Ontogeny of triamcinolone-acetonide binding sites in outer cortical tissue from rat kidneys

The ontogeny of glucocorticoid binding sites and the glucocorticoid hormone (GC) feedback control of available glucocorticoid binding sites was studied using the cytosolic fraction of outer cortical tissue obtained from kidneys in 20- and 40-day-old intact and adrenalectomized rats. Morphometric analysis showed that this tissue contained 85.7% (20 days) and 88.7% (40 days) of proximal tubular cells. Glucocorticoid binding sites were determined by [3H]triamcinolone-acetonide (TA) binding and isoelectric focusing analysis. In intact rats, TA binding sites (fmol/mg DNA) were significantly higher at 20 (3,624) than at 40 (1,640) days. Adrenalectomy significantly increased TA binding sites (fmol/mg DNA) at 40 (to 8,445) but not at 20 days. TA binding sites related to DNA were significantly higher in 20- than in 40-day-old intact rats and significantly higher in 40- than in 20-day-old adrenalectomized rats. Serum corticosterone (nM) was not significantly different in 20- (230) and 40- (189) day-old rats. After in vivo administration of a synthetic GC, TA binding sites were replenished to the cytosol after 20-24 h. Prolonged GC treatment (1-60 micrograms X 100 g body wt-1 X day-1) depressed the replenishment of TA binding sites significantly more in 40- than in 20-day-old adrenalectomized rats. Kd was determined in both intact and adrenalectomized 20- and 40-day-old rats and ranged between 1.30 and 4.33 nM. The steroidal specificity for the TA binding sites was the same in 20- and 40-day-old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of Na-K-ATPase activity in thick ascending limb and of concentrating capacity

Na-K-ATPase activity in the thick ascending limb of Henle (TAL) and the capacity to concentrate urine was determined in 12-, 16-, 20-, 30-, and 40-day-old rats. The most pronounced increase in enzyme activity occurred between 16 and 20 days of age. The relation between enzyme activity in the cortical and medullary TAL was found to be the same in 16-, 20-, and 40-day-old rats, and most enzyme determinations were made in the medullary TAL. The development of Na-K-ATPase activity in TAL and urinary concentrating capacity followed the same pattern. The developmental increase in Na-K-ATPase activity and concentrating capacity between 16 and 20 days of age was accompanied by an increase in serum corticosterone level and was abolished by adrenalectomy. Treatment with glucocorticoid hormones precociously induced Na-K-ATPase activity and concentrating capacity in 13- to 16-day-old rats but had no effect on Na-K-ATPase activity in 17- to 20-day-old rats. The increase in enzyme activity from 20 to 40 days of age was accompanied by an increase in the single nephron glomerular filtration rate. The results suggest that Na-K-ATPase activity in the TAL is an important determinant of the concentrating capacity during development. The developmental surge in Na-K-ATPase activity and concentrating capacity between 16 and 20 days of age is probably set off by the rise in the serum corticosterone level.

Oral rehydration therapy in infectious diarrhoea. Comparison of rehydration solutions with 60 and 90 mmol sodium per litre

The clinical response and changes in water and salt homeostasis as judged from serum sodium levels, salt and water retention and renal handling of sodium was studied during 36 hours following the start of oral rehydration therapy (ORT) with a solution containing 60 mmol Na/l (ORS60) in 17 well-nourished, moderately dehydrated Turkish infants aged 3 to 15 months who had acute infectious diarrhoea (7 with rotavirus, 3 with enteropathogenic E. coli 0 111: B 84, and one with enteropathogenic E. coli 0 125: B 15, one with salmonella and 5 of unknown etiology. In the successfully treated patients sodium and water balance was normalized within 36 hours. In the cases with hypernatremic dehydration the serum sodium concentration rapidly became normal. The results were compared with those obtained in a previous study of the same type of patients who were rehydrated with a solution containing 90 mmol Na/l (ORS90). Although retention was considered to be satisfactory after ORS60 it was less than after ORS90. The changes in the fractionary urinary sodium excretion and the potassium sodium quotient in the urine indicated a less rapid normalization after ORS60 than after ORS90.

