Segmental Nephron Sodium and Potassium Reabsorption in Newborn and Adult Dogs during Saline Expansion

Kleinman, Leonard I.; Banks, Robert O.

doi:10.3181/00379727-173-41637

“…Interestingly, patients carrying KCNJ1 mutations may show hyperkalemia as an initial sign of the disease, soon after birth; then, this defect is even reversed [8]. Micropuncture [9] and clearance [10] studies in young rats have demonstrated limited ability in K + secretion compared with adults. Accordingly, in microperfused CCD from mammalians, K + secretion is low in newborns and cannot be stimulated by tubular flow [11].…”

Section: Hypokalemia: Lessons From the Salt-losing Tubulopathiesmentioning

confidence: 99%

Potassium: From Physiology to Clinical Implications

Zacchia

¹

,

Abategiovanni

²

,

Stratigis

³

et al. 2016

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Background: Potassium (K⁺) is the major intracellular cation, with 98% of the total pool being located in the cells at a concentration of 140-150 mmol/l, and only 2% in the extracellular fluid, where it ranges between 3.5 and 5 mmol/l. A fine regulation of the intracellular-extracellular gradient is crucial for life, as it is the main determinant of membrane voltage; in fact, acute changes of K⁺ plasma levels may have fatal consequences. Summary: An integrated system including an ‘internal' and ‘external' control prevents significant fluctuations of plasma levels in conditions of K⁺ loading and depletion. The internal control regulates the intra-extracellular shift, a temporary mechanism able to maintain a constant K⁺ plasma concentration without changing the total amount of body K⁺. The external control is responsible for the excretion of the ingested K⁺, and it has the kidney as the major player. The kidney excretes nearly 90% of the daily intake. Along the proximal tubule and the thick ascending limb on Henle's loop, the amount of K⁺ reabsorption is quite fixed (about 80-90%); conversely, the distal nephron has the ability to adjust K⁺ excretion in accordance with homeostatic needs. The present review analyzes: (1) the main molecular mechanisms mediating K⁺ reabsorption and secretion along the nephron; (2) the pathophysiology of the principal K⁺ derangements due to renal dysfunction, and (3) the effect of ingested K⁺ on blood pressure and renal electrolyte handling. Key Messages: Maintaining plasma K⁺ levels in a tight range is crucial for life; thus, multiple factors are implicated in K⁺ homeostasis, including kidney function. Recent studies have suggested that K⁺ plasma levels, in turn, affect renal salt absorption in animal models; this effect may underlie the reduction of blood pressure observed in hypertensive subjects under K⁺ supplementation.

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“…This greater avidity of the distal nephron when distal delivery is increased is also observed when distal sodium and chloride delivery are increased (7,32) and thus is probably common to more than one segment of the distal nephron. The factors responsible for this greater propensity for electrolyte reabsorption when delivery is increased cannot be determined from these studies.…”

Section: Discussionmentioning

confidence: 81%

“…It is difficult to identify a single factor that could effect the reabsorption of these electrolytes in different segments. It should be noted that reabsorption of sodium, chloride, and bicarbonate per g kidney are much lower in the newborn than in the adult under all of these experimental conditions, even though the fractions of the distal loads reabsorbed are higher, because the distal loads are much lower as a result of a lower GFR per g kidney in the newborn (7,32). Thus, even if the reabsorptive capacities per g kidney of these segments of the immature distal nephron were less than those ofthe mature distal nephron, it is possible that these capacities might be exceeded in the adult but not in the newborn.…”

Section: Discussionmentioning

confidence: 99%

“…Thus, it seems that suppression of bicarbonate reabsorption by extracellular volume expansion, rather than a limited resorptive capacity, may well have accounted for the lower plasma threshold observed in newborn infants. On the other hand, volume expansion natriuresis is attenuated in the newborn compared with the adult (5)(6)(7)(8). This attenuated natriuresis is due to enhanced fractional reabsorption of sodium by the immature distal nephron (5,7,9,10).…”

mentioning

confidence: 90%

“…This attenuated natriuresis is due to enhanced fractional reabsorption of sodium by the immature distal nephron (5,7,9,10). Volume expansion actually suppresses fractional sodium reabsorption by the proximal nephron more in the newborn than in the adult (7).…”

mentioning

confidence: 99%

See 2 more Smart Citations

Effects of Euvolemic and Hypervolemic Hyperbicarbonemia on Segmental Nephron HCO3 Reabsorption in the Newborn Dog1

