PAF Levels Research Articles

Effect of platelet activating factor on the motility and acrosome reaction of buffalo ( [formula omitted]) spermatozoa

Platelet activating factor (PAF; 1-0-alkyl-2 acetyl-sn-glycerol-3 phosphocholine) has been shown to have a wide range of biological activities. In this study, PAF was used to induce acrosome reactions in fresh as well as frozen-thawed buffalo spermatozoa at different incubation periods and PAF levels. As the period of incubation increased, there was a gradual decrease in motility and increase in acrosome reaction in both fresh and frozen-thawed spermatozoa. With increasing PAF levels, the motility of fresh spermatozoa decreased and acrosome reaction increased whereas in frozen-thawed semen, motility remained almost constant, and the increase in acrosome reaction was not pronounced. Differences in motility and acrosome reaction among different bulls, types of semen, periods of incubation and PAF levels were significant (P < 0.01). A PAF level of 100 μ M and an incubation period of 15 min were found to be optimum for inducing acrosome reaction in buffalo spermatozoa, since at this combination acrosome reaction increased significantly (P < 0.01) over that of the control without much loss of motility.

Quantification of distinct molecular species of platelet activating factor in ulcerative colitis.

The aim of this study was to characterize the synthesis and metabolism of platelet activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) by colonic mucosa from patients with ulcerative colitis and healthy individuals. Tissue was obtained by endoscopic biopsy and by scraping the mucosa from surgical resections. Tissue was assayed for the various molecular species of PAF and its biologically inactive metabolite lyso-PAF using gas chromatography/mass spectrometry. Mucosa from surgical resections for ulcerative colitis contained C16:0 PAF (mean = 156 ng/g of mucosa), but not C18:0 PAF, PAF was not identified in mucosa from normal surgical resections or in endoscopic biopsies from either patients with ulcerative colitis or normal individuals. Both C16:0 lyso-PAF and C18:0 lyso-PAF were found in mucosa from normal and ulcerative colitis surgical resections and in endoscopic biopsies from ulcerative colitis and normal tissue. Levels of lyso-PAF were similar in ulcerative colitis and normal mucosa. Incubation of mucosa from areas of active inflammation in ulcerative colitis with the calcium ionophore A23187 increased the levels of C16:0 PAF by 2-3 fold and also increased the levels of C16:0 lyso-PAF. Addition of 3H-PAF to endoscopic biopsies from either normal individuals or patients with ulcerative colitis resulted in hydrolysis to 3H-lyso-PAF. The data on colonic mucosal levels of PAF are consistent with the results of earlier studies measuring PAF in patients with ulcerative colitis by bioassay. This study examines the synthesis and metabolism of specific molecular species of PAF in ulcerative colitis for the first time.

Blood cardiolipin in haemodialysis patients. Its implication in the biological action of platelet-activating factor

Bovine heart cardiolipin specifically inhibits rabbit platelet aggregation induced by PAF in vitro. In the past we have reported that patients with primary glomerulonephritis have increased PAF levels in plasma (Iatrou et al., 1995b). In this work we investigate the existence of cardiolipin in the blood of end-stage renal patients due to primary glomerulonephritis and we study its implication in the biological study of PAF. Lipids from blood samples of end-stage renal patients were extracted, fractionated onto silicic acid column and onto High Performance Liquid Chromatography (HPLC) cation exchange column. PAF fraction was removed and phospholipids were separated from the rest lipid fraction with current counter distribution and furthermore fractionated onto HPLC silica column. The results show: 1. cardiolipin is present in the blood of end-stage renal patients. 2. Blood cardiolipin specifically inhibits PAF-induced aggregation in washed rabbit platelets. 3. Scatchard plot analysis of PAF binding, in the presence of unlabelled PAF and in the presence of cardiolipin, shows that rabbit platelets possess two different types of binding sites. One of which is saturable and of high affinity, kD = 0.103 ± 0.03 nM (SEM, n = 3) with 337 ± 94 binding sites per platelet for PAF and kD = 0.087 ± 0.02 nM with 371 ± 92.7 binding sites per platelet for cardiolipin while the other one has almost infinite binding capacity. 4. Blood cardiolipin competes [ 3H]PAF binding in rabbit platelets. This work shows that cardiolipin exists in the blood of end-stage renal patients and specifically inhibits PAF-induced aggregation as well as PAF binding in rabbit platelets. The possible implication of the biological actions of cardiolipin in the anticardiolipin-antiphospholipid syndrome is also discussed.

