Zenichi Terashita

Is platelet activating factor (PAF) a mediator of endotoxin shock

To determine whether endogenous PAF contributes to the pathogenesis of endotoxin shock, CV-3988, a specific PAF antagonist, was injected i.v. to rats before, simultaneously with or after endotoxin. CV-3988 (5 mg/kg i.v.) injected 5 min before the endotoxin completely inhibited endotoxin (15 mg/kg i.v.)-induced hypotension, and CV-3988 (0.05-1 mg/kg i.v.) injected 7-10 min after the endotoxin rapidly reversed endotoxin-induced hypotension. A combination of CV-3988 (10 mg/kg) with endotoxin (5 mg/kg) administered i.v. improved the survival rate for 20 h or more. CV-3988 (0.05-1 mg/kg i.v.) rapidly reversed the PAF (1 microgram/kg i.v.)-induced hypotension. These findings strongly suggest that endogenous PAF may play a pivotal role in the pathogenesis of endotoxin shock.

Salutary consequences of blockade of platelet activating factor in hemorrhagic shock.

We studied the effects of a potent, specific platelet activating factor (PAF) antagonist, CV-6209, in a murine model of hemorrhagic shock. Hemorrhaged rats treated with CV-6209 (1 mg/kg) maintained post-reinfusion mean arterial blood pressure (MABP) at significantly higher values than rats receiving either 0.9% NaCl or a lower dose (0.2 mg/kg) of CV-6209 (final MABP 88 +/- 4 vs. 57 +/- 4, vs. 61 +/- 7 mm Hg, respectively). CV-6209 (1 mg/kg) also significantly attenuated the increase in plasma cathepsin D activity following hemorrhage compared with hemorrhaged rats receiving only its vehicle (i.e. 0.9% NaCl). CV-6209 (1 mg/kg) also significantly decreased the plasma accumulation of free amino-nitrogen compounds and the plasma activity of a myocardial depressant factor (MDF) compared to hemorrhaged rats receiving 0.9% NaCl. Rats receiving CV-6209 (1 mg/kg) exhibited a significantly increased survival rate and survival time post-reinfusion compared to rats receiving only the vehicle. These data indicate that PAF is an important mediator of hemorrhagic shock in the rat and that PAF receptor antagonists may be useful in hemorrhagic shock states.

Protective effects of a platelet activating factor (PAF) antagonist and its combined treatment with prostaglandin (PG) E1 in traumatic shock.

We have investigated the role of platelet activating factor (PAF) in the pathogenesis of a murine model of traumatic shock using CV-6209, a specific antagonist of PAF, CV-6209, at a dose of 1 mg/kg (i.v.) given after trauma, significantly improved survival rate at 150 min and overall survival time. Furthermore, the plasma accumulation of the lysosomal hydrolase, cathepsin D, and a cardiotoxic peptide, myocardial depressant factor (MDF), were also attenuated by CV-6209 in traumatic shock. Combined treatment employing low doses of CV-6209 [0.2 mg/kg. i.v. and prostaglandin (PG) E1. 0.8 μg/kg/min] in this shock model was also examined. CV-6209 (0.2 mg/kg) or PGE1 (0.8 μg/kg/min) alone at these doses showed only minimal effects on survival, or plasma cathepsin D or MDF activities. However, combined treatment with CV-6209 (0.2 mg/kg, i.v.) and PGE1 (0.8 μg/kg/min) significantly improved survival rate at 150 min, overall survival time, and decreased the accumulation of plasma MDF. These results suggest that PAF may play an important pathophysiologic role in traumatic shock in rats. Moreover, combination therapy using a PAF antagonist and PGE1 may be useful for the treatment of traumatic shock.

Effects of thromboxane A2 synthase inhibitors (CV-4151 and ozagrel), aspirin, and ticlopidine on the thrombosis caused by endothelial cell injury

The antiplatelet and antithrombotic effects of CV-4151 (isbogrel), a potent selective thromboxane A2 (TXA2) synthase inhibitor, were compared with those of ozagrel (OKY-046), aspirin, and ticlopidine in rats. Two hours after oral administration, CV-4151, ozagrel and aspirin inhibited blood TXA2 generation with ID50 values of 0.04, 0.3 and 6.4 mg/kg, respectively. These values were similar to the oral ID50 values of CV-4151 (0.06 mg/kg), ozagrel (0.92 mg/kg) and aspirin (7.0 mg/kg) for arachidonic acid (AA)-induced platelet aggregation ex vivo. Two hours after p.o. administration, CV-4151 and ozagrel inhibited femoral vein platelet-rich thrombosis caused by endothelial injury with ID50 values of 2.46 and 13.7 mg/kg, respectively. However, aspirin (100 mg/kg, p.o.) only slightly inhibited the thrombosis. Ticlopidine (300 mg/kg, p.o.) slightly but significantly inhibited AA-induced and ADP-induced platelet aggregation, however, it potently inhibited the thrombosis. CV-4151 and ozagrel given by i.v. injection showed therapeutic effects on the thrombosis with ED50 values of 0.026 and 0.066 mg/kg, respectively. These values were similar to the i.v. ED50 values of CV-4151 (0.0056 mg/kg) and ozagrel (0.042 mg/kg) for blood TXA2 generation. However, aspirin (30 mg/kg, i.v.) only moderately reduced the thrombosis. CV-4151 (> 0.3 mg/kg, p.o.), ozagrel (> 3 mg/kg, p.o.) and ticlopidine (300 mg/kg, p.o.) all significantly prolonged tail bleeding time. Aspirin (100 mg/kg, p.o.) tended to prolong the bleeding time. The antiplatelet and antithrombotic effects of CV-4151 are more potent than those of ozagrel, aspirin and ticlopidine in rats. CV-4151 may therefore be a useful drug for the treatment of thrombotic diseases.

