Abstract

The patterns of urinary proteins in healthy full-term neonates were examined by sodium dodecyl sulphate gradient polyacrylamide gel electrophoresis (SDS–PAGE), coupled with the determination of a few parameters related to urinary protein excretion.

Twenty healthy full-term neonates were included in the investigation. Five urine samples from each subject were collected, excreted on days 3, 7, 14, 21 and 28 after birth. Determination of total proteins was performed using the turbidimetric method with sulfosalicylic acid. Urinary creatinine concentration was determined by the Jaffe method. Urinary proteins were separated by horizontal gradient SDS–PAGE according to Görg.

Three types of SDS–PAGE electrophoretic profiles were observed. The first type of electrophoretic profile was characterised by the presence of proteins of mixed glomerular and tubular origin with molecular weights from 10 to 160 kDa. Characteristic of the second type of electrophoretic profile was the presence of two faint fractions with molecular weights of 78 and 90 kDa and several intensive low molecular weight fractions (14–67 kDa). In the third type of electrophoretic profile in all five urine samples only low molecular weight proteins (10–67 kDa) were detected. These findings demonstrate the transitory immaturity of the glomerular filter and tubular protein reabsorbing system of the newborn kidney. Apparently the tubular protein handling normalises later than the glomerular filtration of proteins.