Modulation of human neutrophil superoxide production by selective thromboxane synthetase inhibitor U63,557A

Prostaglandin I2 and prostaglandins of E series have been known to inhibit human neutrophil superoxide production. To examine the effects of selective thromboxane synthetase inhibition on human neutrophil superoxide production (with or without platelets), neutrophils were incubated with U63,557A and stimulated with f-MLP, serum-activated zymosan or calcium ionophore A23187. U63,557A had no significant direct inhibitory effect on neutrophil superoxide production. On the other hand, in the presence of platelets in neutrophil suspension, U63,557A significantly reduced neutrophil superoxide production and increased prostaglandin I2 release. These data suggest that selective thromboxane synthetase inhibition may reduce neutrophil superoxide generation, most likely via increase in prostaglandin I2.

The battered woman

The possibility of physical abuse is seldom raised when battered women seek medical treatment. Physicians are often reluctant to broach the subject, and many of these women do not want to reveal their situations. Apart from the injuries incurred in a battering incident, subtle manifestations of an abusive relationship include psychosomatic complaints, stress, anxiety, fear and depression. Suicide may be contemplated or attempted. The children are always affected.

Activity of calcium/phospholipid dependent protein kinase during rat kidney development

The activity of the calcium sensitive phospholipid dependent protein kinase C (PKC) was studied in cytosol and in the proximal tubular luminal membrane of rats during growth. Cytosolic activity was elevated at 14 and 21 days of age and fell to adult levels by day 60. Luminal brush border membrane activity on the other hand was low on day 14 but reached adult levels by day 21. Changes in brush border membrane PKC activity may have important consequences for the development of electrolyte transport in proximal tubular cells.

Ethanol stimulates prostacyclin biosynthesis by human neutrophils and potentiates anti-platelet aggregatory effects of prostacyclin

Previous reports on the direct effects of ethanol on human platelet aggregation function have been inconsistent. Ethanol ingestion produces vasodilation and raises intracellular cyclic AMP concentrations, effects similar to those of prostacyclin. We, therefore, hypothesized that ethanol may influence biosynthesis and/or bioactivity of prostacyclin. In our experiments, ethanol in concentrations up to 400 mg% had no consistent inhibitory effect on platelet aggregation in response to epinephrine, ADP, or combination of subthreshold concentrations of epinephrine plus ADP. However, ethanol in concentrations as low as 10 mg% potentiated the platelet aggregation inhibitory effects of prostacyclin. In addition, ethanol (20 mg%) decreased formation of thromboxane A2 in whole blood by 41% and stimulated formation of prostacyclin by 160% (both P less than 0.01). Additional studies using isolated human cells demonstrated synthesis of prostacyclin by neutrophils in the presence of platelets, and this neutrophil prostacyclin formation was enhanced in the presence of ethanol. These effects of alcohol in concentrations achieved after moderate intake may relate to the hemodynamic, biochemical, and cardioprotective effects of ethanol.

Inhibition of human platelet and neutrophil function by piriprost (U-60,257)

Platelets and neutrophils are important in determining the extent of myocardial injury following coronary occlusion. The detrimental effects of these blood elements are mediated in part via release of arachidonate metabolites and oxidative species. A new selective inhibitor of leukotriene formation, piriprost (U-60,257), has been observed to decrease both neutrophil accumulation in the myocardium and infarct size following coronary ligation in experimental animals. Since piriprost may have clinical use, we examined its effects on human platelet and neutrophil functions. This compound was found to exert potent inhibitory effects on epinephrine-induced human platelet aggregation and TXA2 biosynthesis (IC50 0.04 microM). Piriprost also inhibited human neutrophil chemotaxis, oxidative species release, aggregation, and LTB4 synthesis with IC50 of 0.1, 0.04, 10 and 14 microM, respectively. Thus, piriprost inhibits a variety of human platelet and neutrophil functions. Because of its suppressive effects on human platelet and neutrophil functions and protective effects in experimental myocardial infarction, this agent may have clinical applications.

