Biomedical subjects

R N Pinckard

Publications and source records attributed to R N Pinckard.

At least 19 recordsLinked to original sources

PubMed1992

Differential responsiveness of human neutrophils to the autocrine actions of 1-O-alkyl-homologs and 1-acyl analogs of platelet-activating factor.

The phlogistic actions of six molecular species of platelet-activating factor (PAF) (1-O-alkyl-PAF homologs, 16:0-, 18:0- and 18:1-alkyl-PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (AGEPC) and their respective 1-acyl-PAF analog counterparts, 16:0-, 18:0- and 18:1-acyl-PAF, 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (AGPC)) were assessed relative to five human neutrophilic polymorphonuclear leukocyte (PMN) functional responses: 1) lysosomal enzyme secretion; 2) specific desensitization to 16:0-AGEPC-induced lysosomal enzyme secretion; 3) O2- production; 4) chemotaxis; and 5) priming for enhanced O2- production. With respect to inducing lysozyme secretion, 18:0-AGEPC was 30- and 75-fold less potent than 16:0-AGEPC and 18:1-AGEPC, respectively, and was 25- and 40-fold less potent for inducing beta-glucuronidase secretion. 18:0-AGEPC was also 10-fold less active than 18:1- and 16:0-AGEPC for inducing O2- production. Thus, the rank order of potency of the alkyl-PAF homologs for inducing both lysosomal enzyme secretion and O2- production was 18:1- greater than or equal to 16:0- much greater than 18:0-AGEPC. In contrast, these three alkyl-PAF homologs had the same potency for desensitizing PMN to subsequent 16:0-AGEPC-induced lysosomal enzyme secretion and for priming PMN for augmented O2- production in response to FMLP or human recombinant C5a. Paradoxically, however, the rank order of potency of the alkyl-PAF homologs for effecting PMN chemotaxis was 18:0- greater than 18:1- much greater than 16:0-AGEPC. At concentrations as high as 1.0 microM, the acyl-PAF analogs did not initiate PMN lysosomal enzyme secretion, O2- production, or chemotaxis. However, the acyl-PAF analogs induced partial PMN desensitization to 16:0-AGEPC. A novel finding of potential (patho)-physiologic significance was the ability of acyl-PAF at nM concentrations to prime PMN for significantly enhanced O2- production after stimulation with FMLP or human recombinant C5a. The priming action of acyl-PAF was due to an increase in the rate as opposed to a prolongation of O2- production. The differing rank orders of potency of the alkyl-PAF homologs and acyl-PAF analogs for stimulating several physiologic responses of the same target cell, the human PMN, support the premise that there may be more than one PAF receptor subtype on the PMN and/or that differences in the biophysical properties of the various molecular species of PAF modulate their interaction with PAF receptor(s) linked to stimulus-response coupling.

Acylation↗

PubMed1991

Electrospray ionization for analysis of platelet-activating factor.

Platelet-activating factor (PAF) was analyzed by electrospray-ionization mass spectrometry (ESI-MS) using a single quadrupole mass spectrometer. The positive-ion spectrum was dominated by an ion corresponding to a sodiated molecule when a low potential difference between the capillary exit (nozzle) and the skimmer was employed, but when the capillary exit voltage was increased, fragmentation of PAF was observed. Initial fragmentation involved the loss of the elements of trimethylamine from the sodiated molecule to yield [M+Na-59]+. An intense ion at m/z 147, generated by the loss of trimethylamine from the sodiated phosphocholine portion of the molecule was also detected, along with a lower intensity ion at m/z 184 which is representative of a protonated phosphocholine moiety. With negative-ion detection the major molecular species was [M+Cl]-. Interpretation of the mass spectral fragments was verified by ESI tandem mass spectrometry on a triple-quadrupole tandem mass spectrometer.

Humans↗

PubMed1991

Isotopic exchange during derivatization of platelet activating factor for gas chromatography-mass spectrometry.

