Renal function in conscious rats after indomethacin. Evidence for a tubular action of endogenous prostaglandins

The renal adverse effects of ibuprofen are not mediated by AQP2 water channels

The aim of this study was to determine (1) whether ibuprofen treatment in very preterm infants causes an increase in the renal water channel aquaporin-2 (AQP2) activity in the collecting duct via prostaglandin synthesis inhibition and (2) whether AQP2 activity remains disturbed long after ibuprofen treatment has ended. This was a prospective study involving premature infants with a gestation age of 27-31 weeks who received treatment between December 2005 and August 2006 in a tertiary Neonatal Intensive Care Unit. Each ibuprofen-treated infant was matched to two controls. Renal glomerular and tubular function were evaluated weekly for 1 month, and urinary AQP2 was measured by immuno-dotting. In total, 166 longitudinal samples were analyzed in 36 infants. Median [interquartile range] gestational age and birthweight were 28 [27.0-29.5] weeks and 1160 [1041-1242] g, respectively. Perinatal factors were similar in both groups. Urine output was significantly decreased in the ibuprofen-treated infants during the treatment. The urinary AQP2 level decreased significantly from day 2 to day 7 in both groups and was similar thereafter for the first month of life in ibuprofen-treated and control groups. Based on our results, we conclude that ibuprofen-induced oligo-anuria is not associated with a change in AQP2 activity and that ibuprofen does not affect AQP2 activity during the first month of life in very preterm neonates.

Cyclooxygenase 2 inhibition exacerbates AQP2 and pAQP2 downregulation independently of V2 receptor abundance in the postobstructed kidney

Previously we demonstrated that ANG II receptor (AT1R) blockade attenuates V2 receptor (V2R), AQP2, and pS256-AQP2 downregulation in the postobstructed kidney and partially reverses obstruction-induced inhibition of cAMP generation and cyclooxygenase 2 (COX-2) induction. Therefore, we speculated whether the effects of AT1R blockade on V2R and the vasopressin-regulated pathway are attributable to attenuated COX-2 induction. To examine this, rats were subjected to 24-h bilateral ureteral obstruction (BUO) followed by 48-h release and treated with the COX-2 inhibitor parecoxib or saline. Control rats were sham-operated. Parecoxib treatment significantly reduced urine output 24 h after release of BUO whereas urine osmolality and solute-free water reabsorption was comparable between saline- and parecoxib-treated BUO rats. Immunoblotting revealed a significant decrease in AQP2 and pS256-AQP2 abundance to 20 and 23% of sham levels in parecoxib-treated BUO rats compared with 40 and 55% of sham levels in saline-treated BUO rats. Immunohistochemistry confirmed the exacerbated AQP2 and pS256-AQP2 downregulation in parecoxib-treated BUO rats. Finally, parecoxib treatment had no effect on V2R downregulation and the inhibited, vasopressin-stimulated cAMP generation in inner medullary membrane fractions from the postobstructed kidney. In conclusion, COX-2 inhibition exacerbates AQP2 and pS256-AQP2 downregulation 48 h after release of 24-h BUO independently of V2R abundance and vasopressin-stimulated cAMP generation. The results indicate that COX-2 inhibition does not mimic AT1R blockade-mediated effects and that AT1R-mediated AQP2 regulation in the postobstructed kidney collecting duct is independent of COX-2 induction.

Comparative effects of indomethacin and nabumetone on urine and electrolyte output in conscious rats

The effects of indomethacin and nabumetone on urine and electrolyte excretion in conscious rats were examined. Male Sprague-Dawley rats were housed individually for a five-week duration, consisting of acclimatization, control, experimental, and recovery phases. During the experimental phase, rats were given either indomethacin (1.5 mg . kg(-1) body weight . day(-1) in 0.5 ml saline, n = 10), nabumetone (15 mg . kg(-1) body weight . day(-1) 0.5 ml saline, n = 10), or 0.5 ml saline alone (n = 10) for a period of two weeks. Water and food intake, body weight, urine output, and electrolyte excretions were estimated. Data were analyzed using two-way ANOVA. Urine output in the indomethacin- and nabumetone-treated groups was not different from the controls, but was significantly different between the drug-treated groups (P<0.01). Sodium, potassium, calcium, and magnesium excretions were not different between nabumetone-treated and control rats. However, sodium and potassium excretion was significantly lower in rats receiving indomethacin when compared to the control rats. Calcium and magnesium outputs, although did not differ from the controls, nevertheless decreased significantly with indomethacin (P<0.01). It appears that indomethacin and nabumetone when given at maximum human therapeutic doses may affect urine and electrolyte output in conscious rats.

