Effect of estrogens on plasma platelet-activating factor acetylhydrolase and the timing of parturition in the rat

In the present study we examined the effects of estrogens on plasma platelet-activating factor acetylhydrolase (PAF-AH) activity in pregnant rats in an attempt to further define the role of platelet-activating factor (PAF) in parturition. The plasma PAF-AH activity decreased starting on Day 13 of pregnancy and reached its lowest level by Day 19 (36.5 +/- 5.7 nmol.min-1.ml-1 plasma, mean +/- SD). The maternal plasma PAF-AH activity rapidly increased to 67.3 +/- 3.5 nmol.min-1.ml-1 plasma by Day 2 postpartum, to 88.8 +/- 14.4 by Day 7, and to 109.1 +/- 4.4 by Day 21, returning to nonpregnant levels by Day 35 in the dams that were allowed to nurse through Day 21. The PAF-AH activity did not increase in dams from which the pups were removed 2 days after delivery. When 17 alpha-ethynylestradiol (0.25 mg/kg) was administered s.c. to pregnant rats for 3 days starting at Day 17 of pregnancy, the plasma PAF-AH activity in the animals decreased by 80% on Day 19, and the rats delivered prematurely on Day 21. When a similar dose of 17 alpha-ethynylestradiol was injected into the pregnant rats for 3 days starting on Day 15, the enzyme activity again decreased by approximately 80% on Day 17 and Day 19 of pregnancy; however, it returned to a value similar to that seen in the controls by Day 21, and the time at which the treated rats delivered was similar to that for the control animals. These observations provide further support for a role of PAF and PAF-AH and their possible regulation by estrogens in the initiation and maintenance of parturition.

Platelet-activating factor acetylhydrolase activity in human follicular fluid

Platelet-activating factor (PAF) has been implicated in a number of reproductive processes ranging from ovulation to parturition. To examine the role of PAF in the human periovulatory processes, the PAF-acetylhydrolase (PAF-AH) activity was assayed in the follicular fluid (FF) obtained in conjunction with the in vitro fertilization and embryo transfer (IVF-ET) procedure and the activity related to oocyte maturation. The PAF-AH activity was also related to the concentrations of estradiol (E2) and progesterone (P) in FF. PAF-AH activity was significantly lower in the FFs obtained from follicles of more than 20 mm in diameter. The enzyme activity was significantly lower in the FFs of patients with a successful outcome of their pregnancies. E2 concentrations were negatively correlated with PAF-AH activities in the FFs. No correlation was found between the PAF-AH activity and concentration of P in the FF. Significantly more mature oocytes were recovered in the group who subsequently become pregnant compared to the non-pregnant group. It is suggested that PAF may be increased following follicular maturation. The increase in PAF may contribute to oocyte maturation and to the successful outcome of pregnancy following fertilization. An additional function of the increased PAF in FF may also be the stimulation of the contraction of smooth muscle in the ovary, thereby assisting the extrusion of the oocyte cumulus cell mass and signaling the completion of ovulation.

Platelet-activating factor-acetylhydrolase activity in follicular fluid of patients undergoing in vitro fertilization and embryo transfer

OBJECTIVE

To examine the role of platelet-activating factor (PAF) metabolism in the periovulatory processes.

DESIGN

The PAF-acetylhydrolase activity in the follicular fluid (FF) obtained in conjunction with IVF-ET procedure was assayed and its activity was related to oocyte maturation. The PAF-acetylhydrolase activity also was related to the concentration of various ovarian hormones.

SETTING

All patients were managed and treated at Oita Medical University Hospital, Oita, Japan.

PATIENTS

The study concerned 30 women between 28 and 36 years of age with tubal infertility.

MAIN OUTCOME MEASURE

The activity of PAF-acetylhydrolase in FF was assayed as well as E2 and P. Oocyte maturation also was evaluated.

