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Query: UMLS:C0029713 (immaturity)
 4,335 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Eighty five 24 hour sodium balance studies and creatinine clearance measurements were performed in 70 infants of gestational age 27-40 weeks and postnatal age 3-68 days. The kidney's capacity to regulate sodium excretion was a function of conceptional age (the sum of gestational age and postnatal age) and an independent effect of postnatal age was also observed--extrauterine existence increased the maturation of this function. The sodium balance was negative in 100% of infants of less than 30 weeks' gestation, in 70% at 30-32 weeks, in 46% at 33-35 weeks, and in 0% of greater than 36 weeks, and the incidence of hyponatraemia closely paralleled that of negative sodium balance. Despite a low glomerular filtration rate (GFR) urinary sodium losses were highest in the most immature babies but fractional sodium excretion (FENa) was exponentially related to gestational age. An independent effect of postnatal age could be identified on FENa but not in GFR. These findings indicate that in infants of greater than 33 weeks' gestation sodium conservation is possible because of a favourable balance between the GFR and tubular sodium reabsorption, but that below this age GFR exceeds the limited tubular sodium reabsorption capacity. The rapid increase in sodium reabsorption in the first few postnatal days seems to be due to maturation of distal tubular function, probably mediated by aldosterone. We suggest that the glomerulotubular imbalance for sodium is a consequence of the immaturity of the tubuloglomerular feedback mechanism, and we estimate that the minimum sodium requirement during the first 2 weeks of extrauterine life is 5 mmol (mEq)/kg/day for infants of less than 30 weeks' gestation and 4 mmol (mEq)/kg/day for those born between 30 and 35 weeks.
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PMID:Sodium homeostasis in term and preterm neonates. I. Renal aspects. 685 12

Water metabolism is a major problem in infants of very low birth weight. Their surface is proportionally larger, they have a relatively low intracellular water volume and a high extracellular and total body volume. Kidney function is immature compared to bigger infants, and the neuroendocrine function is also immature. Finally the large surface and the high skin permeability causes a very high insensible water loss in the early neonatal period. Water imbalance presents itself as either dehydration or overhydration. Dehydration gives poor peripheral--and renal circulation and thereby decreased renal function with acidosis. Furthermore hyperosmolar dehydration will give increased hematocrit and blood viscosity and hyperbilirubinaemia. Excessive administration of water will give oedema and congestive heart failure and possibly an increased risk for patent ductus arteriosus, bronchopulmonal dysplasia and necrotising enterocolitis. The evaporative water losses varies according to the thermal environment and air humidity and it is therefore impossible to give narrow limits for the daily water intake. Clinical examination, frequent controls of body weight (twice daily) and measurements of urine volume and osmolarity serve as guide lines. Yet inappropriate secretion of ADH may confuse the value of measuring urine osmolarity. Finally a neonatal weight loss of 5-10% may be beneficial as a decrease in extracellular water may lessen the working load of the heart and therefore possibly lessen the risk for a patent ductus. Renal immaturity in handling sodium reabsorption on the other hand, will often give an excessive dehydration. For this reason about 2 mmol Na/kg body weight should be given daily to very low birth weight infants from the fourth day of life to the 3rd-4th week if the baby is on human milk or a low salt formula.
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PMID:Water--the major nutrient. 2475 24

Plasma renin (PRC) and aldosterone concentrations are known to be high during early postnatal life. Whether this is related to the low rates of renal blood flow or to sodium homeostasis remains unknown. Measurement of PRC, renal blood flow, and its intrarenal distribution were performed in 1- to 3-wk-old puppies subjected to maneuvers known to stimulate or inhibit renin release. In the awake state, PRC was observed to be higher in 2-wk-old puppies than in older or younger dogs, (P less than 0.0001). Significant differences in PRC were also found between litters (P less than 0.0001), but they did not account for the age-related changes. Anesthesia resulted in a 3- to 5-fold rise in PRC, whereas saline expansion suppressed PRC at all ages, the fall tending to become progressively greater with age (P less than 0.09). There was no significant correlation between the age-related changes in PRC and those in renal blood flow or its intrarenal distribution. The results of these experiments demonstrate that in the newborn from a qualitative point of view, PRC changes appropriately in response to various stimuli. However, quantitative age-related differences exist in this regard, reflecting an initial immaturity of the feedback system.
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PMID:The renin angiotensin system in newborn dogs: developmental patterns and response to acute saline loading. 699 Mar 67

