The need for young, immature animals to maintain positive phosphate balance for growth is well recognized. However, the adaptations that occur in the kidney to facilitate this process have not been clarified. The objective is to evaluate the intrarenal regulation of phosphate reabsorption during development. Micropuncture techniques will be used to examine the nephron sites of phosphate reabsorption and their response to dietary and hormonal factors regulating phosphate homeostasis. Comparisons will be made between immature, weaned rats (3-4 weeks) and adult rats (6 months). The hypothesis to be tested is that the developing animal displays avid phosphate reabsorption due to greater participation of deep nephrons and enhanced reabsorption in distal nephron segments. Furthermore, relative hyporesponsiveness to phosphaturic stimuli also contributes to the renal retention of phosphate. Specific protocols are designed to evaluate the following parameters: a) the nephron sites of phosphate reabsorption, b) the transport capacities of superficial and deep nephron proximal tubules, c) the response of these sites to phosphaturic stimuli (high phosphate diet, PTH, calcitonin), and d) the possible restoration of responsiveness to hhosphaturic hormones (with acute phosphate infusions, diphosphonate treatment). These studies will provide important information regarding the intrarenal mechanisms involved in the adaptations for growth.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
1R01DK036111-01A1
Application #
3234432
Study Section
General Medicine B Study Section (GMB)
Project Start
1986-01-01
Project End
1988-12-31
Budget Start
1986-01-01
Budget End
1986-12-31
Support Year
1
Fiscal Year
1986
Total Cost
Indirect Cost
Name
Georgetown University
Department
Type
School of Medicine & Dentistry
DUNS #
049515844
City
Washington
State
DC
Country
United States
Zip Code
20057
Mulroney, S E; Woda, C; Haramati, A (1998) Changes in renal phosphate reabsorption in the aged rat. Proc Soc Exp Biol Med 218:62-7
Mulroney, S E; Koenig, J I; Csikos, T et al. (1996) Temporal changes in insulin-like growth factor I, c-fos, and c-jun gene expression during hyperplastic kidney growth in weanling rats. Endocrinology 137:839-45
Haramati, A; Lumpkin, M D; Mulroney, S E (1994) Early increase in pulsatile growth hormone release after unilateral nephrectomy in adult rats. Am J Physiol 266:F628-32
Mulroney, S E; Haramati, A; Werner, H et al. (1992) Altered expression of insulin-like growth factor-I (IGF-I) and IGF receptor genes after unilateral nephrectomy in immature rats. Endocrinology 130:249-56
Mulroney, S E; Lumpkin, M D; Roberts Jr, C T et al. (1992) Effect of a growth hormone-releasing factor antagonist on compensatory renal growth, insulin-like growth factor-I (IGF-I), and IGF-I receptor gene expression after unilateral nephrectomy in immature rats. Endocrinology 130:2697-702
Mulroney, S E; Lumpkin, M D; Haramati, A (1991) Suppression of growth hormone release restores phosphaturic response to PTH in immature rats. Am J Physiol 261:F1110-3
Mulroney, S E; Haramati, A (1990) Renal adaptation to changes in dietary phosphate during development. Am J Physiol 258:F1650-6
Corn, P G; Mulroney, S E; Haramati, A (1989) Restoration of a phosphaturic response to parathyroid hormone in the immature rat. Pediatr Res 26:54-7
Mulroney, S E; Lumpkin, M D; Haramati, A (1989) Antagonist to GH-releasing factor inhibits growth and renal Pi reabsorption in immature rats. Am J Physiol 257:F29-34
Lumpkin, M D; Mulroney, S E; Haramati, A (1989) Inhibition of pulsatile growth hormone (GH) secretion and somatic growth in immature rats with a synthetic GH-releasing factor antagonist. Endocrinology 124:1154-9

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