Course of renal function in IgA glomerulonephritis in children and adolescents

The pathophysiology of IgA GN was investigated in different stages of the disease. Seventeen patients who were between 3.5 and 16.5 years of age at the onset were included in the study. Clearance studies were performed repeatedly in 6 patients (in 5 of them over a period extending from the onset to 5-9.5 years) and only once in 9 patients (10-23 years after the onset). Two patients (one with uremia) were only evaluated clinically. CIn, CPAH and UNaV were studied during hydropenia (HP) and 3% isotonic saline volume expansion (VE). Shortly after the onset CIn, CPAH and UNaV were depressed. Renal function was essentially normal and 1 and 2 years after the onset in spite of signs of active disease. A supernormal GFR was found in 7 patients after they had had the condition between 5 and 17 years. After a duration of IgA GN for greater than 9 years 3 of 12 patients had developed hypertension and uremia and 2 had hypertension or labile BP. Three of 10 patients had a normal GFR and BP, but had increased natriuresis during VE. Only 2 of 10 patients were normotensive and had normal renal function. Disturbances in the renal function are thus frequent in all stages of IgA GN and the changes seem to be related to the duration of the disease. Exaggerated natriuresis may indicate progressive disease.

Implications of limitation of renal function for the nutrition of low birthweight infants

Renal function is immature in low-birth-weight infants. The glomerular filtration rate is low during the entire first month of life. It is 20-50% of that observed in older children and adults. This limits the excretory capacity of the kidney and might set an upper limit for the protein intake. The capacity to reabsorb bicarbonate is not fully developed. This predisposes the low-birth-weight infant to metabolic acidosis. The capacities to excrete sodium when in positive sodium balance and to retain sodium when in negative sodium balance are limited. If the daily sodium balance is not well monitored, conditions of negative sodium balance with hyponatremia as well as of positive sodium balance with hypernatremia might occur.

Renal function in dogs with chronic moderate unilateral ureteral obstruction

Partial obstruction of the left ureter was created in seven dogs. Renal function was studied 3 weeks later. Total renal blood flow (RBF) and intrarenal blood flow distribution were studied using the microsphere technique. Glomerular filtration rate (GFR), effective renal plasma flow (CPAH) and the excretion of sodium and osmolar substances were determined using the clearance technique. RBF, GFR and CPAH in the hydronephrotic kidney were reduced to approximately 30% of the same parameters in the contralateral kidney. Urinary sodium excretion was consistently lower in the hydronephrotic than in the contralateral kidney. Volume expansion with isotonic saline solution revealed that this reduction of sodium excretion from the hydronephrotic kidney was out of proportion to the extent of GFR reduction. The contralateral unobstructed kidney did not compensate for this salt retention by increasing its sodium excretion.

The effect of prostaglandin inhibition on renal function in the developing anesthetized lamb

The importance of prostaglandin (PG) compounds for renal function in the developing kidney was studied by comparing renal blood flow (RBF), glomerular filtration rate (GFR) and fractional sodium (Na) excretion in control lambs and lambs treated with a PG synthesis inhibitor, indomethacin. The lambs were 1-2 and 4-6 weeks old and they were studied either during hydropenia (HP) or volume expansion (VE). Indomethacin significantly decreased Na excretion in both groups of hydropenic lambs. Indomethacin also completely blunted the natriuretic response to VE in the older lambs but had no effect on Na excretion in the volume expanded younger lambs. It is concluded that partial lack of PG inhibiting action on tubular Na transport will contribute to the poor natriuretic response to VE in neonatal lambs. Since PG will act locally rather than being blood-borne messengers, The divergent PG action in younger and older lambs might be explained by local differences in maturation of PG metabolism as well as by local differences in the maturation of PG sensitivity.