Urinary nitrite excretion and urinary variables in patients with primary nocturnal frequency of micturition: effects of indomethacin suppositories

Urinary nitrite excretion was measured in patients with primary nocturnal frequency of micturition (PNFM) and in normal individuals. Effects of indomethacin suppository on urine volume and other urinary variables were evaluated. The study comprised seven patients with PNFM and seven healthy control (age range 30-45 years). Nitrite was assayed in spot morning urine samples; urine volume, urine osmolality and electrolytes, serum osmolality and electrolytes and functional bladder capacity (FBC) were assayed. Both groups were then given 100 mg of indomethacin suppository daily for a maximum of 10 days and urinary variables were re-evaluated during day 10. Results showed that urinary nitrite excretion of patients with PNFM was greater than that of the normal subjects (230+/-62 umol/l vs. 42+/-30 umol/l, P<0.05). The mean (SD) 24 h urine volume and osmolality, the night urine volume and osmolality, serum osmolality, FBC, creatinine clearance, fractional excretion of sodium (FENa), fractional excretion of potassium (FEK), and urinary excretion of glucose and potassium were lower in patients with PNFM as compared with normal individuals, although not statistically significantly so, except for FBC that was significantly lower in the patients. Urinary excretion of sodium, calcium, chloride, phosphorus, magnesium, day-night urinary volume ratio, spot morning osmolality, nocturnal index, and nocturnal polyuria index were higher in patients with PNFM. Indomethacin decreased the 24 h urinary volume by 21%, creatinine clearance by 12%, osmolar clearance by 14% and urinary protein excretion by 38% in the patients. These variables decreased by 26, 45, 17 and 12% respectively in the healthy subjects, whereas 24 h urinary protein excretion increased mildly by 9%. Indomethacin increased day-night urinary volume ratio by 73% in the healthy subjects. It might be concluded that urinary nitrite excretion, urinary excretion of sodium, chloride, phosphorus, calcium, and magnesium increased and FBC decreased in patients with PNFM; Indomethacin decreased urinary volume, FENa, FEK, osmolar clearance, and free water clearance in the healthy subjects and the patients. These might explain the mechanism of action of indomethacin to reduce frequency of voiding. The possible interaction of prostaglandin and NO in the pathogenesis of PNFM is discussed.

Cyclooxygenase inhibitors increase Na-K-2Cl cotransporter abundance in thick ascending limb of Henle's loop

Cyclooxygenase inhibitors, such as indomethacin and diclofenac, have well-described effects to enhance renal water reabsorption and urinary concentrating ability. Concentrating ability is regulated in part at the level of the thick ascending limb of Henle's loop, where active NaCl absorption drives the countercurrent multiplication mechanism. We used semiquantitative immunoblotting to test the effects of indomethacin and diclofenac, given over a 48-h period, on the expression levels of the ion transporters responsible for active NaCl transport in the thick ascending limb. Both agents strongly increased the expression level of the apical Na-K-2Cl cotransporter in both outer medulla and cortex. Neither agent significantly altered outer medullary expression levels of other thick ascending limb proteins, namely, the type 3 Na/H exchanger (NHE-3), Tamm-Horsfall protein, or alpha1- or beta1-subunits of the Na-K-ATPase. Administration of the EP3-selective PGE(2) analog, misoprostol, to indomethacin-treated rats reversed the stimulatory effect of indomethacin on Na-K-2Cl cotransporter expression. We conclude that cyclooxygenase inhibitors enhance urinary concentrating ability in part through effects to increase Na-K-2Cl cotransporter expression in the thick ascending limb of Henle's loop. This action is most likely due to elimination of an EP3-receptor-mediated tonic inhibitory effect of PGE(2) on cAMP production.

Physiological responses to repeated endotoxin challenge are selectively affected by recombinant bovine somatotropin administration to calves

The study determined 1) whether the pretreatment of calves with recombinant bovine somatotropin (bST, sometribove) would alter the change in packed cell volume (PCV), rectal temperature (RT), and the plasma concentrations of Ca2+, Fe2+, glucose (G), urea N (PUN), nonesterified free fatty acids (NEFA), albumin (ALB), and blood cell populations after endotoxin challenge (EC) and 2) whether the natural development of physiologic tolerance to repeated EC was affected by bST. Twelve steer beef calves were assigned to either control (-bST) or +bST treatment in equal numbers. Calves were injected intramuscularly with either HCO3(-)-buffered saline or bST (0.1 mg/kg) daily for 5 d. On Day 6, the first EC was administered (Escherichia coli, 055:B5, 0.2 microgram/kg, intravenous bolus in pyrogen-free saline). Saline or bST injections were continued from Day 7 up to the repeat of EC on Day 11. RT and PCV were measured hourly through 12 and 6 hr, respectively. Jugular blood was obtained at 0, +1, 2, 3, 4, 6, 8, 12, and 24 hr relative to each EC. bST had no effect on the increase in RT, the hyperglycemic phase of the G response, the biphasic change in Fe2+, or increases in NEFA and PUN. PCV increased after each EC only in -bST. The mean decrease in G during the hypoglycemic phase was less in +bST. Hypocalcemic responses were significantly less in +bST. ALB concentrations decreased after each challenge; the response was unaffected by bST. CD2+, CD4+, and CD8+ T-lymphocyte populations were unaffected by bST and EC. Overall, the magnitude of change in all plasma variables was less after the second EC compared with the first, either in terms of magnitude or duration. The data suggest that the treatment of calves with bST diminishes the magnitude of hypoglycemic, hypocalcemic, and PCV changes after EC and does not compromise fever response, changes in blood cell populations, or tolerance to repeated EC.

