Renal venous and urinary PGE2 output during intrarenal arachidonic acid infusion in dogs

Angiotensin II and renal prostaglandin release in the dog. Interactions in controlling renal blood flow and glomerular filtration rate

The relationship between angiotensin II and renal prostaglandins, and their interactions in controlling renal blood flow (RBF) and glomerular filtration rate (GFR) were investigated in 18 anaesthetized dogs with acutely denervated kidneys. Intrarenal angiotensin II infusion increased renal PGE2 release (veno-arterial concentration difference times renal plasma flow) from 1.7 +/- 0.9 to 9.1 +/- 0.4 and 6-keto-PGF1 alpha release from 0.1 +/- 0.1 to 5.3 +/- 2.1 pmol min-1. An angiotensin II induced reduction in RBF of 20% did not measurably change GFR whereas a 30% reduction reduced GFR by 18 +/- 8%. Blockade of prostaglandin synthesis approximately doubled the vasoconstrictory action of angiotensin II, and all reductions in RBF were accompanied by parallel reductions in GFR. When prostaglandin release was stimulated by infusion of arachidonic acid (46.8 +/- 13.3 and 15.9 +/- 5.4 pmol min-1 for PGE2, and 6-keto-PGF1 alpha, respectively), angiotensin II did not change prostaglandin release, but had similar effects on the relationship between RBF and GFR as during control. In an ureteral occlusion model with stopped glomerular filtration measurements of ureteral pressure and intrarenal venous pressure permitted calculations of afferent and efferent vascular resistances. Until RBF was reduced by 25-30% angiotensin II increased both afferent and efferent resistances almost equally, keeping the ureteral pressure constant. At greater reductions in RBF, afferent resistance increased more than the efferent leading to reductions in ureteral pressure. This pattern was not changed by blockade of prostaglandin synthesis indicating no influence of prostaglandins on the distribution of afferent and efferent vascular resistances during angiotensin II infusion. In this ureteral occlusion model glomerular effects of angiotensin II will not be detected, and it might well be that the shift from an effect predominantly on RBF to a combined effect on both RBF and GFR induced by inhibition of prostaglandin synthesis is located to the glomerulus. We therefore postulate that renal prostaglandins attenuate the effects of angiotensin II on glomerular surface area and the filtration barrier, and not on the afferent arterioles as previously suggested.

Contraluminal p-aminohippurate transport in the proximal tubule of the rat kidney. VII. Specificity: cyclic nucleotides, eicosanoids

Using the stop-flow peritubular capillary microperfusion method the inhibitory potency (apparent Ki values) of cyclic nucleotides and prostanoids against contraluminal p-aminohippurate (PAH), dicarboxylate and sulphate transport was evaluated. Conversely the contraluminal transport rate of labelled cAMP, cGMP, prostaglandin E2, and prostaglandin D2 was measured and the inhibition by different substrates was tested. Cyclic AMP and its 8-bromo and dibutyryl analogues inhibited contraluminal PAH transport with an app. Ki,PAH of 3.4, 0.63 and 0.52 mmol/l. The respective app. Ki,PAH values of cGMP and its analogues are with 0.27, 0.04 and 0.05 mmol/l, considerably lower. None of the cyclic nucleotides tested interacted with contraluminal dicarboxylate, sulphate and N1-methylnicotinamide transport. ATP, ADP, AMP, adenosine and adenine as well as GTP, GDP, GMP, guanosine and guanine did not inhibit PAH transport while most of the phosphodiesterase inhibitors tested did. Time-dependent contraluminal uptake of [3H]cAMP and [3H]cGMP was measured at different starting concentrations and showed facilitated diffusion kinetics with the following parameters for cAMP: Km = 1.5 mmol/l, Jmax = 0.34 pmol S-1 cm-1, r (extracellular/intracellular amount at steady state) = 0.91; for cGMP: Km = 0.29 mmol/l, Jmax = 0.31 pmol S-1 cm-1, r = 0.55. Comparison of app. Ki,cGMP with app. Ki,PAH of ten substrates gave a linear relation with a ratio of 1.83 +/- 0.5. All prostanoids applied inhibited the contraluminal PAH transport; the prostaglandins E1, F1 alpha, A1, B1, E2, F2 alpha, D2, A2 and B2 with an app. Ki,PAH between 0.08 and 0.18 mmol/l. The app. Ki of the prostacyclins 6,15-diketo-13,14-dihydroxy-F1 alpha (0.22 mmol/l) and Iloprost (0.17 mmol/l) as well as that of leukotrienes B4 (0.2 mmol/l) was in the same range, while the app. Ki,PAH of the prostacyclins PGI2 (0.55 mmol/l), 6-keto-PGF1 alpha (0.77 mmol/l) and 2,3-dinor-6-keto-PGF1 alpha (0.57 mmol/l) as well as that of thromboxane B2 (0.36 mmol/l) was somewhat higher. None of these prostanoids inhibited contraluminal dicarboxylate transport and only PGB1, E2 and D2 inhibited contraluminal sulphate transport (app. Ki,SO4(2-) 5.4, 11.0, 17.9 mmol/l respectively). Contraluminal influx of labelled PGE2 showed complex transport kinetics with a mixed Km = 0.61 mmol/l and Jmax of 4.26 pmol S-1 cm-1. It was inhibited by probenecid, sulphate and indomethacin. Contraluminal influx of PGD2, however, was only inhibited by probenecid. The data indicate that cyclic nucleotides as well as prostanoids are transported by the contraluminal PAH transporter. For prostaglandin E2 a significant uptake through the sulphate transporter occurs in addition.(ABSTRACT TRUNCATED AT 400 WORDS)