Development of colonic fluid and electrolyte transport: influence of weaning pattern

The purpose of this study was to investigate the normal postnatal development of electrolyte and water transport in the large intestines of rats aged 10-20 days, to focus on the events taking place around the time of weaning, and to study the influence of different feeding patterns at the time of weaning on the normal development of the transport mechanisms in the large intestine. The net absorption of sodium, potassium, and water was investigated by using in vivo luminal isotonic perfusion in rats aged 12-40 days. The activity of the active transport enzyme Na-KATPase in the colonic mucosa of rats aged 10-40 days was determined. We found a significant decrease in the net absorption of electrolytes and water that was greatest around the time of weaning. Since the NaKATPase activity was lower in 10-16-day-old rats than in 40-day-old rats, we suggest that the high sodium and water uptake in the colon of suckling rats is independent of the sodium pump. Changes in the feeding patterns around the time of weaning, such as prolonged suckling, were associated with a significantly higher net absorption of electrolytes and water than in rats that were normally weaned at 20 days of age. The Na-KATPase activity was not significantly influenced by the weaning pattern.

Development of urinary concentrating capacity in weaning rats

This study describes the development of the capacity to concentrate urine in 10- to 40-day-old rats that were normally weaned between 16 and 18 days, breast-fed until day 20, or abruptly weaned on day 16. Urine osmolarity after 24 h dehydration was significantly lower in 10- than in 20- and in 20- than in 40-day-old rats. The most pronounced increase occurred between 16 and 20 days in the three groups. The increase in urine osmolality was paralleled by an increase of papillary Na and urea concentrations. The length of the papilla increased linearly from day 10 to 40. Serum arginine vasopressin levels were not significantly different in dehydrated 10- and 20-day-old rats. Serum corticosterone increased significantly between 10 and 20 days of age in both normally weaned and breast-fed rats. The rise was accelerated between days 16 and 18 and paralleled the rise in urinary concentrating capacity. Adrenalectomy on day 16 abolished the increases in urine osmolality and papillary Na and urea concentrations, but not the growth of the papilla between days 16 and 20. The urinary concentrating capacity could be precociously induced by treatment with betamethasone from day 10 to 17 but not from day 17 to 20. Our results indicate that the accelerated development of urine concentrating capacity at the time of weaning is independent of dietary composition and most likely modulated by glucocorticoid hormones.

Renal excretion of calcium and phosphate in preterm and term infants

We studied urinary phosphate and calcium excretion in preterm and term infants during the first 3 months of life. The infants were mainly breast-fed, and the average phosphate intake ranged between 0.5 and 1 mmol/kg/day. During the first week of life urinary phosphate excretion was significantly higher in preterm than in term infants, whereas parathyroid hormone values were the same. After the first week of life urinary phosphate and calcium excretion were the same in preterm and term infants. Fractional excretion of phosphate was low (range 1% to 6%). In both groups calcium excretion was low during the first weeks of life, and increased thereafter to 5 and 3 mmol/1.73 m2/day, respectively. The urinary calcium/creatine ratio generally exceeded 2.0 (mmol/mmol) in preterm infants after the second week of life. These results are compatible with a state of relative phosphate deficiency, resulting in an adaptively low urinary phosphate excretion and an inability to form bone minerals, and therefore relatively high urinary calcium excretion.

