O. Broberger

RENAL RESPONSE TO AN ORAL SODIUM LOAD IN NEWBORN FULL TERM INFANTS

I n the newborn infant renal function is reported to be restricted with regard to filtration rate (16, 22), concentrating (lo), and acidifying capacity (11). Knowledge about the renal control of sodium excretion in the infant kidney is, however, limited. The present study is an attempt to assay the ability of the newborn full term infant to excrete sodium following a standardized oral load of sodium chloride. As a reference the renal effect of a quantitatively corresponding load to older children has been used (2, 5).

SODIUM EXCRETION IN RELATION TO SODIUM INTAKE AND ALDOSTERONE EXCRETION IN NEWBORN PRE‐TERM AND FULL‐TERM INFANTS

Abstract. 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 fist 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.

DEVELOPMENTAL STUDY OF THE RENAL RESPONSE TO AN ORAL SALT LOAD IN PRETERM INFANTS

ABSTRACT. Aperia, A., Broherger, O., Thodenius, K. and Zetterström, R. (Department of Paediatrics, Karolinska Institutet, S:t Görans Childrens Hospital, Stockholm, Sweden). Developmental study of the renal response to an oral salt load in preterm infants. Acta Paediatr Scand 63: 517, 1974.—An evaluation of sodium homeostasis in 44 preterm infants with gestational ages between 29 and 37 weeks has been carried out during the first week after birth and until time of expected term. The natriuretic response to an oral sodium load has been studied in all infants and the GFR (single injection technique of inulin) in 17 infants. The results are compared with those previously found in full‐term infants. The natriuretic response was highest and the GFR was lowest in the very preterm neonates. In the very preterm infants the values for sodium excretion and GFR was just about the same at the time of expected term as in full‐term newborns. Various explanations for the difference between the very preterm neonates and full‐term neonates are discussed. One factor of importance might he the anatomical development. The immature kidney has in comparison to the adult kidney relatively larger glomerular than tubular mass. Extra‐uterine life seems to have little influence on the development of GFR as well as on the development of the response to the oral salt load. Thus in the very preterm infants, the postmenstrual rather than the postnatal age should be considered when prescribing fluid, electrolytes and drugs.

RENAL GROWTH AND FUNCTION IN PATIENTS NEPHRECTOMIZED IN CHILDHOOD

Abstract Aperia, A., Broberger, O., Wikstad, I. and Wilton, P. (Department of Paediatrics and Paediatric Radiology, Karolinska Institute, St. Görans Childrens Hospital, Stockholm, Sweden). Renal growth and function in patients nephrectomized in childhood. Acta Paediatr Scand, 66:185, 1977.—Eight patients nephrectomized in childhood were studied with regard to growth and function of the remaining kidney. The age of the patients ranged between 8½ and 31 years and the follow‐up period was from 1 to 20 years. In most of the patients, repeated renal size determinations were made on postoperative urograms. Normal values for kidney size in childhood are also presented. The structural hypertrophy continued for at least three years after nephrectomy and was most pronounced in patients nephrectomized before three years of age. When more than three years had passed after nephrectomy the remaining kidney was 35–65% larger than normal. Healthy young adults and children with a previous history of urinary tract infection served as controls for function studies. The balance between glomerular and tubular function was well preserved in nephrectomized patients. The renal surface area showed the same relation to GFR and to reabsorption of bicarbonate in nephrectomized patients as in controls. It is therefore concluded that the increase in kidney function following unilateral nephrectomy is, at least in early life, primarily due to structural enlargement.

COURSE OF RENAL FUNCTION IN IgA GLOMERULONEPHRITIS IN CHILDREN AND ADOLESCENTS

ABSTRACT. 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 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 >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. Disturbancies 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.

Maturational changes in glomerular perfusion rate and glomerular filtration rate in lambs.

