Release of platelet-activating factor, slow-reacting substance, and vasoactive amines from isolated rat kidneys

The pathophysiological effects of Russell's viper (Daboia siamensis) venom and its fractions in the isolated perfused rabbit kidney model: A potential role for platelet activating factor

The pathophysiological effects of Russell's viper venom (RVV) and its fractions, including phospholipase A₂ (RvPLA₂), metalloprotease (RvMP), L-amino acid oxidase (RvLAAO), and phosphodiesterase (RvPDE) on renal functions were investigated using the isolated perfused rabbit kidney (IPK) model. Moreover, whether their effects on renal alterations were promoted by platelet activating factor (PAF) was tested using the PAF receptor antagonist, WEB 2086. There was a marked reduction in the perfusion pressure (PP) and renal vascular resistance (RVR) 10 min after RVV administration (1.0 mg/100 ml of perfusate), thereafter both PP and RVR gradually increased and approached the control level within 90 min. These effects were abolished by pretreatment with WEB2086 (2 μg/μl). Administration with RvPLA₂ (280 μg/ml), RvMP (280 μg/ml), or RvLAAO (135 μg/ml) alone increased both the PP and RVR, whereas RvPDE (100 μg/ml) reduced both the PP and RVR. Pretreatment with WEB 2086 completely abolished the effects induced by RvMP, but not the other fractions. The RVV also caused a marked decrease in the glomerular filtration rate (GFR), urinary flow rate (UF), and osmolar clearance (Cosm), and these effects were not inhibited by pretreatment with WEB2086. Each RVV fraction also increased, to varying extents, the GFR, UF, and Cosm, and these effects induced by RvPLA₂ or RvMP, but not the other fractions, were completely blocked by WEB 2086. Changes in percent filtered Na⁺ and K⁺ excreted in the IPK by RVV, RvPDE, and RvMP were abolished by pretreatment with WEB 2086. Histological evaluation profiled mainly tubulonephrosis in the treated kidney. These results reveal that the alterations in renal functions induced by RVV and its fractions are due to the synergistic action of the different components of snake venom, instead of the action of a single component. The effects of RVV and its fractions in rabbit IPK are mediated at least in part by PAF.

The role of platelet-activating factor in mesangial pathophysiology

Platelet-activating factor (PAF) is a powerful proinflammatory mediator that displays an exceedingly diverse spectrum of biological effects. Importantly, PAF is shown to participate in a broad range of pathologic conditions. This review focuses on the role that PAF plays specifically in the pathophysiology of the kidney, the organ that is both a source and a target of PAF. Renal mesangial cells are responsible for glomerular PAF generation and, ultimately, are the victims of its excessive production. Mesangial pathology is widely acknowledged to reflect glomerular damage, which culminates in glomerulosclerosis and proteinuria. Therefore, modulation of mesangial cell responses would offer a pathophysiology-based therapeutic approach to prevent glomerular injury. However, the currently available therapeutic modalities do not allow for targeted intervention into these processes. A more profound understanding of the mechanisms that govern PAF metabolism and signaling in mesangial cells is important, because it could facilitate the quest for improved therapies for renal patients on the basis of PAF as a drug target.

Effect of platelet activating factor antagonist treatment on gentamicin nephrotoxicity

To assess whether PAF could be involved in the gentamicin-induced nephrotoxicity, we have studied the effect of PAF antagonist BN-52021 on renal function in rats after gentamicin (GENTA) treatment. Experiments were completed in 21 Wistar rats divided into three groups: group GENTA was injected with gentamicin 100 mg kg⁻¹ body wt/day s.c. for 6 days. Group GENTA + BN received gentamicin and BN-52021 i.p. 5 mg kg⁻¹ body wt/day. A third group served as control. Rats were placed in meta-bolic cages and plasma creatinine and creatinine clearance were measured daily. GENTA group showed a progressive increase in plasma creatinine, a drop in creatinine clearance and an increase in urinary excretion of N-acetyl-β-D-glucosaminidase and alkaline phosphatase. GENTA + BN group showed a lesser change in plasma creatinine and a creatinine clearance, but no difference with GENTA group in urinary excretion of NAG and AP were observed. Histological examination revealed a massive cortical tubular necrosis in rats treated with gentamicin, whereas in BN-52021 injected animals tubular damage was markedly attenuated. The present results suggest a role for PAF in the gentamicininduced nephro-toxicity.

Purification and biological effects of L-amino acid oxidase isolated from Bothrops insularis venom

Bothrops insularis is a snake from Ilha da Queimada Grande, an island located about 20 miles away from the Southeastern coast of Brazil. Compared with other Brazilian species of Bothrops, the toxinology of B. insularis is still poorly understood, and so far, no fraction from this venom with amino acid oxidase activity had been isolated or its biological activity tested. We investigated the biochemical and biological effects of one l-amino acid oxidase enzyme isolated from B. insularis snake venom (BiLAO), which was purified using HPLC and sequence grade. We also evaluated the renal effects induced by BiLAO. Chromatographic profile of B. insularis whole venom disclosed seven main fractions (I, II, III, IV, V, VI and VII) and the main LAO enzymatic activity was detected in fraction II. The group treated with BiLAO showed a decrease in perfusion pressure (C(120)=110.28+/-3.69; BiLAO(120)=82.2+/-5.6 mmHg*); renal vascular resistance (C(120)=5.48+/-0.53; BiLAO(120)=4.12+/-0.42 mmHg/mL/g/min*), urinary flow (C(120)=0.160+/-0.020; BiLAO(120)=0.064+/-0.012 mL/g/min*), glomerular filtration rate (C(120)=0.697+/-0.084; BiLAO(120)=0.176+/-0.017 mL/g/min*), sodium (C(120)=79.76+/-0.56; BiLAO(120)=65.39+/-6.19%*), potassium (C(120)=69.94+/-6.86; BiLAO(120)=60.26+/-2.24%*) and chloride tubular reabsortion (C(120)=78.53+/-2.33; BiLAO(120)=64.58+/-6.68%*). Acute tubular necrosis foci were observed in the group treated with the LAO fraction of the B. insularis snake venom. Some findings have the same morphological aspect of apoptosis, more evident cortically; otherwise, reversible degenerative phenomena represented by hydropic ballooning with extensive cytoplasmic vacuolization and discontinuity of the cell brush borders in the proximal tubular epithelium were observed; furthermore, necrotic detachment of these cells into the tubular lumina, and increased amount of protein deposits in the distal and proximal tubules were observed. In conclusion, the slowness of blood flow and of glomerular filtration resulted in more time for filtration and tubular reabsorption, with elevation of the total percentage of sodium and chlorine reabsorption. The maintenance of the decrease in glomerular filtration rate would determine the subsequent decreases, which were noticed in these parameters. The necrosis observed was the result of damage cell induced by l-amino acid oxidase isolated from B. insularis venom.