Effect of human tumor cells on platelet aggregation: potential relevance to pattern of metastasis

Tumor metastasis may be facilitated by interaction of tumor cells with platelets. It is not known, however, whether solid tumors which have predisposition to pulmonary metastasis affect platelets differently than lymphoid tumors, which rarely spread to lungs. We therefore examined the effects of cultured osteogenic sarcoma (MG-63, U2-OS), as well as leukemia (NALM-16, LAZ-221, K-562) and lymphoma (RAJI, MOlt 4) cells, on human platelet aggregation. Human osteogenic sarcoma (MG-63) cells alone induced platelet aggregation, whereas U2-OS cells induced platelet aggregation only after preincubation of platelets with subthreshold concentrations of epinephrine. In contrast, neither leukemia nor lymphoma cells affected platelet aggregation. These observations suggest that the platelet proaggregatory potential of tumor cells is variable and that the platelet stimulatory effects of osteogenic sarcoma cells may relate to their high risk of pulmonary metastasis.

The lack of correlation between experimental metastatic potential and platelet aggregating activity of B16 melanoma clones viewed in relation to tumor cell heterogeneity

Two widely used B16 melanoma cell lines of low and high lung colonizing potential (B16-F1 and B16-F10) were compared in their ability to induce platelet aggregation. The results of these experiments showed a reproducible difference in platelet aggregating activity of these two cell lines which directly correlated with their lung colonizing potentials. However, when clones were derived from these heterogeneous cell lines and tested for experimental metastatic potential, platelet aggregating ability and Met-72 expression, no correlation could be attached to the platelet aggregating activity of the clones. Results of these experiments provide direct evidence that platelet aggregation is not an accurate index of experimental metastatic potential of tumor cell clones, nor is it an essential trait of all metastatic cells. The ability of tumor cells to induce platelet aggregation is examined and discussed in the context of cellular heterogeneity.

Spontaneous platelet aggregation: observations on potential mechanisms

We identified SPA in three young apparently healthy women. SPA was associated with release of TXA2 and was only partially inhibited by ADP-inhibitor apyrase and alpha 2-adrenoceptor blocker yohimbine. In vitro incubation of aspirin (90 micrograms/ml) or selective TXA2 synthetase inhibitor OKY-046 (0.1 uM) with platelet rich plasma (PRP) did not abolish SPA, although platelet generation of TXA2 was markedly inhibited. In contrast, oral administration of large amounts of aspirin in one subject or in vitro incubation of PRP with TXA2 -endoperoxide receptor blocker SQ 29,548 (20-100 nM) significantly inhibited SPA. These studies suggest that SPA is associated with TXA2 release. Since TXA2 -endoperoxide receptor blocker completely abolishes the secondary wave, agents like this may be of therapeutic value in individuals with SPA and evidence of tissue ischemia.

Plasma tissue plasminogen activator inhibitor levels in coronary artery disease: correlation with age and serum triglyceride concentrations

Increased levels of an endogenous inhibitor of tissue-plasminogen activator (t-PA) have been thought to relate to the genesis of acute myocardial ischemia. To examine the role of the rapid inhibitor of t-PA, plasma samples were analyzed from 75 patients with chest pain syndrome undergoing coronary angiography (mean age 57 years), 24 patients with clinically documented coronary artery disease (unstable angina, positive exercise stress test or previous history of myocardial infarction; mean age 58 years) and 15 young normal subjects (mean age 26 years). Plasma t-PA inhibitor levels were similar in age-matched patients regardless of the absence or presence (and degree) of coronary artery disease. Plasma t-PA inhibitor levels correlated significantly with age (r - 0.46, p less than 0.005), suggesting an age-dependent decrease in fibrinolytic activity. Plasma t-PA inhibitor levels also correlated significantly with serum triglyceride levels (r - 0.60, p less than 0.001), but not with coronary risk factors such as serum cholesterol, diabetes, hypertension, serum uric acid levels or body weight. Association of high levels of inhibitor of t-PA with hypertriglyceridemia may be of importance in the development of coronary thrombosis, especially in elderly patients. Nonetheless, this study does not suggest a pathogenic role of t-PA inhibitor in coronary atherosclerosis.