Liver and plasma concentrations in paf‐acether and its precursors after partial hepatectomy

Liver and plasma concentrations in paf-acether (paf) and related phosphocholines, i.e., lysopaf and the ether lipid 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (AAGPC) were studied in rats following two-third hepatectomy. We report a rapid increase in hepatic content of the 3 phospholipids at early steps of the regeneration process, when hepatocytes are switching from G0 to G1 (time 2-6 h). Later on, throughout G1 and at the G1-S transition, these concentrations decreased progressively. They were back to sham-operated or intact control levels at 50 h. In the plasma of hepatectomized animals, no comparable changes were detected. However, an increase in both circulating paf and lipoprotein-bound paf concentrations was measured during the regenerating response. This report is, to our knowledge, the first one on paf level variations following 2/3 hepatectomy. In rats, partial resection of the liver was shown to initiate rapid and complex cascades of biochemical changes involving growth factors, neurotransmitters and interleukins among others. Our data are in good agreement with reported increases in both total phospholipid content and synthesis of phosphatidylcholine, a paf precursor, in the regenerating liver. At present, the possible functional significance of high paf concentrations measured over the 'priming' stage of the induced proliferative wave is suggested as a working hypothesis. However, on the one hand, the observed paf response is noteworthy in view of its cytokine-related action, i.e., stimulation of IL-6 production by different cell types (endothelial, macrophagic). On the other hand, it could represent an in vivo confirmation of previously reported in vitro paf effects inducing c-fos and c-jun expression, two members of the so-called 'cellular immediate-early gene' family.

Regulation of Phospholipase A2 Enzymes: Selective Inhibitors and their Pharmacological Potential

The area of PLA2 research has grown immensely over the past 20 years. There is a better understanding of the kinetics, or factors that affect the kinetics, of the different forms of PLA2. New forms of PLA2 are being discovered, such as the cPLA2, which fit the role of an intracellularly regulated enzyme. Multiple forms of PLA2 tend to complicate the elucidation of the cellular mechanisms that regulate AA release and the subsequent eicosanoid production. Because of the factors that affect PLA2 kinetics and the unknown nature of the PLA2 that regulates AA release (there may be more than one), it has been difficult to design or isolate specific inhibitors. This review discussed selected classes of inhibitors because these have generated the most intense research in the field. There is a multitude of structurally diverse compounds reported in the literature that have been reported to be inhibitors of PLA2 in vitro and some have been reported to have anti-inflammatory activity (Wilkerson, 1990; Connolly and Robinson, 1993a). It is clear from a brief survey of the literature that the bulk of PLA2 inhibitors have topical anti-inflammatory activity. This may be due to the nature of these inhibitors: because they are hydrophobic they may be more readily absorbed in the skin whereas when given orally they may not be absorbed. To data, manoalide has been clinically evaluated in man and a new Bristol-Myers Squibb retenoid derivative may enter clinical trials for psoriasis (BMS-181162 (XVI)); however, there are no PLA2 inhibitors on the market or significantly advanced in clinical development (Table III). This indicates the lack of understanding of this enzyme for the development of relevant inhibitors, which is related to the lack of understanding of the relevant PLA2 that regulates AA release and eicosanoid biosynthesis. The concept of regulation of eicosanoid biosynthesis by PLA2 inhibition and decreased AA availability still remains a viable therapeutic approach for the treatment of inflammatory diseases. The proof of this concept has not been obtained because of the complex nature of PLA2 and the multiple forms of PLA2 in the cell. Clinical results with cyclooxygenase inhibitors and recent clinical results with inhibitor of 5-lipoxygenase demonstrate that if inhibition of PLA2 results in reduction in both lipid mediators, a good anti-inflammatory compound should result. The added advantage of PLA2 inhibitors would be the reduction of PAF levels; however, the clinical results with potent and specific PAF antagonists has been less encouraging about the potential benefits of reduction in PAF levels.(ABSTRACT TRUNCATED AT 400 WORDS)

PAF and haematopoiesis. IV. Modifications of spleen and thymus PAF contents after a single dose of the chemotherapeutic drug 5-fluorouracil in mice.