Application of a TCA-precipitation method for the determination of 1-alkyl-sn-glycero-3-phosphate: Acetyl-CoA acetyltransferase in human renal tissue

The activity of 1-alkyl-sn-glycero-3-phosphate:Acetyl-CoA acetyltransferase, which catalyses the first step of the de novo biosynthesis of PAF, was determined and characterised in cortical and medullary human renal tissues. A novel thin-layer chromatographic system as well as a trichloroacetic acid precipitation method, were utilised in order to determine the enzyme's activity. The acetyltransferase activity was associated with the membranous fractions of the renal tissue, it showed an optimum pH of 8.4 and it had a bell-shaped dependence on BSA concentration. One or more disulphide bonds were necessary for the action of acetyltransferase while the enzyme seemed to be independent from divalent cations. Two assay products were extracted from the incubation mixture namely alkylacetylphosphatidic acid, produced by the acetylating action of the acetyltransferase on alkyllyso-phosphatidic acid and alkylacetyl-glycerol, which is produced by the action of a phosphohydrolase on alkylacetylphosphatidic acid. The presence of NaF in the assay mixture resulted to a decreased degradation of alkylacetylphosphatidic acid, as well as to an increased overall product formation. Cortical and medullary acetyltransferases share similar biochemical properties and there is no statistical difference between the two activities.

Renal toxicity of Bothrops moojeni snake venom and its main myotoxins

Acute renal failure is one the most common systemic complications after snakebite, however, its pathogenesis remains obscure. In this study we evaluated the renal effects of Bothrops moojeni venom and its myotoxins (Bmtx-I and BmtxII) in rat isolated perfused kidneys. The myotoxins were purified by ion-exchange chromatography and reverse phase HPLC. The whole venom (10 microg/ml) and myotoxins (5 microg/ml) were added to the perfusion system 30 min after the beginning of each perfusion. The renal effects were compared to a control group perfused with modified Krebs-Henseleit solution alone. B. moojeni venom decreased the perfusion pressure (PP), renal vascular resistance (RVR), and the percent sodium, potassium and chloride tubular transport (%TNa(+), %TK(+), %TCl(-)). In contrast, the venom increased the urinary flow (UF), glomerular filtration rate (GFR), and the sodium, potassium and chloride excretion (ENa(+), EK(+), ECl(-)). The renal effects of myotoxin I was very similar to those of the whole venom, but there was an increase rather than a decrease in the PP and RVR. Myotoxin II had no effect on renal physiology, except for a transient decrease in %TK(+). In conclusion, B. moojeni venom caused intense alterations in renal physiology, including a drop in vascular resistance associated with diuresis, natriuresis and kaliuresis. Bmtx-I had an opposite effect when compared to whole venom, showed in the parameters of PP and RVR. Bmtx-II had a mild effect in %TK(+). The apparent inability of Bmtx-II to induce the renal effect similarly to Bmtx-I should be explained by the absence in the Bmtx-II of the C-terminal lysine rich region.

Glomerular effects of cholera toxin in isolated perfused rat kidney: a potential role for platelet activating factor

Cholera toxin (MW 84 kDa) is now considered a pharmacological tool to study the adenylyl cyclase system and a stimulus to generate platelet activating factor in the intestinal tract. We used this toxin to evaluate the renal haemodynamics, glomerular filtration function, tubular sodium transport and toxicity in isolated perfused rat kidney. Kidneys from adult male Wistar rats were isolated for perfusion. The perfusion fluid was modified Krebs-Henseleit solution and the samples were analyzed for sodium, potassium, inulin and osmolality. Clearance techniques were used to calculate physiological parameters. Cholera toxin (1.0 microg/ml) caused a significant time-dependent reduction of glomerular filtration rate and urinary flow. This toxin also caused a small, but consistent reduction in fractional proximal sodium reabsortion (toxin = 67.43+/-2.42% versus control = 79.26+/-5.80%; P<0.025). WEB 2086, a platelet activating factor receptor antagonist at 100 microg/ml completely blocked the effects induced by cholera toxin on glomerular filtration rate, fractional proximal sodium reabsortion and urinary flow. In contrast to cholera toxin, dibutyryl-cyclic AMP (10(-5) M) significantly increased glomerular filtration rate (Db-cyclic AMP = 0.651+/-0.035 versus control = 0.514+/-0.043 ml x g(-1) x min(-1); P<0.025) in isolated perfused kidneys. Db-cyclic AMP caused a similar, but more severe reduction in fractional proximal sodium reabsortion (Db-cyclic AMP = 54.21+/-2.35% versus control = 70.10+/-3.24%; P<0.025). In addition Db-cyclic AMP increased significantly the urinary flow (Db-Cyclic AMP = 0.290+/-0.018 versus control = 0.179+/-0.026 ml x g(-1) x min.(-1); P<0.025). WEB 2086+ Db-cyclic AMP also caused a significant increase in the urinary flow with maximal effect at 90 min. (WEB+Db-cyclic AMP = 0.26+/-0.01 versus control = 0.15+/-0.01 ml x g(-1) x min.(-1); n = 8, P<0.025). Cholera toxin caused a decrease of urinary flow (toxin = 0.034+/-0.004 versus control = 0.145+/-0.02 ml x g(-1) x min.(-1); P<0.025), this effect was also completely abolished by WEB 2086 when it was injected previously to toxin. When only WEB 2086 was injected, the functional parameters remained stable throughout the perfusion time. Cholera toxin had no effect on renal vascular resistance, renal perfusate flow or tissue potassium, suggesting renal integrity in kidneys treated with this toxin. The results suggest that cholera toxin effects in the perfused rat kidney are primarily mediated by platelet activating factor.