Basal prostaglandin synthesis by the isolated perfused rat kidney

In order to assess the main characteristics of the prostaglandin (PG) biosynthesis by the isolated perfused rat kidney, the urinary and venous outputs of PGE2, PGF2alpha, 6-keto-PGF1alpha and of thromboxane (Tx)B2 were followed during 120 min after an equilibration period of 30 min. Single pass kidneys were perfused with a Krebs-Henseleit solution added with Polygeline at a constant flow rate providing a perfusion pressure about 90 mm Hg. From the beginning of the study, major differences could be observed in the renal biosynthetic rate of the 4 PG studied which were mainly excreted into the venous effluent. During the perfusion, urinary and venous outputs of PGE2, PGF2alpha and of TxB2 remained stable whereas those of 6-keto-PGF1alpha sharply increased and were found inversely related to the glomerular filtration rate (r = -0.95; p n 0.001). Finally, the urinary and venous outputs of each of the four PGs studied were found positively related. It is concluded that the isolated perfused rat kidney is a valuable preparation for studying the biosynthesis of PGs and that, at least in thi model, the urinary excretion of PGs is a good index of their renal synthesis.

Stimulation of renin release by PGE2 and PGI2 infusion in the dog: enhancing effect of ureteral occlusion or administration of ethacrynic acid

This study on 19 anaesthetized dogs had two objectives. The first was to compare the potencies of PGE2 and PGI2 as stimulators of renin release and demonstrate their dependency on activation of intrarenal mechanisms for renin release. The second objective was to demonstrate that ethacrynic acid (ECA) increases renin release not as a stimulator, but by activating intrarenal mechanisms. After inhibiting renal prostaglandin synthesis by indomethacin, PGE2 and PGI2 infused into the aorta proximal to the renal arteries exerted no significant effects on renin release, but increased renin release during ureteral occlusion. At equimolar infusion rates, PGI2 increased renin release twice as much as PGE2, but this difference in potency may reflect differences in degradation since 86% of PGE2 and 29% of PGI2 (measured as 6-keto-PGF1 alpha) were degraded during one passage through the kidney. By infusing PGF2 at 8 nmol min-1 and PGI2 at 2 nmol min-1 renin release increased equally and the prostaglandin outputs increased to the same levels as during ureteral occlusion before indomethacin administration. ECA did not increase renin release after indomethacin administration. However, infusion of PGE2 during continuous ECA administration increased renin release in a dose-dependent manner similar to the experiments performed during ureteral occlusion. We conclude that PGI2 and PGE2 in the amounts synthesized in the kidney seem to be equally important stimulators of renin release but their relative potencies cannot be determined because the site of degradation is uncertain. Renin release is enhanced by intrarenal mechanisms activated by ECA infusion or ureteral occlusion, which both cause autoregulatory vasodilation and reduce NaCl reabsorption at the macula densa.

