TABLE I Levels of PGE in Rat Renal Medulla

A B S T R A C T Tlhe precise role of the kidney in spontaneous experimental hypertension is unknown. We have analyzed the rates of renal prostaglandin synthesis by utilizing a spontaneously hypertensive rat model. The synthetic rate of prostaglandin E2, prostaglandin F2a, and prostaglandin A2-like products was measured in vitro with renal microsomes. In the rabbit and rat there is a steep gradient of microsomal prostaglandin synthetase from papilla to cortex with highest activities in the papilla. Comparison of the activity of prostaglandin synthetase in medullary microsomes from normotensive and hypertensive rats showed accelerated synthesis in the spontaneously hiypertensive rat. These differences appeared after several months of age, were statistically significant from 3 mo of age and, on the average, represented at least a twofold increase of in vitro activity. All classes of prostaglandins were involved with increased synthesis of prostaglandin E2, prostaglandin F2, and prostaglandin A2-like material. These data reenforce and extend previous work showing alterations of granularity and presumably prostaglandin synthesis in renal medullary interstitial cells in various experimental hypertensions. We also measured renal tissue content of prostaglandin E and prostaglandin A-prostaglandin B by radioimmunoassay. Swift and careful handling of the tissue was necessary to avoid extensive postmortem synthesis of prostaglandins. In rapidly-frozen medullary tissue only prostaglandin E was detectable in concentrations ranging from 10 to 200 pg/mg tissue. No significant differences were found in the medullary content of