Potential role of platelet activating factor in acute renal failure

The clinical condition of acute renal failure (ARF) can be caused by a diverse number of renal injuries, but it is generally characterized by a sharp reduction in the glomerular filtration rate (GFR). A lipid mediator, platelet activating factor (PAF), may be one of the entities responsible for causing the hemodynamic changes in the ARF kidney because it can act as a vasodilator or vasoconstrictor, depending upon its concentration. This review examines the action and mechanisms of PAF in experimental animal models of ischemia and nephrotoxicity, as well as renal failure associated with extrarenal disease. While further research is necessary before extrapolating our current knowledge of PAF into the prevention of renal failure of therapeutic intervention using PAF antagonists in human ARF, there is reasonable evidence to support its role as a mediator of the decrease in GFR characteristic of ARF.

Urinary platelet-activating factor excretion is elevated in non-insulin dependent diabetes mellitus

Proteinuria is currently considered a very sensitive predictor of diabetic nephropathy, but 20-25% of all diabetic patients with negative Albustix reaction excrete higher than normal (< 20 mg/24 h) amounts of albumin in their urine. It is our hypothesis that platelet-activating factor (PAF), a potent glycerophospholipid that acts as a chemical mediator for a wide spectrum of biological activities, including increased vascular permeability, may be produced in significant amounts during periods preceding microalbuminuria. In this study, we compared urinary PAF excretion in Mexican-American subjects who were diagnosed with non-insulin dependent diabetes mellitus (NIDDM) with their healthy control counterparts. The age of the NIDDM subjects (45.9 +/- 2.1 years) was not significantly different from the healthy control group, which was 39.4 +/- 2.7 years (P < 0.0672). The NIDDM subjects (body mass index, 29.9 +/- 1.1 compared to 26.1 +/- 0.9 kg/m2 in healthy controls) were characterized by significantly increased (P < 0.05) fasting plasma glucose (192 +/- 11 vs. 97 +/- 4 mg/dl in healthy controls), fasting insulin (20.9 +/- 2.4 vs. 12.3 +/- 1.6 microU/ml), fasting C-peptide (2.93 +/- 1.26 vs. 1.48 +/- 0.51 ng/ml), and hemoglobin A1c (10.3 +/- 0.7 vs. 5.6 +/- 0.3%), respectively. The urine output for the NIDDM and control subjects were 1942 +/- 191 ml/24 h and 1032 +/- 94 ml/24 h, respectively, and urinary albumin excretion (UAE) rates were estimated to be 38 +/- 7 micrograms/min and 11 +/- 1 micrograms/min, respectively. The NIDDM subjects produced significantly increased levels of urinary PAF (2606.3 +/- 513.1 ng/24 h compared with 77.9 +/- 14.1 ng/24 h in controls (or 1706.3 +/- 420.8 ng/ml compared with 85.4 +/- 17.8 pg/ml of urine, in NIDDM and control subjects, respectively). We found that urinary PAF excretion was significantly correlated with microalbumin excretion (r = 0.7) especially at UAE rates greater than 30 mg/day and more importantly, some NIDDM patients with negative Albustix reaction (i.e. normal UAE) produced significantly more PAF, suggesting that PAF excretion may precede microalbuminuria and that subtle injury to the kidneys are present in NIDDM long before overt albuminuria ensues, urinary PAF measurements could potentially therefore serve as a sensitive indicator of renal injury in diabetes mellitus. These results lend further credence to our hypothesis that PAF may be the biochemical compound linking the various members of the insulin resistance syndrome.

Effects of systemic complement activation on renal circulation of rats

In a variety of immunopathological diseases activation of the complement cascade occurs either systemically or localized in the kidney. To elucidate the functional impact of complement activation upon the renal microcirculation, we administered cobra venom factor of Naja naja kaouthia (CVF) i.v. into thiobarbital anaesthetized female rats. CVF is a potent activator of the alternative pathway of complement by forming the C3-convertase CVF, Bb which cannot be downregulated by the natural inhibitor factors H and I and thereby leads to generation of the anaphylatoxins C3a and C5a and formation of the membrane attack complex (MAC). We utilized creatinine clearance and flowmeter measurements in the normal kidney and intravital microscopy of the split hydronephrotic rat kidney model to observe the microvascular changes. Bolus injection of CVF (100 U kg-1) resulted in an immediate reduction of RBF (-68% after 10 min), which remained decreased during the entire experiment (90 min). Systemic blood pressure was significantly reduced only in the early period (-23% of control: 126 mmHg after 10 min). After an initial anuric phase of 30 min duration, the glomerular filtration rate was significantly diminished by 47%. White cell count was decreased by about 50% after the experiments. Application of the competitive thromboxane A2-antagonist, BM 13505, reversed all renal and systemic CVF-effects. Continuous infusion of the competitive leukotriene D4-antagonist, ICI 198615, attenuated the late renal CVF-effects (i.e. 30 min after injection of CVF). Depletion of polymorphonuclear cells (PMN) attenuated the CVF-effects similar to BM 13505. Intravenous administration of CVF in the hydronephrotic kidney model resulted in a massive constriction of the interlobar and arcuate artery, with a fall in glomerular blood flow comparable to the reduction of RBF in the normal kidney. Diameters of the afferent arterioles--most sensitive to many vasoconstricting agents--were not significantly altered. Our results suggest that injection of CVF and the liberation of high amounts of the anaphylatoxins, C3a and C5a, induces the release of TXA2, which contributes to the early renal effects and the formation of cysteinyl-leukotrienes which play an important role in the late phase of systemic complement activation. Utilizing the split hydronephrotic kidney model we demonstrated the predominant action of complement activation on the large preglomerular vessels for the first time. PMN are seemingly involved in the liberation of secondary mediators which appear to reduce renal blood flow and glomerular filtration.