Hormonal induction of Na-K-ATPase in developing proximal tubular cells

The outer 150-micrometers layer of the renal cortex of the rat consists mainly of proximal tubules (PT). In this layer Na-K-ATPase (mumol Pi . mg protein-1 . h-1) increases from 3.45 +/- 0.19 (SE) in 10-day-old rats (R10) to 5.90 +/- 0.28 in 20-day-old rats (R20) to 9.52 +/- 0.42 in 40-day-old rats (R40). Betamethasone in pharmacologic doses increases Na-K-ATPase in R10, R20, and R40 to 11.5 +/- 1.19, 13.4 +/- 0.64, and 13.3 +/- 0.60, respectively. Estrogen in pharmacologic doses increases Na-K-ATPase to 9.1 +/- 0.46 in R20 and decreases Na-K-ATPase to 7.6 +/- 0.39 in R40. Aldosterone in a dose of 10 micrograms/100 g BW increases Na-K-ATPase to 8.7 +/- 0.26 in R20; in a dose of 40 micrograms/100 g BW it increases Na-K-ATPase to 6.9 +/- 0.35 in R10. However, aldosterone in a dose of 80 micrograms/100 g BW is needed to cause an increase in R40 to 13.4 +/- 0.37. Treatment with canrenone from the 10th to the 20th day increases Na-K-ATPase. It is concluded that the immature PT cells are particularly sensitive to hormone induction of Na-K-ATPase and that the sensitivity is maximal during fairly late stages of cellular differentiation. Moreover, the inductive effect is probably mediated via glucocorticoid receptors.

Familial Fanconi syndrome with malabsorption and galactose intolerance, normal kinase and transferase activity. A report on two siblings

Two siblings of Turkish-Assyrian extraction, whose parents were first cousins, had poor appetite, slow weight gain and retarded psychomotor development. When given milk the galactose concentration in blood increased. An oral galactose load showed a markedly reduced capacity to metabolize galactose. Fanconi syndrome was present as in classical galactosemia. A galactose-free diet reduced the aminoaciduria but did not normalize the renal tubular function nor the children's general condition. Galactokinase and galactose-1-phosphate uridyltransferase activities in red blood cells were normal. The physical appearance of the children (sparse subcutaneous fat, thin extremities and distended abdomen) and the results of vitamin A and xylose absorption tests, were in accordance with a malabsorption condition. Glucose, however, seemed to be absorbed normally from the gut. There was no evidence of primary liver disease. Since the condition did not normalize with a galactose-free diet, an enzyme defect of galactose metabolism is unlikely. Instead, a more general transport defect with autosomal recessive inheritance is proposed.

Distal tubular sodium reabsorption in the developing rat kidney

The immature kidney has a blunted natriuretic response to saline loading. to localize the high fractional Na reabsorption in the developing nephron, we determined Na delivery to the early distal tubule (EDT) and the fraction of filtered Na remaining in the tubular fluid [(TF/P)Na/In] in the EDT and late distal tubule (LDT) in 24- and 40-day-old hydropenic (HP) and volume-expanded (VE) rats. During HP the (TF/P)Na/In ratio in EDT was significantly higher in the younger rats (12.6 +/- 2.0%) than in the older rats (4.2 +/- 0.6%), but because of a lower SNGFR in the younger rats th Na delivery to EDT was the same in both age groups. The (TF/P)Na/In ratio in LDT was not different in 24- and 40-day-old HP rats (1.1 +/- 0.4 and 1.7 +/- 0.3%, respectively). During VE th (TF/P)Na/In ratio in LDT was significantly lower in 24- (3.0 +/- 0.7%) than in 40-day-old rats (8.3 +/- 1.1%). The (TF/P)Na/In ratio in LDT correlated well with the urinary fractional Na excretion. It is concluded that the Na reabsorption capacity of the developing nephron is more efficient in the distal tubule than in the more proximal tubular segments.

Long-time effect of large vesicoureteral reflux with or without urinary tract infection

In children more than one year old the growth rate of the renal parenchyma is delayed if the kidney has a large reflux-ureter and is exposed to urinary tract infection. The growth rate of the parenchyma is normal, if the kidney has a large reflux-ureter but no infection. However, since moderate reduction of the renal parenchyma is often observed in patients with large reflux-ureter but without a history of urinary tract infection, it is concluded that a large reflux may cause back pressure injury on the kidney during infancy but, in children more than one year old, will cause renal growth retardation and renal scarring only be predisposing to pyelonephritis.

