Biomedical subjects

M A Javors

Publications and source records attributed to M A Javors.

At least 19 recordsLinked to original sources

PubMed1999

Effects of chronic antidepressant treatments on serotonin transporter function, density, and mRNA level.

To investigate functional changes in the brain serotonin transporter (SERT) after chronic antidepressant treatment, several techniques were used to assess SERT activity, density, or its mRNA content. Rats were treated by osmotic minipump for 21 d with the selective serotonin reuptake inhibitors (SSRIs) paroxetine or sertraline, the selective norepinephrine reuptake inhibitor desipramine (DMI), or the monoamine oxidase inhibitor phenelzine. High-speed in vivo electrochemical recordings were used to assess the ability of the SSRI fluvoxamine to modulate the clearance of locally applied serotonin in the CA3 region of hippocampus in drug- or vehicle-treated rats. Fluvoxamine decreased the clearance of serotonin in rats treated with vehicle, DMI, or phenelzine but had no effect on the clearance of serotonin in SSRI-treated rats. SERT density in the CA3 region of the hippocampus of the same rats, assessed by quantitative autoradiography with tritiated cyanoimipramine ([(3)H]CN-IMI), was decreased by 80-90% in SSRI-treated rats but not in those treated with phenelzine or DMI. The serotonin content of the hippocampus was unaffected by paroxetine or sertraline treatment, ruling out neurotoxicity as a possible explanation for the SSRI-induced decrease in SERT binding and alteration in 5-HT clearance. Levels of mRNA for the SERT in the raphe nucleus were also unaltered by chronic paroxetine treatment. Based on these results, it appears that the SERT is downregulated by chronic administration of SSRIs but not other types of antidepressants; furthermore, the downregulation is not caused by decreases in SERT gene expression.

Adrenergic Uptake Inhibitors↗

PubMed1999

Concentration-dependent effects of muscimol to enhance pulsatile GnRH release from GT1-7 neurons in vitro.

Immortalized GT1-7 neurons were used to characterize the effect of muscimol, a GABAA receptor agonist, to enhance pulsatile gonadotropin-releasing hormone (GnRH) release. GT1-7 neurons were grown on Cytodex-3 beads and placed in special superfusion microchambers. The cells were superfused at a rate of 6.2 ml x h-1 with Media 199 (pH 7.35) using a commercially available perfusion system. After a pre-muscimol period of 120 min, the cells were exposed for 5 min to 0.35, 1, 5 or 10 microM muscimol or 5 microM muscimol+20 microM of the GABAA receptor antagonist, bicuculline. Following removal of the muscimol (and bicuculline, in the case of the latter experiment), the superfusion was continued for another 115 min. Sample fractions were collected at 5 min intervals throughout the perfusion. Basal GnRH release from the GT1-7 neurons was pulsatile with an average interpulse interval of 45.4+/-0.5 min and an average pulse amplitude of 191.5+/-22.6 pg x min x ml-1. Our results also demonstrated that the GABAA receptor agonist, muscimol, enhances pulsatile GnRH release from GT1-7 neurons in culture. The response to muscimol was saturable and concentration-dependent with an EC50 of 0.47 microM. The effects of 5 microM muscimol to increase GnRH pulsatility were blocked by co-exposure to the GABAA receptor antagonist, bicuculline. The average GnRH interpulse intervals were 41.7+/-1.8 min, 32.5+/-2.9 min, 30.6+/-0.7 min and 25.5+/-0.4 min in the period following exposure to 0.35, 1, 5 and 10 microM of muscimol, respectively (post-muscimol period). GnRH pulse amplitude (mean-area for each pulse) was increased during exposure to muscimol but not during the pre- or post-muscimol periods. The GABAA receptor antagonist, bicuculline, itself had no effect on pulsatile GnRH release. These results are consistent with previously published reports suggesting that activation of the GABAA receptor stimulates hypothalamic GnRH release in embryonic and neonatal animals.