The spleen and thymus of mice were examined for the presence of PAF after injection of 5-fluorouracil (5-FU) (200 mg/kg). A significant increase of the spleen (P = 0.005) and thymus (P < 0.05) PAF concentrations was noted 48 h after 5-FU infusion. PAF levels in thymus are similar to those of controls from days 4 to 14. By contrast, spleen PAF significantly decreased (0.005 < P < 0.03) from days 7 to 14. Conversely, the 5-FU administration did not modify the spleen and plasma acetylhydrolase activity, suggesting that the variations of PAF levels in thymus and spleen were mainly due to differences of local PAF production. Thus, the chemotherapeutic drug 5-FU modulates in vivo PAF production in haematopoietic organs of mice. Considering the effects of PAF in the processes of B- and T-cell proliferation and functions, these results could be of importance for the role of PAF during human cancer therapy and haematopoiesis in vivo.

Platelet‐activating factor mediates trinitrobenzene induced dysmotility in the left colon

We investigated whether TNB alters colonic tissue levels of PAF at the expense of changes in colonic motility in the isolated perfused rabbit left colon. Colonic inflammation was induced by the intracolonic administration of 0.25 ml of 50% ethanol containing 30 mg of trinitrobenzene. Strain gauge transducers were sewn onto the serosal surface of the colon to evaluate colonic motility. TNB administration increased tissue levels of PAF and increased the average force of each colonic contraction. Pretreatment with the PAF receptor antagonist WEB-2170 prior to TNB infusion decreased tissue concentrations of PAF and ameliorated the altered motility parameters seen with TNB alone. These results suggest that PAF is stimulated by TNB and may participate in colonic dysmotility during inflammatory states.

Synergy between tumour necrosis factor α and granulocyte-macrophage colony-stimulating factor in neutrophil stimulation

We have examined the interaction between the cytokines, granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumour necrosis factor α (TNFα) on polymorphonuclear leukocyte (PMN) function and on PMN responses to further stimulation with formyl Met Leu Phe (fMLP). Incubation of PMN with TNFα (0.3 nM) and, to a lesser extent, with GM-CSF (1 nM) directly stimulated superoxide anion (O2−) generation and increased the response to subsequent stimulation of PMN by fMLP (100 nM). However, the combination of GM-CSF and TNFα did not result in increased O2− generation and there was no synergistic effect of the combination of these cytokines on the priming of fMLP-induced O2− generation. The combination of TNFα and GM-CSF did result in a striking synergism in the stimulation of PAF generation, and, whereas neither stimulus alone resulted in detectable PAF release, the combination elicited the release of significant levels of PAF. The observation of significant PAF release from PMN exposed to TNFα and GM-CSF indicates that overt neutrophil stimulation with phagocytic or soluble stimuli may not be required for expression of at least some of the PMN pro-inflammatory capacity.

Studies on the etiology of acute acalculous cholecystitis: The effect of lipopolysaccharide on human gallbladder mucosal cells

Previous studies in animals have shown that lipopolysaccharide produces experimental cholecystitis possibly through a platelet-activating factor-prostanoid mediated process. In this study it was intended to evaluate the effect of LPS on primary cultures of human gallbladder mucosal cells. Gallbladder mucosal cells were isolated from gallbladders removed during routine cholecystectomies or other operations. The cells were cultured for 24 h before treatment. Unstimulated cells produced low levels of prostanoids and significant basal levels of PAF. LPS produced stimulation of eicosanoid and PAF secretion. The increased prostanoid formation was not enhanced when LPS and PAF were administered together. Prostanoid synthesis was inhibited by the administration of a cyclooxygenase inhibitor while administration of a PAF receptor antagonist significantly increased prostanoid formation, suggesting that increased PAF levels function as a negative control mechanism to decrease prostanoid synthesis. The results suggest that endotoxemia may produce a cascade of inflammatory processes in human gallbladder mucosal cells resulting in the development of acute acalculous cholecystitis.

Nasal allergen challenge generates 1-0-hexadecyl-2-lyso-sn-glycero-3-phosphocholine.

