The renal haemodynamic and excretory actions of prostacyclin and 6-oxo-PGF1 alpha in anaesthetized dogs

The cooperative roles of inflammation and oxidative stress in the pathogenesis of hypertension

SIGNIFICANCE

Innate and adaptive immunity play fundamental roles in the development of hypertension and its complications. As effectors of the cell-mediated immune response, myeloid cells and T lymphocytes protect the host organism from infection by attacking foreign intruders with bursts of reactive oxygen species (ROS).

RECENT ADVANCES

While these ROS may help to preserve the vascular tone and thereby protect against circulatory collapse in the face of overwhelming infection, aberrant elaboration of ROS triggered by immune cells in the absence of a hemodynamic insult can lead to pathologic increases in blood pressure. Conversely, misdirected oxidative stress in cardiovascular control organs, including the vasculature, the kidney, and the nervous system potentiates inflammatory responses, augmenting blood pressure elevation and inciting target organ damage.

CRITICAL ISSUES

Inflammation and oxidative stress thereby act as cooperative and synergistic partners in the pathogenesis of hypertension.

FUTURE DIRECTIONS

Pharmacologic interventions for hypertensive patients will need to exploit this robust bidirectional relationship between ROS generation and immune activation in cardiovascular control organs to maximize therapeutic benefit, while limiting off-target side effects.

Lymphocyte responses exacerbate angiotensin II-dependent hypertension

Activation of the immune system by ANG II contributes to the pathogenesis of hypertension, and pharmacological suppression of lymphocyte responses can ameliorate hypertensive end-organ damage. Therefore, to examine the mechanisms through which lymphocytes mediate blood pressure elevation, we studied ANG II-dependent hypertension in scid mice lacking lymphocyte responses and wild-type controls. Scid mice had a blunted hypertensive response to chronic ANG II infusion and accordingly developed less cardiac hypertrophy. Moreover, lymphocyte deficiency led to significant reductions in heart and kidney injury following 4 wk of angiotensin. The muted hypertensive response in the scid mice was associated with increased sodium excretion, urine volumes, and weight loss beginning on day 5 of angiotensin infusion. To explore the mechanisms underlying alterations in blood pressure and renal sodium handling, we measured gene expression for vasoactive mediators in the kidney after 4 wk of ANG II administration. Scid mice and controls had similar renal expression for interferon-gamma, interleukin-1beta, and interleukin-6. By contrast, lymphocyte deficiency (i.e., scid mice) during ANG II infusion led to upregulation of tumor necrosis factor-alpha, endothelial nitric oxide synthase (eNOS), and cyclooxygenase-2 (COX-2) in the kidney. In turn, this enhanced eNOS and COX-2 expression in the scid kidneys was associated with exaggerated renal generation of nitric oxide, prostaglandin E(2), and prostacyclin, all of which promote natriuresis. Thus, the absence of lymphocyte activity protects from hypertension by allowing blood pressure-induced sodium excretion, possibly via stimulation of eNOS- and COX-2-dependent pathways.

Prostacyclin protects against elevated blood pressure and cardiac fibrosis

Specific inhibitors of COX-2 have been associated with increased risk for cardiovascular complications. These agents reduce prostacyclin (PGI2) without affecting production of thromboxane (Tx) A2. While this abnormal pattern of eicosanoid generation has been implicated in the development of vascular disease associated with COX-2 inhibition, its role in the development of hypertension, the most common cardiovascular complication associated with COX-2 inhibition, is not known. We report here that mice lacking the receptor for PGI2 (IPKOs) develop salt-sensitive hypertension, cardiac hypertrophy, and severe cardiac fibrosis. Coincidental deletion of the TxA2 (TP) receptor does not prevent the development of hypertension, but cardiac hypertrophy is ameliorated and fibrosis is prevented in IPTP double knockouts (DKOs). Thus, deletion of the IP receptor removes a constraint revealing adverse cardiovascular consequences of TxA2. Our data suggest that adjuvant therapy that blocks unrestrained Tx actions might protect against end-organ damage without affecting blood pressure in patients taking COX-2 inhibitors.

