Renal handling of water and sodium in infancy and childhood: A study using clearance methods during hypotonic saline diuresis

摘要

Renal function is low in infancy, even when the appropriate correction is made for the small body size [1]. Although we know that the maturing kidney seems able to maintain body homeostasis despite wide fluctuations in dietary intake, we know little about the pattern of development of the various tubular functions and especially of sodium and water reabsorption. Even the classical concept that tubular function lags behind glomerular filtration during development [2] has been a matter of recent controversy, and no firm conclusion can be drawn from micropuncture studies about whether glomerulotubular balance exists in the immature animal [3].Clearance techniques, although limited by the necessity for invoking a variety of assumptions, retain the unique advantages of being applicable to human studies and of being relevant to the function of the whole kidney 'in situ' rather than of an isolated population of nephrons. In the present experiments, fractional clearances during hypotonic saline diuresis have been used to study tubular handling of water and sodium in infants and children. With all the limitations in mind, the validity of this methodology is well accepted [4–6], but to our knowledge only a few reports are available of its application to the study of maturation of the renal function in man [7, 8].