Effect of leukotrienes of renal water excretion

To investigate the renal actions of leukotrienes (LT), we infused arachidonic acid into the renal artery of anesthetized dogs during systemic cyclooxygenase inhibition (with ibuprofen) alone or in combination with lipoxygenase inhibition or LTD4/LTE4 receptor antagonism. Renal arachidonic acid infusion following ibuprofen alone decreased urine osmolality (945 +/- 143 to 698 +/- 144 mosm/kg; p < 0.01) and increased urine flow rate (0.34 +/- 0.11 to 0.56 +/- 0.16; p < 0.05) without altering renal blood flow, glomerular filtration rate or sodium excretion. In separate groups, prior inhibition of lipoxygenase (propylgallate) or blockade of LTD4/LTE4 receptors (LY171883) prevented the changes in urine osmolality and urine flow rate. Intrarenal oleic acid infusion following ibuprofen had no effect on renal function. Analysis of the renal papillae at the end of the experiment indicated that interstitial osmolality and sodium, potassium and urea contents were the same in all groups, ruling out a decrease in papillary interstitial osmolality as the cause of the decrease in urine osmolality in the arachidonic acid-infused group. Our experiments suggest that renal LT can decrease urine osmolality and increase urine flow rate and may play a role in renal water excretion.

Effects of PAF antagonists on renal vascular escape and tachyphylaxis in perfused rabbit kidney

Renal vascular escape is a physiological phenomenon of adaptation that occurs in vascular smooth muscle. It has been described in many preparations subjected to electrical stimulation or treated with vasoactive agents, such as noreprinephrine, angiotensin and vasopressin. We have recently demonstrated that a naturally occurring ginkgolide (BN 52021), which is a PAF antagonist, was able to block norepinephrine-induced escape in perfused rabbit kidney. In the present work other PAF antagonists, such as the ginkgolides BN 52022 and BN 52024, and the synthetic compounds 48740 RP and WEB 2086, were tested. Their effects on renal vascular escape, perfusion pressure and tachyphylaxis were evaluated. They all were shown to block the escape. Among the ginkgolides, BN 52024 is generally recognized as one of the weaker PAF antagonists. However, in spite of this, BN 52024 was able to significantly and simultaneously block renal vascular escape and tachyphylaxis in perfused rabbit kidney infused with norepinephrine.

The effects of R-75,317 on antiglomerular basement membrane glomerulonephritis in rats

Platelet-activating factor (PAF) is a potent inflammatory mediator which is released by various inflammatory cells and produced by certain tissues, including the kidney. PAF has been shown to increase glomerular permeability to protein and to decrease glomerular filtration rate (GFR) by contracting mesangium. On the basis of these observations, it has been suspected that PAF may play a role as mediator of glomerular damage in glomerular nephritis. To examine this possibility, we studied the effects of a specific PAF antagonist, R-75,317, on the development of an experimental model of anti-glomerular basement membrane (anti-GBM) glomerulonephritis. Glomerulonephritis was initiated by injecting rabbit anti-rat GBM serum into rats. Proteinuria gradually developed after serum injection, plateaued at week 2, and remained at the high level of week 2 throughout the experimental period (6 wk). Chronic treatment with R-75,317 (10 mg/kg/day i.p.) tended to delay the onset of proteinuria and significantly accelerated the recovery phase. Creatinine clearance (Ccr) fell to 40% at week 3. R-75,317 treatment completely prevented this decline of Ccr. Histological changes in this model (glomerular hypertrophy, proliferation of mesangial matrix and interstitial fibrosis) were also ameliorated by the R-75,317 treatment. The results suggest that PAF may play a role in the development of glomerulonephritis and that PAF antagonists could be used in the treatment of human renal disease.

Platelet-activating factor in cardiovascular stress situations

Since the elucidation of its chemical structure two decades ago, platelet-activating factor (PAF) has emerged as an important mediator of various cardiovascular stress situations. Most notably, PAF was implicated as a key factor in the septic shock syndrome, based on the similarities between endotoxin and PAF biological effects, the elevation of circulating and tissue levels of PAF during endotoxemia, and the protective effect of PAF antagonists in the septic state. In addition, accumulating data suggest the involvement of PAF in the pathophysiological processes associated with ischemia, hemorrhage and trauma, where PAF exerts its effects directly on cells and blood elements or indirectly through interactions with other mediators such as cytokines and prostaglandins. Nevertheless, the relative contribution of PAF to the pathophysiological processes in endotoxemia is still unknown and should await further investigations. The primary aims of this chapter are: to delineate the effects of PAF on the cardiovascular system, to summarize the data which suggest the involvement of PAF in stress situations of the cardiovascular system, and to identify areas where future experimental efforts should be focused.