Effect of NSAID administration on creatinine clearance in healthy dogs undergoing anaesthesia and surgery

Thirty healthy male dogs were randomly assigned to receive carprofen (4 mg/kg intravenously), ketoprofen (2 mg/kg intravenously) or saline (0.2 ml/kg intravenously) at induction of anaesthesia for castration surgery. A routine castration was undertaken and a buccal mucosal bleeding time was assessed at the completion of surgery. Twenty-four hours after surgery a 24-hour endogenous creatinine clearance study was undertaken. Buccal mucosal bleeding time was not significantly different between the three groups. Creatinine clearance was significantly lower (P < or = 0.01) in the two groups of dogs that received a non-steroidal anti-inflammatory drug compared with that in the dogs that received sterile saline. There was no significant difference between the carprofen and ketoprofen groups with respect to creatinine clearance.

Effects of intravenous administration of prostacyclin on regional blood circulation in awake rats

1. The effects of intravenous infusion of prostacyclin (PGI2, 0.1, 0.2, 0.3 and 1.0 microg kg(-1) min(-1) lasting 5 min) on regional blood flow and regional vascular resistance have been studied in awake rats using the radioactive microsphere method. 2. The control values of blood flow to the heart, kidney, small intestine, hind limb muscle, pericranial skin and brain as well as the corresponding vascular resistance were not modified by an i.v. infusion (0.1 ml min(-1)) of Tris-buffer (the vehicle of PGI2). 3. The i.v. infusion of PGI2 produced graded dose-dependent decreases of MAP (r=0.87, P<0.001; ED20=0.73 [0.13-2.55] microg kg(-1) min(-1)) as well as decreases of vascular resistance in the heart (r=0.83, P<0.001; ED30=0.17 [0.09-0.31] microg kg(-1) min(-1)), pericranial skin (r=0.88, P<0.001; ED30=0.28 [0.18-0.43] microg kg(-1) min(-1)) and small intestine (r=0.74, P<0.001; ED30=0.21 [0.11-0.39] microg kg(-1) min(-1)), which led to dose-related increases of blood flow to these territories. 4. On the contrary, PGI2 increased vascular resistance in skeletal muscle (r=0.73, P<0.001; ED30=0.20 [0.10-0.39] microg kg(-1) min(-1)) with corresponding reductions in blood flow. The low doses reduced renal blood flow but there were no significant changes during the high ones. Cerebral vessels did not dilate during any infusion of PGI2 and cerebral blood flow decreased as MAP fell (r=0.56, P<0.01). 5. We conclude that, in awake rats, the coronary vessels are extremely sensitive to the vasodilating effect of PGI2 and that the mesenteric vessels and those of the pericranial skin are very responsive too. Moreover, autoregulation is inefficient to maintain cerebral blood flow during infusion of PGI2.

Renovascular adaptive changes in chronic hypoxic polycythemia

BACKGROUND

Chronic hypoxia in rats produces polycythemia, and the plasma fraction falls, reducing renal plasma flow (RPF) relative to renal blood flow (RBF). Polycythemia also causes increased blood viscosity, which tends to reduce RBF and renal oxygen delivery. We studied how renal regulation of electrolyte balance and renal tissue oxygenation (which is crucial for erythropoietin regulation) are maintained in rats during hypoxic exposure.

METHODS

Rats of two strains with differing polycythemic responses, with surgically implanted catheters in the urinary bladder, femoral artery, and left renal and right external jugular veins, were exposed to a simulated high altitude (0.5 atm) for 0, 1, 3, 14, and 30 days, after which RPF (para-aminohippurate clearance), glomerular filtration rate (GFR, polyfructosan clearance), hematocrit and blood gases were measured, and RBF, renal vascular resistance and hindrance (resistance/viscosity), renal oxygen delivery, and renal oxygen consumption were calculated.

RESULTS

During chronic hypoxia RBF increased, but RPF decreased because of the polycythemia. GFR remained normal because the filtration fraction (FF) increased. Renal vascular resistance decreased, and renal vascular hindrance decreased more markedly. Renal oxygen delivery and consumption both increased.

