Kallikrein excretion: relationship with maturation and renal function in human neonates at different gestational ages.

Kallikrein excretion and renal function were studied on 37 one-day-old newborn infants (14 fullterm and 23 preterm infants). Preterm infants excreted less kallikrein (p less than 0.001), had lower creatinine clearance (p less than 0.02) and urinary osmolality (p less than 0.01). They had higher values on urinary volume (p less than 0.001), FENa (p less than 0.001), FEK (p less than 0.02), and free water clearance (p less than 0.01) than fullterm infants. The excretion of kallikrein correlated directly with gestational age (p less than 0.01) and body weight (p less than 0.01). No correlations were found with FENa, urinary volume, FEK or free water clearance. The values of kallikrein excretion were very low when compared with a young adult population. As kallikrein is synthesized in the distal nephron we advance as an hypothesis that the low levels of kallikrein excretion observed in newborns could be a reflection of immature distal tubular mass, and to the relative unresponsiveness of the distal nephron to hormones known to stimulate renal kallikrein such as aldosterone and antidiuretic hormone.