Nephrotoxicity of cyclosporine: the role of platelet-activating factor and thromboxane

Cyclosporine (CsA), an immunosuppressive agent, is potentially nephrotoxic. We had previously observed that acute administration of CsA to Munich-Wistar rats induced a decrease in single nephron glomerular filtration rate, due to a decline in glomerular plasma flow, and in the glomerular ultrafiltration coefficient. Moreover, these alterations were prevented when an antagonist of platelet-activating factor (PAF) was administered. In the present study we examined whether the protective effect of the PAF blocker in CsA nephrotoxicity could have been mediated by thromboxane (TxA2). Our data show that the PAF effects were not mediated by TxA2, since administration of dazmegrel, a thromboxane synthetase inhibitor, did not ameliorate the acute renal failure caused by CsA. Thus, PAF appears to be a direct mediator of acute CsA nephrotoxicity, while TxA2 is not significantly involved in this process.

Role of platelet activating factor in gentamicin and cisplatin nephrotoxicity

The present study was undertaken to evaluate the effects of platelet activating factor (PAF) antagonists on nephrotoxicity induced by gentamicin (GENTA) and cisplatin (DDP) in rats. PAF infusion provoked a 56% decline in single nephron (SN) GFR due to a decrease in glomerular plasma flow (QA, 55%), glomerular transcapillary hydraulic pressure (delta P, 13%), and glomerular ultrafiltration coefficient (Kf, 37%). Four days after a single dose of DDP (6 mg/kg, i.p.) we observed non-oliguric acute renal failure (ARF) with reduced SNGFR (45%), QA (46%) and delta P (10%) and unchanged Kf. GENTA administration for 10 days (40 mg/kg, i.p. daily) induced a decline in SNGFR (40%), QA (41%) and Kf (41%). Chronic treatment with a GENTA + PAF antagonist (BN 52021) partially prevented the decline in SNGFR (22%) by an amelioration in QA (25%) and Kf (13%). However, simultaneous treatment with DDP and BN 52063 completely prevented the ARF induced by DDP, normalizing all parameters of renal function. Thus, PAF may be a potential mediator involved in the nephrotoxicity induced by GENTA and DDP.

Effects of YM264, a novel PAF antagonist, on puromycin aminonucleoside-induced nephropathy in the rat

We investigated the effects of YM264, WEB2086, methylprednisolone and ticlopidine on puromycin-induced nephropathy in the rat. Puromycin produces marked proteinuria, hypercholesterolemia, and hypoalbuminemia. The structurally differing PAF antagonists YM264 and WEB2086 inhibited proteinuria and improved hypercholesterolemia and hypoalbuminemia. Methylprednisolone also exhibited a beneficial effect on these variables. However, ticlopidine, a platelet inhibitor, showed no inhibitory effect on nephropathy. These results indicate that PAF may play a major role in puromycin-induced nephropathy in the rat, and that PAF antagonists may prove of therapeutic value in the treatment of nephropathy in humans.

Platelet-activating factor (PAF) accumulation correlates with injury in the cornea

This study reports the accumulation of platelet-activating factor (PAF) in corneas injured with either 0.1 N NaOH or 1 N NaOH. The degree of injury in corneas exposed to alkali for 5, 10, 20, or 60 sec was assessed by light microscopy and scanning electron microscopy. PAF accumulation in vivo increased with time (up to 24 hr) after injury and also according to the severity of the alkali injury. PAF was isolated by high-performance liquid chromatography (HPLC) and assayed by platelet aggregation of the HPLC fraction containing PAF. The specificity of the aggregating bioactivity was ascertained from inhibition of platelet aggregation by selective PAF antagonists. BN 50726, a new synthetic PAF antagonist, applied in vivo topically or subconjunctivally, was effective in inhibiting PAF formation. Because PAF is accumulated in vivo as soon as 30 min after corneal injury, this lipid mediator seems to be synthesized by corneal cells and not be recruited inflammatory cells, since they arrive later. Moreover, if the injury causes stromal edema and endothelial damage, the amount of PAF accumulated is even greater. Results from isolated corneas stimulated in vitro with calcium ionophore A23187 suggest that PAF synthesis is the result of stimulation of phospholipase A2 to form lyso-PAF and subsequent activation of an acetyltransferase.

Increased urinary excretion of platelet activating factor in mice with lupus nephritis

Platelet activating factor (PAF) is present in urine from humans and experimental animals in normal conditions. Very little is known about changes in PAF urinary excretion under pathologic conditions and no data are available about the origin of PAF in the urine. In the present study we explored the possibility that immunologic renal disease is associated with an increase in PAF urinary excretion using gas chromatography-mass spectrometry technique. To clarify the renal or extrarenal origin of urinary PAF we evaluated whether exogenously administered PAF (1-[1', 2'-3H]alkyl) is filtered through the glomerulus and excreted in the urine. The results show that: 1) urine from mice with lupus nephritis in the early phase of the disease contained amounts of PAF comparable to those excreted in normal mouse urine, 2) PAF levels increased when animals started to develop high grade proteinuria, 3) after intravenous injection of [3H] PAF in nephritic mice, a negligible amount of [3H] ether lipid, corresponding to [3H]1-alkyl -2-acyl-3-phosphocholine (alkyl-2-acyl-GPC), was recovered from the 24 h urine extract.

Platelet-activating factor (PAF) and its relation to prostaglandins, leukotrienes and other aspects of arachidonate metabolism

This article summarizes some of the previously reported findings regarding a lipid mediator known as platelet-activating factor (PAF), and briefly describes its effects on cells and tissues. The effects of PAF have also been considered in relation to certain products of arachidonate metabolism released in response to PAF.