Blunted pressure natriuresis in the Brattleboro diabetes insipidus rat

Antidiuretic hormone is known to stimulate the renal synthesis of prostaglandins. These autacoids, in turn, modulate the pressure natriuresis phenomenon. Accordingly, the present study was done to test the hypothesis that, in the absence of antidiuretic hormone and antidiuretic hormone-dependent prostaglandin synthesis, the pressure natriuresis response is blunted. Experiments were performed on Brattleboro diabetes insipidus rats (n = 7) and Long Evans control rats (n = 14). A change in perfusion pressure in the Long Evans rats from 89.3 +/- 1.0 to 108.7 +/- 1.1 mm Hg (p less than 0.05) was associated with significant increases in the fractional excretion of sodium (1.1 +/- 0.2 to 2.3 +/- 0.3%) and the urinary prostaglandin excretion (32.6 +/- 6.8 to 56.6 +/- 10.0 pg/min). In contrast, a similar change in perfusion pressure in the diabetes insipidus rat from 88.6 +/- 1.4 to 106.2 +/- 1.5 mm Hg (p less than 0.05) resulted in no significant increases in either sodium or prostaglandin excretions. Treatment of a third group of diabetes insipidus rats (n = 9) with 1-desamino-8-D-arginine vasopressin (1 microgram/day) restored the natriuretic response to increases in renal perfusion pressure. Treated diabetes insipidus and Long Evans control rats had comparable natriuretic responses to increases in renal perfusion pressure. Untreated diabetes insipidus rats, on the other hand, had blunted responses. In summary, the pressure natriuresis response in diabetes insipidus rats is blunted compared with Long Evans control rats. We conclude that antidiuretic hormone is necessary for the complete expression of the pressure natriuresis response.

Haemodynamic regulation of renal prostaglandin and renin release

To examine the relationship between renal release of the prostaglandins E2 (PGE2) and I2 (PGI2) and renin during autoregulatory vasodilation, experiments were performed in anaesthetized dogs with denervated kidneys. Autoregulatory vasodilation was induced by reducing renal arterial pressure (RAP) or by raising ureteral pressure in steps. During progressive renal arterial constriction, PGE2 and PGI2 release reached maximal values (10.6 +/- 1.7 for PGE2 and 6.6 +/- 1.1 pmol min-1 for PGI2 release) at RAP of 70-80 mmHg, associated with almost no increase in renin release. By further reduction of RAP, prostaglandin release was not significantly altered, whereas renin release reached maximal values (18.7 +/- 2.4 micrograms AI min-1) when autoregulatory vasodilation was complete at RAP below 55-60 mmHg. During progressive elevation of ureteral pressure, the release of PGE2, PGI2 and renin increased in concert in a curvilinear fashion, reaching maximal values at a ureteral pressure of 85 mmHg. There was no further increase during ureteral occlusion and the plateau values averaged 23.6 +/- 3.7 pmol min-1 for PGE2, 8.0 +/- 1.6 pmol min-1 for PGI2 and 16.6 +/- 3.4 micrograms AI min-1 for renin. We conclude that vascular dilation enhances both prostaglandin and renin release. During reduction of RAP, preglomerular arteries are dilated at higher RAP than are afferent arterioles. Release of prostaglandins synthetized in arteries consequently occurs at higher RAP than release of renin, which is not enhanced until afferent arterioles ultimately dilate at RAP approaching 60 mmHg. In contrast, elevation of ureteral pressure provides nearly uniform enhancement of prostaglandin and renin release, indicating a more uniform dilation of the whole preglomerular vascular tree.

Tubular mechanisms determining the urinary excretion of tritiated prostaglandin E2 in the anaesthetized rat

