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Summary. After acute administration of ammonium chloride, infants 1 to 16 months of age were similar to older children in their capacity to acidify their urine. The infants had a higher rate of excretion of titratable acid and a lower rate of excretion of ammonium but were similar in their rate of excretion of total hydrogen ion.Bicarbonate titrations performed in infants during the first year of life demonstrated a threshold ranging from 21.5 to 22.5 mmoles per L, maximal rate of reabsorption from 2.6 to 2.9 mmoles per 100 ml glomerular filtrate, and marked titration splay. A nephronic frequency distribution curve of the ratio of glomerular filtration rate to tubular reabsorptive capacity demonstrated both heterogeneity and skewing to the right, suggesting the presence of significant numbers of nephrons with low tubular transport capacity relative to filtration rate.

Hypertension is common in children after renal transplantation and is associated with multiple factors. Data regarding the prevalence of post-transplant hypertension and the relationship between immunosuppressive drugs and the persistence of hypertension in a large population of North American children have not been available. This study was designed by the North American Pediatric Renal Transplant Cooperative Study to evaluate in a large diverse multicenter population of children the prevalence of hypertension post transplantation, the type of antihypertensive medications used to treat this hypertension and to determine the relationship between the blood pressure control and the immunosuppressive therapy. Analysis of 277 patients showed the following: (1) 70% of recipients required antihypertensive medications 1 month post transplant compared with 48% pre transplant; the incidence decreased to 59% at 24 months; (2) the majority of children received multiple drug therapy to control blood pressure; (3) hypertension can be controlled effectively despite inherent etiological factors, such as allograft source, prior hypertension and immunosuppressive therapy.

ExtractCardiac output, renal blood flow, and intrinsic renal vascular resistance were measured in piglets ranging in age from 6 h to 45 days. During this period of time the mean cardiac output increased from 0.9 to 6.5 liters/min/m . These data demonstrate that the large increase in renal blood flow in the pig during the first 6 weeks of life was due to both an increase in cardiac output as well as a decrease in renal vascular resistance. By 6 weeks of age, cardiac output was at adult levels. Since in the adult pig the kidney receives 20 % of the cardiac output, increases in renal blood flow beyond 6 weeks of age must result from further decreases in renal vascular resistance. SpeculationIn the human infant, cardiac index is comparable to values observed in the adult. It appears, therefore, that the entire increase in renal blood flow observed during year 1 of life is due to steadily decreasing renal vascular resistance. Since glomerular filtration rate is modified by the relative resistances in the glomerular afferent and efferent arterioles, the parallel increases in filtration rate during infancy may be related to the same mechanism.Introduction mates renal plasma flow by not more than 30-40%. Rates of flow reach mature levels (1,200 ml/min/1.73 Numerous studies have shown that renal blood flow m

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This report of the North American Pediatric Transplant Cooperative Study summarizes data contributed by 57 participating centers on 754 children with 761 transplants from 1 January 1989 to 16 February 1989. Data collection was initiated in October 1987 and follow-up of all patients is ongoing. Transplant frequency increased with age; 24% of the patients were less than 5 years, with 7% being under 2 years. Common frequent diagnoses were: aplastic/dysplastic kidneys (18%), obstructive uropathy (16%), and focal segmental glomerulosclerosis (12%). Preemptive transplant, i.e., transplantation without prior maintenance dialysis, was performed in 21% of the patients. Dialytic modalities pretransplant were peritoneal dialysis in 42% and hemodialysis in 25%. Bilateral nephrectomy was reported in 29%. Live-donor sources accounted for 42% of the transplants. Among cadaveric donors, 41% of the donors were under 11 years old. During the first post-transplant month, maintenance therapy was used similarly for live-donor and cadaver source transplants, with prednisone, cyclosporine, and azathioprine used in 93%, 83%, and 81%, respectively. Triple therapy with prednisone, cyclosporine, and azathioprine was used in 78%, 75%, and 75% of functioning cadaver source transplants at 6 months, 12 months, and 18 months as opposed to 60%, 63%, and 54% for live-donor procedures, with single-drug therapy being uncommon. Rehospitalization during months 1-5 occurred in 62% of the patients, with treatment of rejection and infection being the main causes. Additionally, 9% were hospitalized for hypertension. During months 6-12 and 12-17, 30% and 28% of the patients with functioning grafts were rehospitalized. Times to first rejection differed significantly for cadaver and live-donor transplants. The median time to the first rejection was 36 days for cadaver transplants and 156 days for live-donor transplants. Overall, 57% of treated rejections were completely reversible although the complete reversal rate decreased to 37% for four or more rejections. One hundred and fifty-two graft failures had occurred at the time of writing, with a 1-year graft survival estimate of 0.88 for live-donor and 0.71 for cadaver source transplants. In addition to donor source, recipient age is a significant prognostic factor for graft survival. Among cadaver donors, decreasing donor age is associated with a decreasing probability of graft survival. Thirty-five deaths have occurred; 16 attributed to infection and 19 to other causes. The current 1-year survival estimate is 0.94. There have been 9 malignancies.

There are several methods to evaluate renal function during childhood. The use of serum creatinine, either alone or in combination with the Schwartz formula, is reliable and quick, but requires knowledge of conceptual age. A plasma creatinine concentration of 88.4 mumol/L (1.0 mg/dL), for example, represents normal renal function in an adolescent but more than 50% loss of renal function in a 5-year-old child. A timed urine collection for creatinine clearance is another evaluative method, but the adequacy of the urine collection always should be determined first. Urea clearance rarely is used to measure GFR because of the complex factors that influence urea excretion. Measurement of the disappearance of radioactive-labeled substances in plasma can be used to determine GFR. Radionuclide renal scans also can be used and offer the advantage of estimating the GFR of each kidney. Although infants and newborns have an intact urine diluting ability, their concentrating ability is impaired. The maximal urinary concentration in the neonatal period is less than 700 mOsm/kg, but reaches adult values of 1200 mOsm/kg by 6 to 12 months of life. Similarly, the infant kidney has a limited capacity for salt regulation, predisposing the infant to salt disturbances.

MENG, AND MILTON ELKIN. Validation of use of xenon 133 to measure intrarenal distribution of blood flow. Am. J. Physiol. 219(Z) : 440-444. 1970.-The gamma camera has been used to evaluate the distribution of radioxenon in man after injection into the renal artery. Combined gas-washout curves performed according to the method of Thorburn and associates and gamma-camera studies confirm the relationship between the first component of the gas-washout curve and clearing of radioactivity from the renal cortex. The mean cortical renal blood flow in patients with no known renal disease on a normal diet was 413 ml/min per 100 g of kidney =t 27 (SE). This represented 76.4% =t 2.7 of the total renal blood flow. The method was found to be reproducible and safe. These studies suggest that the xenon washout study is a reliable method for the determination of the intrarenal distribution of blood flow in man.