Prostaglandin E2 in renal transplant recipients

The concentrations of prostaglandin E2 (PGE2), sodium, potassium and creatinine were determined in the blood and urine of 50 renal transplant recipients treated with cyclosporine A or azathioprine, as immunosuppressive agents, for at least one year post transplantation. Fourteen healthy subjects served as control group. The urinary PGE2 excretion was significantly decreased in all treated renal transplant recipients and this reduction was associated with significant decrease in urinary excretion of sodium and potassium. On the other hand, a high elevation in blood PGE2 concentration was observed while no significant changes were seen in sodium and potassium levels in the blood of these renal transplant recipients. The observations suggest an association between urinary PGE2 reduction and immunosuppressive treatments in renal transplant recipients; also, PGE2 may regulate intra-renal haemodynamics and influence the renal tubular electrolyte excretion. Moreover, urinary PGE2 can be used as an indicator of successful renal transplantation.

Chloride secretion stimulated by prostaglandin E1 and by forskolin in a canine renal epithelial cell line

1. The actions of prostaglandins upon ion transport in a renal-derived cultured epithelium (MDCK) have been investigated. 2. Prostaglandin E1 (PGE1) stimulates an inwards short-circuit current (SCC) in voltage-clamped epithelial layers mounted in Ussing chambers. Measurements of transepithelial Cl- fluxes, cation and anion replacement of the bathing media and the use of the Cl- channel blocker 3-nitro-2(3-phenylpropylamino)-benzoic acid (NPPB) are consistent with the PGE1-stimulated inward SCC resulting predominantly from basal to apical Cl- secretion. 3. The response of MDCK epithelia is relatively specific for prostaglandins of the E series. PGE1 is most effective when applied to the basal bathing solutions, though near-maximal stimulation of SCC was possible with 1 microM-PGE1 added to the apical bathing solution. 4. Forskolin addition (10 microM) stimulates an inwards SCC in MDCK epithelia which displays similar characteristics and is of a similar magnitude to that observed with PGE1. In the presence of isobutylmethylzanthine, PGE1 and forskolin are capable of elevating intracellular cyclic AMP accumulation, suggesting that stimulation of inward SCC is mediated via a cyclic AMP-dependent mechanism.

Role of prostaglandins in tumour necrosis factor induced weight loss

Administration of either tumour necrosis factor alpha (TNF-alpha) or 16,16-dimethylprostaglandin E2 (PGE2) to female NMRI mice caused a decrease in body weight accompanied by a reduction in both food and water intake and a decrease in carcass water content. A single injection of TNF-alpha caused an enhanced production of PGE2 by spleen cells from treated animals, that was significant within 1 h of treatment, and persisted until at least 6 h. These results suggest that the anorectic effect of TNF-alpha may be mediated by a prostaglandin intermediate. Indomethacin (10 mg kg-1) administered 2 h before TNF-alpha (7.5 x 10(7) U kg-1) caused a significant reduction in the extent of weight loss and inhibited PgE2 production. Administration of indomethacin 0.5-1.5 h before the TNF-alpha had no significant effect on loss of body weight, but still inhibited PgE2 production. Also PgE2 production was still enhanced in response to TNF-alpha administered chronically, despite the inability of prolonged TNF-alpha administration to produce continued loss of body weight. These results suggest that prostaglandins are not involved in the anorectic effect of TNF-alpha.

Eicosanoids in renal function

The major role of renal eicosanoid synthesis appears to be a protective one. In the cortex, prostaglandin synthesis minimises potential anoxic and ischaemic damage by vasodilatation. In the medulla, prostaglandin synthesis appears to stabilise the corticomedullary solute gradient and may play a role in cell volume regulation. Mono-oxygenase production at this site, by modifying blood flow and cellular active transport processes could again serve a protective function against anoxia and ischaemia. The release of erythropoietin also appears to be prostaglandin dependent. It is likely that leukotrienes released from inflammatory cells within the kidney will affect renal haemodynamics and capillary permeability as in other tissues.

