Prostaglandins play an important role in renal physiology. We have studied the prostaglandin synthetase system in 10 human newborn kidneys ranging from 22 to 40 weeks of gestation who succumbed within 40 hr postnatally. Slices of medulla and cortex were incubated within 2 hr of death in a medium containing 50 μg arachidonic acid and 50 μCi [3H]arachidonic acid. The incorporation of [3H]AA into prostaglandin (PG)E and PGF was determined at 30-min intervals in medulla and cortex tissue and in the incubation media over 120 min and at 180 min, using silicic acid chromatography and scintillation counting. The study showed that biosynthesis of the primary prostaglandins occurs mainly in the renal medulla as early as 22 weeks of gestation, with the biosynthetic activity increasing concomitantly with advanced gestation. The ratio of PGE to PGF in the medulla and cortex was always greater than 1. The highest ratio was obtained in kidneys from neonates born before 28 weeks of gestation. Because prostaglandins are biosynthesized in the neonatal kidney, it is conceivable that hemodynamic and fluid and electrolyte homeostasis functions of prostaglandins may exist at this very early stage of development.SpeculationBecause prostaglandins are biosynthesized early in the development of the neonatal kidney, it is conceivable that hemodynamic and fluid and electrolyte homeostasis functions for prostaglandins might exist at this very early stage of development. Further information into the significance of these findings awaits measurement of age-dependent biologic activity profiles of prostaglandins and their metabolites and prostaglandin-metabolizing enzymes which influence the net production of renal prostaglandins.