Dietary casein promotes a progressive decline in the glomerular filtration rate (GFR) of remnant kidneys associated with metabolic acidosis and an endothelin-mediated increase in renal acidification. We tested whether diets that affect the acid-base status contributes to the decline of GFR through endothelin receptors in rats with a remnant kidney. Rats on a casein diet had metabolic acidosis at baseline and developed a progressive decline in GFR after renal mass reduction. Dietary sodium bicarbonate but not sodium chloride ameliorated metabolic acidosis and prevented the decrease in GFR but only after the sodium bicarbonate-induced increase in blood pressure was treated. Dietary soy protein did not induce baseline metabolic acidosis and rats with remnant kidney on a soy diet had no decrease in their GFR. By contrast, rats with a remnant kidney on soy protein given dietary acid developed metabolic acidosis and a decreased GFR. This decline in GFR was prevented in either case by endothelin A but not endothelin A/B receptor antagonism. Our study suggests that the casein-induced decline in GFR of the remnant kidney is mediated by metabolic acidosis through endothelin A receptors.

Abstract. The hypothesis that increased dietary protein augments distal nephron acidification and does so through an endothelin (ET-1)-dependent mechanism was tested. Munich-Wistar rats that ate minimum electrolyte diets of 50% (HiPro) and 20% (CON) casein-provided protein, the latter comparable to standard diet, were compared. HiPro versus CON had higher distal nephron net HCO 3 reabsorption by in vivo microperfusion (37.8 Ϯ 3.2 versus 16.6 Ϯ 1.5 pmol/mm per min; P Ͻ 0.001) as a result of higher H ϩ secretion (41.3 Ϯ 4.0 versus 23.0 Ϯ 2.1 pmol/mm per min; P Ͻ 0.002) and lower HCO 3 secretion (Ϫ3.5 Ϯ 0.4 versus Ϫ6.4 Ϯ 0.8 pmol/mm per min; P Ͻ 0.001). Perfusion with H ϩ inhibitors support that increased H ϩ secretion was mediated by augmented Na ϩ /H ϩ exchange and H ϩ -ATPase activity without augmented H ϩ ,K ϩ -ATPase activity. HiPro versus CON had higher levels of urine ET-1 excretion, renal cortical ET-1 addition to microdialysate in vivo, and renal cortical ET-1 mRNA, consistent with increased renal ET-1 production. Oral bosentan, an ET A/B receptor antagonist, decreased distal nephron net HCO 3 reabsorption (22.4 Ϯ 1.9 versus 37.8 Ϯ 3.2 pmol/mm per min; P Ͻ 0.001) as a result of lower H ϩ secretion (28.4 Ϯ 2.4 versus 41.3 Ϯ 4.0 pmol/mm per min; P Ͻ 0.016) and higher HCO 3 secretion (Ϫ6.0 Ϯ 0.7 versus Ϫ3.5 Ϯ 0.4 pmol/mm per min; P Ͻ 0.006). The H ϩ inhibitors had no additional effect in HiPro ingesting bosentan, supporting that ET mediated the increased distal nephron Na ϩ /H ϩ exchange and H ϩ -ATPase activity in HiPro. Increased dietary protein augments distal nephron acidification that is mediated through an ET-sensitive increase in Na ϩ /H ϩ exchange and H ϩ -ATPase activity.The routine acid challenges to systemic acid-base status faced by humans are modest compared with the large acid loads administered to animals in most experimental protocols. 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).In contrast with the acid-producing mineral salts that are most commonly used to induce an acid challenge in experimental protocols, increased intake of dietary protein that contains acid-producing amino acids constitutes the acid challenge that humans more routinely face. 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 ...

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to June 30, 2004, were reviewed and data were collected. Results: 486 infants of 30-33 weeks gestation had screening cranial US performed. IVH occurred in 22 of 486 (4.5%). Of the 22 infants, 4 infants had significant IVH (grade III and/or grade IV). Of the 4 infants with significant IVH, 2 were 30 weeks and 2 were 31 weeks gestation. All 4 infants had either significant risk factors for brain injury (abruption, asphyxia) or clinical symptoms (seizures) that would warrant US during their hospital course. Of the 486 infants who had US, 5 additional infants (1%) had PVL, and 2 of these 5 had risk factors (abruption, shock) that warranted obtaining a sonogram. There was a statistically significant trend towards fewer abnormal sonograms from 33 weeks to 30 weeks gestation (p = .04).