Dose-response effects of pressor doses of arginine vasopressin on renal haemodynamics in the rat

1. Dose-response effects of arginine vasopressin on renal haemodynamics were studied in conscious and in pentobarbitone-anaesthetized rats infused with 77 mM-NaCl at 5.2 and 2.6 ml h-1 respectively. 2. Vasopressin at 0.8 pmol h-1 (100 g body weight)-1 did not have a significant effect on arterial blood pressure in conscious or anaesthetized rats. Increasing the dose to 2.5 pmol h-1 (100 g body weight)-1 induced a pressor effect in conscious rats but not in anaesthetized rats. A pressor response was observed in the latter at a dose of 10 pmol h-1 (100 g body weight)-1. 3. Pressor doses of vasopressin of 100 pmol h-1 (100 g body weight)-1 and less did not significantly alter the clearance of p-aminohippurate (PAH) in either conscious or anaesthetized rats. A dose of 1000 pmol h-1 (100 g body weight)-1 significantly decreased PAH clearance in both conscious and anaesthetized animals. 4. Inulin clearance was unchanged by non-pressor doses of vasopressin in both conscious and anaesthetized rats. Moderately pressor doses decreased inulin clearance in conscious animals only. The highest dose administered (1000 pmol h-1 (100 g body weight)-1) decreased inulin clearance in both conscious and anaesthetized rats. 5. Pressor doses of vasopressin had a biphasic effect on the filtration fraction in conscious rats. The filtration fraction decreased with doses of vasopressin at the lower end of the pressor range but increased with the highest dose of 1000 pmol h-1 (100 g body weight)-1. In contrast the filtration fraction did not change significantly with moderate pressor doses in anaesthetized rats but was increased by doses of 100 and 1000 pmol h-1 (100 g body weight)-1. 6. It is concluded that pressor doses of vasopressin lower than 100 pmol h-1 (100 g body weight)-1 do not decrease renal plasma flow rate in conscious or pentobarbitone-anaesthetized rats. The results suggest that the inconsistent effects of vasopressin on renal blood flow reported in the literature are due, at least in part, to the wide range of doses used.

Effect of maximal hydration on the renal responses to pretreatment with nonsteroidal anti-inflammatory drugs and probenecid in man

The renal response to a challenge of maximal water diuresis has been studied in seven subjects pretreated over 48 h with either placebo, probenecid, indomethacin or piroxicam. Probenecid did not alter the excretion of water and sodium chloride when compared with placebo responses, but increased both phosphate and urate clearances. Indomethacin reduced significantly both water and sodium chloride clearances by approximately 40%. Piroxicam reduced water excretion to a similar extent but did not influence salt output. In parallel with these changes, both drugs caused significant phosphaturia. It is concluded that the renal actions of nonsteroidal anti-inflammatory drugs (NSAIDs) are individually distinct and involve direct effects on tubular transport of ions and water to differing extents within both the proximal and distal portions of the nephron.

Renal haemodynamic actions of pressor doses of lysine vasopressin in the rat

1. Dose-response effects of lysine vasopressin on renal haemodynamics were studied in conscious rats infused with 2.5% (w/v) dextrose solution at 5.8 ml/h. 2. Lysine vasopressin was maximally antidiuretic in the absence of a significant pressor effect at a dose of 2.5 pmol h-1 100 g body weight-1. Doses of vasopressin greater than this induced a dose-dependent increase in arterial blood pressure. 3. The clearance of p-aminohippurate (PAH) was not significantly changed by vasopressin, even at pressor doses. Rats pre-treated with indomethacin to inhibit prostaglandin synthesis showed a decrease in PAH clearance during the infusion of vasopressin at a dose of 30 pmol h-1 100 g body weight-1, and this suggests that the renal vasoconstrictor actions of vasopressin are attenuated by dilator prostaglandins. 4. Inulin clearance was unchanged by non-pressor doses of vasopressin but was decreased in a dose-dependent manner by pressor doses. A maximal effect was induced by a dose of 30 pmol h-1 100 g body weight-1 which decreased inulin clearance from 3.23 +/- 0.76 (mean +/- S.E. of mean) to 1.60 +/- 0.37 ml/min (P less than 0.02). A change in inulin clearance (from 3.42 +/- 0.46 to 2.17 +/- 0.33 ml/min, P less than 0.01) was also observed in rats pre-treated with indomethacin and infused with vasopressin at the same dose. The magnitude of the change was not significantly different from that observed in rats which were not treated with indomethacin. 5. Control rats infused with dextrose showed a slight but significant increase in sodium excretion during the course of the experiment. A similar natriuresis was observed in rats infused with non-pressor doses of vasopressin but was considerably enhanced in rats infused with pressor doses of the peptide. The antidiuresis induced by vasopressin remained maximal in rats infused with pressor doses. 6. Potassium and osmolal outputs were unchanged by non-pressor doses of vasopressin but significantly increased during administration of pressor doses. 7. It is concluded that pressor doses of lysine vasopressin do not alter total renal perfusion in conscious rats when the prostaglandin system is intact. Glomerular filtration is, however, decreased in a dose-dependent manner by these amounts but the mechanism is unclear.