RESULTS

Platelet-activating factor-acetylhydrolase activity was decreased significantly in the FFs of patients with a successful outcome of their pregnancies compared with the nonsuccessful group. Estradiol levels were negatively correlated with PAF-acetylhydrolase activities in the FFs. No correlation was found between the PAF-acetylhydrolase activity and P concentration in the FF. Significantly more mature and less immature oocytes were recovered in the group who subsequently became pregnant compared with the nonpregnant group.

CONCLUSIONS

It is suggested that the decrease in PAF-acetylhydrolase activity may result in an increase of PAF in the FFs, which in turn may contribute to a successful pregnancy. The determination of PAF-acetylhydrolase activity in FF may serve as a prognostic marker for the evaluation of oocytes that are utilized in IVF-ET procedure.

Evaluation of bedside blood glucose monitoring by the phlebotomy team in an acute general care hospital

A feasibility study was undertaken to evaluate laboratory phlebotomists performing bedside glucose monitoring (BGM) over a 3-month period on a medical and surgical floor. Specific questions included: feasibility of providing testing on a 24-h basis, accuracy, appropriate utilization, effect on patient care, and an analysis of cost. In all, 1975 tests were performed on 114 patients. BGM results were within 15% of the laboratory's result 97% of the time. Patient and physician satisfaction was high. Although the cost of BGM is slightly higher than a laboratory glucose test, its use appeared to reduce the length of hospital stay by 0.47 days. Practical information on initiating a highly successful BGM program is provided.

The inhibitory effect of 1,25-dihydroxyvitamin D3 on the secretion of platelet-activating factor acetylhydrolase by human decidual macrophages

The effects of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and 25-hydroxyvitamin D3 on the secretion of a platelet-activating factor (PAF)-inactivating enzyme, PAF-acetylhydrolase (PAF-AH), by decidual macrophage populations were examined. 1,25-(OH)2D3 inhibited PAF-AH secretion by either decidual cells or flow cytometrically purified decidual macrophages. 25-Hydroxyvitamin D3 also decreased the enzyme secretion but at higher concentrations than those required for 1,25-(OH)2D3. The 1,25-(OH)2D3-induced inhibition was partially blocked by protein kinase C (PKC) inhibitors, sphingosine and 1-(5-isoquinolinesulfonyl)-2-metylpiperazine (H-7). An intracellular calcium channel blocker, bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl)-ester (BAPTA/AM), also partially blocked the inhibition by 1,25-(OH)2D3, whereas extracellular calcium channel blockers, verapamil and nifedipine, failed to prevent the inhibition. H-7 and BAPTA/AM additively blocked the 1,25-(OH)2D3-induced inhibition. A PKC activator, 12-O-tetradecanoylphorbol 13-acetate, also decreased PAF-AH secretion. The decrease was abolished by sphingosine or H-7. It is suggested that 1,25-(OH)2D3 may increase the concentration of PAF in the decidua via its inhibitory effect on PAF-AH secretion by decidual macrophages and that the inhibitory action may be mediated by intracellular calcium and PKC-dependent signal transduction. PAF and 1,25-(OH)2D3 may, therefore, play a cooperative role in the regulation of PAF metabolism at the maternal-fetal interface.

Treatment of active refractory rheumatoid arthritis with humanized monoclonal antibody CAMPATH-1H administered by daily subcutaneous injection

OBJECTIVE

To investigate the dose tolerance and potential clinical activity of a humanized antilymphocyte monoclonal antibody, CAMPATH-1H (C1H), in patients with active, refractory rheumatoid arthritis (RA).

METHODS

Thirty adult patients with active, refractory RA were treated in an open-label, 3-center, dose-escalation study of subcutaneously injected C1H. Six patients were assigned to each of 5 dosage groups (0.3, 1.0, 3.0, 10.0 or 30.0 mg/day), and received 10 daily injections of C1H over a 12-day period.