One approach to the quantitative analysis of platelet activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycerol-3-phosphocholine; also referred to as AGEPC, alkyl glyceryl ether phosphocholine) is hydrolytic removal of the phosphocholine group and conversion to an electron-capturing derivative for gas chromatography-negative ion mass spectrometry. [2H3]Acetyl-AGEPC has been commonly employed as an internal standard. When 1-hexadecyl-2-[2H3]acetyl glycerol (obtained by enzymatic hydrolysis of [2H3]-C16:0 AGEPC) is treated with pentafluorobenzoyl chloride at 120 degrees C, the resulting 3-pentafluorobenzoate derivative shows extensive loss of the deuterium label. This exchange is evidently acid-catalyzed since derivatization of 1-hexadecyl-2-acetyl glycerol under the same conditions in the presence of a trace of 2HCl results in the incorporation of up to three deuterium atoms. Isotope exchange can be avoided if the reaction is carried out at low temperature in the presence of base. Direct derivatization of [2H3]-C16:0 AGEPC by treatment with pentafluorobenzoyl chloride or heptafluorobutyric anhydride also results in loss of the deuterium label. The use of [13C2]-C16:0 AGEPC as an internal standard is recommended for rigorous quantitative analysis.

Carbon Isotopes↗

PubMed1990

Analysis of platelet-activating factor by GC-MS after direct derivatization with pentafluorobenzoyl chloride and heptafluorobutyric anhydride.

Parallel analysis of platelet-activating factor (PAF) using chemical ionization gas chromatography-mass spectrometry after direct derivatization with pentafluorobenzoyl chloride (PFB) and heptafluorobutyric anhydride (HFB) provides a facile and highly sensitive means for detecting and elucidating the structure of the numerous alkyl-chain homologs of this acetylated phospholipid autacoid. In the present study, the PFB derivative was used for initial electron capture negative ion chemical ionization analysis of PAF candidate molecules in human PMN extracts of unknown composition. Subsequent pulsed positive ion/electron capture negative ion chemical ionization evaluation of the HFB derivative furnished a measure of the molecular weight from [MH]+ and yielded the required structural information from characteristic negative ions, in particular [M-(2HF + ketene)]- and [M-(HF + acetic acid)]-. These procedures easily permitted confirmation of the presence of C16:0-, C17:0-, C18:0-, and C18:1-AGEPC (acetyl glyceryl ether phosphocholine) in extracts of stimulated human PMN and also demonstrated that the C17:0- homolog was comprised of both straight-chain and branch-chain varieties.

Benzoates↗

PubMed1989

Alkyl chain homologs of platelet-activating factor and their effects on the mammalian heart.

Platelet-activating factor (PAF; AGEPC) is a potent negative inotropic and coronary-vasoconstricting agent. Minor structural alterations in the PAF molecule are known to greatly affect its biological activity; thus, we have investigated the effects of selected synthetic saturated and unsaturated alkyl chain PAF homologs on the isolated guinea pig heart. The rank order of potency for the negative inotropic effect was C16:0- greater than C18:1- greater than beef-heart AGEPC greater than C15:0- greater than C18:0- greater than C14:0-AGEPC; the rank order for the coronary-vasoconstricting effect was C16:0- approximately C18:1- approximately beef-heart AGEPC greater than C15:0- greater than C18:0- approximately C14:0-AGEPC. With the exception of C16:0- and C18:1-AGEPC, the relative potencies for the cardiac and coronary effects of the alkyl chain AGEPC homologs did not correlate well with their relative potencies in stimulating rabbit platelets and human neutrophils. The differences in the rank order of potency for these AGEPC homologs suggest the presence of species and/or target cell PAF receptor heterogeneity.

Alkylation↗

PubMed1989

A novel method for the analysis of platelet-activating factor: direct derivatization of glycerophospholipids.

A novel, facile, and sensitive method for the quantitative and complete structure-proof analysis of platelet-activating factor (PAF) and other glycerophospholipids is described. 1-O-Alkyl/acyl-2-acyl-3-glycerophospholipids were treated with heptafluorobutyric anhydride in a one-step reaction to yield 1-O-alkyl/acyl-2-acyl-3-heptafluorobutyroyl-sn-glycerols as gas-liquid chromatography (GLC)-compatible derivatives. Furthermore, the components of the polar head group were also analyzed from the aqueous extract of the same reaction mixture as t-butyldimethylsilyl derivatives. Thus, this new method eliminates the need for phospholipase C treatment and subsequent purification procedures. Moreover, the direct derivatization of PAF homologs and analogs with hepatofluorobutyric anhydride does not result in positional isomerization of the product, providing increased specificity for gas-liquid chromatography-mass spectrometric (MS) analysis. It has also been shown that the heptafluorobutyroyl (HFB) derivative can easily be converted to the respective t-butyldimethylsilyl analog in a one-step reaction using t-butyldimethylsilyl chloride/imidazole reagent. Analogous to the formation of heptafluorobutyroyl derivatives, PAF also was reacted with pentafluorobenzoyl chloride to generate the pentafluorobenzoyl derivative. Therefore, this method has wide applicability for the formation of GLC-compatible derivatives of various glycerophospholipids. Our successful HFB derivatization and GLC-MS detection of subnanogram quantities of PAF indicate that this analytical procedure will greatly facilitate complete and quantitative identification of each of the molecular species of biologically derived PAF.