The effects of naproxen and sulindac on renal function and their interaction with hydrochlorothiazide and piretanide in man

We have studied the effect of a single dose challenge of naproxen (500 mg) and sulindac (200 mg) on renal function in five volunteers, and the effect of a single dose challenge of the thiazide, hydrochlorothiazide (100 mg), and loop diuretic, piretanide (6 mg) on renal function when the diuretics were given alone or when superimposed on chronic therapy of either naproxen or sulindac. None of the nonsteroidal anti-inflammatory drug (NSAID) or diuretic exposures significantly influenced glomerular filtration rate, as measured by creatinine clearance. Over the first 4 h of the study, both naproxen and sulindac reduced fractional excretion of sodium by approximately 50%. Sulindac also caused a significant uricosuria whilst naproxen promoted urate retention. Similar changes were observed over 8 h. Superimposition of either hydrochlorothiazide or piretanide on top of chronic sulindac therapy resulted in a blunting of the natriuresis by approximately 30% compared to when these diuretics were given alone: the action of the diuretics was unchanged by naproxen. Sulindac pretreatment did not alter the urinary excretion of either hydrochlorothiazide or piretanide; naproxen did not alter hydrochlorothiazide excretion. On the basis of these findings, it is concluded that NSAIDs exert direct tubular effects that do not necessarily interfere with the delivery of diuretics to their sites of action within the nephron.

Evidence against the hypothesis that prostaglandins are the vasodepressor agents of pregnancy. Serial studies in chronically instrumented, conscious rats

Renal hemodynamics increase dramatically during pregnancy, and pressor responsiveness to exogenous administration of vasoconstrictors is attenuated. We investigated whether or not vasodilatory prostaglandins mediate these phenomena. Trained, chronically instrumented, conscious pregnant rats were used. Control values of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were elevated at midgestation (P less than 0.01 and P = 0.05 from prepregnant means, respectively), and effective renal vascular resistance was decreased (P = 0.05). Indomethacin (4.5-6.5 mg/kg body weight [BW]) failed to decrease renal hemodynamics at this stage of pregnancy; in fact, it raised GFR somewhat further (P less than 0.05). Systemic pressor responsiveness to bolus administration of norepinephrine and angiotensin II (AII) was significantly attenuated by at least gestational day 20. Neither indomethacin (7 mg/kg BW) or meclofenamate (6 mg/kg BW) affected the refractory response. The renal vasculature was also relatively unresponsive to an intravenous infusion of AII (5 ng X kg-1 X min-1) during late gestation (day 19); in particular, the fall in ERPF in response to AII (16 +/- 3%) was markedly less than that observed in the prepregnant condition (34 +/- 3%; P less than 0.05). Indomethacin (6 mg/kg BW) failed to restore this blunted response, and further attenuation was evident, despite the presence of the inhibitor (gestational day 21). We conclude that vasodilatory prostaglandins do not appear to mediate the rise in renal hemodynamics, and the attenuation of the systemic and renal pressor responsiveness observed during pregnancy, insofar as these phenomena were unaffected by acute cyclooxygenase inhibition in unstressed, conscious rats.

Renal extraction and clearance of p-aminohippurate during saline and dextrose infusion in the rat

The reliability of the use of p-aminohippurate (PAH) as a clearance marker for the determination of renal plasma flow during saline or dextrose infusion was investigated in conscious and anaesthetized rats. In the conscious rat (wt. 350-400 g) infused for 4 h with 0.85% saline followed by 3 h of 2.5% dextrose, PAH clearance averaged 11.50 +/- 1.45 ml/min during saline infusion and 7.83 +/- 0.82 ml/min during dextrose infusion. The difference was significant (P less than 0.02). Inulin clearance, however, was unchanged. With dextrose as the initial infusate, PAH clearance averaged 5.86 +/- 0.65 ml/min and increased (P less than 0.01) to 8.74 +/- 0.71 ml/min following a change of infusate to saline, although inulin clearance was again unchanged. In separate groups of rats anaesthetized with sodium pentobarbitone, a comparison was made between renal blood flow values calculated from PAH clearance and haematocrit, and those determined simultaneously using an electromagnetic flow probe placed on the left renal artery. During 0.85% saline infusion, the calculated value was 88.1 +/- 8.4% of that measured using the flow probe. During 2.5% dextrose infusion the value determined from PAH clearance was only 47.3 +/- 4.2% of that obtained using the flow probe, and this is significantly (P less than 0.01) lower than the ratio found during saline infusion. In another study, renal venous blood samples were obtained from sodium-pentobarbitone-anaesthetized rats during 0.85% saline or 2.5% dextrose infusions, for calculation of the renal PAH extraction ratio. During saline infusion, PAH extraction averaged 68.3 +/- 2.5%, whereas during dextrose infusion PAH extraction was lower (P less than 0.001) and averaged only 48.8 +/- 3.2%. It is concluded that PAH clearance grossly underestimates renal plasma flow during 2.5% dextrose infusion in the rat.