RESULTS

Side effects occurred primarily during the first 1-2 days of dosing, and included mild fever, chills, nausea, vomiting, headache, and, in a minority of patients, hypotension. All patients developed some discomfort at the injection site. Self-limited infections occurred in 5 patients during the 6-month study period. Peripheral blood lymphocyte counts fell promptly after initial dosing and recovered slowly, usually over 2-3 months. Serum antibodies to C1H developed in 54% of patients following treatment. Clinical improvement was observed in 56% of patients, based on the composite Paulus criteria, with a median time-to-response of 22 days and a median response duration of 32 days.

CONCLUSION

C1H is a lymphocyte-depleting antibody that exhibits biologic potency when administered subcutaneously to patients with refractory RA. Its use is associated with mild to moderate toxicity and short-term amelioration of disease activity.

Platelet-activating factor. Role in fetal lung development and relationship to normal and premature labor

In this overview on the role of PAF in reproductive biology, we have emphasized its relationship to fetal lung maturation and the initiation and maintenance of parturition. In addition, we have discussed the role of this autacoid in certain complications of premature delivery. It should be pointed out, however, that it is our view that other mediators and cytokines also play a role in these processes. In the past, many investigators have suggested a central role for one of these mediators that serves as the "trigger" of these biologic events. It is our view that these systems are regulated by a number of effectors, among which PAF may play an important role.

Metabolic fate of platelet-activating factor in the rat enterocyte: the role of a specific lysophospholipase D

The metabolism of platelet-activating factor (PAF) by isolated rat intestinal epithelial cells was investigated using 1-[3H]octadecyl-2-acetyl-sn-glycero-3-phosphocholine. The principal metabolite produced by the cells was 1-O-alkylglycerol, which was found in association with the cells and the medium. When similar studies were conducted employing an intestinal epithelial cell line (INT 407), PAF was almost quantitatively converted into 1-alkyl-2-acyl-sn-glycero-3-phosphocholine (AAGPC). When the intestinal epithelial cell microsomes were incubated in the presence of fluoride to inhibit phosphohydrolase activity, the formation of 1-alkylglycerol was decreased in association with a stoichiometric increase in 1-alkyl-glycerophosphate, indicating the presence of a lysophospholipase D in the intestinal cells. When the phospholipase D activity was examined in the microsomal fraction prepared from intestinal epithelial cells, lyso-PAF was the preferred substrate and only trace amounts of lyso-PAF were converted into alkylacyl-GPC. Acyllyso-GPC was rapidly cleaved to form free fatty acids. The absence of lysophospholipase D activity in INT 407 cells cannot be attributed to the absence of brush border in these cells since no lysophospholipase D activity was present in isolated brush border preparations.

Coenzyme A-independent transacylation in amnion-derived (WISH) cells

Total membranes or microsomal fractions prepared from the amnion-derived WISH cell line posses a coenzyme A-independent transacylase activity. The transacylase utilizes 1-alkenyl- and 1-alkyl-2-lysoglycerophospholipids as preferred acceptors. Marginal transacylation was observed with 1-acyl-2-lysoglycerophospholipids. The reaction occurred in the presence of ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid and was not affected by phospholipase A2 inhibitors. Both 1-acyl- or 1-alkyl-glycerophosphocholines containing an arachidonoyl residue in the sn-2 position were effective as donors, while 2-oleoyl- or 2-palmitoyl-glycerophosphocholines were ineffective. The presence of the transacylase, the specificity of the substrates, and the stability of the 1-alkenyl bond provide a biochemical model that may explain the increased proportion of a highly enriched arachidonate-containing phosphatidyl-ethanolamine-plasmalogens fraction that is found in amnion at term.