Lorenz

¹

1990

Pediatr Res

0

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ABSTRACT. Studies were undertaken to determine the effect of elevated plasma bicarbonate concentration (PHC03) with and without volume expansion on segmental nephron H C 0 3 reabsorption in newborn and adult dogs using the technique of distal blockade. Reabsorption of bicarbonate per mL glomerular filtrate (RHC03lGFR) in the proximal nephron was more suppressed in euvolemic newborns than euvolemic adults as PHC03 was increased from baseline to 50-70 mM. Inasmuch as total nephron reabsorption has been shown to be essentially complete under these conditions in both newborns and adults, distal nephron H C 0 3 delivery and the fraction of the distal H C 0 3 load reabsorbed must have been greater in euvolemic newborns than adults when P H C 0 3 was elevated. Total nephron RHC03/GFR was less suppressed by NaHC03 volume expansion in the newborn than it was in the adult. However, proximal nephron RHC03/GFR was similarly suppressed by NaHC03 volume expansion in newborns and adults. Thus, the NaHC03-expanded newborn must have reabsorbed a greater proportion of the increased distal HC03 load than did the NaHC03-expanded adult. Proximal nephron H C 0 3 reabsorption is a balance between reabsorption effected by active proton secretion and passive H C 0 3 back leak. Euvolemic increase in peritubular HCO3 concentration has been shown to suppress proximal tubular proton secretion; volume expansion increases proximal tubule H C 0 3 permeability and back leak. Thus, we interpret these results to indicate that: 1 ) the limited capacity of the immature proximal tubule for proton secretion is most likely responsible for the greater suppression of proximal RHC03/GFR by increased PHC03 in euvolemic newborn dogs compared with adults; 2) the increase in H C 0 3 permeability of the immature proximal nephron with volume expansion is no greater than that which occurs in the mature proximal nephron with volume expansion; and 3) the immature distal nephron displays a greater propensity for HCO3 reabsorption as PHC03 is increased than does the mature distal nephron, with or without volume expansion. (Pediatv Res 27: 604-611, 1990) Abbreviations FRHC03, fractional reabsorption of the filtered bicarbonate load GFR, glomerular filtration rate PHC03, plasma bicarbonate concentration

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The Kidney During Development

Spitzer

¹

,

Schwartz

²

1992

Comprehensive Physiology

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The sections in this article are: Historical Perspective Standards of Reference for Comparison of Renal Function Between Infants and Adults Morphogenesis of the Kidney Embryologic Origin of the Kidney Subsequent Development of the Kidney Glomerulus Renal Tubule Renal Blood Flow and its Control During Development Total Renal Blood Flow Intrarenal Distribution of Blood Flow Renal Microvasculature Control of Renal Circulation Glomerular Filtration Net Ultrafiltration Pressure Hydraulic Conductivity and Ultrafiltration Coefficient Glomerular Capillary Surface Area Factors That Affect GFR during Development Autoregulation of GFR Renal Energy Metabolism Development of Renal Cortical Metabolic Pathways Tubular Functions Renal Reabsorption of Sodium Reabsorption of Bicarbonate and Excretion of Hydrogen Ions Glucose Transport Transport of Amino Acids Transport of Organic Acids Phosphate Transport Control of Renal Transport during Development Calcium Transport Magnesium Transport Potassium Transport Concentration of Urine Developmental Renal Physiology as A Tool for Understanding the Emergence and Integration of Renal Transport Systems

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Segmental Nephron Sodium and Potassium Reabsorption in Newborn and Adult Dogs during Saline Expansion

Cited by 28 publications

References 0 publications

Potassium: From Physiology to Clinical Implications

Potassium: From Physiology to Clinical Implications

Effects of Euvolemic and Hypervolemic Hyperbicarbonemia on Segmental Nephron HCO3 Reabsorption in the Newborn Dog1

The Kidney During Development

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