Animals↗

PubMed1999

Thrombin-stimulated increases in cytosolic Ca2+ level and gonadotropin-releasing hormone release in GT1-7 neurons.

The effects of thrombin on cytosolic calcium levels ([Ca2+]cyt), and on gonadotropin-releasing hormone (GnRH) release, were characterized in cultured GT1-7 neurons. GnRH release from GT1-7 neurons was pulsatile with an average pulse amplitude of 14.3+/-5.8 pg x min x ml(-1) and an average pulse duration of 21.3+/-4.2 min. The [Ca2+]cyt response to 0.005 to 0.2 U/ml thrombin was saturable and concentration dependent (EC50 = 0.0268 U/ml). Ethyleneglycotetraacetic acid (EGTA) chelation of extracellular Ca2+ resulted in an approximately 70% attenuation of thrombin-stimulated increase in [Ca2+]cyt. By use of a special superfusion system, a 5-min exposure to 0.1 U/ml thrombin significantly increased the amplitude (193.2+/-67.8 pg x min x ml(-1); P = 0.001) but not the duration (22.5+/-2.4 min; P = 0.8) of GnRH release. These results suggest that thrombin increases [Ca2+]cyt and GnRH release from GT1-7 neurons via specific membrane-bound receptors.

Animals↗

PubMed1999

Biphasic changes in left ventricular function during hyperdynamic endotoxemia.

Cardiac contractility was studied in a clinically relevant conscious swine model simulating human hemodynamics during endotoxemia. The slope of the end-systolic pressure-volume relationship [end-systolic elastance (EES)] was used as a load-independent contractility index. Chronic instrumentation in 10 pigs included two pairs of endocardial ultrasonic crystals for measuring internal major and minor axial dimensions of the left ventricle, a micromanometer for left ventricular pressure measurement, and a thermodilution pulmonary artery catheter. After a 10-day recovery period, control measurements of cardiac hemodynamic function were obtained. The following week, Escherichia coli endotoxin (10 micrograms . kg-1. h-1) was administered intravenously for 24 h. EES increased 1 h after endotoxin infusion and decreased beyond 7 h. The later hemodynamic changes resembled human cardiovascular performance during endotoxemia more closely than the changes during the acute phase. EES decreased in the later phase. A similar biphasic response of EES has been reported during a tumor necrosis factor-alpha (TNF) challenge. Even though plasma TNF was highest at 1 h and declined thereafter in this study, no consistent relationship between TNF and EES was identified, and TNF levels did not correlate directly with the changes in EES.

Animals↗

PubMed1998

Characterization of chloride efflux from GT1-7 neurons: lack of effect of ethanol on GABAA response.

The purpose of this study of GT1-7 neurons was to partially characterize basal Cl- transport and GABAA mediated Cl- efflux and to test the effect of ethanol on a GABAA receptor that lacks a gamma subunit. We measured GABAA function and Cl- transport with 36Cl-. Our results show that basal 36Cl- efflux varied with temperature at 4 degrees C, 23 degrees C, and 37 degrees C. At 23 degrees C, DIDS, an inhibitor of anion exchange, reduced basal 36Cl- efflux maximally by 79.6% with an IC50 of 42.1 microM, whereas bumetanide, an inhibitor of (Na-K-Cl) cotransport, had no effect on basal 36Cl- efflux at concentrations up to 150 microM. At 4 degrees C, muscimol, a GABAA receptor agonist, stimulated 36Cl- efflux with an EC50 of 1.47 microM. Bicuculline, a GABAA receptor antagonist, completely reversed the effect of 20 microM muscimol with an IC50 of 6.08 microM. Ethanol, at concentrations up to 87 mM (0.4% (w/v)), had no effect on muscimol-induced 36Cl- efflux at 4 degrees C or at 32 degrees C. Our results indicate that stimulation of GABAA receptors causes an efflux of Cl- from GT1-7 neurons. This finding is consistent with the concept that stimulation of GABAA receptors produces depolarization of the plasma membrane, increase in cytosolic [Ca2+], and GnRH release. Our results represent the first description of chloride transport in GT1-7 neurons and suggest the presence of a Cl- exchange, but not (Na-K-Cl), transporter mechanism. Furthermore, the lack of an effect of ethanol observed in this study is consistent with the idea that a gamma 2L subunit may be necessary for the effects of low concentrations of ethanol at GABAA receptors.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1998

Effects of suramin on human platelet aggregation and Ca2+ mobilization induced by thrombin and other agonists.