We studied antigen-induced platelet activating factor and the 1-0-hexadecyl-2-lyso-sn-glycero-3-phosphocholine (lyso-PAF) in nasal lavage fluids (NLF) by combined gas chromatography/mass spectrometric analysis (GC/MS). During the early allergic reaction, there was a dramatic increase in the levels of lyso-PAF that peaked at 15 min (2.6 +/- 5.2 ng/ml, mean +/- SEM, n = 6). Increasing doses of antigen produced a dose-dependent increase in the levels of lyso-PAF that peaked at the highest dose. Levels of lyso-PAF correlated strongly with those of N-alpha-tosyl-L-arginine methyl ester (TAME)-esterase activity (rs = 0.82, p = 0.0001) and histamine (rs = 0.57, p = 0.002). There was a no significant increase in the quantity of lyso-PAF found in NLF from allergic individuals challenged with diluent or nonallergic individuals challenged with antigen. In subjects showing a late phase reaction, as indicated by symptoms and histamine release, we detected lyso-PAF along with TAME-esterase activity and histamine during the late phase reaction. In contrast to lyso-PAF, PAF levels were near or below the detection limit of the assay in NLF and remained unchanged after antigen challenge. We also investigated the potential pathways for lyso-PAF generation from 2-acetylated phospholipids. We found that the time required for deacetylation of 50% of [3H]PAF (t1/2) to lyso-PAF was 50 min in baseline secretions and 10 and 22 min in NLF obtained 10 min and 24 h after antigen challenge, respectively. These data suggested that catabolic pathways were present in NLF.(ABSTRACT TRUNCATED AT 250 WORDS)

血管内皮細胞を介する好中球遊走における血小板活性化因子の役割解析

In an air pouch type allergic inflammation model in rats, PAF antagonists inhibit neutrophil migration into the pouch fluid although levels of PAF in the pouch fluid are less than the detectable amount. To clarify roles of PAF in neutrophil migration, effects of PAF antagonists (CV-6209, L-652, 731, Y-24180) on transendothelial migration of neutrophils were examined in vitro. Histamine and thrombin stimulated LTB4-induced transmigration of neutrophils through the confluent monolayer of human umbilical vein endothelial cells (HUVEC) . Treatment with PAF antagonists selectively inhibited the histamine- and thrombin-induced transendothelial migration, suggesting that PAF plays some significant roles in endothelial cell recognition by neutrophils.Treatment of HUVEC with TNF-α or IL-1/β induced neutrophil adherence to HUVEC monolayer and expression of adhesion molecules, such as ICAM-1, ELAM-1 or GMP-140. However, PAF antagonists showed no effect on the cytokine-induced neutrophil adherence to HUVEC nor the expression of these adhesion molecules. Furthermore, histamine- and thrombin-induced neutrophil adherence to HUVEC was inhibited by PAF antagonists without altering the expression of these adhesion molecules.Transendothelial migration of neutrophils was not inhibited by antibodies to GMP-140 and ELAM-1, but was completely inhibited by an antibody to LFA-1/β. An antibody to ICAM-1 partially inhibited the transendothelial migration of neutrophils.These results suggest that PAF produced by HUVEC plays important roles in signaling for neutrophil adherence to endothelial cells without affecting the expression of these adhesion molecules.

Inhaled Nitric Oxide Reverses Vascular and Respiratory Effects of ET-1 and PAF in Pigs

In anaesthetized paralysed, mechanically ventilated pigs, the vascular and respiratory effects of 80 ppm nitric oxide (NO) inhaled for 6 min were evaluated. To evoke different levels of smooth muscle contraction ET-1 or PAF, mediators involved in pulmonary disorders, were used. In control conditions, inhaled NO caused selective pulmonary vasodilatation without affecting respiratory resistances. This pulmonary vascular activity influenced the distensibility of the respiratory system and decreased inspiratory work. ET-1 administration significantly increased pulmonary arterial pressure and modestly changed mechanical properties of the respiratory system, while PAF caused potent vasoconstriction and bronchoconstriction associated with a marked change in volume-pressure relationship. In both cases, the changes in vascular and mechanical properties of the respiratory system increased inspiratory work. The vascular and respiratory activities of inhaled NO were correlated with preconstriction levels. The data show that the combination of vascular and respiratory effects improves pulmonary function, suggesting that inhalation of NO is a possible therapeutic approach for obstructive and inflammatory pulmonary diseases.

Cvtokines and Paf Release from Human Monocytes and Macrophages: Effect of Hemoglobin and Contaminants