Cumulative effects of quinidine and aspirin on bleeding time and platelet alpha 2-adrenoceptors: potential mechanism of bleeding diathesis in patients receiving this combination

We observed quinidine-induced prolongation of bleeding time without thrombocytopenia in three subjects. In addition, we noticed a cumulative prolongation of bleeding time by a combination of quinidine and aspirin. We postulated that because both quinidine and aspirin inhibit epinephrine-induced platelet aggregation, a cumulative effect of the two drugs might be responsible for the hemostatic defect. In studies using normal human platelets, we confirmed a marked reduction in epinephrine-induced platelet aggregation by the combination of these two agents. To further study the potential mechanism of this cumulative effect, platelet lysates were incubated with the alpha 2-adrenoceptor antagonist tritiated yohimbine in the presence of quinidine and aspirin. On the basis of the radioligand binding data, the dissociation constant (KD) of alpha 2-adrenoceptors was observed to increase in the presence of quinidine as well as aspirin. The combination of these two agents caused a marked increase in the KD of platelet alpha 2-adrenoceptors without alteration in the number of receptor sites. These data suggest that the cumulative effects of quinidine and aspirin on platelet alpha 2-adrenoceptor KD may relate to the significant reduction in epinephrine-induced platelet aggregation. This phenomenon, coupled with other well-known effects of aspirin on the platelet release reaction and arachidonate metabolism, may lead to bleeding problems in some patients receiving this combination.

Effects of thromboxane A2 inhibition on osteogenic sarcoma cell-induced platelet aggregation

There is evidence that tumors may stimulate platelet aggregation, causing release of thromboxane A2. Thromboxane A2 may potentiate tumor metastasis by stimulating tumor cell growth and proliferation and by enhancing platelet-tumor cell aggregate formation. Despite potential significance of thromboxane A2 in tumor metastasis, agents which inhibit thromboxane A2 synthesis have not been uniformly effective in reducing tumor metastasis. We, therefore, evaluated the effects of a thromboxane A2 receptor antagonist SQ-29,548 compared to those of a thromboxane A2 synthetase inhibitor OKY-046 on osteogenic sarcoma-induced platelet aggregation and thromboxane A2 release. Osteogenic sarcoma cells added to platelet-rich plasma caused complete and irreversible platelet aggregation as well as thromboxane A2 release. Preincubation of platelet-rich plasma with SQ-29,548 (2 to 20 nM) decreased platelet aggregation induced by tumor cells, but it had no effect on thromboxane A2 release. In contrast, preincubation of platelet-rich plasma with OKY-046 (0.1 to 10 microM) had no effect on platelet aggregation despite a decrease in thromboxane A2 synthesis. These results suggest that thromboxane A2 receptor blockers, rather than synthetase inhibitors, may prevent tumor cell-induced platelet aggregation.

Antiemetics in children receiving cancer chemotherapy: a double-blind prospective randomized study comparing metoclopramide with chlorpromazine

This is the first prospective randomized study comparing commonly used antiemetics in children receiving cancer chemotherapy. We compared metoclopramide (MCP) with chlorpromazine (CLP), both administered in conventional doses, in 50 cancer patients aged 6 to 18 years who were receiving emetic chemotherapy. CLP proved significantly better than MCP in reducing both the frequency of vomiting (P less than .05) and the duration of nausea and vomiting (P less than .025). Extrapyramidal reactions (EPRs) were more common in MCP-treated patients. We conclude that, in the standard doses used, CLP is a better overall antiemetic than MCP for children receiving intensive chemotherapy. However, further prospective pediatric studies of antiemetic combinations are needed.

Leukotrienes potentiate the effects of epinephrine and thrombin on human platelet aggregation

A cooperation between leukocytes and platelets relative to metabolism of arachidonic acid has been observed in animal studies. To determine potential stimulatory effects of leukotrienes (LTs) on human platelets, LTs were incubated with platelet rich plasma followed by addition of subthreshold concentration of aggregatory stimulus. LTs (LTE4 LTD4 LTC4) alone had no direct effect on platelet aggregation, but potentiated the effects of subthreshold concentrations of epinephrine and thrombin and caused complete platelet aggregation. This potentiation was similar in citrated or heparinized blood and was unaffected by exogenous CaCl2. LTs did not induce secondary wave of aggregation in aspirin or selective TXA2-synthetase blocker OKY-046-treated platelets. In addition, LTs stimulated TXA2 biosynthesis by platelets in the presence of subaggregatory concentrations of epinephrine, but not when platelets had been pretreated with OKY-046. These data indicate that LTs potentiate epinephrine-induced platelet aggregation by modulating TXA2 synthetase activity.