Interleukin-6 production by tumor necrosis factor and lipopolysaccharide-stimulated rat renal cells

Interleukin-6 (IL-6) is produced by various cell types, including monocytes, fibroblasts, and endothelial cells. IL-6 has also been detected in the urine of normal and renal transplant patients. Thus, the possible production of this cytokine by glomeruli and mesangial cells was investigated. Rat glomeruli were obtained by serial sieving of cortical homogenates of blood-free kidneys. Mesangial cells were obtained from the glomeruli and cultured under standard methods in RPMI 1640 medium containing 15% fetal calf serum. Glomeruli or confluent monolayers cells were then incubated in RPMI 1640 for 18 hr, in the presence or not of tumor necrosis factor-alpha (TNF alpha), lipopolysaccharide (LPS), or platelet-activating factor (PAF). IL-6 activity was measured using the IL-6-dependent cell line subclone (B 9-9) and expressed with respect to a standard curve established with recombinant IL-6. Glomeruli generate IL-6 upon TNF alpha (100 ng/ml) and LPS (1 microgram/ml), 11,500 +/- 3000 and 22,000 +/- 7500 U/ml, respectively. Nonstimulated mesangial cells produced 50 +/- 5 U/ml (mean +/- SEM, n = 4) of IL-6. TNF alpha (1 ng/ml) and LPS (1 microgram/ml) induced the production of 800 +/- 90 and 40,000 +/- 5000 U/ml, respectively (n = 4). In contrast, PAF (0.1 nM-1 microM) did not increase IL-6 production from glomeruli or mesangial cells. These results demonstrate that renal cells spontaneously generate minimal amounts of IL-6 and that this production is significantly increased by TNF alpha or LPS. A synergy between LPS and TNF alpha was induced in glomerular cells with 10 ng/ml of TNF alpha and graded concentrations of LPS. Thus, the production of IL-6 by glomerular cells and its modulation by other cytokines or endotoxins may play a role in the local immunological processes leading to immune glomerular diseases.

Involvement of platelet activating factor and thromboxane A2 in the renal response to unilateral ureteral obstruction

Platelet activating factor (PAF) and thromboxane A2 (TxA2) are two vasoactive mediators which can decrease renal blood flow. Both are synthesized by various intrarenal cell types or by macrophages which may infiltrate the kidney during unilateral ureteral obstruction (UUO). In several experimental systems, PAF receptor activation is accompanied by TxA2 release; pharmacological modification of TxA2 synthesis or receptor activation modulates the response to PAF. The involvement of PAF in UUO has not been studied previously, and the role of TxA2 has not been clearly defined by previous investigations. The hemodynamic response to acute UUO is characterized by decreases in renal blood flow (RBF) and glomerular filtration rate and an acute increase in ureteral pressure. In the present experiments, the involvement of either PAF or TxA2 in the acute response to UUO was studied by determining if blockade of either the TxA2 or PAF receptor would affect the renal hemodynamic response to UUO. In addition, the effect of blockade of the TxA2 receptor on the renal response to PAF was determined. Our results indicate that only a small portion of the renal response to PAF is mediated by TxA2, and that neither PAF nor TxA2 can be implicated in the acute hemodynamic response to UUO. TxA2 or PAF involvement in the chronic response to UUO still remains to be determined.

Immune release of histamine and other lipid mediators from guinea-pig isolated kidney: antagonism by BN-52021

The ability of a specific PAF-receptor antagonist, BN-52021, to control the release of mediators of anaphylaxis from actively sensitized (ovalbumin) guinea-pig has been investigated "in vitro". BN-52021 perfused through the kidney at different molar concentrations (1 x 10(-4)-1 x 10(-5)-1 x 10(-6] prior to antigen challenge neither modified the basal values of perfusion pressure nor stimulated mediator release from the organ. On the contrary, the compound antagonized in a concentration dependent way both vasoconstriction of the renal vessels and the increase in the perfusate of histamine, TXB2 and SRS-A due to antigenic shock. The antagonistic activity of BN-52021 was very consistent at 1 x 10(-4) M at which concentration the immunological release of histamine and TXB2 was reduced by 75%. The beneficial effect of BN-52021 in experimental anaphylaxis of the kidney may have some therapeutic implications principally in those pathological conditions where an abnormal increase of renal histamine and other mediators may compromise the haemodynamic function of this organ.

Direct effects of endotoxin on the function of the isolated perfused rat kidney

When the endotoxin-lipopolysaccharide (LPS) derived from the cell wall of gram-negative bacteria is given to the rat in vivo, there are prompt, marked decreases in glomerular filtration rate (GFR), renal blood flow (RBF) and % Na+ reabsorption (%T-Na+). However, it has not been determined whether the endotoxin itself has a direct effect on these renal functions. To test whether endotoxin has a direct renal effect, isolated rat kidneys (N = 8) were perfused for 160 minutes with a Krebs-Ringer-HCO3- solution containing substrate-free albumin (40 g/liter), glucose (5 mM) and L(+) lactate (7.5 mM). After control observations (20 to 80 min) were made, purified LPS from E. coli was added (N = 4) to the perfusate to achieve [endotoxin] of 0.01 micrograms/ml (80 to 120 min) and 0.1 micrograms/ml (120 to 160 min). Endotoxin had no effect on GFR, Na+ reabsorption or tissue K+ content when compared to timed-control perfusions (N = 4). There was a small (approximately 10%) but significant decrease in mean perfusion flow rate (PFR) at the highest [endotoxin] when compared to the low [endotoxin]p but no change in GFR occurred. When the same LPS was given to four rats in vivo at a dose which achieved an [endotoxin] of approximately 0.08 micrograms/ml plasma, there were prompt decreases in GFR and %T-Na+ and an increase in body temperature when compared with timed-controls; there also was a large loss of K+ from the kidney tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoaffinity labeling of platelet activating factor binding sites in rabbit platelet membranes

