Gregory L. Stahl

Prostacyclin Mediation of Vasodilation Following Mesenteric Traction

Eight untreated patients (group I) and four patients who received ibuprofen preoperatively (group II) scheduled for elective abdominal aortic ancurysm repair were studied. Heart rate (HR); systolic, diastolic, and mean arterial pressure (MAP); systolic and diastolic pulmonary artery pressure; pulmonary capillary wedge pressure (PCWP); cardiac output (CO); and central venous pressure (CVP) were recorded pre-induction, before mesenteric traction, and 5, 15, and 30 min post-mesenteric traction. Plasma samples were obtained at these times for analysis of six-keto-prostaglandin Flα (PGF1α) concentration by radioimmunoassay. Group II patients received ibuprofen 12 mg/kg orally 11/2 h before surgery. Plasma samples from six group I patients and all group II patients taken 5 min after mesenteric traction were added to isolated helical strips of cat superior mesenteric arteries precontracted with norepinephrine (200 ng/ml) for analysis of reduction in developed force. In group I, abdominal mesenteric traction resulted in a significant decrease in MAP (P < 0.03) and SVR (P < 0.005) with an increase in CO (P < 0.05) at 5 min post-mesenteric traction. which returned to mean pre-mesenteric traction values by 30 min and a significant increase in PGF,α concentrations. There was a significant positive correlation between PGF,α and CO (P < 0.001) and a significant negative correlation between PGF,α and SVR (P < 0.01) at 5 min post-mesenteric traction. Post-mesenteric traction plasma samples added to the cat mesenteric artery preparation resulted in vasodilation, as demonstrated by a reduction in developed force of 0.563 ± 0.092 grams, as compared to the reduction by pre-mesenteric traction plasma values of 0.12 ± 0.11 grams (P < 0.01). Group II patients did not develop significant increases in PGF,α, and 5-min post-mesenteric traction plasma samples did not significantly relax the cat mesenteric artery preparations. There were no changes in MAP, SVR, and CO in group II patients. Flushing of the head and neck in association with mesenteric traction was noted in group I only.

PAF-acether induced cardiac dysfunction in the isolated perfused guinea pig heart

SummaryPAF-acether (1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) has been implicated in a variety of inflammatory and ischaemic disorders (e.g., myocardial ischemia, anaphylactic shock). Recently, the peptide leukotrienes (i.e., LTC4, LTD4) have been shown to mediate the increase in coronary vascular resistance induced by PAF-acether in the isolated perfused rat heart. In isolated perfused guinea pig hearts, PAF-acether produced a dose-dependent increase in coronary perfusion pressure (CPP) and a decrease in contractile force (CF). At 50 μmol/l, PAF increased CPP by 13 ± 3 mm Hg and decreased CF by 47 ± 12% in 8 hearts. Radioimmunoassay of the coronary effluent did not detect peptide leukotrienes or thromboxane B2 (TxB2) in response to PAF. Addition of a specific PAF-acether receptor antagonist, CV-6209 (25 nmol/l), blocked the increase in coronary perfusion pressure and decrease in contractile force. OKY-1581 (400 nmol/l), a thromboxane synthetase inhibitor or LY-171,883 (7.3 μmol/l) a leukotriene D4 receptor antagonist, failed to prevent the increase in CPP or the decrease in CF. These data indicate that the PAF-acether induced increase in CPP is not mediated by the peptide leukotrienes or thromboxane A2 (TxA2). Possible mechanisms for the increase in CPP induced by PAF-acether in the isolated perfused guinea pig heart include a direct receptor mediated constriction of coronary resistance vessels, release of a non-eicosanoid coronary constrictor as a mediator of the response, or via enhancement of coronary microvascular permeability.

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 specific platelet activating factor (PAF) antagonist, WEB 2086, in traumatic shock

We have investigated the role of platelet activating factor (PAF) in the pathogenesis of a murine model of traumatic shock using WEB 2086, a specific antagonist of PAF. WEB 2086 (0.5 mg/kg) significantly reversed the decrease in mean arterial blood pressure (MABP) induced by PAF (0.3 micrograms/kg) in anesthetized rats. Anesthetized rats were subjected to Noble-Collip drum trauma. Traumatized rats treated with WEB 2086 (0.5 mg/kg bolus followed by infusion at 0.5 mg/kg/hr) maintained a higher MABP than those receiving only the vehicle (0.9% NaCl). Improvement in MABP paralleled a significant increase in overall survival time (p less than 0.01) in rats receiving WEB 2086 (0.5 mg/kg). WEB 2086 also significantly attenuated the plasma accumulation of the lysosomal hydrolase, cathepsin D and of free amino-nitrogen compounds, compared to shocked rats receiving only the vehicle. Furthermore, the production of the cardiotoxic peptide, myocardial depressant factor (MDF) was also blunted by WEB 2086. These results suggest that PAF may be an important mediator in the pathogenesis of traumatic shock in rats. Furthermore, PAF receptor antagonists may be useful as therapeutic agents when given early in the course of ischemic and shock states.