Unsuccessful oral rehydration therapy in an infant with enteropathogenic E. coli diarrhoea. Studies of fluid and electrolyte homeostasis

A 4-month-old male infant with severe hyponatremic dehydration due to an enteropathogenic E. coli O125: B15-induced diarrhoea had continued very high stool fluid output with a very elevated sodium concentration after hospitalization and the institution of oral rehydration therapy (ORT). Thirty-six hours after start of ORT intravenous therapy was required. The results of studies of fluid and salt homeostasis in this patient have been compared with those obtained in 3 other patients who had acute diarrhoea of the same severity but caused by another strain of enteropathogenic E. coli (O111:B14) and who were successfully treated with ORT. On ORT the patient with treatment failure had a stool volume which was almost 8 times larger and a stool sodium output which was about 5 times higher than in the successfully treated patients. During the 36-hour-period of ORT fluid losses were about the same as the fluid intake. The results as regards urinary fractional sodium excretion and the urinary potassium/sodium quotient indicate that the severe sodium depletion which was present on admission in the unsuccessfully treated patient persisted during ORT. The reason for ORT failure may be that the infectious E. coli strain had bacilli-adherent qualities that cause damage of microvilli.

Regulation of renal water excretion in newborn full-term infants

The renal response to low (45 ml/kg) and high (73 ml/kg) fluid intake was studied during an 8-hour period in healthy 3-4-day-old full-term infants. 20 infants received low fluid (LF) intake and 15 infants received high fluid (HF) intake. HF significantly increased urine flow and significantly decreased urine osmolality but did not influence glomerular filtration rate measured as the clearance of creatinine. Serum arginine vasopressin (s-AVP) was not different in the LF and HF groups and did not correlate to urine osmolality. Urinary sodium excretion was significantly correlated to the diuresis.

CONCLUSION

Following high fluid intake full-term infants are capable to adaptively excrete larger urine volumes and more dilute urine by mechanisms independent of AVP. S-AVP appears to relate differently to the state of hydration and to urine osmolality in infants than in adults.

Pathophysiological changes in rat kidneys with partial ureteral obstruction since infancy

A partial ureteral obstruction (PUO) was created in 5-day-old rats by implanting the left ureter in the psoas muscle. The surgical technique was modified to produce mild or severe hydronephrosis [Hn (m) and Hn (s)]. The rats were studied at ages between 45 and 65 days with regard to kidney weight, number of functioning glomeruli, mean arterial blood pressure (MAP), total glomerular filtration rate (GFR), nephron filtration rate (SNGFR), tubular free-flow pressure (PT, and stop-flow pressure (SFP). Total GFR was determined after the release of obstruction. The other studies were performed in the obstructed state. Reference values were obtained from sham-operated and untouched control rats. The number of functioning nephrons was depressed 38% in Hn (m) and 73% in Hn (s). Total GFR was preserved in Hn (m) and depressed 54% in Hn (s). SNGFR in the remaining nephrons was significantly elevated in Hn (m) and normal in Hn (s). SFP was significantly elevated in Hn (s). The Hn (s) rats were hypertensive. The glomerular density was lower in the hydronephrotic than in the contralateral kidneys. This suggests a compensatory growth of the remaining nephrons in the Hn kidneys. We conclude that PUO present since infancy will either destroy the nephrons or elicit an adaptive response that will tend to preserve GFR.

Role of arginine vasopressin in blood pressure control in young rats

We investigated the importance of arginine-vasopressin (AVP) for blood pressure control in young and adult rats. Most of the studies were performed on Brattleboro rats with complete diabetes insipidus (DI). In some protocols, Sprague-Dawley rats (SD) were also used. The rats were age 20-24 days (young) or 50-80 days (adult). Adult DI rats have a significantly higher mean arterial pressure (MAP) than adult SD rats. The studies were performed during normovolemia and hypovolemia. Hypovolemia was created by the rapid withdrawal of blood, 0.5-1.5% of body weight. Following bleeding 0.5% of the body weight, young DI rats had a significantly larger decrease in MAP than adult DI and young and adult SD rats. Continuous infusion of AVP (2000 pg X 100 g-1 min-1) blunted the hemorrhagic hypotension in the DI rats. In all groups of rats studied, AVP had little effect on the MAP during normovolemia. The effect of AVP (given in a bolus dose of 20 or 2000 pg X 100 g-1) on the MAP was in DI rats significantly related to the MAP immediately prior to the AVP administration. No effect on MAP was observed when the initial MAP was 105-112 mm in the young DI rats and 148-157 mm in the adult DI rats. The effect of AVP (20 pg X 100 g-1) appeared to be submaximal to maximal. In anaesthetized SD rats, the basal AVP production was higher in the young than in the adult animals. Following bleeding, serum AVP increased in both young and adult rats but the increase was significant only in the adult rats.