The purpose of this study was to investigate the effect of suramin, a polyanionic napthalene sulfonic acid, on human platelet aggregation and Ca2+ mobilization induced by various agonists. Our results show that suramin completely inhibited aggregation by thrombin, platelet activating factor (PAF), alkyllysophosphatidic acid (ALPA), or arachidonic acid in a concentration-dependent manner. The IC50 values of suramin for inhibition of aggregation by PAF, arachidonic acid, and thrombin were 76.7, 239, and 1.49 microg/ml, respectively. Ca2+ mobilization induced by thrombin was inhibited by suramin with an approximate IC50 value of 20 microg/ml. This concentration of suramin had no effect on PAF or oleic acid-induced Ca2+ mobilization. The mechanism by which suramin inhibits aggregation is not clear, but our results suggest that suramin inhibits the ligand-receptor interaction.

Antineoplastic Agents↗

PubMed1997

Oleic acid-induced Ca2+ mobilization in human platelets: is oleic acid an intracellular messenger?

The purpose of this study was to explore the effect of oleic acid (OA) on intracellular Ca2+ mobilization in human platelets. When applied extracellularly, OA produced a concentration dependent rise in cytosolic [Ca2+] ([Ca2+]cyt) when extracellular [Ca2+] (Ca2+]ext) was zero (presence of EGTA), suggesting that OA caused an intracellular release of Ca2+. Intracellular Ca2+ release was directly proportional to entry of OA into platelets and OA entry was indirectly proportional to [Ca2+]ext. In permeabilized platelets, OA caused the release of 45Ca2+ from ATP dependent intracellular stores. Finally, our results show that thrombin stimulated the release of [3H]OA from platelet phospholipids. The saturated fatty acids stearic and palmitic acid did not stimulate an increase in [Ca2+]cyt under these conditions, but the unsaturated fatty acid, linolenic acid produced effects similar to those of OA, suggesting specificity among fatty acids for effects on [Ca2+]cyt. Taken together, our experiments suggest that OA which has been incorporated into platelet phospholipids was released into the cytosol by thrombin stimulation. Our experiments also show that OA stimulates Ca2+ release from intracellular stores. These results support the hypothesis that OA may serve as an intracellular messenger in human platelets.

Blood Platelets↗

PubMed1997

Schizophrenia, psychosis, and cerebral spinal fluid homovanillic acid concentrations.

Neuroleptic drugs block brain dopamine receptors and are effective in treating psychoses of diverse origins. This finding has become a cornerstone of the dopamine theory of schizophrenia, but clinical studies relating schizophrenia, per se, to brain dopamine metabolism have ranged from controversial to negative. This article presents new evidence that cerebrospinal fluid levels of the dopamine metabolite homovanillic acid are related to the severity of psychosis in schizophrenia. These results support the concept that homovanillic acid levels in cerebrospinal fluid vary as a function of psychosis rather than being related to the diagnosis of schizophrenia per se.

Adult↗

PubMed1995

Partial characterization of K(+)-induced increase in [Ca2+]cyt and GnRH release in GT1-7 neurons.