1. The renal excretion of arterially injected tritiated prostaglandin E2 ([3H]PGE2) and its metabolites has been examined in the anaesthetized rat before and after the administration of probenecid (an inhibitor of proximal organic acid secretion). [14C]Inulin was employed as a freely filtered, non-reabsorbable marker, while [3H]p-aminohippurate was used to assess the inhibitory effect of probenecid. The experiments allowed us to quantify the tubular delivery, proximal secretion, intratubular metabolism, and tubular reabsorption of [3H]PGE2 by the whole kidney in vivo. 2. Following a single pass through the left kidney 25% of an injected dose of [3H]PGE2 was excreted, although only 1.7% of the injected 3H co-chromatogrammed with cold PGE2. The chemical content of PGE2 in the isotope employed, produced a slight but significant (P less than 0.05) fall (12%) in the single-pass excretion of [14C]inulin. 3. Intravenous probenecid (100 mg kg-1 + 100 mg kg-1 h-1) completely inhibited the proximal tubular secretion of [3H]p-aminohippurate, while the single-pass excretion of [14C]inulin remained unchanged. Probenecid also reduced the blood pressure and urine flow, and decreased the binding of [3H]PGE2 to plasma protein from 59 to 41%. 4. Probenecid administration reduced the single-pass excretion of 3H following an injection of [3H]PGE2 by 65% down to 8.5% of the injected dose. Due to the change in protein binding however, probenecid also increased the filtered load of [3H]PGE2 from 12 to 16% of the injected dose. 5. The following calculations were made concerning the tubular handling of [3H]PGE2 by the whole kidney in vivo. (i) Thirty-five per cent of the injected dose of [3H]PGE2 was secreted by the proximal tubules on a single pass through the kidney, in addition 12% was filtered while 59% was protein bound. (ii) The tubular reabsorption of [3H]PGE2 was 47% of the filtered load. (iii) [3H]PGE2 was subject to a high degree of intratubular metabolism which at a minimum value represented about 50% of the filtered load. The metabolism of [3H]PGE2 also occurred during proximal tubular secretion.

Effects of ureteral occlusion and ethacrynic acid infusion on renal prostaglandin degradation in the dog

The two major renal prostaglandins PGE2 and PGI2 are partly metabolized during a single passage of the kidney. To examine whether stopping glomerular filtration affected the renal degradation, PGE2 and PGI2 were infused into the suprarenal aorta of dogs during ureteral occlusion. Prostaglandin synthesis was blocked by indomethacin, 10 mg kg-1 b.w. i.v. About 20% of PGI2 and 80-90% of PGE2 were metabolized during one passage through the kidney. Prostaglandin degradation and arterial input were proportional (r greater than 0.95). Compared to control conditions at free urine flow, PGI2 degradation was not changed, whereas the degradation of PGE2 was slightly increased by ureteral occlusion. Ethacrynic acid might reduce degradation of PGE2 by inhibiting two degradation enzymes. To examine the influence of ethacrynic acid, PGE2 was infused in different doses into the suprarenal aorta of dogs before and after administration of ethacrynic acid 3 mg kg-1 b.w. i.v. At all dose levels of PGE2, 75-80% was degraded by one passage through the kidney, whether ethacrynic acid was administered or not. However, although ethacrynic acid did not alter the total renal output, the urinary fraction was reduced from 20-30% to 10-15%. We conclude that degradation of both PGE2 and PGI2 is mainly confined to the blood vessels, and that ethacrynic acid in conventional doses does not prevent degradation of PGE2, but redistributes PGE2 output from urine to renal venous blood.

Renal degradation and distribution between urinary and venous output of prostaglandins E2 and I2

To examine renal degradation and distribution between urine and renal venous blood, prostaglandins E2 and I2 (PGE2 and PGI2), and a metabolite of PGI2, 6-keto-PGF1 alpha, were infused into the suprarenal aorta of anaesthetized dogs after blocking prostaglandin synthesis by indomethacin, 10 mg kg-1 body wt iv. During one passage through the kidney 80% of PGE2 and only 25% of PGI2 and 6-keto-PGF1 alpha were metabolized. Prostaglandin degradation and arterial input were proportional (r greater than 0.90). To stimulate the intrarenal prostaglandin synthesis in unblocked kidneys, arachidonic acid was infused at rates ranging from 24 to 160 micrograms min-1 kg-1 body wt. During arachidonic acid and PGE2 infusion the urinary excretion of PGE2 was about 20% of the renal venous output over a wide range of infusion rates. During arachidonic acid and PGI2 infusion urinary excretion of 6-keto-PGF1 alpha was about 10% of total renal output, but failed to increase further when total renal output exceeded 70 pmol min-1. Further increase in output occurred only in the renal vein. In contrast, during 6-keto-PGF1 alpha infusion the urinary excretion and the renal venous output of this metabolite were related as 1:2 over a wide range of infusion rates. Thus, PGI2 is much less degraded by renal tissue than PGE2, and the distribution patterns differ. Similar distributions between urine and renal venous blood during aortic infusion and stimulated intrarenal synthesis suggest a pre-glomerular vascular origin of both prostaglandins.