CONCLUSIONS

During chronic hypoxia GFR homeostasis apparently took precedence over RBF autoregulation. The large decrease in renal vascular hindrance suggested that renal vascular remodeling contributes to GFR regulation. The reduced hindrance also prevented a vicious cycle of increasing polycythemia and blood viscosity, decreasing RBF, and increasing renal hypoxia and erythropoietin release.

Prostaglandins in liver disease and liver transplantation

This brief review summarizes the physiology and pharmacology of eicosanoids and describes how they have been tested for possible application in liver disease and transplantation. The objective is to trace the stepwise application from the laboratory to the bedside. Although many questions remain to be answered, the observations summarized in this article have opened up new and potentially rewarding prospects in application to liver disease.

Opposite renal effects of a PGE1 analog and prostacyclin in humans

Renal effects of prostaglandins have been widely investigated in anesthetized animals, but in contrast only few studies have been devoted to healthy and diseased humans. Recently, both prostacyclin and a stable analog of PGE1, misoprostol, have been available for therapeutic purposes in clinical conditions associated with peripheral or renal vasoconstriction; however, the renal effects have not been defined. We have therefore studied the acute renal effects of PGI2 5 ng.kg/min intravenously and of misoprostol, a stable PGE1 analogue, 400 micrograms orally in two groups of respectively 8 and 12 healthy supine subjects on normal sodium diet using sodium, lithium, inulin, PAH and neutral dextran clearances. PGI2 induced a slight natriuretic effect, a systemic and renal vasodilation with a decrease in mean arterial pressure from 85.3 +/- 1.1 to 80.2 +/- 1.6 mm Hg (P < 0.01) and in renal vascular resistance from 94 +/- 6 to 75 +/- 5 mm Hg.min/ml (P < 0.001). GFR did not change whereas fractional clearance of dextran decreased over the 34 to 48 A radius range. Applying these changes on a hydrodynamic model of filtration of macromolecules through water-filled pores, we calculated that PGI2 decreased the glomerular transcapillary pressure gradient from 35 +/- 1 to 32 +/- 1 mm Hg (P < 0.001), decreased nonsignificantly the ultrafiltration coefficient Kf and did not affect the membrane parameters r0 and omega 0. Misoprostol had no natriuretic effect, induced slight renal vasoconstriction and moderate decrease in GFR from 124 +/- 9 to 114 +/- 10 ml/min.1.73 m2 (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Biologic differences between vasodilator prostaglandins and medullipin I

Vasodepressor prostaglandins (PGs), PGE2, PGI2, and medullipin I (Med I) are synthesized in the kidney. These vasodilator substances are thought to be involved in the antihypertensive function of the kidney. At issue is whether there are biologic differences between the vasodilator PGs and Med I. Two separate studies have shown that Med I's vasodepressor action is inhibited by four procedures: mixing with Tween 20; treatment with n-butyl boronic acid; treatment of the assay animal with SKF 525A, an inhibitor of cytochrome P-450; and removing the liver from the circulation. These same procedures were applied to the vasodilator PGs. All four failed to inhibit the vasodepressor action of the PG's. It is concluded that Med I and vasodilator PGs of the kidney are separate and distinct biologic entities.

Renal prostaglandin production is increased during abdominal sepsis in the rat and unaffected by the infusion of different amino acid formulations

Renal prostaglandin (PG) production was studied in 32 laparotomized (control) and 33 septic rats (cecal ligation and puncture). Control and septic rats were infused for 18 hr with 5% glucose or 5% glucose and one of three amino acid formulations containing 22, 35, or 45% branched chain amino acids. When comparing renal PG production from endogenous precursors in septic versus control rats, significant increases (P less than 0.01) could be detected for PGE2, 6-keto-PGF1 alpha, and TxB2. The infusion of either 5% glucose alone or 5% glucose with 4.25% of any of the three amino acid formulations tested did not change renal PG production in either control or septic rats.

