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This Article Full Text Full Text (PDF) All Versions of this Article: 287/1/F117    most recent 00357.2002v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Woda, C. B. Articles by Mulroney, S. E. Search for Related Content PubMed PubMed Citation Articles by Woda, C. B. Articles by Mulroney, S. E.

Regulation of renal NaPi-2 expression and tubular phosphate reabsorption by growth hormone in the juvenile rat

¹Department of Physiology and Biophysics, Georgetown University School of Medicine, Washington, District of Columbia 20057; and ²Division of Renal Diseases and Hypertension, Departments of Medicine, Physiology, and Biophysics, University of Colorado Health Sciences Center, Denver, Colorado 80262

Submitted 20 February 2002 ; accepted in final form 29 February 2004

Growth hormone (GH) is an important factor in the developmental adaptation to enhance P_i reabsorption; however, the nephron sites and mechanisms by which GH regulates renal P_i uptake remain unclear and are the focus of the present study. Micropuncture experiments were performed after acute thyroparathyroidectomy in the presence and absence of parathyroid hormone (PTH) in adult (14- to 17-wk old), juvenile (4-wk old), and GH-suppressed juvenile male rats. While the phosphaturic effect of PTH was blunted in the juvenile rat compared with the adult, suppression of GH in the juvenile restored fractional P_i excretion to adult levels. In the presence or absence of PTH, GH suppression in the juvenile rat caused a significant increase in the fractional P_i delivery to the late proximal convoluted (PCT) and early distal tubule, so that delivery was not different from that in adults. These data were confirmed by P_i uptake studies into brush-border membrane (BBM) vesicles. Immunofluorescence studies indicate increased BBM type IIa NaP_i cotransporter (NaPi-2) expression in the juvenile compared with adult rat, and GH suppression reduced NaPi-2 expression to levels observed in the adult. GH replacement in the [N-acetyl-Tyr¹-D-Arg²]-GRF-(1-29)-NH₂-treated juveniles restored high NaPi-2 expression and P_i uptake. Together, these novel results demonstrate that the presence of GH in the juvenile animal is crucial for the early developmental upregulation of BBM NaPi-2 and, most importantly, describe the enhanced P_i reabsorption along the PCT and proximal straight nephron segments in the juvenile rat.

development; sodium-phosphate cotransporters; parathyroid hormone; antagonist to growth hormone-releasing factor; brush-border membrane vesicles

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