Comparison of PGE2, 6-keto PGF1 alpha and renin release from dog kidneys

Several renal cell types synthesize prostaglandin E2 (PGE2) and prostacyclin (PGI2). To examine whether the release of these prostaglandins varies in proportion, prostaglandin synthesis was stimulated in anaesthetized dogs by renal arterial constriction, ureteral occlusion, intrarenal angiotensin II infusion and infusion of arachidonic acid, the precursor of PG synthesis. PGI2 was measured as its stable hydrolysed product, 6-keto PGF1 alpha. The two former procedures raised PGE2 release to 13 +/- 2 pmol min-1, 6-keto PGF1 alpha release to 5 +/- 2 pmol min-1 and renin release to 23 +/- 5 micrograms AI min-1. Angiotensin II infusion, reducing the renal blood flow by 30%, increased PGE2 and 6-keto PGF1 alpha release only half as much as ureteral and renal arterial constriction, and exerted no significant effect on renin release. By increasing the infusion rate of angiotensin II up to 10 times, the renal blood flow remained unaltered in four dogs and fell to 50% of control in two dogs, but PGE2 and 6-keto PGF1 alpha release did not increase further in any of the experiments. Arachidonic acid, infused at 40 and 160 micrograms kg-1 min-1, increased prostaglandin release in proportion to the infusion rate. At the highest infusion rate, PGE2 release averaged 166 +/- 37 pmol min-1 and 6-keto PGF1 alpha release 98 +/- 28 pmol min-1. All procedures increased PGE2 and 6-keto PGF1 alpha release in a fixed proportion of about 2.5:1, whereas renin release increased only during autoregulatory vasodilation.

Haemodynamic conditions for renal PGE2 and renin release during alpha- and beta-adrenergic stimulation in dogs

Constriction of the renal artery and infusion of an alpha-adrenergic agonist induce autoregulated vasodilation and increase prostaglandin E2 (PGE2) and renin release. The enhancement of renin release during autoregulated vasodilation might be mediated by prostaglandins. To examine this hypothesis, experiments were performed in three groups of anaesthetized dogs. In six dogs constriction of the renal artery to a perfusion pressure below the range of autoregulation raised renin release from 2 +/- 1 to 27 +/- 6 micrograms AI X min-1 and PGE2 release from 1 +/- 1 to 10 +/- 2 pmol X min-1. After administration of indomethacin (10 mg X kg-1 b.wt), PGE2 release was effectively blocked and constriction of the renal artery raised renin release only from 0.1 +/- 0.1 to 6 +/- 1 micrograms AI X min-1. During subsequent continuous infusion of a beta-adrenergic agonist, isoproterenol (0.2 micrograms X kg-1 X min-1), constriction of the renal artery raised renin release from 0.1 +/- 0.1 to 52 +/- 11 micrograms AI X min-1, although there was no rise in PGE2 release. In six dogs, intrarenal infusion of phenylephrine, an alpha- adrenergic agonist, increased PGE2 and renin release before, but not after, indomethacin administration. In six other dogs, phenylephrine infused during isoproterenol infusion increased renin release equally before and after indomethacin administration. Thus the enhancing effect of constricting the renal artery or infusing an alpha-adrenergic agonist is not dependent upon prostaglandins. We propose that autoregulated dilation enhances renin release whether the stimulatory agent is a prostaglandin or a beta-adrenergic agonist.

Relationship between PGE2 and renin release in dog kidneys. Effects of afferent arteriolar dilation and adrenergic stimulation

To study the relationship between PGE2 and renin release from the kidney, examinations were performed on anesthetized dogs during afferent arteriolar dilation. This condition is known to increase renin release and enhance the stimulatory effects on renin release of beta-adrenergic agonists, such as isoproterenol. Afferent arteriolar dilation induced by constricting the renal artery or occluding the ureter increased PGE2 and renin release before, but not after, indomethacin administration. Isoproterenol infusion during afferent arteriolar dilation increased renin release but not PGE2 release both before and after indomethacin administration. Phenylephrine, an alpha-adrenergic agonist, which also induces afferent arteriolar dilation, increased PGE2 and renin release at control blood pressure but not when the afferent arterioles already were dilated by ureteral occlusion. We conclude that afferent arteriolar dilation caused by renal arterial constriction, ureteral occlusion or infusion of phenylephrine increases prostaglandin synthesis which stimulates renin release. The effect of isoproterenol on renin release is independent of prostaglandin synthesis.