Renal Excretion of Inorganic Phosphate in Newborn Infants 12

McCrory, Wallace W.; Forman, Carolyn; McNamara, Helen; Barnett, Henry L.

doi:10.1172/jci102616

Cited by 77 publications

(26 citation statements)

References 17 publications

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“…Perinatal calcium homeostasis is regulated by a number of endocrine (13,21,38,46) and nonendocrine (4,10,27,28,44) factors. Although PTH would be expected to play a key role among the endocrine factors involved, this has been difficult to document.…”

Section: Discussionmentioning

confidence: 99%

Parathormone and Perinatal Calcium Homeostasis

et al. 1979

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Summawand Rudd (49) have observed mean PTH concentrations in cord Plasma measured the first parathormone (PTH) and calcium concentrations were in 309 specimens collected from 190 newborns during 7 days of life. The patient material consisted of 51 preterm, 130 term, and 9 postterm infants, including 22 infants of diabetic mothers (IDM), 38 infants with hypocalcemia, and 25 asphyxiated infants. PTH was detectable, although in low concentrations, in cord blood samples despite the presence of elevated calcium concentrations. Postpartum, PTH concentrations in term, appropriate for gestational age (AGA) infants remained low during the first 2 days of life; a significant ( P < 0.05) and sustained increase in plasma hormone levels was noted starting on day 3. PTH concentrations in IDM and preterm infants remained low for 3 days and a significant hormone increase did not occur until day 4.Hypocalcemia was common in IDM and asphyxiated infants; these infants accounted for two-thirds of all hypocalcemic infants. The profde of plasma calcium in IDM during the fust week of life was different than that of any other group of infants. Plasma calcium concentrations remained depressed over this period of time and exhibited a temporary drop on day 4 accompanied by an increase in plasma PTH levels. Asphyxiated infants exhibited low plasma calcium concentrations, despite PTH levels that were significantly ( P < 0.007) higher than those of age-matched term AGA newborns. SpeculationBasal PTH secretion is present at birth, several days before the parathyroid glands appearto become responsive to hypocalcemia. Furthermore, in cord blood PTH is detectable in spite of elevated calcium concentrations. The present observatiois suggest that nonsuppressible PTH secretion, previously described in short-term animal ex~eriments. also occurs in the human fetus ex~osed to long-standing intrauterine hypercalcemia, with the implication that PTH secretion in man may be regulated by control mechanisms in addition to calcium feedback. There is anatomical and pharmacologic evidence to implicate the autonomic nervous system in this control.Hypocalcemia is a frequent problem in early postnatal Life (1 1, 20, 37, 47). Between 1970 and 1971,44 of 1390 newborns (3.2%) delivered at Harbor General Hospital, UCLA, presented with socalled "first day hypocalcemia" defmed as serum calcium levels of 5 7 mg/dl during the first 36-48 hr of life (32). Two-thirds of these infants were premature (gestation less than 38 weeks). The etiology of first day hypocalcemia remains unclear. A number of authors (17,19,46) (1 17 k 17), but were unable to detect any correlation between serum-ionized calcium on the one hand and PTH levels on the other in either maternal, cord, or infant blood between birth and age 7 days. David and Anast (13) reported similar results, yet they did observe an increase in plasma PTH in 23 of 36 infants beyond age 48 hr, and this increase correlated with a gradual rise of the low neonatal calcium concentrations toward normal. Finally, there are conflic...

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Section: Discussionmentioning

confidence: 99%

Parathormone and Perinatal Calcium Homeostasis

et al. 1979

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“…On the basis of these morphologic findings, as well as of functional data suggesting that proximal tubular function during immaturity is relatively lower than glomerular function, we have suggested that fractional reabsorption in the proximal tubule may be less in the immature than in the mature animal [7]. Support for this is found in a number of functional studies, such as the high rate of clearance of free water in young infants, when expressed per 100 ml glomerular filtration rate (GFR) [1], and their higher fractional excretion of amino acid [2] and of phosphate [2,5,16,22].…”