Induced development of proximal tubular NaKATPase, basolateral cell membranes and fluid reabsorption

We have previously demonstrated that adrenal corticoid hormones (ACH) induce NaK-ATPase activity in immature proximal tubular (PT) cells in rats. We have now determined the effect of betamethasone (beta) and aldosterone (aldo) on the size of PT basal and lateral cell membranes (BLM), PT fluid reabsorption (J v (a] measured in vivo with the split drop technique and PT NaKATPase activity in 20-day-old (young) and 40-day-old (adult) rats. Serum levels of ACH were the same in young and in adult rats, but adrenalectomy caused a significantly larger fall in NaKATPase activity in young than in adult rats. BLM surface area (micron 2/micron -3 cell volume), J v (a) and NaKATPase were significantly lower in young than in adult rats. Three-day treatment with high doses of beta (60 micrograms X 100 g-1 or aldo (40 micrograms X 100 g-1) significantly increased BLM surface area. J v (a) and NaKATPase activity in young but not in adult rats. Three days after adrenalectomy, J v (a) was significantly depressed in adult rats. There was a significant correlation between the ACH-dependent changes in NaKATPase activity and J v (a). Short-term treatment (2-3 hours) with high doses of ACH did not significantly increase NaKATPase activity and J v (a) in young rats.

Colonic water and electrolyte transport in young and adult rats

The development of colonic water and electrolyte transport was studied in rats. The colon of 20-day-old (young) and 40-day-old (adult) rats was perfused with either a hypotonic (200 mosmol/L) or a hypertonic (450 mosmol/L) solution. The solutions had identical electrolyte contents. Polyethylene glycol was used as a marker of water absorption. Na,K-Adenosine triphosphatase (Na,K-ATPase) activity was determined in nonperfused colonic segments in 10- to 40-day-old rats. Water absorption was always higher in young rats than in adult rats. In the young rats but not in the adult rats increased osmotic pressure of the luminal fluid resulted in a significant decrease in water absorption. The secretion of K was observed only in adult rats. Na,K-ATPase activity increased significantly from 10 to 20 and from 20 to 40 days of age. The results imply that the immature colon has higher water conductivity and low active electrolyte transport.

Comparison of plasma clearances of polyfructosan and 51Cr-EDTA in children

Plasma clearances of polyfructosan and 51Cr-EDTA were determined in 38 children with renal diseases and in five healthy children in order to compare the values for the glomerular filtration rate (GFR) obtained by single injection procedures. Both one-compartment (Cr-EDTA-1) and two-compartment (Cr-EDTA-2) analyses were made of the isotope decay curve. The children were divided into two age groups: (a) 24 children below 6 years, and (b) 19 children between 8 and 16 years of age. In both groups Cr-EDTA-1 GFR and Cr-EDTA-2 GFR correlated significantly with polyfructosan GFR. The correlation coefficients, however, were somewhat lower in the younger (r = 0.74, r = 0.73) than in the older children (r = 0.91, r = 0.93). There were no significant differences between simultaneously obtained polyfructosan GFR and Cr-EDTA-2 GFR based on paired observations while Cr-EDTA-1 GFR was somewhat higher (16%) than the simultaneously obtained polyfructosan GFR. We conclude that estimates of GFR from polyfructosan and Cr-EDTA clearances based on two compartment analyses and single injection procedures are interchangeable.