Antidiuresis induced by β1- and β2-adrenergic agonists in ethanol-anesthetized rats

Abstract The β1- and β2-adrenergic in antidiuresis and sodium retention induced by β-adrenergic agonists were analysed in ethanol-anesthetized, water-diuretic rats. Intravenous infusions of isoprenaline, salbutamol and carbuterol did not affect inulin clearance but all increased plasma renin concentration to the same extent. Propranolol completely blocked the decreases in urine volume (V) and urinary sodium excretion (UNaV) induced by isoprenaline; practolol (β1-blocker) inhibited only the decrease in UNaV and butaxamine (β2-blocker) inhibited only the decrease in V. The ratios of doses of β-agonists which decreased UNaV and V by 50% %ED50 UNaV decrease/ED50 V decrease) were 0.34, 0.68, 1.56 and 2.36 for isoprenaline, tretoquinol, salbutamol and carbuterol, respectively. This increasing order of the ratios coincided with the order reported for the preponderance of the β2- over β1-component of these agonists. These results indicate that the decrease in UNaV induced by β-antagonists is related to β1, while the decrease in V is related to β2 stimulation.

Protective action of prostaglandin E1 (PGE1) against constrictor mediators in isolated rat heart and lung.

Prostaglandin (PG) E1 (2.8 to 280 nmol/L) dose-dependently inhibited the platelet-activating factor (PAF)-induced increase in coronary perfusion pressure (CPP) in isolated constant flow perfused rat hearts. The PAF-induced release of immunoreactive leukotrienes (iLT) and thromboxane B2 (iTxB2) in isolated rat hearts was also attenuated. PAF induced a significant decrease in left ventricular cAMP content, which was antagonized by PGE1. PGE1 also decreased the production of iLT, but not of iTxB2, in A23187-stimulated minced rat lung tissue. Furthermore, PGE1 inhibited the increase in CPP induced by LTD4 and arginine vasopressin (AVP) in the isolated perfused rat heart. The inhibitory effects of PGE1 on coronary vasoconstrictor substances were not due to a nonspecific vasodilator effect since sodium nitroprusside neither inhibited the increase in CPP nor the release of eicosanoids induced by PAF. Moreover, PGE1 did not inhibit the PAF-induced hypotension in vivo, indicating that PGE1 is not a PAF receptor antagonist. These results suggest that PGE1 may exert an important regulatory effect on coronary vascular homeostasis by stimulation of cyclic AMP and may be important in controlling eicosanoid metabolism in the rat heart. Furthermore, beneficial effects of PGE1 in circulatory shock and myocardial ischemia may be related to this inhibitory effect of PGE1.

Mechanisms of Action of PGE1 in Hemorrhagic Shock in Rats

We studied the effects of prostaglandin E1 (PGE1) in a severe model of hemorrhagic shock in rats. PGE1 was administered as a continuous IV infusion of either 0.1 microgram/kg/min or 1.0 microgram/kg/min starting 30 minutes after the onset of bleeding and continuing until one hour after reinfusion. Hemorrhaged rats treated with PGE1 (1 microgram/kg/min) maintained post-reinfusion mean arterial blood pressure (MABP) at significantly higher values than rats receiving only the vehicle (ie, 0.9% NaCl) (final MABP 84 +/- 3 vs 57 +/- 4 mm Hg, P less than .01). PGE1 at 1 microgram/kg/min also attenuated the increase in plasma activities of cathepsin D (P less than .01), and at both doses blunted the plasma accumulation of free amino-nitrogen compounds (P less than .02 at 0.1 microgram/kg/min and P less than .01 at 1.0 microgram/kg/min). Furthermore, the plasma activity of a myocardial depressant factor (MDF) was significantly lower in rats treated with PGE1 (1 microgram/kg/min) than in rats receiving the vehicle (35 +/- 4 U/mL vs 74 +/- 12 U/mL, P less than .01). Rats receiving PGE1 (1.0 microgram/kg/min) also exhibited a significantly increased survival rate (P less than .01) and post-reinfusion survival time (P less than .01) compared with rats receiving only the vehicle. Our data suggest that antiproteolytic and membrane-stabilizing actions of PGE1 are important and may contribute to its beneficial effects in hemorrhagic shock. Other mechanisms (eg, inhibition of platelet aggregation and vasodilation) may also be involved.