ONTOGENY OF AROMATIC L-AMINO-ACID DECARBOXYLASE-CONTAINING TUBULE CELLS IN RAT-KIDNEY

Dopamine plays an important role in regulation of renal sodium transport. Proximal tubule cells produce dopamine after decarboxylation of L-DOPA via the enzyme aromatic L-amino acid decarboxylase (AADC). The presence and cellular localization of AADC-like immunoreactivity (-LI) and AADC mRNA were examined during pre- and postnatal development in rat kidney by indirect immunofluorescence and in situ hybridization histochemistry. Few scattered condensations of AADC-immunoreactive (-IR) tubule cells forming a lumen were detected on gestational day 18. From gestational day 21, many AADC-IR tubule cells were observed in the inner cortex, whereas the outer cortex lacked AADC-LI. Within 24 hours of birth, AADC-IR cells in the inner cortex could be identified as proximal tubule cells. During day 3 and 5 there was an increase in number of AADC-IR proximal tubule cells in the inner cortex, leaving less amount of AADC-negative cells in the outer cortex. Starting from day 8, AADC-IR cells could be seen in the outer cortex. An apparent decrease in AADC-immunofluorescence intensity was observed at 40 days, and at 80 days virtually no AADC-LI could be demonstrated. Intrarenal levels of dopamine showed a tendency to increase between 3 and 20 days, and showed significant decreases between 20 to 40 days and between 40 to 80 days. AADC mRNA was not detected in the kidney at 18 hours after birth, but could be observed in the inner cortex at 6 days. At 12, 19 and 40 days AADC mRNA was seen in the entire cortex. The results indicate that dopamine can be formed prenatally in the proximal tubules of the rat kidney and that the levels of dopamine increase postnatally to reach a peak at one month.