Calcium blocker diltiazem inhibits platelet activation and stimulates vascular prostacyclin synthesis

The effects of slow channel calcium blocker diltiazem on platelet aggregation and on the generation of vasoactive prostanoids, thromboxane A2 and prostacyclin were examined. Diltiazem, in therapeutic concentrations (50-200 ng/ml), inhibited human platelet activation induced by cumulative subthreshold concentrations of calcium ionophore A 23187 plus ADP or epinephrine. However, platelet activation induced by cumulative effects of ADP plus epinephrine was inhibited by diltiazem only in very high concentrations (greater than 5 micrograms/ml). These data indicate that platelet aggregation mediated only through calcium flux is inhibited by diltiazem in therapeutic concentrations. In other experiments, diltiazem significantly potentiated prostacyclin release from human umbilical veins. These effects of diltiazem may contribute to efficacy of this compound in ischemic heart disease.

Increase in human platelet alpha 2-adrenergic receptor affinity for agonist in unstable angina

Spontaneous increase in platelet activity and change in coronary vasomotor tone have been implicated in the pathogenesis of acute myocardial ischemia. To define the mechanism of platelet "hypersensitivity" in acute myocardial ischemia, we examined the status of platelet alpha 2-adrenergic receptors in patients hospitalized with severe unstable angina. With the use of the specific alpha 2-receptor antagonist 3H-yohimbine, we identified a 26% decrease in the receptor binding sites on platelet membranes from patients with unstable angina compared with controls (155 +/- 32 vs. 210 +/- 29 fmol/mg protein, P less than or equal to 0.005). The dissociation constants of 3H-yohimbine binding to platelet alpha 2-receptors were similar in both groups (3.3 +/- 1.1 and 4.1 +/- 1.6 nmol/L, P not significant). To study the alterations in the affinity of platelet alpha 2-receptors for the agonists, effects of 1-epinephrine on specific binding of 3H-yohimbine were examined. We observed a marked reduction in 1-epinephrine concentration for inhibition of antagonist binding by 50% in acute myocardial ischemia (IC50: 4.2 +/- 3.9 X 10(-8) vs. 6.7 +/- 3.4 X 10(-7) mol/L, P less than or equal to 0.01), indicating increase in platelet alpha 2-receptor affinity for the agonist. Platelet aggregation and thromboxane A2 generation in response to epinephrine were also significantly increased in the acute phase of myocardial ischemia. This study suggests enhanced affinity of platelet alpha 2-receptors to the agonist 1-epinephrine as a possible mechanism of platelet hypersensitivity in acute myocardial ischemia.

Influence of selective thromboxane synthetase blocker CGS-13080 on thromboxane and prostacyclin biosynthesis in whole blood: evidence for synthesis of prostacyclin by leukocytes from platelet-derived endoperoxides

Increase in thromboxane A2 (TXA2) generation has been proposed as a mechanism of dynamic vaso-occlusion and in vivo platelet thrombus formation. We have examined the effects of CGS-13080, an imidazole derivative, on rabbit and human TXA2-prostacyclin (PGI2) "balance." In rabbits given CGS-13080, serum levels of TXB2 (stable metabolite of TXA2) were inhibited 81% at 2 hours and 56% at 24 hours (both P less than or equal to 0.01). Collagen-induced platelet aggregation was inhibited at 2 hours after CGS-13080 administration. In contrast, serum levels of 6-keto-PGF1 alpha (stable hydrolysis product of PGI2) increased 587% compared with control values at 2 hours (P less than or equal to 0.01). Platelet and white blood cell counts were not significantly altered. In human blood incubated in vitro with CGS-13080, serum TXB2 was completely inhibited, whereas PGI2 generation was stimulated (both P less than or equal to 0.001). In other experiments, we demonstrated uptake of platelet-generated cyclic endoperoxides by leukocytes and generation of PGI2 in the presence of CGS-13080 but not indomethacin. Thus, CGS-13080 inhibits TXA2 and stimulates PGI2 production in rabbit and human blood. Increase in PGI2 generation with TXA2 inhibition may be of potential benefit in conditions characterized by platelet hyperactivity.