Heterogeneity of uridine incorporation along the rabbit nephron. II. Effect of DOCA

Uridine uptake was investigated in microdissected segments from the entire length of tubules from normal rabbit kidneys and the effect DOCA treatment was studied. Uridine uptake was measured after in vitro incubation of kidney pyramids with [14C]uridine (0.25 mM). Determinations were done on intact segments, and also using TCA precipitation on both the acid-soluble fraction considered as representative of the pyrimidine nucleoside precursor pool and the acid-insoluble one containing the precipitated nucleic acids. In normal rabbits the fraction of uridine incorporated in the insoluble fraction represented about 5% of that in the soluble one for all segments. Maximal values were found in the distal convoluted tubule (DCT) and the connecting tubule (CNT), where uridine uptake was two- to fourfold higher than in other segments. After DOCA treatment, a significant increase in uridine uptake in the soluble fraction was present in the cortical collecting (CCT) (+90%, P less than 0.001) and medullary collecting tubules (MCT) (+63%, P less than 0.05) when values were corrected for the cellular swelling induced by DOCA in all segments. An even more marked rise in uridine incorporation was observed in the insoluble fraction of the DCT (+88%, P less than 0.05), CCT (+291%, P less than 0.001), and MCT (+422%, P less than 0.05). These results indicate that 1) the level of uridine uptake in soluble and insoluble fractions widely differs along the tubular length of the normal rabbit nephron; and 2) DOCA treatment induces an increase of uridine incorporation in both the pyrimidine precursor pool and nucleic acids of the collecting tubule, known to be the target site for corticosteroid hormones.