Inhibition of prostaglandin synthesis in chloralose-anesthetized dogs reduced renal blood flow, and this reduction closely correlated (r = 0.92, P<0.01) with a decline in the renal efflux of a substance having the properties of PGE 2 . We used solvent extraction and thin-layer chromatography coupled with parallel bioassay to identify and assay the PGE-and PGF-like substances (expressed as PGE 2 and PGF 2a equivalents). Either of two antunflaiunatory acids, indomethacin or meclofenamate, that inhibited conversion of 14 C-arachidonic acid to prostaglandins in renal homogenates decreased the basal concentration of a PGE-like substance in renal venous blood to 0.06 ±0.02 ng/ml from a mean control value of 0.34 ±0.10 ng/ml (P<0.01). This change was associated with a mean reduction in renal blood flow of 45% in spite of increased renal perfusion pressure. Femoral blood flow and cardiac output were variably and insignificantly affected. Changes in the renal efflux of a PGF-like substance induced by indomethacin were unrelated to the decline in renal blood flow. Changes in the efflux of a PGE-like substance from the femoral vascular bed were unrelated to the small and variable changes in femoral blood flow. Extrarenal factors, i.e., humoral, nervous, or cardiopulmonary factors, did not account for the decline in renal blood flow produced by the inhibitors of prostaglandin synthesis, since the inhibitors produced identical effects in the isolated blood-perfused canine kidney. We concluded that PGE 2 participates in maintaining renal vascular tone which heretofore has been ascribed to autonomous, intrinsic renal arteriolar activity.

Renal prostaglandins (PC s ) might mediate an antihypertensive function of the kidney. The blood-superfused organ technique possesses the sensitivity (threshold < 0.4 ng/ml blood) and specificity required for identification of PGs in blood. Induction of unilateral renal ischemia in 14 chloraloseanesthetized dogs reduced renal blood flows from a mean value of 257 to 109 ml/min on the ischemic side and from 250 to 209 ml/min on the contralateral side. Concomitantly, PG-like substances were detected by assay organs in the venous blood of ischemic (13 experiments) and contralateral (11 experiments) kidneys. In one experiment, in a spontaneously hypertensive dog, PGs were not detected during renal ischemia. Renal venous blood and renal medullary tissue were extracted for acidic lipids and assayed for PG-like substances. Extracts of venous blood collected during renal ischemia and extracts of renal medulla yielded substances with biological activity indistinguishable from PG-like substances or PG standards. Chromatographic characterization of PG-like substances suggests that they are predominantly a mixture of PGE 2 and PGF 2α .

Rabbit kidney medulla (10kg.) was homogenized in 5mm-disodium hydrogen phosphate and deproteinized with ethanol, and the concentrated supernatant solution was extracted at pH8 with light petroleum and at pH2 with chloroform. The acidic lipids present in the chloroform phase were separated on silicic acid columns into three biologically active fractions. The first fraction contained only vasodepressor activity; the second fraction contained both vasodepressor and non-vascular-smooth-muscle-stimulating activity; the third fraction contained both vasopressor and non-vascular-smooth-muscle-stimulating activity. Purification of each fraction by reversed-phase partition and thick-layer chromatography yielded three pure acids. Thin-layer chromatographic, spectroscopic and mass-spectral analysis of the acids and their methyl esters established their structures as prostaglandins E(2), F(2alpha) and A(2). Evidence is presented demonstrating that part or all of the prostaglandin A(2) is formed during the isolation procedures from endogenous prostaglandin E(2).

S U M M A R Y1. The concentrations of prostaglandin E(PGE)-and prostaglandin F(PGF)-like substances in renal venous blood were determined by parallel bioassay of extracts of renal venous effluent before and during adrenergic stimulation of the kidney and were related to simultaneous measurements of renal blood flow and urine flow.2. When noradrenaline was infused continuously into the renal artery, its initial vasoconstrictor and antidiuretic effects diminished on seven of eight occasions in six dogs. Rapid recovery of renal blood flow and urine flow was invariably associated with increasing concentration in renal venous blood of a substance having the physicochemical, chromatographic and biological properties of a prostaglandin of the E series. In the one instance when rapid early recovery of renal blood flow was not observed the concentration of PGE-like substance was not increased.3. In contrast, during renal nerve stimulation early rapid recovery of renal blood flow and urine flow did not occur and the concentration of a PGE-like substance in renal venous blood did not increase. The concentration of a PGF-like substance in renal venous effluent did not increase in response to either stimulus. 4. Since PGE,, unlike PGF2=, is a potent renal vasodilator and diuretic, the intrarenal release of this substance by noradrenaline in concentrations similar to those determined for a PGE-like substance (> 0.50 ng/ml assayed as PGE, equivalents) would account for the changes in renal blood flow and urine flow in these experiments when the renal actions of noradrenaline were attenuated. 5. These results support the proposal that renal prostaglandins function in an intrarenal negative feedback control system which regulates antidiuretic and vasoconstrictor systems.