Phospholipid content and metabolism were studied in rat renal papillary, medullary and cortical slices. The highest concentration of phospholipids was found in cortex and the lowest in papilla samples (ratio cortex/medulla, 1.3; cortex/papilla, 3.7). The profile of the various phospholipids was different depending on the zone. The most important difference was the relative concentrations of sphingomyelin (CerPCho) and phosphatidylinositol (PtdIns) with ratios for PtdIns/CerPCho of 5.0, 3.3 and 2.5 in papilla, medulla, and cortex, respectively. In the three zones, PtdIns showed the highest specific activity for [2-14C]glycerol and [1-14C]arachidonic acid incorporation. By contrast, a higher amount of [1-14C]palmitic acid was incorporated into phosphatidylcholine than into any other phospholipid. The various radioactive precursors were only poorly incorporated into phosphatidylethanolamine. No radioactivity was associated with phosphatidylserine. The papilla possesses the most active phospholipid metabolism of all the pathways studied.

We have studied microsomal phospholipid, cholesterol and protein concentration in rat renal papilla, medulla and cortex during postnatal development, and the relationship between these membrane biochemical parameters and morphological changes. We also determined DNA concentration in each kidney zone. No changes were observed either in papillary microsomal phospholipids, proteins and cholesterol or in DNA concentration from 10- to 70-day-old rats. Medullary microsomal proteins and cholesterol did not change but a significant increase was observed in the microsomal phospholipid concentration during development; in this case, medullary DNA was significantly lower at 70 than at 10 days. In contrast, all biochemical parameters in renal cortex were significantly higher during development except for DNA concentration which suffered a great decrease. These biochemical findings agree with the morphological changes observed. Our results demonstrate that the developmental pattern is different in each zone of the kidney and confirm the fact that the papilla, in newborn rats, is almost fully developed whereas the renal cortex and medulla are immature.

We have examined the phospholipid content and metabolism in renal papilla, medulla and cortex in 10- to 70-day-old rats. No changes in papillary and medullary phospholipids with an increase in cortical phosphatidylcholine and phosphatidylethanolamine were evident during maturation. Phopshatidylinositol de novo synthesis did not change with age, but a decrease in medullary and cortical phosphatidylcholine and phosphatidylethanolamine was observed. In the three zones [¹⁴C]arachidonic acid incorporation into all the phospholipids was the highest at 10 days with a gradual decrease with age, while the [¹⁴C]palmitic acid incorporation remained unchanged except for phosphatidylinositol which decreased from 10 to 70 days.