Reduction of urinary excretion of PGE2 and 6 keto PGF1 alpha by tiaprofenic acid

Tiaprofenic acid (Surgam, Cassenne) was administered intravenously to saline-diuretic conscious rats, at doses of 2, 10 and 25 mg kg-1 body weight. Tiaprofenic acid significantly reduced urinary prostaglandin E2 (PGE2) and 6 keto PGF1 alpha excretion, at all three doses employed. The extent of the reduction was similar for both PGE2 and 6 keto PGF1 alpha output; hence no evidence of 'selectivity' (i.e. sparing of PGI2 synthesis) was observed. Tiaprofenic acid was also administered to rats receiving an infusion of 5% dextrose. The dose employed (0.5 or 1 mg kg-1 body weight) was submaximal and elicited reductions in PGE2 output to values still more than 60% of the control period values. In this group of animals, the percentage change in 6 keto PGF1 alpha excretion was again not significantly different from that of PGE2. The maximal extent of reduction in urinary PGE2 excretion with tiaprofenic acid (25 mg kg-1 body weight) was not significantly different from that elicited by indomethacin (10 mg kg-1 body weight), although the time course of the reduction was different.

Pressure natriuresis and prostaglandin secretion by perfused rat kidney

Isolated rat kidneys respond to elevations of perfusion pressure with an increase in glomerular filtration rate (GFR), filtration fraction (FF), and sodium excretion (UNaV) and a fall in fractional sodium reabsorption (FRNa). Significant linear correlations exist between each of these dependent variables and the renal artery pressure (P). In control kidneys, pressure natriuresis is seen to result both from an increase in filtered sodium load and a decrease in FRNa. In kidneys treated with indomethacin in doses which curtail the release into the perfusate of prostaglandin E2 (PGE2) and the prostacyclin metabolite, 6-keto-PGF1 alpha, the regression lines relating GFR, FF, and UNaV to P are shifted to the right. Thus, prostaglandin-inhibited kidneys require higher pressures than control kidneys to maintain comparable rates of filtration and sodium excretion. Total renal vascular resistance (RVR) is also higher in inhibited kidneys. These findings suggest that in the isolated perfused rat kidney, prostaglandins promote pressure natriuresis by maintaining afferent arteriolar dilation. Their inhibition leads to afferent constriction, which raises RVR, lowers FF and GFR, and reduces sodium excretion.

Prostaglandin E2 excretion, urine flow and papillary osmolality during saline or dextrose infusion in the conscious rat

Conscious rats received infusions at 5.8 ml./hr of either 0.9% NaCl or 5% dextrose, via a tail vein, for 6 hr. During this infusion period, urine was collected from the animals, and the urine volume, sodium concentration and immunoreactive PGE2 were determined. Urine flow in both groups was stable during the 2-6 hr period of the infusion and was not significantly different between the two groups. Sodium output was also stable over the 2-6 hr infusion period but obviously the output of the saline-infused group was higher than that of the dextrose-infused group. Urinary PGE2 output was not significantly different between the groups in the 2-4 hr period (79.4 +/- 8.6 p-mole/2 hr in the saline-infused group, 82.1 +/- 5.7 p-mole/2 hr in the dextrose-infused group). In the 4-6 hr period, PGE2 output remained at this level (82.0 +/- 7.8 p-mole/2 hr) in the dextrose-infused group, but fell significantly (to 53.7 +/- 5.0 p-mole/2 hr) in the saline-infused group. In separate groups of animals which received saline or dextrose infusions as above, renal papillary osmolality was determined. The osmolality was significantly (P less than 0.001) higher in the saline-infused group. It is concluded that renal PGE2 synthesis is unlikely to be directly involved in sodium homeostasis and that PGE2 synthesis as measured by urinary PGE2 excretion is not controlled by the papillary osmolality.

The influence of renal prostaglandins on urinary calcium excretion in idiopathic urolithiasis

Hypercalciuria is well recognized as an important factor in the cause of idiopathic calcium stone disease. Identification of the exact mechanism for the renal tubular handling of calcium has proved elusive, hence, treatment methods to alter the concentration of urine calcium in hypercalciuric stone formers have hitherto been non-specific. It is now well established that renal prostaglandins influence intrarenal hemodynamics and tubular electrolyte excretion. As the renal handling of sodium and calcium is intimately related, the possibility that the mechanism underlying hypercalciuria may be prostaglandin mediated was considered. Experiments were performed in conscious Sprague-Dawley rats (n = 10) to determine the changes in calcium excretion following prostaglandin synthetase inhibition with indomethacin. Calcium excretion was significantly reduced (p less than 0.01), compared with control animals (n = 10). Further experiments were performed in anesthetized monkeys (Macaca fascicularis) to see if the inhibitory effect of indomethacin was reversible. Exogenous prostaglandin (PGE2) infusion resulted in a marked calciuretic response without producing changes in glomerular filtration rate or blood pressure. Forty-three hypercalciuric patients were treated with a prostaglandin inhibitor for periods ranging from 2 to 4 weeks, and all showed a significant fall in urinary calcium excretion to within the normal range. This clinical and experimental study suggests that prostaglandin (PGE2) is a hormone which determines the renal handling of calcium by influencing renal tubular function.

