Title: Regulation of renal NaPi-2 expression and tubular phosphate reabsorption by growth hormone in the juvenile rat
Abstract: 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-Tyr 1 -d-Arg 2 ]-GRF-(1-29)-NH 2 -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.
Publication Year: 2004
Publication Date: 2004-03-09
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 34
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