Mesencephalic type 1 astrocytes rescue dopaminergic neurons from death induced by serum deprivation

We have established a primary neuronal culture of the embryonic day 14 rat, ventral mesencephalic region, centered on the A8, A9, and A10 dopaminergic nuclei (approximately 1.0 mm3 of tissue). At 16 hr after plating on a substrate of poly-D-lysine, in a serum-free or serum-supplemented growth medium, using a microisland culturing method, 95% of the cells stained positive for neuron-specific enolase, 20% for tyrosine hydroxylase, and < 5% for vimentin. When the growth medium was supplemented with 10% fetal calf serum, the percentage of tyrosine hydroxylase-positive neurons increased significantly (p < 0.05) at the 7th and 10th days in culture, compared with the percentage present at 16 hr after plating. When cultured in a serum-free growth medium, the percentage of tyrosine hydroxylase-positive neurons decreased to < 5% and to 0% by the 5th and 7th days, respectively, while the percentage of GABA-IR neurons increased. The addition of serum to the serum-free culture rescued dopaminergic neurons from death induced by serum deprivation. The effect of serum was dependent both on the time of addition after plating, and on the percentage added. When the cells were plated in a serum-free medium, on a confluent, type 1 astrocyte monolayer, prepared from the ventral mesencephalon of the embryonic day 16 rat, the survival of dopaminergic neurons increased significantly (p < 0.01) at DIV5, versus survival after plating on poly-D-lysine. Conditioned medium prepared from the same mesencephalic type 1 astrocyte monolayer also rescued dopaminergic neurons from death. The rescue mediated by the astrocyte monolayer or the conditioned medium was not inhibited by the mitotic inhibitor cytosine arabino furanoside (1.0 microM). Type 1 astrocyte monolayers and conditioned media prepared from the striatum and cerebral cortex of the embryonic day 16 rat had weaker trophic effects than those mediated by mesencephalic glia. We conclude that serum deprivation causes the selective death of dopaminergic neurons in a primary culture of the rat E14 ventral mesencephalon. Type 1 astrocytes or the conditioned medium from type 1 astrocytes can rescue dopaminergic neurons from death induced by serum deprivation.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of alcohol on platelet-activating factor acetylhydrolase activity in pregnant and nonpregnant mice

Platelet-activating factor (PAF) induces platelet aggregation and hypotension. It has been implicated in embryonic implantation, fetal lung maturation, and parturition. Alcohol abuse is associated with platelet dysfunction, chronic hypertension, and alcohol-related birth defects. We hypothesized that alcohol may cause, in part, these effects by increasing the activity of PAF-acetylhydrolase (PAF-AH), thereby decreasing PAF concentration. Pregnant mice were given 3.5 g/kg of alcohol orally twice daily from gestation days 7-17. PAF-AH was measured on gestation days 5, 14, and 19 in pregnant females. Nonpregnant females were treated and sampled at parallel time intervals. Pair-fed and untreated control groups were also used. The maternal plasma PAF-AH decreased with gestational age in the untreated controls. Alcohol significantly increased PAF-AH levels in both the pregnant and nonpregnant animals. PAF deficiency might contribute to the tocolytic action of alcohol, as well as some alcohol-related pregnancy complications.

Platelet-activating factor acetylhydrolase in term and preterm human milk: a preliminary report

Human milk may protect against necrotizing enterocolitis (NEC). Since platelet-activating factor (PAF) may participate in the pathophysiology of NEC, we measured PAF acetylhydrolase (PAF-AH), which metabolizes PAF, in term and preterm human milk. The activity of PAF-AH in term milk collected 2-4 days after delivery (n = 17) was 2.7 +/- 1.2 nmol x min-1 x ml-1. A higher activity was found in milk collected at similar times from mothers who delivered between 33 and 36 weeks of gestation (n = 6, 5.6 +/- 2.1 nmol x min-1 x ml-1, p < 0.01). However, milk from mothers who delivered between 26 and 32 weeks of gestation had a PAF-AH activity similar to that of term milk (n = 6, 3.0 +/- 0.7 nmol x min-1 x ml-1). With advancing lactational age, PAF-AH activity in term milk decreased, whereas the activity of this enzyme in preterm milk remained unchanged. In milk samples collected beyond 14 days after delivery from women who gave birth between 33 and 36 weeks or 26 and 32 weeks of gestation, PAF-AH activity was fivefold higher than that found in milk for women delivering at term (3.7 +/- 1.3 and 3.6 +/- 3.6 nmol x min-1 x ml-1 serum 0.7 +/- 0.4 nmol x min-1 x ml-1, respectively, p < 0.05). We speculate that the presence of PAF-AH in human milk may protect against NEC in preterm newborns.