Secretion of pituitary gonadotropins is regulated centrally by the hypothalamic decapeptide gonadotropin releasing hormone (GnRH). Using the immortalized hypothalamic GT1-7 neuron, we characterized pharmacologically the dynamics of cytosolic Ca2+ and GnRH release in response to K+-induced depolarization of GT1-7 neurons. Our results showed that K+ concentrations from 7.5 to 60 mM increased [Ca2+]cyt in a concentration-dependent manner. Resting [Ca2+]cyt in GT1 -7 cells was determined to be 69.7 +/- 4.0 nM (mean +/- S.E.M.; n = 69). K+-induced increases in [Ca2+]cyt ranged from 58.2 nM at 7.5 mM [K+] to 347 nM at 60 mM [K+]. K+-induced GnRH release ranged from about 10 pg/ml at 7.5 mM [K+] to about 60 pg/ml at 45 mM [K+]. K+-induced increases in (Ca2+]cyt and GnRH release were enhanced by 1 microM BayK 8644, an L-type Ca2+ channel agonist. The BayK enhancement was completely inhibited by 1 microM nimodipine, an L-type Ca2+ channel antagonist. Nimodipine (1 microM) alone partially inhibited K+-induced increases in [Ca2+]cyt and GnRH release. Conotoxin (1 microM) alone had no effect on K+-induced GnRH release or [Ca2+]cyt, but the combination of conotoxin (1 microM) and nimodipine (1 microM) inhibited K+-induced increase in [Ca2+]cyt significantly more (p < 0.02) than nimodipine alone, suggesting that N-type Ca2+ channels exist in GT1-7 neurons and may be part of the response to K+. The response of [Ca2+]cyt to K+ was linear with increasing [K+] whereas the response of GnRH release to increasing [K+] appeared to be saturable. K+-induced increase in [Ca2+]cyt and GnRH release required extracellular [Ca2+]. These experiments suggest that voltage dependent N- and L-type Ca2+ channels are present in immortalized GT1-7 neurons and that GnRH release is, at least in part, dependent on these channels for release of GnRH.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1994

Impaired surface expression of PAF receptors on human neutrophils is dependent upon cell activation.

The capacity of human neutrophils to bind PAF was rapidly diminished upon cell stimulation with both physiological agonists (N-formylmethionylleucylphenylalanine (FMLP), leukotriene B4 (LTB4)) and pharmacologic agonists (phorbol 12-myristate 13-acetate (PMA), A23187). As a consequence, PAF responses in neutrophils were blunted, as monitored by an inhibition of intracellular Ca2+ mobilization. Downregulation of the PAF receptor in neutrophils by diverse agonists was temperature-sensitive and required intact cells. Scatchard analysis of binding data revealed that PAF binding sites were lost without an appreciable change in the affinity of the ligand for the receptor. The binding of the PAF receptor antagonist WEB2086 to neutrophils decreased in parallel with PAF binding. PMA-induced PAF receptor downregulation was staurosporine-sensitive while PAF receptor downregulation by A23187, FMLP, or LTB4 was staurosporine-resistant. Both neutrophil aggregation (a form of intercellular adhesion) and PAF receptor downregulation occurred only at high concentrations of agonists while other signaling processes such as the increase in [Ca2+]i, PKC activation, and PAF synthesis were stimulated at low concentrations of agonists. Furthermore, agonist-induced PAF receptor downregulation was observed only under conditions in which the activated neutrophils were stirred (or shaken) and were allowed to aggregate. Additionally, chelation of extracellular Ca2+ with EGTA minimized cell aggregation and also inhibited PAF receptor downregulation. While the nature of the biochemical signal or the physical changes in the plasma membrane associated with aggregation or that follow aggregation remain to be elucidated it is clear that full expression of cell activation (i.e., neutrophil aggregation) is required for PAF receptor downregulation.

Calcimycin↗

PubMed1994

Urinary catecholamines in attention-deficit hyperactivity disorder with and without comorbid anxiety.