Prostaglandins in the semicircular canal of the frog

The synthesis of prostaglandins by ampulla and duct tissue isolated from the frog posterior semicircular canal was investigated in vitro. Ampulla and duct produced PGE2 (9 and 6 pg/structure, respectively) and prostacyclin (26 and 12 pg/structure). In the ampulla, prostaglandins mostly originated from the part containing dark and sensory cells and was not altered by 10(-3) M streptomycin. Prostaglandin levels were time-dependent and temperature-dependent. Arachidonic acid (3 X 10(-5) M) stimulated PGI2 synthesis by ampulla and duct (by 11.4 and 17 times) and PGE2 synthesis by 50 times in both structures. Ionophore A23187 stimulated ampulla and duct PGI2 synthesis (by 4.8 and 5.6 times) and PGE2 synthesis (by 2.4 and 1.8 times). Subcutaneous 100 mg/kg aspirin reduced PGI2 and PGE2 synthesis (ampulla: -87%, -33%; duct: -100%, -33%). Indomethacin (10(-6) M), in vitro, decreased PGI2 and PGE2 synthesis (ampulla: -47%, -47%; duct; -22%, -77%). Within 3 h, aspirin (5 X 10(-6) M) or arachidonic acid (2 X 10(-5) M) did not change Na and K concentrations in endolymph. It is concluded that frog inner ear produces PGI2 and PGE2, mostly from the part containing the dark cells, and that prostaglandins could be involved in the physiology of inner ear.

Prostaglandins and nonsteroidal anti-inflammatory drugs. Effects on renal hemodynamics

Renal prostaglandins are important modulators of renal hemodynamic function. Their synthesis from arachidonic acid precursor is regulated by neurohumoral vasoactive substances as well as by intrarenal factors. Endogenous renal prostaglandins exert little influence on renal blood flow and glomerular filtration rate in the basal state. In contrast, inhibition of cyclooxygenase-dependent arachidonic acid metabolism with nonsteroidal anti-inflammatory drugs in states of decreased renal perfusion causes marked alterations in these variables. Thus, clinical states characterized by decreased intravascular volume (decreased effective blood volume) with decreased renal perfusion augment the activity of various neurohumoral vasoactive systems and result in an increased dependence of renal hemodynamics on endogenous renal prostaglandin synthesis, which is stimulated, in a compensatory manner, by these same systems. The development of newer drugs that undergo biotransformation in the kidney between active and inactive forms may permit a lesser degree of renal cyclooxygenase inhibition, with the possibility of a reduction in the adverse effects on renal blood flow and glomerular filtration rate. Appropriate clinical use of nonsteroidal anti-inflammatory drugs requires careful consideration of the potential deleterious consequences of prostaglandin synthesis inhibition. Prostaglandins are considered to be autacoids and, as such, they exert their physiologic actions close to or at the site of synthesis. Therefore, production of prostaglandins, thromboxanes, and, possibly, leukotrienes in the renal cortex by the constituent cells of the glomeruli and the arterioles would be anticipated to influence their hemodynamic functions, that is, glomerular filtration rate, renal blood flow, renal vascular resistance, and juxtaglomerular granular cell renin release.

Effect of spironolactone on renal prostaglandin excretion in patients with liver cirrhosis and ascites

The effect of spironolactone on the urinary excretion of prostaglandins was studied in patients with liver cirrhosis and ascites. Patients were kept in bed and given a sodium-restricted diet for at least 4 days before spironolactone treatment was considered. Starting from the 5th day of protocol, patients were treated with this diuretic if their spontaneous weight loss had been less than 600 g during the 2 previous days. Patients were distributed in groups according to weight loss during the first 4 days on diuretic therapy: Group I (high responders), II (medium responders) and III (low responders). Group I patients showed higher basal values (4th day of protocol) of urinary sodium (P less than 0.02) and urinary 6-keto-PGF1 alpha (P less than 0.02) than the other patients, but there were no significant differences in the basal excretion rates of PGE2 nor TXB2 among the groups. The therapeutic requirement for spironolactone treatment in patients from Group I was delayed as compared with the other two groups (P less than 0.001) due to the fact that their spontaneous weight loss took place over a long period. For all patients, spironolactone administration produced a significant increase in 6-keto-PGF1 alpha excretion (P less than 0.01) without affecting significantly urinary elimination of PGE2 nor TXB2. A close relationship was found between the spironolactone-induced increments in urinary sodium and urinary 6-keto-PGF1 alpha excretion (r = 0.74, P less than 0.001). It is suggested that the ability of the kidney to synthetize prostacyclin can influence the natriuretic response to spironolactone therapy in patients with liver cirrhosis.