Chemical Phenomena↗

PubMed1988

Complement and neutrophil activation in the pathogenesis of ischemic myocardial injury.

Complement depletion with cobra venom factor (CVF) before coronary artery ligation has been previously shown to reduce subsequent ischemic myocardial tissue injury in the baboon; however, whether complement depletion after the initiation of acute myocardial ischemia affords similar myocardial preservation is not known. Both complement depletion with CVF or the administration of certain nonsteroidal anti-inflammatory drugs, including ibuprofen, are thought to decrease myocardial infarct size by reducing polymorphonuclear leukocytic (PMN) infiltration; nevertheless, complement activation also could alter tissue injury by PMN-independent actions. Thus, the relative effects of CVF administered after coronary artery ligation on the subsequent development of myocardial tissue injury were assessed in a baboon myocardial infarction model. The animals were randomized into three treatment groups (n = 6): either CVF (125 units/kg) or saline was given 30 minutes after coronary artery ligation, and ibuprofen (12.5 mg/kg) was administered 30 minutes and 4 hours after ligation. The extent of ischemic myocardial injury was assessed 24 hours later. Relative to saline-treated baboons, both CVF and ibuprofen reduced PMN infiltration (36 +/- 4 vs. 24 +/- 4 and 24 +/- 4 PMN/mm2, respectively; mean +/- SEM) and histological evidence of transmural myocardial infarction (100% vs. 47% and 53%, respectively) in electrocardiographically designated, expected infarct sites. In both saline- and ibuprofen-treated animals, there was extensive localization of C4, C3, and C5 in all infarct sites; in contrast, there was only C4 localization in the CVF-treated baboons. When expected infarct sites were assessed for creatine kinase content as an indicator of tissue injury, there was significantly less epicardial and endocardial creatine kinase depletion in the CVF-treated animals (31.7 +/- 5.6% and 39.3 +/- 4.8%) than in the saline-treated animals (54.1 +/- 5.4% and 59.0 +/- 4.7%; p = 0.012 and 0.011, respectively). The percent creatine kinase depletion in the ibuprofen-treated animals was intermediate between the two other groups. These results suggest that depletion of complement after coronary ligation has beneficial effects in reducing tissue injury that cannot be explained solely on the basis of reducing PMN infiltration into the ischemic myocardium.

Animals↗

PubMed1988

Platelet-activating factor in the rabbit uterus during early pregnancy.

Platelet-activating factor (PAF) concentrations were low in the non-pregnant, oestrous uterus (mean +/- s.e.m.: 2.2 +/- 1.2 pmol/g, n = 3). However, uterine PAF increased dramatically during pregnancy to a maximum of 37.8 +/- 4.90 pmol/g (n = 7) on Day 5. By Day 7, PAF concentrations in the uteri of pregnant rabbits had returned to levels similar to those found at oestrus. In contrast, uterine PAF in pseudopregnant rabbits peaked at 30.6 +/- 2.8 pmol/g (n = 8) on Day 4, declined to 20.5 +/- 2.4 pmol/g (n = 8) on Day 5 and then remained at that concentration through Day 7. Uterine PAF co-migrated with synthetic PAF (1-O-hexadecyl-2-acetyl-sn-glycero-phosphocholine) in both thin-layer and normal-phase high-performance liquid chromatography. PAF activity in the uterus during pregnancy and pseudopregnancy was found almost exclusively in the endometrium; little or no PAF was found in myometrium, uterine flushings or blastocysts. While no PAF was detected in blastocysts on Days 5 and 6 of pregnancy, the presence of the embryo appears to modulate biosynthesis and/or degradation of PAF by the uterus, since PAF decreased significantly in uterine tissue apposed to the implanting embryo (but not in similar areas between such attachment sites). Increased concentrations of PAF in the preimplantation rabbit uterus followed by a dramatic decrease on the day of blastocyst attachment suggest that this potent inflammatory autacoid may play a vital role in implantation.