Absorption of platelet-activating factor acetylhydrolase by rat intestine

Platelet-activating factor acetylhydrolase (PAF-AH) is a 43-kDa protein that catalyzes the degradation and inactivation of this potent phospholipid mediator. PAF plays an important role in the pathogenesis of necrotizing enterocolitis (NEC), and the elevation of the plasma PAF-AH activity may be beneficial in the prevention of this disease. The activity of PAF-AH was transferred from the mucosal to the serosal fluid in intestinal sacs from neonatal rats. Translocation was highest on day 15, decreased by day 21, and disappeared by day 24. Greater transport of the enzyme was noted in the neonatal jejunum compared with duodenum or ileum. PAF-AH absorption in 15-day-old rats was decreased by the addition of inhibitors of energy production and by low temperature. We have, therefore, concluded that the enzyme transport is an energy-dependent process. It is suggested that PAF-AH found in milk may prove to be beneficial in the prevention of NEC by its translocation across the intestinal mucosa. The absorption of macromolecules in the neonate, in addition to providing a passive immunity, may also serve a protective role by inactivating certain proinflammatory agents, such as PAF.

Platelet activating factor-acetylhydrolase activity following chorionic villus sampling and amniocentesis

OBJECTIVE

Platelet activating factor (PAF) is essential for embryonic development and is a potent vasodilator. It increases vascular permeability and stimulates prostaglandin E2 (PGE2) production. Platelet activating factor-acetylhydrolase (PAF-AH), the enzyme that degrades PAF, is synthesized by decidual macrophages. The aim of this study was to test the hypothesis that chorionic villus sampling (CVS) and/or amniocentesis might cause an increase in maternal PAF-AH activity.

METHODS

Maternal plasma PAF-AH activity was evaluated before and after genetic amniocentesis (N = 13) and transcervical CVS (N = 29). A control group (N = 9) was evaluated to study the effects of venipuncture.

RESULTS

Chorionic villus sampling caused a significant elevation in PAF-AH activity (P < .0005). No changes were noted in PAF-AH activity in the amniocentesis or the control group.

CONCLUSIONS

Chorionic villus sampling causes subclinical release of PAF-AH, possibly from the decidual macrophages. Increased PAF-AH activity might result in decreased PAF levels, which might lead to vasoconstriction in the placental circulation due to lack of the vasodilator effects of PAF and possibly PGE2. This mechanism might explain the increased risk for fetal limb reduction noted with CVS performed at very early gestational ages.

Binding and metabolism of platelet-activating factor (PAF) by isolated rat type II pneumonocytes

The specific binding of platelet-activating factor (PAF) to isolated type II pneumonocytes from rat lung has been investigated employing an intact cell preparation. The dissociation constant (Kd) for the autacoid has been determined to be 0.46 x 10(-9) M and approximately 3000 receptor sites per cell are present. In studies conducted on the metabolism of PAF in these cells, it was demonstrated that PAF is rapidly converted into 1-alkyl-2-acylglycerophosphocholine (alkyl-acyl GPC). After longer time intervals there was a substantial conversion of alkyl-acyl GPC into alkyl-acylglycerophosphoethanolamine (alkyl-acyl GPE). Both the alkyl-acyl GPC and alkyl-acyl GPE fractions were devoid of plasmalogens. The alkyl-acyl GPC fraction was further characterized and a distinct double peak could be visualized following thin-layer chromatography and the same lyso-compound was produced from both peaks following mild alkaline hydrolysis. By using appropriate standards it was concluded that the dual alkyl-acyl GPC peaks represent differences in the fatty acid present in the sn-2 position. One peak corresponds to the presence of saturated fatty acid in the sn-2 position and is probably due to the characteristic high capacity of the type II cells to produce disaturated glycerophospholipids.