A photoreactive, radioiodinated derivative of platelet activating factor (PAF), 1-O-(4-azido-2-hydroxy-3-iodobenzamido)undecyl-2-O-acetyl-sn- glycero-3-phosphocholine ([125I]AAGP), was synthesized and used as a photoaffinity probe to study the PAF binding sites in rabbit platelet membranes. The nonradioactive analog, IAAGP, induced rabbit platelet aggregation with an EC50 value of 3.2 +/- 1.9 nM as compared to 0.40 +/- 0.25 nM for PAF. Specific binding of [125I]AAGP to rabbit platelet membranes was saturable with a dissociation constant (Kd) of 2.4 +/- 0.7 nM and a receptor density (Bmax) of 1.1 +/- 0.2 pmol/mg protein. Photoaffinity labeling of platelet membranes with [125I]AAGP revealed several 125I-labeled components by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A protein species with apparent molecular weight of 52,000 was consistently observed and inhibited significantly by unlabeled PAF at nanomolar concentrations. The labeling was specific since the PAF antagonists, SRI-63,675 and L-652,731, at 1 uM also blocked the appearance of this band; whereas lysoPAF was not effective at the same concentration. These results suggest that the binding sites of PAF receptor in rabbit platelets reside in the polypeptide of Mr = 52,000.

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.

Role of thromboxane A2, leukotriene C4 and histamine in the antigen-induced vasoconstriction in perfused, sensitized guinea-pig kidney

The existence of a role for TXA2, histamine, and possibly LTC4 in the antigen-induced renal vasoconstriction in isolated, perfused kidney of sensitized guinea-pigs is demonstrated.

The detection of platelet-activating factor in inflamed human gingival tissue

Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine; PAF) is a biologically active lipid, like the prostaglandins, which mediates allergic and inflammatory reactions. Aggregation of washed rabbit platelets was induced by a lipid prepared from inflamed gingiva. The mobility of the active lipid was coincident with that of authentic PAF on thin-layer chromatography. The aggregation was dose-dependent and inhibited by pretreatment with a specific PAF antagonist, ONO 6240, but not by indomethacin or creatine phosphate/creatine phosphokinase, which inhibit the platelet aggregation due to arachidonic acid or ADP, respectively. Thus the active lipid was identified as PAF; the amount of PAF detected was 118.1 +/- 79.7 pg/50 mg tissue (n = 6, mean +/- SD), the amount in normal tissue being 13.0 +/- 11.3 pg/50 mg tissue (n = 6). There was therefore a significant difference between the tissues. Lyso PAF, the metabolite of PAF with acetylhydrolase, was not detectable in either gingival tissue. Thus PAF was produced more in inflamed gingival tissue than in normal tissue; PAF may be involved in the occurrence and maintenance of periodontal disease.

Acetylcholine and dopamine promote the production of platelet activating factor in immature cells of chick embryonic retina

We have previously shown that platelet-activating factor (PAF), a naturally occurring lipid mediator of cell-to-cell communication, was produced by 3-day-old chick retina stimulated with acetylcholine (ACh) and dopamine (DA), but not with other neurotransmitters. ACh and DA stimulated PAF synthesis via a dithiothreitol (DTT)-insensitive cholinephosphotransferase, without affecting the acetyltransferase pathway, which was stimulated only by the calcium ionophore A23187. Therefore, we attempted to study the effects of neurotransmitters on PAF production and on the activities of the DTT-insensitive cholinephosphotransferase and acetyltransferase in the developing chick embryo retina up to hatching. Our results show that PAF was produced already at 8 days of development, when retinal cells are still rather immature and ganglion and Mueller cells are the only differentiated cells. The stimulation of PAF production occurred with ACh and not with other neurotransmitters. In older stages, DA also stimulated PAF production, as already described in the chick after hatching. DTT-insensitive cholinephosphotransferase and acetyltransferase activities were present in 8-day-old embryos, the earliest stage analyzed. Both enzymatic activities increased with age; DTT-insensitive cholinephosphotransferase increased rapidly from day 12 up to day 18, whereas acetyltransferase activity increased linearly up to the time of hatching. To promote PAF production, ACh and DA activate DTT-insensitive cholinephosphotransferase, but not acetyltransferase.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet activating factor antagonism with BN52021 protects the kidney against acute ischemic injury

The present study has been conducted to evaluate the eventual role of the platelet activating factor (PAF) in post-ischemic recovery of renal function, using BN52021, a PAF receptor antagonist, in the anesthetized rat. In Groups 1 and 2, animals were maintained hydropenic (fractional excretion of sodium less than 1%), while in Groups 3 and 4, studies were performed under extracellular expansion (0.9% NaCl, 5% of body weight), a procedure known to protect the kidney from ischemic injury. Groups 1 and 3 (control animals) were untreated, whereas Groups 2 and 4 received an intravenous bolus of BN52021 (3mg/kg), immediately before clearance studies. After three 20-minute control periods, the left renal artery was occluded during 30 minutes. Four consecutive 20-minute clearance periods were taken after the release of occlusion. In Groups 1 and 2, urine flow (UV) increased from 3.1 +/- 0.9 to 20.9 +/- 3.6 ml/min, and from 6.8 +/- 0.3 to 40.4 +/- 4.5 ml/min, respectively, from control to the last period of recovery. Glomerular filtration (GFR) recovered to 38% of control values, from 0.58 +/- 0.09 to 0.22 +/- 0.10 ml/min in Group 1, as opposed to Group 2, where GFR recovered to 69%, from 0.61 +/- 0.07 to 0.42 +/- 0.06 ml/min. Urinary sodium (UNaV) increased from 0.3 +/- 0.1 to 3.0 +/- 0.9 microEq/min, and from 1.0 +/- 0.3 to 6.0 +/- 0.7 microEq/min, in Groups 1 and 3. UV rose from 14.3 +/- 2.5 to 35.3 +/- 3.5 microliters/min, and from 14.2 +/- 2.1 to 68.6 +/- 9.3 microliters/min, in Groups 3 and 4, during the same periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effect of platelet-activating factor (PAF) receptor antagonists on peptide and PAF-stimulated prostaglandin release in unilateral ureteral obstruction