Extract: The developmental pattern of the glomerular filtration rate (GFR), the regional glomerular density, and glomerular blood flow, as well as that of the cardiac output, blood pressure, and hematocrit has been followed in 2—79-day-old lambs. The glomerular perfusion rate (GPR), i.e., the glomerular blood flow, has been derived by determining the regional renal blood flow with microspheres and dividing it by the number of glomeruli per unit of renal tissue at that cortical depth assuming that practically all of the spheres are trapped in the glomeruli. The GFR per gram of renal tissue increased more rapidly during the first days of life, whereas the total GFR appeared to increase more linearly with age. The glomerular density fell in all cortical layers. The fall was slightly more pronounced in the inner cortex. The glomerular blood flow was recorded in three zones: the outer 10% of the cortex, which contained an aglomerular as well as a high density glomerular zone; the mid 65% of the cortex, which on gross inspection appeared fairly homogeneous; and the inner 25% of the cortex, which corresponded to the juxtamedullary zone. In all zones the GPR increased with age. The increase was most pronounced in the inner cortex in the oldest animals. The largest scatter of data was found in the outer cortex as a result of the heterogeneity of that zone. The cortical profile for the GPR did not change much with age, which indicated that in the lamb no intrarenal redistribution of blood flow of greater importance occurs during the postnatal development. In the inner and midcortex the GPR increased in proportion to the cardiac output. In the outer cortex the data indicate that GPR increased somewhat more rapidly than cardiac output. The development of the total GFR has been related to the development of the GPR in the inner and midcortex since those two zones contain more than 90% of all glomeruli. During the first period of life the GFR increased more rapidly than the GPR. This coincided with the time when the most rapid fall in hematocrit was recorded. Thus the development of the glomerular plasma flow and the GFR appeared to follow closely.Speculation: In the growing animal as well as in the adult the glomerular plasma flow appears to be the main determinator of the glomerular filtration rate (GFR). Inasmuch as the arterial blood pressure in infants is close to the level at which the renal blood flow is autoregulated in the mature kidney, the GFR might be more susceptible to fluctuations in infants.

Salt content in human breast milk during the three first weeks after delivery.

During a study of electrolyte balance in newborn infants, the concentration of sodium and potassium in breast milk was determined on different days after delivery. Material and Methods. Mothers who were delivered at term were studied on the first ( n = 5 ) , second (n=5) , third (n=17), fourth (n=14), fifth (n=19), sixth (n=6), seventh (n=5), eighth and ninth ( n = 5 ) , tenth and eleventh (n =5) , and twenty-second to twentysixth (n=12) days after delivery. In addition, 19 samples were obtained 1-11 days after delivery from mothers who were delivered during the 32nd-34th gestational week. A 1 ml sample of breast milk was obtained at the beginning and/or at the end of the feeding. The concentration of sodium and potassium in 1/50 diluted breast milk was determined with a flame photometer. Results and Comments. In 11 mothers delivered at term and studied 3-6 days after delivery, the concentration of sodium and potas-

POSTNATAL CONTROL OF WATER AND ELECTROLYTE HOMEOSTASIS IN PRE-TERM AND FULL-TERM INFANTS

Aperia, A., Broberger, O., Herin, P., Thodenius, K. and Zetterström, R. (Department of Paediatrics, Karolinska Institute, St. Görans Childrens Hospital, Stockholm, Sweden). Postnatal control of water and electrolyte homeostasis in pre‐term and full‐term infants. Acta Paediatr Scand, Suppl. 305: 61–65, 1983.—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 IN RELATION TO METABOLIC CONTROL IN CHILDREN WITH DIABETES OF DIFFERENT DURATION

ABSTRACT. 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 >10 years. Glomerular filtration rate (GFR) measuerd as inulin clearance or creatinine clearance, clearance PAH (CPAH), filtration fraction (FF), 24‐hour urinary excretion of β2‐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 >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 β2‐microglobulin was similar in diabetics and controls. In the total material no significant correlation could be found between inulin clearance and creatinine clearance. On the other hand significant inverse correlations were found between creatinine clearance and indices of metabolic control. It is concluded that GFR as measured by inulin clearance is related to indices of metabolic control in a different way with different duration of diabetes. As long as the relation between the increased GFR detectable early in the disease to diabetic nephropathy is unknown the predictable value of this kidney function test is low and prospective studies are necessary. Creatinine clearancee assayed by the method of Jaffé is a poor indicator of GFR in diabetics with a poor metabolic control. 24‐hour urinary excretion of albumin measured by sensitive techniques might be predictive for diabetic nephropathy.

RENAL COMPENSATORY HYPERTROPHY IN CHILDREN WITH UNILATERAL RENAL DISEASE

Abstract. Wilton, P., Aperia, A., Broberger, O. and Wikstad, I. (Departments of Pediatrics and Pediatric Radiology, Karolinska Institute, St. Görans Childrens Hospital, Stockholm, Sweden). Renal compensatory hypertrophy in children with unilateral renal disease. Acta Paediatr Scand, 69:83, 1980.—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 contra‐lateral 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