Postnatal development of renal function in pre-term and full-term infants

This study has been designed to examine the effect of gestational age (GA) on the postnatal development of renal function and has been performed in pre-term (PT) infants (GA=30-34 weeks) and in full-term (FT) infants (GA=39-41 weeks). Postnatal age has ranged from 1-35 days. From 8 hour urine samples collected after spontaneous voiding and a capillary blood sample, determinations have been made of the clearance of creatinine (CCr), the fractional excretion of beta 2-microglobulin (FE beta 2) and the fractional excretion of sodium (FENa). In some infants receiving fluid parenterally, simultaneous determinations were made of the clearance of creatinine and inulin. As judged from this study, CCr is a reliable indicator of the glomerular filtration rate (GFR). GFR was almost the same in newborn PT and FT, but from 0.3--1 week of age GFR increased significantly more rapidly in FT than in PT. From 1--5 weeks of age GFR increased at approximately the same rate in PT and FT infants. The absolute value for GFR in 3--5 weeks old infants was lower in PT than in FT. FE beta 2 was higher in PT than in FT infants during the entire first month of life and FENa was higher in PT than in FT infants during the first week of life, suggesting a glomerular tubular imbalance at least at the level of the proximal tubule in PT infants. It is concluded that different stages of maturation will alter the preconditions for the renal adaptation to extrauterine life during at least the first month of life. Therefore special attention must be paid to the limited renal function in PT during their entire first month of life.

Effect of normal development on compensatory renal growth

Sprague-Dawley rats were nephrectomized unilaterally, or sham-operated at 5, 12, and 40 days of age. The kidney weight, number of glomeruli, GFR, and single nephron GFR (SNGFR) were determined in about 60 days of age. In both sham-operated and nephrectomized rats operated on at 5 and 12 days of age, the kidney was studied with light microscope for 1 to 14 days. Unilateral nephrectomy performed just before or just after completion of nephrogenesis or in adulthood did not result in formation of new nephrons. Renal structural development followed the same pattern in nephrectomized and sham-operated rats. A compensatory increase in renal size and GRF was inversely related to the age at which the nephrectomy was carried out but was more pronounced if nephrectomy had been performed just before rather than just after completion of nephrogenesis. In all nephrectomized rats, the compensatory increase in filtration rate appears to be the same in nephrons at all cortical levels judging by comparison of SNGRR and GFR. Conclusion. Compensatory renal growth does not involve the formation of new nephrons in the postnatal kidney of the rat. The potentiation of compensatory changes after nephrectomy at an early age is largely dependent on the development stage of the kidney at the time of nephrectomy.

Effect of isotonic volume expansion on glomerular filtration rate and renal hemodynamics in the developing rat kidney

Young rats (20-24 days) and adult rats (40-45 days) were studied during hydropenia and volume expansion with regard to glomerular filtration rate (GFR) and the determinants of GFR. During hydropenia, GFR and renal blood flow (RBF) were significantly lower in younger than in adult rats both in absolute terms and when related to bodyweight. Equivalent degrees of volume expansion (6% of b.wt.) resulted in a much more pronounced increase in GFR and RBF in younger than in older rats. This suggests that the high renal vascular resistance in hydropenic young rats is primarily due to vasoconstriction. The relationship between the filtration rate of superficial nephrons and the total GFR was the same in hydropenic and volume expanded rats in both age groups. The tubular stop flow pressure, the calculated hydrostatic glomerular capillary pressure and ultrafiltration pressure in the afferent part of the glomerular capillaries was slightly lower in hydropenic young rats than in hydropenic adult rats. The pressures did not rise after volume expansion. It is concluded that the marked increase in GFR in volume expanded young rats is mainly due to increased renal plasma flow.

Renal compensatory hypertrophy in children with unilateral renal disease

Kidney parenchymal size was estimated on urograms from 22 children with unilateral vesico-ureteral reflux (VUR), 14 children with bilateral VUR and seven children with unilateral heminephrectomy. In the bilateral VUR group, one kidney was roentgenologically normal and the other was growth-retarded. The GFR was estimated in 19 of the children. The age of the children was 3-17 years and all had a history of urinary tract infection. The size of the smaller kidney varied between 33-97% of normal. Children in the unilateral VUR group with a small kidney due to scarring and/or growth retardation showed a varying degree of compensatory hypertrophy in the contralateral kidney, which was proportional to the parenchymal reduction. This compensation was inhibited in the bilateral VUR group. There was a positive correlation between the GFR and kidney size.