Section: Discussionmentioning

confidence: 99%

Renal Reabsorption of Bicarbonate in Puppies: Effect of Extracellular Volume Contraction on the Renal Threshold for Bicarbonate

et al. 1972

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It has been recognized for many years that infants have lower concentrations of bicarbonate in plasma than older children and adults, due neither to a limited renal capacity to excrete hydrogen ion nor to a reduced capacity for reabsorption of bicarbonate, but to a low renal threshold for bicarbonate. The purpose of the present investigation was to determine whether the neonate and young of another species also could be shown to have a "physiologic acidosis" and, if so, to use this model for exploration of factors that might influence the threshold for bicarbonate. Mean pH of blood and concentration of bicarbonate in plasma in 11 young suckling puppies were 7.24 ± 0.018 and 18.2 ± 0.55 mmoles/liter, respectively, levels considerably lower than those found in adult dogs. In all but one animal pH of urine was below 6.0. Inasmuch as puppies thus appear to be in a state of "physiologic acidosis" and to have no limitation in acidification of the urine, we feel that this animal provides a suitable model for further examination of the characteristics of renal reabsorption and excretion of bicarbonate during immaturity. Titrations of bicarbonate performed in the usual manner demonstrated a threshold of 17-20 mmoles/liter, with a mean of 18.3. In the absence of significant volume expansion, maximal rates of reabsorption of bicarbonate were not observed despite filtered loads that were double those at threshold. Fractional excretion of sodium during control periods in animals which were not dehydrated averaged 2.9 ± 1.8% compared with 0.16 ± 0.08% in animals which were slightly dehydrated by their previous treatment with ammonium chloride. In this group, by replacement of gastric fluid (primarily sodium and potassium chloride) with a solution of sodium and potassium bicarbonate, renal handling of bicarbonate at varying filtered loads could be studied in the absence of volume expansion and with the continued stimulus for reabsorption of sodium. Under these circumstances, the renal threshold for bicarbonate was found to be markedly increased (25.2 ± 1.12). Saline was administered to two animals after the threshold had been passed. At any given level of filtered load the rate of excretion of bicarbonate in urine after administration of saline greatly exceeded the rate of excretion during gastric suction. The data in the present study thus indicate that the decreased threshold for bicarbonate in the young animal is not due to a limitation in intrinsic capacity for reabsorption of bicarbonate, inasmuch as capacity could be increased markedly under the stimulus 859 860 MOORE ET AL.for extracellular volume contraction, but is a consequence of the various factors that influence reabsorption of bicarbonate in the proximal portion of the nephron. Speculation

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“…It is well established that the urinary excretion of Pi is related to its dietary intake. This relation has been described by balance and clearance techniques in normal human adults and patients with parathyroid disease (1)(2)(3)(4)(5), in newborn children (6), and in both intact and parathyroidectomized rats (1,7,8). In these studies it has mostly been shown that dietary Pi (9).…”

Section: Introductionmentioning

confidence: 99%

Inorganic phosphate homeostasis. Renal adaptation to the dietary intake in intact and thyroparathyroidectomized rats.

Tröhler¹,

Bonjour²,

Fleisch³

1976

J. Clin. Invest.

182

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A B S T R A C T The possibility of renal tubular adaptation to variations in dietary inorganic phosphate (Pi) was investigated in intact and thyroparathyroidectomized (TPTX) rats pair-fed diets containing low, normal, and high amounts of Pi for periods up to 10 days. Clearances were measured before and during acute i.v. infusions with Pi in conscious animals. Thus tubular reabsorption of phosphate (TRPi) could be assessed over a wide range of plasma phosphate concentrations ([Pt]Pi). It was found that the renal tubule could adapt its capacity to transport Pi according to the dietary Pi: TRPt was always higher, for a given [Pt]P1, in the animals fed low than in those fed higher Pi diets. This diet-induced modification also occurred in the absence of thyroparathyroid glands, in the presence of the same calcemia and urinary pH, and during marked extracellular volume expansion. A time-course study in rats TPTX both before and during the administration of the experimental diets showed that a difference in the tubular handling of Pi was detectable as early as 3 days after switching the animals from a normal to low-or high-Pi diets. These results indicate that factors other than parathyroid hormone are implicated in the tubular response to variations in the dietary intake of inorganic phosphate.

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Renal Excretion of Inorganic Phosphate in Newborn Infants 12

Cited by 77 publications

References 17 publications

Parathormone and Perinatal Calcium Homeostasis

Parathormone and Perinatal Calcium Homeostasis

Renal Reabsorption of Bicarbonate in Puppies: Effect of Extracellular Volume Contraction on the Renal Threshold for Bicarbonate

Inorganic phosphate homeostasis. Renal adaptation to the dietary intake in intact and thyroparathyroidectomized rats.

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