Tubular handling of Pi in young growing and adult rats

Caverzasio, Joseph; Bonjour, J.-P.; Fleisch, H.

doi:10.1152/ajprenal.1982.242.6.f705

Cited by 24 publications

(16 citation statements)

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“…The maximal transport was not reached in the basal state, as was indicated by the increase in Pi QR/GFR after the Pi load. In agreement with the reports of Caverzasio et al (4) and Karlen (5) on 2-mo-old rats, the plasma Pi of early weaned 21-d-old rats fed an LPD was higher than that of adult rats, although it was lower than that of control rats of the same age. Pi depletion, which is accompanied by the release of calcium and Pi from bone, may explain the maintained phosphatemia (25).…”

Section: Animalssupporting

confidence: 93%

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Effects of an Early Weaning on Phosphate Transport Maturation in the Rat Kidney: Influence of the Phosphate Content of the Diet

et al. 1992

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ABSTRACT. The renal phosphate (Pi) transport system matures during the 3rd postnatal wk in the rat by an increase in the carrier affinity for sodium-cotransported phosphate. This study examines the ability of pups to adapt their renal Pi transport to the dietary phosphorus content during this period of carrier affinity maturation, corresponding to the weaning period in the rat. Clearance experiments and brush border membrane studies were performed on 21-d-old rats weaned early on d 16 onto a low phosphate diet (LPD, 0.19 g/100 g), a normal phosphate diet (control, 0.78 g/100 g), or a high phosphate diet (HPD, 1.5 g/100 g). In LPD rats, the Pi fractional excretion (0.3 f 0.1%) was lower than in controls (18 f 3%, p < 0.001). It remained very low (0.21 f 0.05% in LPD rats versus 40.5 2 6.3% in controls, p < 0.001) after Pi perfusion (1.5 pmol.min-'. 100 g-') and the reabsorbed Pi per min, corrected for the glomerular filtration rate. was higher than in the two othergroups. The calcium fractional excretion (12.6 2 1.02%) in the LPD rats was much higher than in the controls (0.42 2 0.2%, p < 0.001). In contrast, HPD rats had an elevated Pi fractional excretion (41 f 4%, p < 0.001), whereas reabsorbed phosphate per min corrected for the glomerular filtration rate was not increased by a Pi load. The membrane vesicles from 21-dold LPD rats had a higher V,,, (1 1 466 2 1 840 pmol. mg protein-'.I0 s-') than the controls (7 019 f 1 112 pmol. mg protein-'. 10 s-', p < 0.01), whereas those from HPD rats had a lower V,,, (5 161 2 956,p < 0.01). The apparent Km values were unchanged. The LPD rats had high plasma calcium levels. The parathyroid hormone level was depressed by this hypercalcemia 121.97 2 1.9 pg/mL (2.31 f 0.2 pmol/L) in LPD and 38.54 f 2.01 pg/mL (4.05 2 0.21 pmol/L) in normal Pi diet rats, n = 8, p < 0.001j. This plus their LPD explains the lower Pi fractional excretion of these rats and the low Pi V,,, in their brush border membrane. The plasma parathyroid hormonal level of HPD rats was normal (35.07 f 2.23 pg/mL (3.69 f 0.23 pmol/L), n = 81. We conclude that the young 3-wk-old rat can adapt its renal Pi transport capacity to the dietary phosphorus content during the weaning period by varying the number of functional units of the sodium Pi cotransporter or by increasing its turnover rate. Changing the Pi content of the diet induces no apparent change in Pi transport maturation during this period, as there was no change in the carrier affinity. (Pediatr Res 32: 704-709, 1992)

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Section: Animalssupporting

confidence: 93%

“…PiR also increases brush border enzymes over the homogenate activity (Table 4). when growing weaned rats are placed on an LPD (4,5). As in This indicates that the quality of the membrane preparations the adult, the response to change in Pi diet persists when the was not different.…”

Section: Animalsmentioning

confidence: 96%

Effects of an Early Weaning on Phosphate Transport Maturation in the Rat Kidney: Influence of the Phosphate Content of the Diet

et al. 1992

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“…Fractional reabsorption of phosphate is higher in infants than in older children (II). Maximal tubular reabsorption of phosphate per volume glomerular filtration rate is higher in neonatal rats than in adult rats, a difference that persists after thyroparathyroidectomy (12)(13)(14). There is also direct evidence that the higher rate of phosphate reabsorption by the neonate is due in part to a higher intrinsic rate of phosphate reabsorption by the neonatal kidney (15,16).…”

mentioning

confidence: 99%

Maturational Effects of Glucocorticoids on Neonatal Brush-Border Membrane Phosphate Transport