The concentrations of aldosterone in the plasma and adrenal glands, the concentrations of sodium and potassium in the plasma and the hematocrit were estimated from birth to day 6 after birth in premature mice removed by Caesarean section on day 19 of pregnancy in comparison with newborn mice delivered spontaneously vaginally on day 20 of pregnancy. In premature mice, the plasma aldosterone concentrations increased twice: at birth after reanimation, then at 6 h after birth. The first increase at birth resulted probably from ACTH stimulation. Several factors could be involved in the peak at 6 h after birth: ACTH stimulation, the decrease in the level of sodium in the plasma and the increase in the hematocrit due to kidney immaturity of premature mice. The results suggest that the renin-angiotensin-aldosterone system is able to respond to stimulations in the first 6 h after birth in premature mice. The rise in the level of plasma aldosterone which has been found at birth in newborns delivered spontaneously vaginally on day 20 of pregnancy (control animals) did not result from variations of plasma electrolytes, plasma volume and ACTH; this rise has been induced by labor of the parturition which caused the aldosterone release from adrenal glands.
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PMID:Plasma and adrenal aldosterone levels in premature mice at birth and during neonatal development. 718 5

Calcium and sodium permeability of erythrocytes from patients with untransfused alpha- or beta- thalassemia major has been studied and compared to mature erythrocytes or control cells with comparable reticulocytosis. Isotopic Na(+) influx was increased a mean fourfold greater than normals and threefold greater than reticulocyte rich control. Passive net leak of Na(+) into thalassemic cells incubated with ouabain was also increased corresponding to their greater (22)Na(+) influx. Erythrocyte Na(+) and K(+) concentrations and cell water content per unit volume of cells were normal. Quantitation of active cation pumps in the cell membrane by the technique of [(3)H]ouabain binding showed a 2.6- to 9.9-fold increase above normal. Inward Ca(2+) movement was studied in cells with absent Ca(2+) pumping produced by depletion of either ATP or Mg(2+)-ions. Calcium uptake by ATP depleted thalassemic cells was increased 12-fold above normals and 3.6-fold above reticulocyte-rich controls. The Ca(2+) uptake by Mg(2+)-depleted thalassemic cells was also increased above normal confirming that erythrocyte Ca(2+) permeability is increased in this disease. Osmotic fragility measurements show that the surface area to volume ratio of thalassemic erythrocytes was increased by 15 to 25% above mature erythrocytes. The increased passive cation permeability of thalassemic erythrocytes cannot be explained by either reticulocytosis or an increased surface area to volume ratio of these cells. Moreover, erythrocyte Na(+) and Ca(2+) influxes in congenital dyserythropoietic anemia (CDA type 2) were increased 2- and 14-fold, respectively, above normal. The increased cation fluxes and cation pump numbers in thalassemic and congenital dyserythropoietic anemia erythrocytes are consistent with the hypothesis of membrane immaturity arising from rapid marrow transit times, a concept previously advanced to explain the persistence of i-antigen on these cells.
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PMID:Increased erythrocyte cation permeability in thalassemia and conditions of marrow stress. 720 77

The permeability of the ocular blood vessels to sodium fluorescein (NaFl) was evaluated in neonatal and adult cats by fluorescence microscopy. The iris, ciliary body, and choroidal vessels were markedly permeable, whereas the mature and immature retinal vessels were impermeable. Since there is no apparent barrier to NaFl at the level of the iris vessels, the role of those vessels in aqueous formation is possibly significant. The fact that the immature retinal vessels are impermeable suggests that abnormal permeability to NaFl in retinal neovascularization is a consequence of pathology rather than immaturity.
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PMID:Permeability of blood-ocular barriers of neonatal and adult cat to sodium fluorescein. 740 82