Sodium excretion in relation to sodium intake and aldosterone excretion in newborn pre-term and full-term infants

The importance of aldosterone for the control of salt balance has been examined in pre-term infants (gestational age 28--34 weeks) and in full-term infants. The post-natal age has varied from 2--21 days. Eight-hour urinary specimens have been analysed with regard to sodium, potassium and aldosterone. The daily sodium intake has been recorded following determination of milk intake and analyses of sodium in breast milk. Due to variations of sodium content of breast milk, the daily sodium intake in pre-term infants was lower than in full-term infants during the first 10 days of life. The sodium excretion was significantly higher in pre-term infants than in full-term infants during the first six days of life. During the first week of life the sodium balance is negative in pre-term infants and positive in full-term infants. Aldosterone excretion is high during the first week of life and increases further from the 2nd to the 3rd week of life in both pre-term and full-term infants. The correlation between aldosterone excretion and urinary potassium/sodium quotient is 0.87 in full-term infants, 0.57 in pre-term infants aged 13--20 days and does not exist in pre-term infants aged 2--10 days. It is suggested that the high sodium excretion in newborn pre-term infants can in part be explained by an unresponsiveness to aldosterone at this developmental stage.

Beta-2-microglobulin, an indicator of renal tubular maturation and dysfunction in the newborn

The urinary excretion and proximal tubular reabsorption of beta-2-microglobulin was studied in 17 healthy newborn infants in relation to gestational and post-natal age. The effect of IRDS and non-conjugated hyperbilirubinemia on the tubular reabsorption of the protein was evaluated in 10 IRDS infants and 14 infants with non-conjugated hyperbilirubinemia. The urinary excretion of beta-2-microglobulin was determined under standardized conditions. When GFR was determined, the single injection clearance method was used. The filtered load of beta-2-microglobulin was found to increase with increasing gestational age. This was due to a rise in plasma beta-2-microglobulin concentration as well as to a rise in the GFR. Although the smallest filtered load was recorded in infants with a mean GA of 32.4 weeks, these infants had a lower fractional reabsorption of the protein (88%) than infants with a mean GA of 35.0 weeks or more (98%). In infants with a GA of 35 weeks or more a glomerulo-tubular balance for beta-2-microglobulin apparently was established. In these infants the filtered load of beta-2-microglobulin increased rapidly during the first days of life. This was paralleled by an increase in the reabsorptive capacity for the protein. In infants with IRDS and in infants with non-conjugated hyperbilirubinemia the fractional reabsorption of beta-2-microglobulin was lower than in control infants of a corresponding gestational and postnatal age. This indicates, that in the neonatal period, the proximal tubular transporting capacity is more vulnerable than the glomerular filtration rate in states of hypoxia and hyperbilirubinemia.

Studies of renal urea cycle enzymes. I. Renal concentrating ability and urea cycle enzymes in the rat during protein deprivation

Activities of renal urea enzymes were studied in normally fed (21% dietary protein) rats and rats deprived of protein (6% dietary protein) for 3 weeks. Protein deprivation resulted in growth retardation and defective urine concentrating ability. Compared to rats on an optimal diet containing 21% of protein, the protein starved animals had decreased concentrations of protein and urea in serum, reduced urinary excretion of urea and decreased levels of all five urea cycle enzyme activities in the liver. In the kidney, however, protein malnutrition resulted in a significant increase in arginase specific activity from 11.5 +/- 1.1 to 16.3 +/- 1.5 (M +/- SD) whereas the other urea cycle enzymes remained unchanged. It is postulated that this increase in renal arginase might be an early compensatory mechanism to preserve a net synthesis of urea in a situation involving arginine deficiency, thereby preserving an intact hypertonic gradient in the renal medulla.

