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 < 0.001), had lower creatinine clearance (p < 0.02) and urinary osmolality (p < 0.01). They had higher values on urinary volume (p < 0.001), FE(Na) (p < 0.0001), FE(K) (p < 0.02), and free water clearance (p < 0.01) than fullterm infants. The excretion of kallikrein correlated directly with gestational age (p < 0.01) and body weight (p < 0.01). No correlations were found with FE(Na), urinary volume, FE(K) 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.