Clinical and laboratory-based studies of pulmonary edema have usually focused on the mechanisms responsible for the production of the edema and how therapeutic maneuvers can oppose or treat such processes. Recently, there has been increasing interest in the mechanisms involved in the clearance of airspace fluids. These studies have demonstrated that active transport of Na+ by the distal lung epithelium plays an important physiologic role in the clearance of pulmonary edema fluid. Specifically, the ability of the lung to clear its fluid by active transport processes correlates with survival from high-pressure or high-permeability pulmonary edema. Also, studies have shown that immaturity of Na+ transport processes and, specifically, inadequate expression of Na+ channels contribute to the pathogenesis of respiratory distress syndrome in the newborn.
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PMID:The role of active Na+ transport by lung epithelium in the clearance of airspace fluid. 758 65

Numerous clinical studies during the past two decades have indicated that kidney function and regulation of electrolyte and fluid balance undergo profound changes in the neonatal period. The genetic mechanisms behind these developmental changes have recently been the topic for many investigations and has led to the identification of factors, reviewed here, that seem to be of extraordinary importance for the induction of kidney differentiation and maturation. For a long time it has been debated whether immaturity of renal function might have any clinical consequences. It now seems clear that at least one aspect of renal immaturity, namely the high urinary sodium excretion in preterm infants, which often results in negative sodium balance, should be paid more attention to because it might interfere with growth. Two recent review articles discuss this issue. The profound changes in fluid and electrolyte homeostasis that occur in the neonatal period, involves most tissues. This is exemplified with some recent exciting studies on the changes in ion transport that occur in the lung around birth.
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PMID:Neonatal kidney, fluids, and electrolytes. 803 94

The renal effects of endothelin-1 were investigated in 16 anesthetized and mechanically ventilated newborn rabbits. Renal blood flow and glomerular filtration rate were determined by the clearance of para-aminohippuric acid and inulin, respectively. Each animal acted as its own control. In eight newborn rabbits, a bolus injection of 5 nmol.kg-1 of endothelin-1 caused an initial fall in mean arterial blood pressure followed by a gradual, significant increase in mean arterial blood pressure that lasted for 45 min. The dramatic increase in renal vascular resistance (+28 +/- 4%) induced by endothelin led to a fall in glomerular filtration rate (-12 +/- 4%) and renal blood flow (-16 +/- 3%). In spite of the reduction of glomerular filtration rate and renal blood flow, urine flow and sodium excretion rates increased significantly (+20 +/- 5% and +49 +/- 9%, respectively). In eight additional newborn rabbits, a bolus injection of 1 nmol.kg-1 of endothelin--a dose that usually induces marked renal and systemic vasoconstriction in adult models--did not affect systemic or renal hemodynamics. In conclusion, endothelin induces renal and systemic vasoconstriction and affects water and sodium homeostasis during the neonatal period. These effects occur under higher doses than those used in adult animals. This age difference in systemic and renal responsiveness is probably mediated by receptor immaturity and/or interference of high levels of counteracting hormones present during the neonatal period.
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PMID:Effects of endothelin on renal function in newborn rabbits. 823 10

Renal immaturity is pronounced in very low-birth-weight infants with a gestational age < or = 30 weeks. We attempted to elucidate if conditions requiring mechanical ventilation, including patent ductus arteriosus, might further compromise renal function due to decreased renal perfusion. Forty infants studied between 4 and 28 days of age were divided into four groups: Control with no patent ductus or mechanical ventilation (n = 8); PDA+MV, with both patent ductus and mechanical ventilation (n = 17); PDA, with patent ductus (n = 6); MV, with mechanical ventilation (n = 9). The groups PDA+MV and MV had significantly lower creatinine clearances and significantly higher fractional sodium excretions than controls. Mean arterial pressure was significantly lower in all groups compared to controls and correlated significantly with creatinine clearance (r = 0.47, p < 0.02). In conclusion, low renal function in these infants is further compromised by a patent ductus arteriosus and/or the use of mechanical ventilation.
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PMID:Renal function in sick, very low-birth-weight infants. 824 64


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