Animals↗

PubMed1987

Ontogeny of the responsiveness to intravenous platelet-activating factor.

Neonatal and young animals fail to develop antigen-induced, lethal, systemic anaphylactic reactions. Recent evidence has documented that, in the adult rabbit, an unusual phospholipid autacoid, platelet-activating factor, induces almost all of the physiologic events associated with IgE-induced anaphylaxis. Thus, in the present study, the intravascular alterations after intravenous infusion of synthetic platelet-activating factor (1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine; AGEPC) into young rabbits were examined. In comparison to 13-week-old, adult rabbits, the intravascular infusion of greater than 1.0 micrograms/kg AGEPC was not lethal in rabbits of 8 weeks of age or less. In dose-response studies, the amount of AGEPC required to induce a lethal response in 50% of the animals tested (LD50) was found to inversely correlate with age. In contrast, AGEPC-induced platelet aggregation in vitro was not affected by the age of the donor animal. Consistent with age-independent platelet responsiveness in vitro, AGEPC-induced thrombocytopenia and intravascular accumulation of platelet factor 4 and thromboxane B2 were also unaffected by animal age. Neutropenia and basopenia, as well as platelet and neutrophil sequestration in the pulmonary microvasculature after intravenous AGEPC infusion also were similarly unaffected by animal age. Although the mechanisms which modulate the profound and lethal physiologic responses following AGEPC infusion in the adult rabbit remain to be established, the current study clearly documents an age-dependent acquisition of systemic physiologic sensitivity to AGEPC and/or other mediators released as a result of intravascular AGEPC administration.

Aging↗

PubMed1986

Characterization of inflammatory mediator release from purified human lung mast cells.

The release of inflammatory mediators (histamine, PGD2, TxB2, and LTC4) from purified human lung mast cells was characterized by kinetic and anti-IgE dose-response parameters. The relative rate of mediator release was histamine greater than PGD2 = TxB2 greater than LTC4, with one half maximal release occurring at approximately 2, 5, and 10 min, respectively. In 2 experiments, stimulation with anti-IgE caused significant quantities of platelet-activating factor (PAF) to appear rapidly (2 min) in the cell pellet; cell-associated PAF declined to low levels by 45 min. The optimal concentration of anti-IgE for the release of the arachidonate cyclooxygenase metabolites PGD2 and TxB2 (0.3 microgram/ml) was 10- to 30-fold less than that required for the release of histamine and LTC4 (3 to 10 micrograms/ml), suggesting that these release processes may have differential IgE Fc receptor cross-linking requirements. At optimal histamine release, the magnitude of the release of each arachidonate metabolite was found to correspond to the magnitude of histamine release, however, suggesting that the 2 processes are linked either in series or in parallel.

Antibodies, Anti-Idiotypic↗

PubMed1986

Age-dependent differential development of leukotactic and vasoactive responsiveness to acute inflammatory mediators.

Age-associated development of increased cutaneous vascular permeability and neutrophil accumulation in response to several inflammatory mediators was examined in young rabbits. The development of increased cutaneous vascular permeability was mediator-, age- and dose-dependent and was potentiated by prostaglandin E2 (PGE2). While 4-week-old rabbits responded to bradykinin, they did not develop increased vascular permeability in response to histamine, acetyl glyceryl ether phosphocholine (AGEPC), N-formyl-methionyl-leucyl-phenylalanine, or zymosan-activated plasma at doses which induced significant increases in vascular permeability in 13-week-old rabbits. Dose-dependent increases in vascular permeability after intracutaneous injection of AGEPC and histamine were observed by 6 weeks of age although fewer animals responded to histamine as compared to AGEPC. In addition, coadministration of PGE2 allowed the expression of increased vascular permeability to AGEPC, N-formyl-methionyl-leucyl-phenylalanine and zymosan-activated plasma in all 4-week-old animals. Interstitial neutrophil accumulation as well as increased vascular permeability was also age-, time-, mediator- and dose-dependent. Compared to 13-week-old rabbits, fewer numbers of interstitial neutrophils were observed in 4-week-old animals for up to 4 hours after intracutaneous injection of AGEPC. PGE2 potentiated the neutrophil response to N-formyl-methionyl-leucyl-phenylalanine and zymosan-activated plasma in both young and adult rabbits; nevertheless, the response in young animals was never as extensive as in the adult animal with the exception of the neutrophil infiltrative response after administration of AGEPC and PGE2. These results suggest that PGE2 synthesis and/or reactivity in young animals may be significantly different from adult animals and in part may account for the lowered reactivity to acute inflammatory mediators in the young animal.

