStart DNA Master SYBR Green I mix (Roche) in a 20-l final volume. Samples were then placed in the LightCycler instrument in duplicate and underwent the following thermal cycling profile: cDNA was denatured by a preincubation of 30 s at 95°C, and the template was amplified for 35 cycles of (1) denaturation for 0 s at 95°C, (2) annealing at 48°C for 10 s, and (3) extension at 72°C for 25 s. The increase in fluorescence, dependent on the initial template concentration, was acquired after each extension phase at 83°C, a temperature above the Tm of the primer dimers and below the Tm of the specific PCR product, thus minimizing acquisition of nonspecific fluorescence intensities. After amplification, a melting curve was generated by cooling the samples to 55°C for 30 s and slowly heating the samples at 0.1°C/s to 95°C while the fluorescence was measured continuously.…”

“…Intake of acid-producing amino acids increases systemic acid production and urine net acid excretion (6), but its effect on distal nephron acidification or its hormonal and/or transport mediators are not known. Recognizing that ET mediate increased distal nephron acidification induced by modest dietary acid loads as a result of intake of acid-producing mineral salts (1,2), the present studies tested the hypothesis that increased intake of acid-producing amino acids as dietary protein increases distal nephron acidification and that this increased acidification is mediated by enhanced ET activity.…”

“…Augmented distal rather than proximal nephron acidification is the predominant renal regulatory response in experimental animals to modest dietary acid loads induced by acid-producing mineral salts (1,2). Augmented distal nephron acidification induced by dietary acid is mediated by multiple mechanisms, including (1) increased net HCO 3 reabsorption (3), consistent with increased H ϩ secretion; (2) reduced HCO 3 delivery to the terminal distal nephron (4) that facilitates NH 4 ϩ secretion (5) and permits secreted H ϩ to effect acid excretion rather than HCO 3 reclamation; and (3) decreased distal nephron HCO 3 secretion (1) mediated by endogenous endothelins (ET) (2).…”