Increased fractional excretion of phosphate and beta 2-microglobulin in unilateral renal disease

Following progressive nephron loss tubular reabsorption in the remaining nephrons will fall to preserve solute and electrolyte excretion. We have examined the fractional excretion (FE) of phosphate, sodium, beta 2-microglobulin (beta 2M) and tubular glucose reabsorption (T glucose) in children with unilateral renal disease to find 1) the threshold for this response and 2) whether intrinsic renal mechanisms can elicit this response. Separate renal function studies were performed using unilateral ureteral compression. Total glomerular filtration rate (GFR) was 93.7 +/- 2.99 ml/1.73(m2)-1 X min-1, and 110.25 +/- 5.40 in control children. GFR in the scarred kidney (SK) was 22.4 +/- 2.46 and in the contralateral kidney (CIK) 67.2 +/- 4.60 ml X 1.73 (m2)-1 X min-1. The kidney area was reduced in proportion to GFR in SK. FE phosphate and beta 2M were significantly higher in SK than in CIK (sign test), but absolute values for FE phosphate and beta 2M were not higher in SK than in control kidneys. FE sodium and T glucose were the same in SK and CIK.

CONCLUSION

Following moderate unilateral reduction of GFR selective depression of tubular reabsorption can occur without extrarenal impulses.

Effect of metabolic control and duration on exercise-induced albuminuria in diabetic teen-agers

Nineteen type I diabetic teen-agers without clinical signs of nephropathy with a duration of diabetes varying from 3 to 16.8 years were examined by a standardized exercise test for analysis of urinary excretion of albumin and beta 2-microglobulin. The patients were studied both in poor and improved (but not perfect), metabolic control as defined by HbA1c and blood glucose profiles, and the values were compared to those of 14 age-matched healthy controls. The controls showed no increase in albumin excretion rate during exercise as was found in diabetic patients. The albumin excretion rate during exercise was significantly correlated (p less than 0.05) to systolic blood pressure in the diabetic patients. Blood pressure in the diabetic patients was, however, similar to that of controls both at rest and during exercise. Urinary beta 2-microglobulin did not change during exercise. The urinary albumin excretion during exercise decreased significantly with improved metabolic control in diabetic patients, but the albumin excretion rate was not correlated with either blood or urinary glucose or diuresis during the exercise test. When metabolic control was improved there was a significant correlation between the increase in albumin excretion rate during exercise and the duration of diabetes, indicating that part of the exercise-induced albumin excretion might reflect irreversible morphological changes in the diabetic kidney. This test might therefore have a predictive value for diabetic nephropathy if performed during strict metabolic control.

Renal function in relation to metabolic control in children with diabetes of different duration

To evaluate the interpretation of different kidney function tests in diabetic children and teenagers we have studied 47 children with a duration of diabetes up to 5 years, 61 children with a duration of 5.1-10 years and 49 children with a duration of greater than 10 years. Glomerular filtration rate (GFR) measured as inulin clearance or creatinine clearance, clearance PAH (CPAH), filtration fraction (FF), 24-hour urinary excretion of beta 2-microglobulin and albumin were examined and correlated with short- and longterm indices of metabolic control. In all groups of duration GFR as measured by inulin clearance was increased compared with reference values from age matched controls. In patients who had had diabetes for 0-5 years a significant positive correlation was found between inulin clearance and blood glucose during the examination. Inulin clearance was also correlated to HBA1c as well as to 24-hour urinary glucose (mean of 4-6 samples during two years). No such correlation was found in the group who had had diabetes for 5-10 years but in patients with a duration of diabetes greater than 10 years a significant inverse relation was found between GFR and HbA1c. The 24-hour urinary excretion of albumin was significantly higher in all groups of diabetics compared with controls. The urinary excretion of beta 2-microglobulin was similar in diabetics and controls. In the total material no significant correlation could be found between inulin clearance and creatinine clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of diuresis on the degree of vesicoureteral reflux. An experimental investigation in rats

The influence of bladder filling volume (BV), bladder pressure (BP) and diuresis (V) on the occurrence of vesicoureteral reflux (VUR) in Sprague-Dawley rats, where spontaneous VUR is common, has been investigated. The BV and BP at which VUR occurred during constant low diuresis (group I), high inconstant diuresis (group II) and moderately high, constant diuresis (group III), was measured. The abdomen was opened for visual observation of the VUR. The bladder was catheterized with a double-lumen metal catheter for infusion of a Lissamine green saline solution and to enable recording of BP. VUR occurred at significantly lower BV in group II than in group I and at significantly lower BV and BP in group I than in group III.

