Postnatal development of renal tubular amino acid reabsorption in canine pups

The renal clearance of amino acids in canine pups 5 days and 3, 8, and 12 weeks of age was studied. The 5-day-old pups had incomplete reabsorption of most amino acids. At 3 weeks, fractional reabsorption of 16 of 21 amino acids was complete; between 3 and 8 weeks, an adult pattern of reabsorption was present. Seemingly, a rapid development of amino acid transport precedes anatomic development or functional maturation of other transport systems.