Renal handling of indomethacin and its relationship with the secretory pathway of prostaglandins

The uptake of prostaglandin E2, one of the main renal prostaglandins and of p-aminohippurate, an indicator of the anion organic transport, by slices of kidney cortex from adult female rats was studied in the presence and in the absence of indomethacin. The drug's inhibitory effect on the uptake of prostaglandin E2 was observed both after in vivo administration as well as when it was present in the bathing media. The effect was more pronounced when the drug was given in vivo and in addition, was present in the bath. [14C] PAH uptake was inhibited by indomethacin in a dose-related pattern and the kinetic analysis of this effect is indicative of a competitive inhibition. As expected, uptake of PAH by medullary slices was not affected by the presence of either indomethacin of PGE2. Indomethacin was more potent in inhibiting PGE2 uptake than PAH uptake.

Reduction of the effects of diuretics or sodium chloride loading in the conscious rat by inhibitors of prostaglandin synthesis

In conscious rats pretreatment with indomethacin or flurbiprofen, two chemically unrelated inhibitors of prostaglandin synthesis, reduced urine volume and sodium excretion induced by four diuretics, acetazolamide, amiloride, bendrofluazide and frusemide, or oral sodium chloride loads. The maximum reduction in sodium excretion was limited to approximately 2 mmol/kg Na+ even when sodium excretion was greatly increased. In contrast these inhibitors did not appreciably affect potassium excretion. These results indicate that part of the natriuretic response in the rat to highly and moderately efficacious diuretics and to sodium chloride loading is modified by prostaglandins. We suggest that the lack of effects on potassium excretion indicate that the collecting tubule is the probable site of action.

Renal vasodilator activity of prostaglandin E2 in the rat anaesthetized with pentobarbitone

1 The effect of intra-aortic administration (i.a.) of prostaglandin E2 (PGE2) on renal blood flow was studied in the rat anaesthetized with pentobarbitone. Renal blood flow was assessed in two ways, either by use of an electromagnetic flow probe or by measurement of the renal clearance of p-aminohippurate (PAH). 2 PGE2 (0.1 microgram/min, i.a.) increased renal blood flow measured by either method. However, PAH clearance overestimated the degree of vasodilatation compared to that obtained using the flow meter. The possibility that PGE2 or a metabolite may increase PAH extraction by the kidney was considered. 3 The sensitivity of the rat to the renal vasodilator actions of PGE2 was enhanced by using a flank retro-peritoneal approach from which to insert the flow probe, rather than a mid-line abdominal incision. 4 Dose-response curves demonstrate that under the conditions used, PGE2 produced a biphasic change in renal vascular resistance, vasodilatation started at 0.01 microgram/min and was maximal at about 3 micrograms/min, while at the highest dose used (20 micrograms/min) PGE2 induced renal vasoconstriction. 5 The results indicate that contrary to previous reports, the rat does not exhibit an important species difference in the response of its renal vasculature to PGE2. Therefore, physiological and pathophysiological roles which have previously been attributed to vasoconstriction produced by PGE2 synthesized in the kidney may now have to be considered.

The influence of renal prostaglandins on glomerular filtration rate (GFR) and calcium excretion in urolithiasis

In a clinical study of 275 idiopathic stone formers the GFR was significantly raised in hypercalciuric patients compared with normal controls P less than 0.001). The possibility that the mechanism underlying hypercalciuria and raised GFR may be prostaglandin-mediated was considered because it is now well established that prostaglandins regulate intra-renal haemodynamics and influence tubular electrolyte excretion. Experiments were performed in conscious Sprague Dawley rats to determine the changes in calcium and sodium excretion following prostaglandin synthetase inhibition with indomethacin. Both calcium and sodium excretion together with urine flow were significantly reduced (P less than 0.002). Further experiments were performed in anaesthetised monkeys (Macacca fascicularis) to see if the inhibitory effect of indomethacin was reversible. Exogenous prostaglandin (PGE2) infusion resulted in a marked calciuretic response without producing changes in GFR or blood pressure. Selected hypercalciuric patients were treated with indomethacin, which resulted in a significant fall in urinary calcium excretion (P less than 0.001). This clinical and experimental study suggests that PGE2 is the hormone which determines the renal handling of calcium by controlling renal tubular function.

On the relationship between urinary PGE2 and PGF2 alpha excretion rates and urine flow, osmolar excretion rate and urinary osmolality in anesthetized rats

A strong inverse relationship was found between the excretion rates of the prostaglandins PGE2 and PGF2 alpha and urine flow (and osmolar excretion rate) over a range of urine flow rates from 1.5 to 40 microliters . min-1 . g kidney weight-1, covering spontaneous variations and isotonic saline diuresis. These results suggest the operation of a negative feedback mechanism by which the diuretic action of the prostaglandins, as part of a defence system, counteracts excessive oliguria. PGE2 excretion did not correlate with either urinary kallikrein excretion or plasma renin concentration. When the concentrating mechanism was interfered with by reducing renal perfusion pressure to, or below 65 mmHg, and vasopressin was given i.v. PGE2 excretion rate roughly parallelled urine--and probably medullary interstitial osmolar activity. However, in hydropenic rats there was no correlation between urine osmolality (Uosm) and PGE2 excretion over a range of osmolalities from 500 to 2 500 mOsm . kg-1, nor any relationship between delta Uosm and delta PGE2 excretion. Thus, a high interstitial osmolar activity appears to be a prerequisite for the activation of PG-synthesis in the renal medulla, but another (other) yet undefined factor(s) play the major role as (a) determinant(s) for PG-excretion in vivo.