Studies of renal urea cycle enzymes. II. Human renal arginase activity and location of the adaptive changes of renal arginase in the protein deprived rat

Rats fed 6% protein for 3 weeks with growth retardation and urinary concentration defect had 3 times higher arginase activity in the kidney cortex (10.8 +/- 28, M +/- SD) compared with controls fed 21% protein (3.3 +/- 0.9, M +/- SD). In the outer medulla there was a 50% increase of arginase activity whereas no change was observed in the inner medulla and papilla. Arginase activity in fresh human cortical tissue was of the same magnitude as in the rat. The results are in agreement with the hypothesis that intrarenal urea synthesis contributes to the maintenance of the intrarenal urea gradient in the protein deprived state. The response in the protein deprived rat might thus be an adaptation to a situation with substrate deficiency.

Renal sodium excretory capacity in infants under different dietary conditions

An evaluation of dietary effects on sodium (Na) homeostasis was performed in 28 healthy infants 7--13 weeks of age. Each infant received during one week an ordinary formula where either the Na and/or the protein content was increased twice. The high Na diets induced a significant elevation of the natriuretic response to an oral Na load. The response was most pronounced in those infants receiving a high Na as well as a high protein diet. The diet that was only high in protein resulted in an increased osmotic load to the kidneys but did not affect the Na excretion. The maturation of renal Na excretion thus seems to be accelerated by a high Na intake and further potentiated by a high protein intake. The Na excretory capacity was, even after the period of a high Na diet, well above the level of Na then given.

Renal functional changes in acute glomerulonephritis in children. A one-year follow-up

Renal function was studied in three patients with post-streptococcal, four patients with IgA and one patient with non-streptococcal proliferative glomerulonephritis (GN) at the onset of the disease and two, six and 12 months later. Renal biopsies were performed at the onset of the disease and 12 months later. Standard clearance techniques were used for the functional studies. The latter were performed during hydropenia and continuous isotonic saline infusion. During hydropenia, the GFR was uniformly depressed shortly after the onset of the disease, but it normalized during the following two months. The filtration fraction was depressed in poststreptococcal GN at the onset and it normalized with the GFR. In IgA GN, the filtration fraction remained within normal limits during the entire course of the illness. The natriuretic response to isotonic saline volume expansion was low in all patients at the onset of the disease, but normalized in post-streptococcal and IgA GN during the one-year follow-up. In spite of normalized renal function, biopsy findings in IgA GN were unchanged 12 months later. An episode of macroscopic hematuria in one patient with IgA GN at the six-month investigation had no apparent effect on renal function.

Renal function in infants with hyperbilirubinemia

A total of 45 infants were studied on the fourth or fifth day of life: 13 term and 10 pre-term infants with serum bilirubin levels ranging between 257 and 390 mumol/l were compared with 12 term and 10 pre-term infants with serum bilirubin levels below 195 mumol/l. The groups did not differ with regard to mean gestational age or mean post-natal age. GFR and CPAH were determined with the single injection clearance method and ability to excrete Na+ was determined following an oral loading of sodium chloride. GFR was lower in infants with hyperbilirubinemia and correlated negatively to the highest recorded serum bilirubin value. CPAH was similar in hyperbilirubinemic infants and controls. The urinary sodium excretion was significantly higher in infants with hyperbilirubinemia.

Correlation between fluid reabsorption and proximal tubule ultrastructure during development of the rat kidney

Parallel functional and ultrastructural studies were performed in maturing rats in order to elucidate factors determining the development of proximal tubular fluid reabsorption. Three groups of hydropenic animals, which were 22 to 24, 28 to 32 and 40 to 45 days old, were studied. Nephron function was evaluated at the single nephron level by micropuncture technique. The ultrastructure of the developing proximal tubules was analysed by morphometric techniques following fixation of single nephrons. Kidney weight, proximal convoluted tubule length and diameter increased during postnatal development. SNGFR increased from 2.98 to 8.57 and to 20.5 nl/min in respective group of rats whereas proximal tubular fluid reabsorption Jv (a) increased from 0.15 to 0.22 and 0.34 micron3.micron-2.s-1. Parallel to the functional development the relative area of lateral and basal cell membrane increased, resulting in a constant relationship between net fluid reabsorption and the lateral and basal cell membrane area during the fourth postnatal week and then only a slight increase in this relation during the further development. The results suggest that net fluid transport during hydropenia is determined by the amount of available lateral and basal cell membranes where the transporting enzyme for sodium is located.