Monocytes [M] were isolated from venous blood of healthy volunteers and activated macrophage-leukocytes (Mø-L] were obtained from peritoneal fluid of patients with mild endometriosis. The M were incubated with pyrogen free CELLGRO culture medium [Control], and with 0.2 mM of [A] unmodified bovine hemoglobin (UHb), [B] Hb crosslinked to form polymers with M.W. < 400 kDa (LMWHb), [C] Hb crosslinked to form large polymers (< 1,020 kDa) (HMWHb), and Mø-L additionally with [D] UHb contaminated with endotoxin (Hb+E) (2.5 EU/mL), and [E] UHb contaminated with phospholipids (Hb+PLs). The Mø-L medium of incubation was tested for TNF alpha, IL-1 alpha, IL-6, GM-CSF and PAF after 6 and 24 hours, but M for TNF alpha and GM-CSF at 12, 24 and 36 hours. Mø-L were found more responsive than M colonies. The strongest reaction of Mø-L was to Hb+E, which produced levels of cytokines and PAF higher than Controls (p < 0.001). Hb+PLs induced smaller increases of TNF and IL-6, and a decrease in the levels of IL-1 and GM-CSF. However, the release of PAF was much greater with this Hb than with Hb+E. UHb caused an increase in TNF, as compared to control (p < 0.01). LMWHb generated a similar increase in TNF, but also a decrease in IL-1. Both polymerized Hb forms inhibited expression of GM-CSF. HMWHb induced high levels of TNF, IL-1 and PAF. UHb, LMWHb and HMWHb significantly increase levels of TNF in M cultures after 36 hours of incubation.

Inflammatory mediator changes in cotton-top tamarins (CTT) after SC-41930 anti-colitic therapy.

Use of the CTT model provides insight into the inflammatory mediator contribution in the pathogenesis of idiopathic colitis. To evaluate anti-colitic efficacy, the leukotriene B4 receptor antagonist and anti-inflammatory agent, SC-41930, was administered (10 mg/kg BW by gavage BID) for 8 weeks to CTTs with histologically confirmed persistent and defined active colitis. The inflammatory mediators LTB4, PGE2, TXB2, and PAF were assayed in colonic dialysate that was collected after 1 1/2 h from four CTTs pre-, mid-, and post-treatment, frozen at -70 degrees C, and analyzed by RIA after HPLC purification. LTB4 levels were lower at mid- and post-treatment and had little inter-animal variation post-treatment. PGE2 and PAF levels were elevated during SC-41930 treatment, but there was a trend towards lower thromboxane B2 levels. Reduced LTB4 (PMN degranulation and chemotaxis) and increased PGE2 (mucosal-protective effect) may, in part, explain the observed efficacy of SC-41930 in active tamarin colitis.

Study on the metabolism of lyso-platelet activating factor (lyso-PAF) in human paranasal sinus mucosa. The cultured ciliated epithelium can convert lyso-PAF to PAF

The conversion of lyso-platelet activating factor (lyso-PAF) to PAF in cultured paranasal sinus mucosa obtained from normal human subjects was studied. The PAF concentration in the medium was determined after addition of lyso-PAF. PAF became detectable at 10 minutes after the addition of 10 −8M lyso-PAF, and reached a maximum concentration (3.25×10 −9M) at 20 minutes. The PAF level then gradually declined to become undetectable at 60 minutes after addition of lyso-PAF. Thus PAF is very unstable having a half-life calculated to be 12.8 minutes with an elimination constant of k=0.05377 minutes −1. In contrast, lyso-PAF is known to be a stable metabolite of PAF as well as a precursor of PAF. The results obtained from this study suggest that the turnover of lyso-PAF to PAF may play a role in evoking prolonged inflammation in target organs or tissues.

Metabolism of platelet-activating factor in the guinea-pig heart

Platelet-activating factor (PAF; 1-alkyl-2-acetyl-glycerophosphocholine) is a biologically active phospholipid which is synthesized by a variety of blood cells and organ systems. PAF exerts many effects on the cardiovascular system including hypotension, depression of myocardial contractility and coronary constriction. The present study has examined the capacity of the guinea-pig heart to regulate the levels of exogenous PAF in two different models: isolated perfused heart and isolated ventricular myocytes. In the first model, isolated hearts were perfused with labeled PAF (10 −10 m) in a recirculating manner at flow rates of 15 ml/min (normal flow perfusion; NFP) and 2 ml/min (low flow perfusion, LFP). Exogenously provided PAF appeared in the tissue in a time-dependent manner. The rate of extraction of PAF was higher during LFP than during NFP. PAF was metabolized by the heart to two major products, lyso-PAF and 1-alkyl-2-acyl-sn-glycero-3-phosphocholine (1-alkyl-2-acyl-GPC). Lyso-PAF was found primarily in the perfusion buffer while both lyso-PAF and 1-alkyl-2-acyl-GPC were detected in the tissue. No qualitative difference in the metabolic products derived from PAF catabolism was observed between hearts undergoing NFP and LFP. Acetyl hydrolase activity was detected in the perfusion fluid at both flow rates, probably accounting for the formation of lyso-PAF in the perfusate. However, perfusion fluid from LFP contained a higher acetyl hydrolase activity per μg of protein as compared to fluid from NFP. Isolated ventricular myocytes incubated with labeled PAF (3 × 10 −9 m) also converted it to 1-alkyl-2-acyl-GPC. Kinetic experiments suggested that PAF was initially deacetylated to form lyso-PAF and that this intermediate was then rapidly reacylated with a fatty acyl moiety at the sn-2 position. HPLC analysis of the fatty acids inserted at the sn-2 position of 1-alkyl-2-acyl-GPC revealed that the myocytes reacylated lyso-PAF predominantly with arachidonic acid. These data indicate that the guinea-pig heart may regulate PAF levels by at least two mechanisms: (1) it may release acetyl hydrolase into the vascular compartment, particularly under low flow conditions; and (2) the ventricular myocyte has the capacity to take up PAF and catabolize it to inactive products.

