Postnatal development of renal function: micropuncture and clearance studies in the dog

Abstract

A B S T R A C T Postnatal renal development was studied in dogs between 2 and 77 days. Single, superficial nephrons were evaluated by micropuncture, concurrently with measurements of total renal function and morphometric analyses in the same animals.Glomerular filtration rate for the entire kidney increased linearly from 0.13 ml/min per g kidney weight at 2 days to 0.91 at 77 days. Extraction of p-aminohippurate increased from about 20 to 80%, and renal plasma flow per g kidney weight, measured as CPAH/EPAH, increased threefold during the same period. Filtration fraction increased to the mature value during the first half of the postnatal period studied.The clearance of urea per unit of renal mass increased with age, whereas the fraction of filtered urea reabsorbed declined during the early part of the postnatal period. The pattern of fractional urea reabsorption may be due mainly to increased medullary recycling of urea and to a rise in the reabsorption of water from the medullary collecting duct.Urine osmolality was higher than plasma from birth onward and rose with age. Osmolal equality of collecting duct fluid and medullary interstitium reflected mature vasopressin (ADH)-induced water permeability. The rise in urinary concentration was predominantly due to increasing medullary sequestration of urea.Glomerular filtration rate of the superficial nephron A preliminary report on part of this work appeared in abstract form: Horster, M. 1970. Postnatal fluid reabsorption in single nephrons of the dog kidney. J. Clin. Invest.

Developmental changes in nephron number, proximal tubular length and superficial nephron glomerular filtration rate of rats.

“…g for Wistar rats). Measurements in GFR of animals younger than this show the previously described age dependent increase Horster & Valtin, 1971;Solomon & Capek, 1972b). Fig.…”

Effect of amiloride on the renal response to saline expansion in new‐born dogs.

“…Current evidence suggests that this attenuated natriuretic response to saline expansion in the new-born animal is primarily a reflexion of differences in distal nephron function between the neonate and the adult (Baker & Solomon, 1976;Kleinman, 1975 (Kleinman, 1975). As the animal matures the fractional sodium reabsorption in the proximal tubule remains relatively constant (Horster & Valtin, 1971). In the new-born dog, acute changes in filtered sodium loads result in proportional changes in proximal tubular sodium reabsorption, demonstrating good glomerulo-tubular balance (Kleinman, 1975).…”

Hypouricemia in Neonates with Syndrome of Inappropriate Secretion of Antidiuretic Hormone

“…In the renal tubule urate is reabsorbed and secreted by relatively specific tubular transport processes (18); the amount of urate finally excreted in the urine appears to depend on the balance between tubular secretion and postsecretory reabsorption (1 1, 19, 20). Renal tubular urate transport is sensitive to many influences including the serum concentration of urate, changes in ECFV (12,13), and age-related maturation of renal function during the early days of life (21). Expansion of ECFV increases urate clearance by inhibiting tubular reabsorption (12,13); contraction of ECFV decreases the urate clearance, probably by enhancing tubular reabsorption.…”