1994

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ABSTRACf. Previous studies have implicated glucocorticoids as an important factor in the postnatal maturational increase in proximal tubule volume absorption, Na+[H+ antiporter, Na(HC0 3)3 symporter, and Na"-K+-ATPase activity. The present study examined whether glucocorticoids are also a potentially important factor in the maturational decrease in proximal tubule phosphate transport. Renal BBMs were prepared from neonatal rabbits who received dexamethasone (10 j.lgJI00 g body weight) or vehicle. Brush-border membrane vesicles from dexamethasone-treated neonates had a lower rate of Na-phosphate cotransport than controls (50.8 ± 3.6 versus 29.2 ± 2.6 pmol 32PJI0 s[mg protein, p < 0.001). This decrease was due to a decrease in the Vmax with no change in the affinity of the transporter for phosphate. The dexamethasoneinduced decrease in BBM Na-phosphate transport was not due to a reduction in transporters as assayed by phosphateprotectable Na-dependent equilibrium binding of phosphonoformic acid. Dexamethasone treatment caused an increase in the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene and trimethylammonium-l,6-diphenyl-1,3,5-hexatriene (i.e. a decrease in membrane fluidity). Brush-border membranes from dexamethasone-treated neonates had a decrease in sphingomyelin and an increase in phosphatidylcholine and phosphatidylinositol content but no change in cholesterol or total phospholipid content. These data are consistent with glucocorticoids playing a role in the postnatal maturational decrease in proximal tubule phosphate transport by altering membrane characteristics. (Pediatr RfS 35: 474-478,1994) Abbreviations BBM, brush-border membrane DPH, 1,6-diphenyl-l,3,5-hexatriene TMA, trimethylammonium PFA, phosphonoformic acid BLM, basolateral membrane PI, phosphate imal tubule is due, in part, to a lower rate of glucose transport (2-4) and bicarbonate transport (2,3) by the immature segment. The rate of apical sodium-glucose cotransport (4), Na"IH+ antiporter activity (5-7) and H+-ATPase activity (6), and basolateral Na+-K+-ATPase (I, 8-10) and Na(HC0 3 h symporter (5) activity are all significantly less than that in the mature proximal tubule.Substantial evidence exists that unlike the proximal tubule transport processes described above, renal phosphate transport is higher in neonates than adult animals. Fractional reabsorption of phosphate is higher in infants than in older children (II). Maximal tubular reabsorption of phosphate per volume glomerular filtration rate is higher in neonatal rats than in adult rats, a difference that persists after thyroparathyroidectomy (12-14). There is also direct evidence that the higher rate of phosphate reabsorption by the neonate is due in part to a higher intrinsic rate of phosphate reabsorption by the neonatal kidney (15, 16). Neonatal guinea pig kidneys perfused in vitro had a higher maximal tubular reabsorption of phosphate per glomerular filtration rate than adult kidneys (15). In addition, neonatal guinea pig BBM vesicles had a higher Vrna. for phosphate...

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“…This was seen in rats that received parathyroidectomy indicating that an altered response to parathyroid hormone was not the factor that caused the disparity in renal phosphate uptake [143]. Finally both young and adult rats responded to a low-phosphate diet with an increase in the fractional reabsorption of phosphate; the magnitude of phosphate absorption was again higher in young animals than adults [143].…”

Section: à2mentioning

confidence: 96%

“…Animal studies demonstrated that young rats had a greater rate of phosphate reabsorption than adults [143]. This was seen in rats that received parathyroidectomy indicating that an altered response to parathyroid hormone was not the factor that caused the disparity in renal phosphate uptake [143].…”

Section: à2mentioning

confidence: 99%

Renal Tubular Development

Baum

2014

Pediatric Nephrology

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The nephron is faced with the enormous task of maintaining a constant composition and volume of the extracellular fluid. The amount of electrolytes and water ingested and absorbed must be eliminated, and the waste products from metabolism must also be excreted. This challenge is all the more complex as our dietary intake is quite variable from day to day. Despite this variable intake, there is virtually no change in the volume or composition of the extracellular fluid volume from day to day.There are two possible ways that our kidney could balance ingestion and excretion. The kidney could be a secretory organ where all the excess solutes and water ingested would be excreted by tubular secretion. This would be very inefficient and require an enormous amount of energy. In addition, in times of a disturbance in the extracellular fluid volume such as a high salt intake or volume loss from diarrhea, the regulatory systems necessary to maintain a constant extracellular fluid volume and composition while excreting waste products would be very complex. On the other hand, the kidney could filter an enormous quantity of extracellular fluid, which would be very efficient in removing waste products, and reclaim the desired salt, organic solutes, and water. With volume depletion, a greater fraction of salt and water could be reabsorbed, and when one has a dietary indiscretion such as the salt intake from a pepperoni pizza, there could be a reduction in sodium reabsorption leading to an increase in excretion to bring us back into balance. The mammalian kidney actually uses both mechanisms to perform its job which is necessary for our survival on land. The adult kidney filters~150 l of isotonic fluid a day and reclaims most of it, leaving the waste produces to be excreted in about 1.5 l of urine. In addition, there are secretory processes for solutes such as organic anions and cations in the proximal tubule and secretory mechanisms to excrete the excess acid generated from metabolism in the distal nephron which aid in maintaining homeostasis.To accomplish the remarkable task of reclamation of the necessary solutes and water to maintain a constant composition of the extracellular fluid volume, the mammalian kidney has evolved into a highly specialized organ with thousands of units called nephrons. Each human kidney has approximately one million nephrons. Each nephron is a tube consisting of epithelial cells and is divided into 12 specialized segments as shown in Fig. 1. The epithelial cells allow for the vectorial transport of solutes. The proximal tubule is responsible for the bulk reclamation of solutes and water and for the secretion of organic cations and anions. Approximately two-thirds of the glomerular filtrate is reabsorbed by the proximal tubule in an isotonic fashion. Virtually all of the organic solutes, as well as the majority of bicarbonate, phosphate, and chloride, are reabsorbed in this segment. The proximal tubule is divided into S 1 , S 2 , and S 3 segments based on the rates of transport of some solutes and mor...

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Tubular handling of Pi in young growing and adult rats

Cited by 24 publications

References 0 publications

Effects of an Early Weaning on Phosphate Transport Maturation in the Rat Kidney: Influence of the Phosphate Content of the Diet

Effects of an Early Weaning on Phosphate Transport Maturation in the Rat Kidney: Influence of the Phosphate Content of the Diet

Maturational Effects of Glucocorticoids on Neonatal Brush-Border Membrane Phosphate Transport

Renal Tubular Development

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