Measurement of PAF in blood by radioimmunoassay: Examination of interfering factors and problems involved in accurate quantification

A recently developed radioimmunoassay for PAF was applied to blood extracts with the aims of defining and overcoming problems that lead to erroneous results and establishing optimum conditions for the accurate determination of PAF levels. The high lipid content of blood was found to interfere with the assay, and it appeared that phosphatidylcholine and/or sphingomyelin might be among the lipids responsible. Interference was eliminated by either dilution or preparative TLC of blood extract prior to RIA although dilution is unlikely to be generally useful due to the low amounts of PAF normally present in human blood. Lipid extraction of whole blood followed by preparative TLC proved to be necessary in the preparation of samples prior to performance of the RIA. The problems encountered in the measurement of PAF levels in blood by RIA highlight the importance of determining the correct method of sample preparation for any tissue/fluid prior to its inclusion in the assay.

Blood levels of PAF are elevated during induction of immune complex mediated enteropathy in the rat

Intravenous injection into rats of immune complexes (IC) prepared in 5 × antigen excess rapidly induces annular bands of vascular congestion and transmural haemorrhage producing a striped appearance of the small intestine. Indirect evidence suggested a major role for PAF in the induction of lesions. In the present study, we showed that blood and leukocyte levels of PAF were elevated in most rats injected 10 min earlier with sufficient IC to induce lesions of 3+ to 4+ intensity. There was no significant difference in the number of rats with elevated plasma levels of PAF. The possibility that changes in blood PAF levels might be mirrored at sites closer to the lesions was considered. The overall effect of PAF on the small intestine of the rats is to induce stasis of flow; the precise target of PAF in mediating this effect is unknown.

Paf-acether acetylhydrolase activity is increased in patients with rheumatic diseases.

Paf-acether (platelet-activating factor) is a phospholipid described as a potent mediator of inflammatory response. We have recently shown that the level of paf bound to lipoproteins was significantly higher in the serum from patients with rheumatic diseases, compared to that of control subjects. In serum, paf is inactivated in part by a paf acetylhydrolase that catalyses the hydrolysis of the acetate residue. Acetylhydrolase activity was measured in the serum and synovial fluid of patients with rheumatoid arthritis and other arthritides, i.e. osteoarthritis and chondrocalcinosis. In serum, the activity of acetylhydrolase was significantly increased in patients with rheumatic diseases when compared with that in the control group. However, it was enhanced to a lesser degree in rheumatoid arthritis than in non inflammatory rheumatic diseases. These results suggest a role for acetylhydrolase in controlling paf levels in rheumatic diseases.

Quantitation by radioimmunoassay of PAF in human saliva

Approximately 75% of the PAF present in saliva is recovered on extraction of whole saliva (0.8 vol) with chloroform/methanol/water (2:2:1, v/v/v). PAF levels, determined by our recently developed radioimmunoassay, in saliva extracts ranged from 0.5-21 ng/mL with 59% between 2-6 ng/mL. These figures, for apparently healthy subjects, are higher than previously reported levels obtained by platelet assays. The validity of our radioimmunoassay results was checked by isolating and quantitating the PAF fraction from whole saliva. In addition, when we examined our saliva samples by platelet aggregation, low levels of PAF, comparable with the values found in the literature, were detected. Investigations revealed the presence of a substance(s) which inhibited PAF-induced platelet aggregation but which did not affect the radioimmunoassay.