Suckling-induced attenuation of plasma cortisol concentrations in postpartum lactating women

The effect of suckling on serum cortisol concentrations was assessed in postpartum lactating women studied during serial breast feeding sessions 1-24 weeks postpartum. The mean +/- SD serum cortisol concentration at 15 min after the start of nursing, 9.8 +/- 3.89 micrograms/dl, was significantly lower, P = 0.001, than prior to the start of nursing, 13.2 +/- 5.92 micrograms/dl. The decline in the serum cortisol concentrations in the breast feeding women was not due entirely to the normal metabolism of the hormone or the normal circadian variation in cortisol secretion. These studies complement and expand upon a recent report [3] of a significant decrease in plasma adrenocorticotrophic hormone in breast feeding women studied one week postpartum. The neuroendocrine mechanisms responsible for this effect in women have yet to be defined.

Oligodendrocyte-type-2 astrocyte (O-2A) progenitors increase the survival of rat mesencephalic, dopaminergic neurons from death induced by serum deprivation

When a primary culture of E16 rat striatal cells was grown in a serum-free medium, treatment with basic fibroblast growth factor (bFGF, 10 ng/ml) caused the generation of the progenitor cell for oligodendrocytes and type-2 astrocytes (O-2A). Immunostaining tests confirmed that > 90% of the cells were positive for A2B5, and < 5% positive for glial fibrillary acidic protein (GFAP). When E14, mesencephalic, dopaminergic neurons were co-cultured with established O-2A progenitor cells in a serum-free growth medium, the survival of tyrosine hydroxylase-positive (TH+) neurons increased 23-fold and 668-fold at the 5th and 10th days, respectively, compared with control cultures plated on poly-D-lysine. Conditioned medium from the O-2A progenitor cultures also decreased the death of TH+ neurons. The mitotic inhibitor, cytosine arabinoside (1.0 microM), did not block the protective effect of the O-2A progenitor cells. O-2A progenitor cells produce a potent, soluble factor, that mediates the increased survival of dopaminergic neurons in vitro.

Smoking and preterm labor: effect of a cigarette smoke extract on the secretion of platelet-activating factor-acetylhydrolase by human decidual macrophages

OBJECTIVE

Maternal smoking in pregnancy is associated with a significant increase in the incidence of preterm labor, premature rupture of membranes, and premature delivery. Our aim was to clarify the cause underlying this association.

STUDY DESIGN

The effect of cigarette smoke extract on the secretion of platelet-activating factor-acetylhydrolase by both decidual macrophages and peripheral blood monocytes and macrophages was investigated.

RESULTS

The cigarette smoke extract inhibited the platelet-activating factor-acetylhydrolase secretion by these cells. The inhibitory effect of cigarette smoke extract on the secretion was a hundred times more potent compared with its direct effect on the plasma enzyme. Glutathione and dithiothreitol blocked the inhibition, whereas catalase or superoxide dismutase did not. Nicotine and cotinine have no effect on the secretion.

CONCLUSION

The presence in cigarette smoke extract of a potent inhibitor(s) of platelet-activating factor-acetylhydrolase secretion by decidual macrophages may provide an insight into the pathogenesis of preterm labor, premature rupture of membranes, and premature delivery in women who smoke during pregnancy.

Secretion of platelet-activating factor acetylhydrolase by human decidual macrophages

Platelet-activating factor (PAF) metabolism in the maternal-fetal decidual interface has been investigated. Human decidua was obtained from patients at term and not in labor after cesarean section. The cells were isolated by enzymic digestion, followed by Ficoll-Paque centrifugation, or were purified further by discontinuous Percoll density gradient centrifugation. Cell populations were analyzed by flow cytometry after labeling with macrophage-specific antibodies. Twenty-seven percent of the cells obtained after enzymic digestion and Ficoll-Paque density gradient centrifugation had macrophage surface markers. The decidual cell population secreted PAF-acetylhydrolase (PAF-AH) activity. The secreted PAF-AH was the plasma-type isozyme. Synthesis and secretion was inhibited by actinomycin-D or cycloheximide. The PAF-AH activity secreted into the culture medium correlated positively with the number of macrophages. Flow cytometric purification yielded a 96% macrophage marker-positive population. The macrophages were shown to be the only cell types of decidual tissue that secreted PAF-AH. Treatment with anti-CD14 monoclonal antibody and complement specifically blocked PAF-AH secretion by collagenase-dispersed cells. It is concluded that decidual macrophages produce and secrete PAF-AH of the plasma type, and it is suggested that these cells may play an important role in PAF metabolism during parturition.