OBJECTIVE: To determine whether there are differences in noradrenergic or adrenergic functioning in children with attention-deficit hyperactivity disorder (ADHD) with and without anxiety. METHOD: ADHD children with and without a comorbid overanxious (ANX) disorder were compared to each other and to normal controls in terms of 2-hour urinary excretion of norepinephrine (NE), epinephrine (EPI), and their metabolites. All subjects performed a fixed series of mentally stressful tasks during the collection period. RESULTS: Children with ADHD, regardless of comorbid anxiety, excreted more normetanephrine (NMN), the chief extracellular metabolite of NE, than controls, as well as more vanillylmandelic acid. Children with ADHD alone had lower NE/NMN and EPI/metanephrine ratios compared to controls. Children with ADHD/ANX excreted more EPI than ADHD children without anxiety. CONCLUSIONS: Children with ADHD may have a higher tonic activity of the noradrenergic system than controls, while children with comorbid ADHD/ANX may be differentiated from those with ADHD alone by higher adrenergic activity.

Anxiety Disorders↗

PubMed1993

Bradykinin receptors and signal transduction pathways in human fibroblasts: integral role for extracellular calcium.

Bradykinin receptors have been identified in human gingival fibroblasts; the primary signal transduction pathways and their dependence on calcium have been characterized. Binding data revealed a calcium-independent binding of bradykinin to the cell membrane with a receptor density of 25,000 receptors per cell and a Kd of 1.6 nM. The bradykinin receptor-mediated activation of phospholipase C (PLC) resulted in an extensive and rapid stimulation of phosphoinositide metabolism. Using radioreceptor assay techniques, in the absence of LiCl, the inositol 1,4,5-trisphosphate (Ins 1,4,5P3) generation was found to be transient, with maximal levels attained within 15 s. An EC50 of 12 nM was observed for the accumulation of total inositol polyphosphates. The activation of phospholipase A2 (PLA2), and the subsequent release of arachidonic acid and the primary metabolite prostaglandin E2, also was found to be time- and concentration-dependent. Stimulation of tyrosine kinase activity by bradykinin was concentration-dependent and resulted in the phosphorylation of three substrates of unknown identity. Bradykinin stimulation did not activate adenylate cyclase as there occurred no increase in the generation of cyclic AMP. The mobilization of intracellular calcium stores followed closely the Ins 1,4,5 P3 kinetics and had an EC50 of 11 nM. Chelation of extracellular calcium reduced significantly the duration of the calcium response, while only minimally lowering the rapid, maximal increase in intracellular free calcium concentration ([Ca2+]i). A sustained elevation of [Ca2+]i was found to be essential in PLC and PLA2 signaling, as well as in tyrosine kinase activation, suggesting a major role for membrane calcium channels in bradykinin stimulation of cellular responses in these cells. Bradykinin was found to inhibit dramatically epidermal growth factor-induced DNA synthesis in confluent cells, although to a much lesser degree in subconfluent cells. This pattern was similar to the observed maximal specific increase in bradykinin binding with confluency. Together these results demonstrate the presence of bradykinin receptors in human gingival fibroblasts; these receptors are coupled to signal transduction mechanisms involving the PLC, PLA2, and tyrosine kinase effector systems, all of which require extracellular calcium to achieve maximal activation.

Arachidonic Acid↗

PubMed1993

Effects of fire ant venom alkaloids on platelet and neutrophil function.

About 95% of venom of the imported fire ant Solenopsis invicta is composed of dialkyl piperidines. These alkaloids produce a distinct pustule at the site of injection. The formation of this pustule may involve the activation of platelets and neutrophils. The purpose of this paper was to characterize the effects of fire ant venom alkaloids (FAVA) on certain physiological and biochemical functions of human platelets and neutrophils. In platelets, FAVA caused a rise in intracellular [Ca2+], secretion of dense granules as measured by ATP release, and aggregation as measured by light transmission through a suspension of platelets. Aggregation response was less complete with FAVA than with thrombin or PAF. However, secretion response was greater with FAVA than thrombin. One of our most significant findings was that pretreatment of platelets with subthreshold concentrations of FAVA produced enhanced PAF-induced increase in [Ca2+]cyt, suggesting that synergism between the two agonists might play an important role in the physiological response to FAVA. In neutrophils, FAVA produced a rise in intracellular [Ca2+] and aggregation, although the responses were more moderate than those observed in platelets. These results suggest that FAVA activation of platelets and neutrophils may occur in vivo as a response to stings by red fire ants.