Essential fatty acid supplemented diet increases renal excretion of prostaglandin E2 and water in essential fatty acid deficient rats

Weanling male rats were fed an essential fatty acid (EFA)-deficient diet for 25 weeks and then switched to an EFA-supplemented diet for 3 weeks. Control rats received the EFA-supplemented diet for 25 weeks and then the EFA-deficient diet for 3 weeks. Throughout the last 19 weeks, the rats were housed in metabolic cages once a week for a 24-hr period. urinary excretion of prostaglandin E2 (PGE2) was estimated by radioimmunoassay. Throughout a period of 12 weeks (weeks 13-24) water consumption increased ca. 60%, and urine output and PGE2 excretion decreased ca. 45% and 70%, respectively, in the EFA-deficient rats, Feeding EFA-supplemented diet to the EFA-deficient rats for 3 weeks decreased the water consumption and raised the urine output to that observed in the controls. However, the urine output was corrected within 1 day whereas the water consumption was not corrected until the second measurement 8 days after the dietary change. The PGE2 excretion increased more than 9-fold (from 18 +/- 8 ng/24 hr to 165 +/- 51 ng/24 hr) 1 day after EFA-supplementation, followed by a decrease to 86 +/- 29 ng/24 hr over the following 24 weeks. On the basis of the present data, it is suggested that EFA deficiency in rats causes diminished PGE2 excretion, which can be normalized by EFA supplementation. The normalization of the urine flow may, in part, be caused by the concomitant considerable increase in endogenous PGE2 synthesis.

A study of the effect of stimulated endogenous prostaglandin synthesis on urine flow, osmolar excretion rate, and renin release in hydropenic and saline loaded, anesthetized rats

The purpose of the study was to investigate the effects on urine flow and osmolar excretion of arachidonic acid (C20:4) infused in the renal artery of anaesthetized rats under conditions in which indomethacin previously was found to reduce urine flow and to prevent the development of a moderate saline diuresis. C20:4 caused a reversible increase in the urinary excretion rates of PGE2 and PGF2 alpha both in hydropenic rats and in rats during a saline diuresis. Renal venous plasma concentration of PGE2 increased significantly while the increase in PGF2 alpha was insignificant. C20:4 infusion was followed by an increase in urine flow and osmolar excretion rate in hydropenic rats, and it augmented urine flow (but not solute excretion) in saline-loaded rats. This latter effect was blunted by indomethacin treatment and inactin anaesthesia. Increased endogenous PG-levels were associated with only a modest (insignificant) increase in renin release under the present conditions. Saline loading acutely depressed PGE2 and PGF2 alpha urinary excretion rates and plasma renin concentration (PRC). The fall in PRC was unaffected by indomethacin. The main conclusions are that endogenous renal PG's have a diuretic effect in the amytal anaesthetized rat, while an effect on osmolar excretion rate is apparent only under hydropenic conditions. Acute saline loading depresses renal PG-synthesis, but this depression is not the only cause of the fall in PRC following saline loading. The saline diuresis is caused by a mechanism(s) not involving prostaglandins.

Prostaglandin synthesis and renal function in man

1. Experiments were performed to determine the changes in renal function which occur following prostaglandin synthetase inhibition in healthy conscious humans. It was hoped that such experiments could provide information on the mechanism by which renal prostaglandin synthesis influences urinary excretion. 2. In water-diuretic male subjects (receiving a slow saline infusion) the renal excretion of sodium and water was reduced following I.V. acetylsalicylic acid (1 g) administration, while the effective renal plasma flow (p-aminohippurate clearance), and glomerular filtration rate (inulin clearance) remained unaltered. 3. In normally hydrated female subjects on an unrestricted diet, the mean urinary prostaglandin E output was 8.5 ng/hr. The renal excretion of sodium, water and urinary prostaglandin E were significantly reduced (P less than 0.05) following oral acetylsalicylic acid (1.2 g) administration. 4. In normally hydrated female subjects on an unrestricted diet the renal excretion of sodium and water was reduced following oral paracetamol (1.5 g) administration. 5. It is concluded that following renal prostaglandin synthetase inhibition in conscious humans, the excretion of sodium and water can be reduced without measurable changes in the glomerular filtration rate or effective renal plasma flow. It is suggested that in conscious healthy humans, the kidney may continually synthesize prostaglandin which might help to maintain sodium and water excretion by a direct action on the renal tubule without influencing renal blood flow. The relevance of this hypothesis to the intrarenal location of prostaglandin synthetase is discussed.