Aging↗

PubMed1985

Fast atom bombardment-mass spectrometric identification of molecular species of platelet-activating factor produced by stimulated human polymorphonuclear leukocytes.

Fast atom bombardment mass spectrometry was used to identify molecular species of platelet-activating factor (PAF) produced by stimulated human neutrophilic polymorphonuclear leukocytes. Normal and reverse-phase high performance liquid chromatography were employed to separate the individual regions with PAF activity prior to mass spectrometric analysis. The following alkyl chain homologs of acetyl glyceryl ether phosphorylcholine (AGEPC) were found: C16:0, C17:0, C18:0 and C18:1. There was also evidence for the presence of the C15:0 homolog, as well as other species which have not yet been identified.

Chromatography, High Pressure Liquid↗

PubMed1985

Modulation of platelet-activating factor (PAF) synthesis and release from human polymorphonuclear leukocytes (PMN): role of extracellular albumin.

Human neutrophilic polymorphonuclear leukocytes (PMN) stimulated with N'-formyl-methionyl-leucyl-phenylalanine (FMLP) in the presence of cytochalasin B but in the absence of human serum albumin (HSA) synthesized only small amounts of platelet-activating factor (PAF) that attained maximum levels within 60-120 s after stimulation; in addition, no release of PAF occurred. However, in the presence of 2.5 mg HSA/ml, there was a threefold increase in PAF synthesis, 30-40% of which was released within 5 min after FMLP stimulation. In the presence of 50 mg HSA/ml there was at least a fourfold increase in PAF synthesis and release, with maximal synthesis occurring 10-20 min after stimulation. Thus, the presence of HSA during PMN stimulation not only induced an albumin dose-dependent increase in PAF release but significantly augmented the synthesis of PAF. In contrast to PAF synthesis and release, the presence or absence of HSA had no effect upon lysosomal enzyme secretion from FMLP-stimulated PMN, which was maximal within 30-60s after stimulation. These results demonstrate that HSA plays an essential role in vitro in the synthesis and release of PAF from human PMN, and support the hypothesis that there is a cyclic PAF synthesis-release coupling mechanism in the stimulated human PMN.

Calcium↗

PubMed1985

The role of complement in the pathogenesis of postischemic acute renal failure.

One hour occlusion of total renal blood flow results in oliguric acute renal failure as defined by an abrupt and severe diminution in glomerular filtration rate. In rats, after 1-2 h of such ischemia, the acute renal failure which follows is characterized by decreased renal blood flow and by intratubular obstruction with necrotic cellular debris. The present study has examined the possible role of the complement system in the development of this model of acute renal failure. Immunoreactive C3 was extensively localized within necrotic tubular epithelial cells and the walls of small muscular arteries in reperfused kidneys after 1 h of total renal ischemia. Depletion of complement by the administration of cobra venom factor 18 h prior to the induction of ischemia abrogated C3 localization and significantly attenuated the subsequent fall in renal blood flow following reperfusion but did not alter the oliguria or marked fall in glomerular filtration.

Acute Kidney Injury↗

PubMed1985

Kinetics of acetyl glyceryl ether phosphorylcholine (AGEPC)-induced acute lung alterations in the rabbit.

Acetyl glyceryl ether phosphorylcholine (AGEPC; 1-O-hexadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) was infused intravenously into rabbits (0.5 micrograms/kg); subsequently, temporal pulmonary alterations were assessed histologically. Within 30 seconds after AGEPC infusion, widespread platelet and neutrophil aggregates were distributed throughout the pulmonary microvasculature. Concomitantly, small muscular arteries and bronchioles throughout the lungs were contracted. Five minutes after AGEPC infusion, intravascular pulmonary platelet aggregates were less frequent and smaller than those observed at 30 seconds after infusion; however, AGEPC-induced pulmonary neutrophil sequestration persisted. Moreover, at this time, large mononucleated cells and damaged endothelial cells were prevalent throughout the pulmonary microvasculature. Sixty minutes after infusion, neither platelet aggregates nor arterial or bronchiolar constriction was observed. However, in most animals, neutrophils and large mononucleated cells were still abundant, and focal endothelial cell alterations persisted. In addition, discrete areas of interstitial hemorrhage around small and medium-sized arteries were present. These studies suggest that the intravascular release of AGEPC could initiate significant pulmonary injury and therefore could be an important etiologic factor in the development of inflammatory lung diseases.