Adenosine Triphosphate↗

PubMed1993

Studies of catecholamine metabolism in schizophrenia/psychosis--I.

Acutely psychotic schizophrenic patients not taking antipsychotic medications and control subjects were studied before and during treatment with debrisoquin (DBQ), an inhibitor of monoamine oxidase, which does not penetrate into brain. Homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) were measured in plasma, urine, and cerebrospinal fluid (CSF). Significant differences between patients and control subjects were more easily discerned during treatment with DBQ. In patients, HVA was increased in plasma but not in urine or CSF, although MHPG was increased in all three fluids. There were many significant correlations between plasma MHPG and HVA levels and clinical ratings of psychoticism. Plasma MHPG correlated positively with both the severity of positive and negative symptoms and plasma HVA correlated only with positive symptom severity. These data suggest that both dopamine and norepinephrine (NE) metabolism are disturbed in acutely psychotic schizophrenic patients; disturbed NE metabolism may relate to negative symptoms as well.

Adult↗

PubMed1993

Studies of catecholamine metabolism in schizophrenia/psychosis--II.

Acutely psychotic schizophrenic patients were maintained on debrisoquin (DBQ) throughout 5 weeks of treatment with haloperidol. Treatment with haloperidol caused initial increases in urinary homovanillic acid (HVA) output that returned toward baseline by the 5th week. During haloperidol treatment, plasma levels of HVA tended to decrease, concurrent with increased renal clearance of HVA. Plasma 3-methoxy-4-hydroxyphenylglycol (MHPG) levels and urinary MHPG output both decreased over the course of treatment. The differences in HVA and MHPG metabolism suggest differential effects of treatment on dopamine and norepinephrine systems. Neuroleptic treatment also abolished the marked morning decreases in plasma HVA concentrations (reported in part I).

Adult↗

PubMed1993

Chronic cocaine disruption of estrous cyclicity in the rat: dose-dependent effects.

The effects of cocaine on cyclic reproductive function in females remain largely unknown. In this study, we sought to define the range of doses of cocaine effective in disrupting estrous cyclicity and inhibiting ovulation. Estrous cyclicity was monitored daily by vaginal cytology. Group 1 consisted of rats receiving no treatment. Group 2 consisted of rats injected daily with saline s.c. Groups 3 to 6 consisted of rats injected with 1, 5, 10 and 20 mg/kg/day of cocaine HCl s.c., respectively. Group 7 consisted of rats that were food-restricted to allow weight gains comparable to those of group 6. Our results indicate a dose-dependent effect of cocaine on estrous cyclicity with an estimated IC50 of 8.5 mg/kg/day (i.e., the dose of cocaine required to inhibit the number of proestrus: estrus events per 3-week period of analysis by 50%). Over 50% of the rats with cycle disruption on 10 mg/kg/day of cocaine, but almost none of those with cycle disruption on 20 mg/kg/day, returned to normal cyclic patterns after cessation of cocaine treatment. Serum luteinizing hormone levels were reduced 53 and 74% by 10 and 20 mg/kg/day of cocaine, respectively, with an IC50 of 8.9 mg/kg/day. In contrast, cocaine had no significant effect at any of the tested dosages on serum follicle-stimulating hormone or prolactin levels. Ovulation rates were significantly reduced at both 10 and 20 mg/kg/day of cocaine (IC50 = 11 mg/kg/day of cocaine).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Dual effects of oleic acid on Ca2+ mobilization and protein phosphorylation in human platelets in presence or absence of platelet activating factor.

