Elevated blood levels of endogenous ouabain-like factor in preterm versus mature newborns at birth

Compared to healthy adults, elevated levels of endogenous ouabain-like factor (OLF) have already been shown in the cord blood, and a role of OLF in the maintenance of high Na(+) excretion by reducing tubular sodium reabsorption during intrauterine life was suggested. In this study, we aimed to measure OLF cord blood levels of premature and mature newborns to provide further data on the possible physiological significance of this compound in neonates. OLF was assessed in the cord blood of newborns (28-41 weeks) and in the blood of healthy adults using ouabain radioimmunoassay. HPLC was employed to isolate endogenous OLF. Newborns had about twelve times higher OLF levels than healthy adults (41.96 +/- 4.64 vs. 3.1 +/- 1.1 pg/ml, p < 0.001). Further, there was a highly significant correlation (p < 0.004) between maturity and OLF concentration; OLF level increased with gestational age, however there was a rapid drop in its concentration at week 39 (43.26 +/- 7 vs. 35.47 +/- 1.84 pg/ml, p = NS). Further studies are needed to evaluate the physiological relevance of higher OLF in preterm versus mature newborns.