Metabolism of hexadecanol by rat type II pneumonocytes

Type II pneumonocytes isolated from adult rats incorporate radioactivity from 1-[3H]hexadecanol into either lipids. The radioactivity is distributed between the neutral lipids, phosphatidylcholines, and phosphatidylethanolamines. The neutral lipid fraction is almost exclusively composed of triradylglycerols. The potent ether-containing glycerophospholipid, platelet-activating factor, has been shown to stimulate glycogen breakdown and surfactant secretion. In consideration that a long chain alcohol (hexadecanol) is added to certain artificial surfactant preparations which are utilized in the treatment of respiratory distress syndrome of the newborn, the metabolism of hexadecanol by the type II pneumonocytes should be taken into account.

Effects of endotoxins and cytokines on the secretion of platelet-activating factor-acetylhydrolase by human decidual macrophages

OBJECTIVE

The aim was to clarify the role of platelet-activating factor in parturition, preterm labor, and premature rupture of membranes.

STUDY DESIGN

Decidual macrophage populations were obtained by enzymic digestion, Ficoll-Paque centrifugation, or flow cytometric sorting. The effects of endotoxins and cytokines on platelet-activating factor-acetylhydrolase secretion by these cells were examined.

RESULTS

Lipopolysaccharide inhibited the platelet-activating factor-acetylhydrolase secretion by decidual macrophages. The inhibition was partially reversed by interleukin-1 receptor antagonist or by neutralizing antibodies against interleukin-1 alpha, interleukin-1 beta, or tumor necrosis factor-alpha. Tumor necrosis factor-alpha, interleukin-1 alpha, and interleukin-1 beta also decreased the enzyme secretion. The inhibitory actions of tumor necrosis factor-alpha and interleukin-1 beta were specifically neutralized by the corresponding antibodies. The effect of interleukin-1 alpha or interleukin-1 beta on the secretion was abolished by interleukin-1 receptor antagonist.

CONCLUSION

It is suggested that platelet-activating factor is involved in the pathogenesis of preterm labor or premature rupture of membranes caused by endotoxins and the subsequent activation of cytokine network.

Presence of platelet-activating factor-acetylhydrolase in milk

Human milk contains numerous factors such as immunoglobulins, lactoferrin, lysozyme, macrophages, etc., which serve an immunoprotective role. Platelet-activating factor (PAF) is one of the most proinflammatory agents thus far described. PAF is metabolized to the biologically inactive lysoPAF by the enzyme PAF-acetylhydrolase (PAF-AH). In the present study we have demonstrated that PAF-AH activity is present in human milk. The activity was associated with aqueous phase and was not stimulated by the addition of bile salts or Ca2+. The activity of PAF-AH in human milk was not affected by the addition of propranolol or NaCl. PAF, and 1-acyl-2-acetyl-glycerophosphocholine were the only substrates cleaved by the enzyme. Based on these properties it is concluded that the milk PAF-AH is not the lipoprotein or bile salt-stimulated lipase known to be present in milk. Inhibitor studies revealed that the enzyme in human milk was the plasma type PAF-AH. The activity of PAF-AH was stable at pH 4.0 at 37 degrees C and the activity varied in milk samples obtained from various species. The enzyme was secreted by milk macrophages. The presence of PAF-AH in human milk may explain, in part, the beneficial effects of breast feeding in the prevention of necrotizing enterocolitis by inactivating the potent proinflammatory autacoid, PAF.