Development of renal control of salt and fluid homeostasis during the first year of life.

This study describes the development of renal control of salt and water homeostasis. Twenty-three infants aged 3 weeks to 13 months were studied with respect to glomerular filtration rate (GFR) using single injection technique, ability to excrete an oral salt load, ability to excrete water, and diluting capacity. GFR developed exponentially, salt excretion linearly, water excretion was unchanged and diluting capacity actually decreased. A hypothesis is presented for the theoretical basis of this functional development taking into account the interdependence of the functional parameters studied. This theory might well explain the high incidence of hypernatremic dehydration in infants.