Salt and water homeostasis during oral rehydration therapy

Changes in sodium balance and urinary and stool output during orally administered rehydration therapy were studied in 22 well-nourished Turkish infants, aged 2 to 13 months, with acute diarrhea mainly of viral origin. The infants randomly received a rehydration solution containing either 90 mmol Na/L (ORS90) or 40 mmol Na/L (ORS40). Slight transient hypernatremia was noted in a few infants receiving ORS90, and slight transient hyponatremia in a few infants receiving ORS40. In both groups, sodium balance increased most rapidly during the first 12 hours of rehydration, and then more slowly because of increased urinary as well as stool sodium output. Sodium balance was always more positive after ORS90 than after ORS40, but the difference did not change much from 12 to 36 hours after therapy was started. Changes in fractional sodium excretion, urinary K/Na quotient, and urinary aldosterone-creatinine quotient were used as indexes of changes in sodium balance. All values were interpreted to indicate that the sodium deficit on admission was corrected within 12 to 18 hours after ORS90 and, in most cases, after 24 to 36 hours after ORS40. Both groups of infants responded well to orally administered rehydration therapy from the clinical viewpoint.

Effect of betamethasone on Na-K-ATPase activity and basal and lateral cell membranes in proximal tubular cells during early development

The mechanism by which betamethasone induces Na-K-ATPase activity in developing tissue was studied in homogenates of proximal tubular cells from 10-day-old rats. A significant increase in Na-K-ATPase activity occurred after 5 micrograms . 100 g-1 . 12 h-1 X 2 beta-methasone and a maximal increase after 15-60 micrograms . 100 g-1 . 12 h-1 X 2. Following a single dose of 60 micrograms . 100 g-1 betamethasone Na-K-ATPase activity increased significantly after 16 h and maximally after 24-30 h. The 16-h time lag suggests that betamethasone does not act only directly on Na-K-ATPase synthesis. Betamethasone 60 micrograms . 100 g-1 increases Na-K-ATPase activity significantly in kidneys in which glomerular filtration rate is reduced by ureteral ligation, but the increase is significantly less pronounced than in kidneys with intact ureters, suggesting that the induction is not mediated only by alterations in sodium supply. Twenty-four hours after 10-60 micrograms . 100 g-1 betamethasone there was no significant increase in glucose-6-phosphatase and Mg-ATPase activity in 10-day-old rats or in Na-K-ATPase activity in 40-day-old rats. The basal and lateral cell membranes of the proximal tubular cells were not significantly increased 24 h after 60 micrograms . 100 g-1 betamethasone. Accordingly, structural development is not a prerequisite for enzymatic differentiation.

Development of glomerular filtration rate and excretion of beta 2-microglobulin in neonates during gentamicin treatment

Ten infants of different gestational ages (GA) and postnatal ages (PNA), treated with gentamicin, were compared with 10 control patients of similar GA and PNA to evaluate the possible nephrotoxic effects of this drug. Changes in the glomerular filtration rate (GFR) and the fractional excretion of beta 2-microglobulin in urine (FE beta) were used as indicators of renal dysfunction. In the control infants there was a postnatal increase in the GFR that was higher in full-term than in preterm infants. The FE beta decreased logarithmically as a function of both the GA and the PNA. The GFR was statistically lower in 5/10 and 6/10 of the patients on the first and the last days of gentamicin treatment (GT) respectively. Three weeks after GT, 8/10 had a normal GFR. The FE beta was statistically higher in 4/10 of the patients on their first day of GT and 7/10 on their last day of GT. Three weeks after GT, 9/10 of the patients had a normal FE beta for their postnatal and gestational ages. It is concluded that GT influences filtration and proximal reabsorption in GT infants by decreasing the GFR and increasing the FE beta. However, the observed renal dysfunction seemed to be reversible.

