Indicators of functional differentiation of the chick embryonic kidney

Relevant indicators of the functional capability of the embryonic kidney were tested in the chick mesonephros chosen as an ideal model accessible to direct observation in vivo. Evidence of glomerular filtration (GF) was checked up by the arterial injection of 2% lissamine green (LG) followed by measurement of the LG passage time on days 5, 6 and 7. Presence of the electrogenic transport was investigated by determining the transepithelial potential difference (TPD) which distinguished proximal and distal tubules of the 6-day nephrons. GF and tubular reabsorption could be demonstrated from day 5 by the storage of trypan blue (TB) in proximal tubules after intra-amniotic administration of the dye. The distribution of tubule staining corresponded to the proximal-distal gradient of the nephron differentiation. Activities of embrane enzymes, alkaline phosphatase and 5'-nucleotidase, were detected from day 4. They preceded the ultrastructural maturation in the differentiating proximal tubule epithelia. A semiquantitative evaluation of enzyme activities by the method of measuring of the minimum incubation time (MIT) together with the TB storage, appeared reliable and relevant indicators of the functional properties of mesonephric nephrons, suitable for distinguishing between more and less advanced stages of the nephron development.