Cyclooxygenases in the collecting duct of neonatal rabbit kidney

COX 1 and 2 expression during the terminal phase of kidney development is poorly understood. To obtain information about this process we followed the primary appearance of cyclooxygenases in collecting duct (CD) epithelia of the neonatal rabbit kidney with immunohistochemical and two dimensional electrophoretical methods. In the fully embryonic cortical zone immunohistochemical expression of COX 1 is seen in all cells of the CD ampulla, while COX 2 is lacking within the nephron inducer. Within the matured cortical collecting duct (CCD) COX 1 and 2 immunoreactivity could not be detected. In contrast, a heterogeneous expression profile for COX 1 and 2 is found in the outer medullary CD (OMCD), since not all cells showed immunohistochemical labeling. Within the inner medullary CD (IMCD) nearly all cells express both cyclooxygenases. As revealed by western blot experiments generated embryonic CD epithelia in perfusion culture demonstrate high COX 1 presence at the begin of culture, while COX 2 is found to a minor degree. From day 3 until day 14 continuous levels of COX 1 and 2 expression are detected. Administration of 1 x 10(-7) mmol/l aldosterone does not influence COX expression, while application of 100 mmol/l NaCl increases COX 2 fourfold. The upregulation of COX 2 by a chronic NaCl load in embryonic epithelia suggests in part a constitutive and in part a facultative expression during CD cell differentiation.