Glomerular tubular balance in preterm and fullterm infants

The development of glomerular and tubular function was studied in preterm and fullterm infants of varying gestational and postnatal age. The results indicate that glomerular functional development precedes tubular functional development until the 34th postmenstrual week. After the 34th week the tubular transport capacity seems to be more vulnerable than the glomerular filtration rate in states of disease. The release of a postulated renal vasoconstriction could account for the rapid changes in renal function after birth. The purpose of such a vasoconstriction could be to protect the tubules from an overload.

Structural and functional development of the nephron

The present review deals with structural and functional relationships during the development of the nephron. Ultrastructural morphometric technique has been used to obtain quantitative data on structural observations in order to make correlations between structure and function possible. The area of the glomerular basement membrane was found to increase by a factor 1.7 when relating the change in glomerular basement surface area to kidney weight. Furthermore it is suggested that a permeability change of the glomerular basement membrane occurs during development and that this change probably is the result of an increased area of endothelial pores and epithelial slits. The increased capacity of different nephron segments to transport Na and fluid is directly correlated to the increase in the area of the basal and lateral cell membranes as well as the amount of Na-K-ATPase. This suggests a significant contribution of these factors to the maturation of solute and fluid transport through the tubular wall.

Postnatal control of water and electrolyte homeostasis in pre-term and full-term infants

A review is given of the progress which has been made during the last decade within the field of renal control of water and sodium homeostasis in newborn infants of varying gestational age. Both preterm and full-term infants have a low capacity for rapid excretion of a salt load. The natriuretic response improves gradually up to the age of 15 months. The capacity to excrete a load of sodium bicarbonate is higher than to excrete a load of sodium chloride. Under basal conditions preterm infants of a gestational age below 35 weeks have a higher renal sodium excretion than full-term infants. They also appear to be unable to retain sodium when in negative balance. The capacity to concentrate the urine is low in newborn infants, the maximal osmolality being only slightly above that of plasma. The concentrating capacity increases relatively fast during the first 4-6 postnatal weeks in full-term as well as in pre-term infants but does not reach the adult level until the second year. Water loaded newborn infants are able to excrete a urine with a osmolality as low as 30-50 mOsm per kg. In full-term infants free water clearance per unit filtered water is higher than in adults. Water-loaded pre-term infants with a gestational age of more than 30 weeks also have a supernormal diluting capacity.

Renal function and biopsy changes during the course of Henoch-Schönlein glomerulonephritis

Renal function studies were performed in 18 subjects in different stages of Henoch-Schönlein glomerulonephritis (HS GN). Nine children were serially investigated, and nine adolescents or young adults, who were considered to have clinically recovered, were investigated only once, 10.5-14 years after the onset. Inulin and PAH clearance, as well as sodium excretion, were determined during hydropenia (HP) and 3% volume expansion (VE) with isotonic saline. In most patients in the former group a renal biopsy was performed during the first investigation and again one year later. The early disturbances in renal function resembled those we have found in other types of GN. The GFR was normal during HP or after VE in most cases one year after the onset. The natriuretic response to VE was decreased in most patients initially, and this was found to persist in half of the patients 2-3 years after the onset. Pathological urinalyses then indicated disturbances in the renal handling of sodium. A reduced capacity to excrete sodium, however, did not seem to be of prognostic significance since all patients, except one who developed renal insufficiency and hypertension, had normal urinalyses and blood pressure six years after the onset. This study provides no evidence that subjects with previous HS GN will later develop impaired renal function or be predisposed to hypertension.