Unilateral ureteral obstruction (UUO) results in increased renal resistance as well as in exaggerated prostaglandin (PG) release from the obstructed hydronephrotic kidney (HNK). We have reported previously that platelet-activating factor (PAF) dose-dependently stimulates the release of PGs from both the HNK and unobstructed contralateral kidney (CLK), with CLK release being 10% that of the HNK. In the present report, we studied the interaction of PAF with its receptor by examining the effects of PAF-receptor antagonists on the release of PGs from the isolated perfused rabbit HNK and CLK stimulated by PAF; angiotensin II (AII), and bradykinin (BK) were also used as agonists. In the HNK, kadsurenone (3 microM) inhibited PAF-stimulated PGE2 and thromboxane B2 (TxB2) release by 28.2 and 62.5% respectively. CV-3988 (20 microM) and triazolam (5 microM) also preferentially diminished PAF-stimulated TxB2 release. In addition, all three drugs significantly diminished BK- and AII-stimulated TxB2 release, while CV-3988 was the only antagonist to affect peptide-stimulated PGE2 release. While effective against agonist-stimulated PG synthesis, these drugs had no direct effect on arachidonic acid metabolism to PGs. Furthermore, in the CLK, CV-3988 had no effect on BK- or AII-stimulated PGE2 release, whereas it totally inhibited PAF-stimulated release of PGE2. These results show that PAF-receptor antagonists in the HNK preferentially inhibit TxB2 release whether stimulated by PAF, AII or BK; in the CLK only PAF-stimulated PG release is affected. This biochemical difference may be of physiological significance and explain some of the functional differences between the HNK and CLK. Therefore, PAF may be an important mediator of some of the biochemical and functional changes associated with UUO.

Leukotriene A4: metabolism in different rat tissues

The transformation of leukotriene A4 into dihydroxyeicosatetraenoic acids and sulfidopeptide leukotrienes was determined in homogenates of rat tissues supplied with glutathione and albumin. The highest production of leukotriene B4 was found in spleen, lung and small intestine, while leukotriene C4 dominated in liver and lung. 5(S),6(R)-Dihydroxy-7,9-trans-11,14-cis-eicosatetraenoic acid (5,6-DHETE) was formed in all tissues, most prominently in kidney, heart and brain. We also found another isomer of 5,6-dihydroxyeicosatetraenoic acid produced in the kidney. This compound was derived from 5,6-DHETE by isomerization, probably of the 11-cis double bond to 11-trans, and the process appeared to be catalyzed by a membrane-bound factor.

A possible role for leukotrienes in the regulation of glomerular haemodynamics in the dog

In anaesthetized beagles, saralasin, phentolamine, 1-penicillamine-2-O-methyl-tyrosine-8-arginine-vasopressin and SCH 23390, a DA1 antagonist, were infused into the left renal artery (i.r.a.) and indomethacin and aprotinin intravenously (Group 1). In Groups 2 and 3, i.r.a. infusion of two chemically different putative leukotriene (LT) antagonists, FPL 55712 (100 micrograms/kg/min) and LY 171883 (500 micrograms/kg/min), respectively, was superimposed in the fourth period of experiments. In comparison to Group 1, there was an increase (40% in Group 2 and 33% in Group 3) in renal blood flow and a decrease in glomerular filtration rate (16% and 17%, respectively) and filtration fraction (36% and 41%, respectively). Similar changes were observed on the single nephron level. Directly measured glomerular capillary pressure decreased by 10% and 12%, respectively. A decrease in total arteriolar resistance by 34% and 25%, respectively, was caused by a comparatively higher decrease in efferent (44% and 34%, respectively) than afferent (26% and 15%, respectively) arteriolar resistance values. No change in the ultrafiltration coefficient, Kf, was detected. Providing FPL 55712 and LY 171883 are specific LT antagonists, these experiments suggest a possible constrictory role of LT (expressed more on the efferent than afferent arteriole) in anaesthetised mildly surgically stressed dogs.

The potential pathophysiological role of platelet-activating factor in human diseases

Platelet-activating factor (PAF) is a new phospholipid mediator released from various cell types and tissues by the catalytic action of phospolipase A2 and acetyl transferase upon immunological and non-immunological stimuli. It activates the cells by binding to specific binding sites. PAF exhibits a broad range of biological and pharmacological activities including platelet and neutrophil aggregation, eosinophil chemotaxis, bronchoconstriction, hypotension, and acute renal failure. In addition, PAF is involved in acute graft rejection, endotoxin shock, and gastrointestinal ulceration. Furthermore, it closely mimics the pathology of bronchial asthma and is cabable of producing most of the phenomena seen in inflammation. So far several PAF antagonists have been described and shown to afford protection. In future, pharmacological studies using such antagonists will help to elucidate the pathophysiological role of PAF in human diseases.

Cardiac and renal mast cells: morphology, distribution, fixation and staining properties in the guinea pig and preliminary comparison with human

In guinea pig (GP) and human heart and kidney cell or tissue preparations fixed with Carnoy's fluid (but not with formol-saline), mast cells (MC) were extremely well preserved and could be detected after staining with alcian blue (AB). Although histamine content and distribution in GP and human heart appeared to be different, morphological and histochemical studies of MC suggested a similarity between the two species and a clear distinction from rat peritoneal MC.

Anaphylatoxin-induced release of histamine from in vitro perfused guinea pig kidney

The effect of porcine C5a des Arg and C3a, given as a bolus injection, in the isolated constant flow pump-perfused guinea-pig kidney was investigated. Only C5a des Arg showed activity which was manifested by a dose-dependent increase in perfusion pressure (PP, due to vasoconstriction) and histamine release. Although histamine release was substantial, it alone could not account for the increase in PP. The two more likely causes are a direct vasoconstrictor effect and the release of other mediators.