This laboratory demonstrated earlier that oleic acid inhibited platelet activating factor (PAF)-induced aggregation and serotonin release of rabbit platelets (M. Miwa, C. Hill, R. Kumar, J. Sugatani, M. S. Olson, and D. J. Hanahan, 1987, J. Biol. Chem. 262, 527-530). More recently, we reported that oleic acid caused a decrease in phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2), but did not affect the level of inositol-1,4,5-trisphosphate (IP3), in rabbit platelets (D. Nunez, J. Randon, C. Gandhi, A. Siafaka-Kapadai, M. S. Olson, and D. J. Hanahan, 1990, J. Biol. Chem. 265, 18330-18838). These results suggested that oleic acid did not stimulate phospholipase C. In contrast, PAF induced a decrease in PIP2 and an increase in PIP level and IP3. These effects were shown to be attenuated by oleic acid. In this current study, our experiments show that (a) oleic acid blocked PAF-induced rise in intracellular [Ca2+] (to provide a mechanism in agreement with our previous experiments which showed that oleic acid inhibited PAF-induced IP3 rise in platelets) and (b) oleic acid itself induced a gradual rise in [Ca2+]i, which would provide a mechanism for oleic acid-induced aggregation despite the fact that oleic acid did not cause the production of IP3 (Nunez et al., 1990). Oleic acid, in a dose-dependent manner, was shown to inhibit PAF-induced Ca2+ mobilization from intra- and extracellular sources. The inhibition was closely related to the suppressive effect of oleic acid on PAF-induced aggregation. Furthermore, oleic acid inhibited the PAF-stimulated phosphorylation of the 20- and 40-kDa proteins. At concentrations above 20 microM, oleic acid itself could induce platelet aggregation and Ca2+ mobilization, but the time sequence of these two responses in human platelets was significantly different from those obtained with PAF. Oleic acid alone, at 20 microM, caused a 1.4-fold increase in the cAMP level in platelets which was followed by a decline to a basal value at higher concentrations of this fatty acid. It seemed clear that elevation of adenylate cyclase activity was not associated with free fatty acid inhibition of platelet activation. Interestingly, both PAF and oleic acid added separately to human platelets induced protein-tyrosine phosphorylation, but oleic acid did not cause any inhibition of PAF-induced protein-tyrosine phosphorylation.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Platelets↗

PubMed1992

Platelet-activating factor as an intercellular signal in neutrophil-dependent platelet activation.

The role of platelet-activating factor (PAF) in heterotypic cell to cell interactions in a rabbit neutrophil-platelet mixture model was investigated. Platelets were exposed to each of three chemotactic agonists: PAF, leukotriene B4 (LTB4), or FMLP. Only PAF stimulated aggregation, [3H]serotonin secretion, and cytosolic Ca2+ mobilization in platelets alone. However, platelets were stimulated by LTB4 and FMLP in the presence of neutrophils. This neutrophil-dependent platelet activation was blocked by pretreatment of platelets with PAF receptor antagonists, and was prevented by desensitization of platelets to PAF. Furthermore, the time-course of platelet activation showed a positive correlation with PAF production by neutrophils stimulated with either LTB4 or FMLP. The PAF-mediated neutrophil-platelet interaction was dependent on direct cell to cell contact, as demonstrated by experiments in which the majority of newly formed PAF was neutrophil associated (rather than released). Platelet activation did not occur when the neutrophil-platelet mixture was not stirred, minimizing cell to cell contact, or when platelets were challenged with a cell-free supernatant prepared from neutrophils activated with LTB4 or FMLP. Finally, the neutrophil-platelet interaction was abolished by SC-49992, a peptidomimetic of the fibrinogen binding sequence Arg-Gly-Asp-Phe, indicating a Arg-Gly-Asp-specific recognition mechanism. Our results demonstrate that neutrophil-generated PAF plays a crucial role in neutrophil-dependent platelet activation in this model system. This type of intercellular signaling event may be important in certain inflammatory or thrombotic processes.

Amino Acid Sequence↗