Improvement in the preservation of ischemically impaired renal transplants of pigs by iloprost (ZK 36 374)

Kidneys of five pigs were preoperatively perfused with iloprost in situ (infusion of 0.5 microgram X kg-1 for 15 minutes) and exposed to a warm ischemic period of 45 minutes. The behaviour of these kidneys during initial perfusion by gravity and hypothermic mechanical perfusion for 24 hours was comparable to that of kidneys having had a warm ischemic period of less than 5 minutes. After retransplantation all kidneys showed a sufficient blood flow and immediate production of urine during the test period of 3 hours.

Effect of indomethacin on clinical progress and renal function in cystinosis

Three children with nephropathic cystinosis were treated with indomethacin 3 mg/kg a day for periods ranging from 9 to 18 months. The drug produced worthwhile clinical improvement in all, with marked beneficial effects on polyuria, polydipsia, and general wellbeing. Clearance studies performed under conditions of maximal water diuresis showed that proximal tubular sodium reabsorption was increased in all children, with consequent reduction in sodium delivery to the distal nephron leading to reduced free water clearance and distal tubular cation exchange. Plasma sodium and potassium concentrations became normal in all patients, with improvement in phosphate and bicarbonate concentrations in one. Renal function continued to deteriorate, but without obvious acceleration of the process by the drug. We were unable to demonstrate a beneficial effect on growth; nevertheless, indomethacin is a useful adjunct to the symptomatic treatment of children with severe nephropathic cystinosis.

Arachidonic acid metabolism, prostaglandins and the kidney

Renal prostaglandins are gaining increasing recognition as important modulators of hemodynamics and excretory function in the mammalian kidney. Synthesis of these unsaturated fatty acids from arachidonate precursors is closely regulated by intrarenal factors, and circulating angiotensin II, catecholamines, arginine vasopressin and bradykinin. Endogenous prostaglandins exert little influence on renal blood flow and glomerular filtration rate in the basal state, but inhibition of arachidonate metabolism when renal perfusion is impaired causes marked alterations in these parameters. Renal salt and water excretion is modified by the effects of prostaglandins on glomerular filtration rate, proximal tubule fluid reabsorption, medullary solute gradients, and the intrinsic water and ion reabsorptive properties of distal nephron segments. Prostaglandins also mediate renin release under basal conditions and in response to intravascular volume depletion. Abnormalities of renal prostaglandins are evident in various clinical disorders of renal function including hypertension, ureteral obstruction, Bartter syndrome, hypokalemic nephropathy and drug-induced disorders of water metabolism. Appropriate clinical use of nonsteroidal anti-inflammatory agents requires consideration of the potential renal consequences of inhibiting prostaglandin biosynthesis.

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.

Effects of prostacyclin and prostaglandin E1 on cyclic AMP metabolism and calcium efflux in isolated renal cortical tubules

Comparative effects of prostaglandin E1 (PGE1) prostacyclin (PGI2) on cyclic AMP (cAMP) metabolism and efflux of 45Ca in isolated renal cortical tubules from hamsters were investigated. Both PGE1 and PGI2 increased tissue concentrations and production of cAMP in isolated tubules with effects of PGE1 being slightly greater than those of PGI2. Both prostaglandins produced dose-related increases in cAMP production over identical concentration ranges (0.01-15 micrograms/ml). Degradation of cAMP, estimated as the difference in tissue levels of cAMP in the presence and absence of maximal amounts of the phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (MIX), increased following addition of either prostaglandin with increases paralleling increases in cAMP production. Simultaneous addition of maximal amounts of both prostaglandins resulted in a combined effect on cAMP production which was nonadditive. Both prostaglandins produced dose-related increases in efflux of 45Ca from isolated tubules. Changes in 45Ca efflux were closely related to changes in cAMP levels produced by either prostaglandin. Simultaneous addition of maximal concentrations of PGE1 and PGI2 produced changes in 45Ca efflux which were nonadditive. The results indicate that both prostaglandins increase cAMP production and efflux of calcium in isolated renal cortical tubules and may share a common target cell type in these responses.