Animals↗

PubMed1984

Molecular heterogeneity of platelet-activating factor produced by stimulated human polymorphonuclear leukocytes.

The molecular heterogeneity of platelet-activating factor (PAF) produced by stimulated human neutrophilic polymorphonuclear leukocytes (PMN) was assessed by both normal and reverse phase high performance liquid chromatography (HPLC). As detected by rabbit platelet stimulation, at least 5 PAF molecules were separated by HPLC. Fast atom bombardment (FAB) mass spectrometry revealed one of these PAFs was acetyl glyceryl ether phosphorylcholine (AGEPC) with a C16:0 alkyl chain in the sn-1 position. Although the structures of the remaining PAFs are unknown, two of the peaks of PAF activity had the same retention times on reverse phase HPLC as the C15- and C18-saturated alkyl chain AGEPC homologues. These studies indicate that the human PMN produces multiple molecular species of PAF.

Amino Acid Sequence↗

PubMed1984

Modulation of platelet-activating factor (PAF) synthesis and release from human polymorphonuclear leukocytes (PMN): role of extracellular Ca2+.

Extracellular Ca2+ regulated the synthesis and release of platelet-activating factor (PAF) from human polymorphonuclear leukocytes (PMN) stimulated with N'-formyl-methionyl-leucyl-phenylalanine (FMLP) in the presence of cytochalasin B. Maximum PAF synthesis and release required the presence of 0.14 mM Ca2+ whereas 1.4 mM Ca2+ was necessary for maximum lysosomal enzyme secretion. The synthesis of PAF occurred within 2.5 min after PMN stimulation in the presence of 1.4 mM Ca2+; however, PAF release did not occur until 5 min after stimulation. Peak PAF release occurred by 7.5 min but accounted for only 30-40% of the total amount of PAF synthesized, the remainder being retained on or within the PMN. Stimulation of PMN in the presence of 0.01 M EDTA or EGTA decreased PAF synthesis and release by greater than 95%. In the absence of extracellular Ca2+, stimulated PMN synthesized PAF in amounts that were 10-30% of maximum, but there was no release of the newly synthesized PAF. At Ca2+ concentrations greater than 0.01 mM, there was a dose-dependent (up to 0.14 mM) increase in PAF synthesis that was associated with the initiation and concomitant increase in the amount of PAF released. These data suggest the presence of a PAF synthesis-release coupling mechanism in which the extracellular Ca2+-dependent release of PAF stimulates additional PAF synthesis.

Adult↗

PubMed1984

Observations on the critical micellar concentration of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine and a series of its homologs and analogs.

In a study designed to explore the physical chemical characteristics of platelet activating factor (PAF), or 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, the critical micellar concentration of this compound, as well as the propionyl, butyryl and hexanoyl homologs was determined. In addition, an analogous series of compounds, in which the 1-O-alkyl was replaced by a 1-O-hexadecanoyl or a 1-O-octadecanoyl group, were examined for their critical micellar concentration. A variety of analytical techniques including NMR, gas liquid chromatography, infra-red spectrometry, thin layer chromatography, phosphorus, choline, glyceryl ether and fatty acid analyses were used to confirm the high purity of the individual derivatives. A dye binding assay and a surface tension technique were compared as to their suitability for determination of the critical micellar concentration of these compounds. Whereas the dye binding method proved highly variable, the surface tension procedure proved to be a facile, reproducible technique and was the assay of choice. The critical micellar concentration of the 1-O-alkyl and the 1-O-acyl derivatives showed comparable values for each short chain substituent at carbon 2, with values, in microM, ranging from 1.3 +/- 0.03 for 1-O-hexadecanoyl-2-acetyl-sn-glycero-3-phosphocholine and 1.1 +/- 0.10 for 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine to 0.22 +/- 0.01 for 1-O-hexadecanoyl-2-hexanoyl-sn-glycero-3-phosphocholine and 0.18 +/- 0.03 for 1-O-hexadecyl-2-hexanoyl-sn-glycero-3-phosphocholine. The data show that at the molar concentration usually employed in biological studies with these compounds, i.e., 1 X 10(-7) to 10(-11) M, one can assume that they will be present as monomolecular species. Thus, it seems unlikely that the widely diverse biological activities of these compounds can be explained by this physical parameter.

Acylation↗