Pharmacologic profile of lipoxins A5 and B5: new biologically active eicosanoids

In this study, we have investigated the biological activities of LxA5 and LxB5 in isolated smooth muscle preparations of the guinea pig. LxA5 slowly contracted pulmonary parenchymal strips isolated from guinea pigs in a concentration-dependent manner over the range of 0.1-2.2 microM. This bronchoconstrictor effect was not associated with release of peptide leukotrienes (i.e. LTC4, LTD4 and LTE4) and only a slight increase in thromboxane B2. Furthermore, the bronchoconstrictor effect was not blocked by lipoxygenase inhibitors, suggesting the pulmonary effect is not mediated by lipoxygenase products. However, a peptide leukotriene receptor antagonist (e.g. SK&F-104353) inhibited or reversed the LxA5 response indicating that LxA5 and the peptide leukotrienes may share the same receptor. In contrast to LxA5, LxB5 displayed no significant bronchoconstrictor effect at concentrations up to 2.2 microM. Moreover, LxA5 and LxB5 did not exert a significant endothelium-dependent vasorelaxation in aortic vascular smooth muscle as do LxA4 and LxB4. Thus, LxA5 and LxB5 display a unique biological profile which differs from LxA4 and LxB4. LxA4 may be a mediator in circulatory disease states (e.g. myocardial ischemia, circulatory shock), but LxA5 and LxB5 are not as likely candidates as mediators of disease.

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.

Heterogeneity of Vascular Smooth Muscle Responsiveness to Lipid Vasoactive Mediators

Thromboxane A2 (TxA2), leukotriene C4 (LTC4), leukotriene D4 (LTD4), and platelet-activating factor (PAF) are novel lipids which exert a variety of biological actions. TxA2, LTC4 and LTD4 have been shown to induce direct vasoconstriction in several species, while PAF contracts isolated guinea pig ileum and lung parenchyma. We studied the direct vasoconstricting activities of these lipid mediators in isolated cat renal, superior mesenteric and coronary arteries. The TxA2 analog 9,11-methanoepoxy PGH2 (U-46619) constricted both perfused and helical strips, with the renal and mesenteric arteries being 4 times more responsive than the coronary arteries. LTC4 and LTD4 constricted coronary arteries to a significantly greater extent than renal and superior mesenteric arteries in both perfused arteries and helical strips. Furthermore, PAF failed to contract any of the perfused arteries or helical strips at concentrations from 1 ng to 20 micrograms. TxA2 was a potent vasoconstrictor in all the vessels studied, suggesting a role for this substance as a vasoactive mediator in ischemia and shock. The coronary arteries were more responsive to the leukotrienes than the mesenteric and renal arteries, suggesting that the leukotrienes may play an important role in myocardial ischemia. Moreover, both thromboxane and leukotriene effects were blocked in all preparations by specific receptor antagonists. While the biological effects of PAF are still poorly understood, PAF does not directly vasoconstrict large arteries of the feline renal, superior mesenteric or coronary vasculatures.

Coronary vascular actions of synthetic atrial natriuretic factor in isolated vascular preparations.

Summary: Administration of atrial natriuretic factor (ANF) in animals results in increases in renal blood flow, natriuresis, and a decrease in arterial blood pressure, supporting a role for the atrial peptide system in cardiovascular regulation. However, little is known about the vascular effects of synthetic ANF (26 amino acid) on coronary artery smooth muscle. We studied the coronary vascular effects of synthetic ANF in feline artery preparations in vitro. In isolated coronary arteries perfused at constant flow, ANF (3–300 nM) concentration dependency decreased perfusion pressure ranging from 2.6 ± 0.7 mm Hg (p < 0.02) at 3 nM to 28.6 ± 3.7 mm Hg (p < 0.001) at 300 nM. Perfusion with the prostacyclin analog, iloprost (20–100 nM), failed to alter the coronary vasodilator response to ANF. ANF also relaxed feline coronary helical strips when contracted by U-46,619 (an en-doperoxide analog), serotonin, and leukotriene D4. This relaxant effect was independent of the presence of endothelial cells and occurred in the presence of a guanylate cyclase inhibitor, methylene blue. The ANF had no direct effect on electrically driven isolated feline papillary muscles, signifying a lack of direct inotropic activity of ANF in cat cardiac muscle. These results suggest that ANF may produce coronary vasodilation that therefore could contribute to coronary regulation, without directly altering myocardial performance.

Efficacy of a combination thromboxane receptor antagonist and lipoxygenase inhibitor in traumatic shock.

The effects of a thromboxane receptor antagonist having lipoxygenase inhibitory activity, L-655,240 (3-[1-(4-chlorobenzyl)-5-fluoro-3-methyl-indol-2-yl]2,2-dimethylpropa noic acid) (1 mg/kg per h) were studied in a standardized model of traumatic shock. Pentobarbital (35 mg/kg) anesthetized rats subjected to Noble-Collip drum trauma were characterized by a 82 +/- 12 min survival time, a 20-fold increase in plasma cathepsin D activity, and a 6-fold increase in plasma myocardial depressant factor (MDF) activity. L-655,240 significantly attenuated the accumulation of MDF activity in the plasma (74 +/- 3 vs. 46 +/- 4 units/ml), vehicle vs. drug, respectively, and significantly (P less than 0.01) prolonged survival time to 206 +/- 26 min. However, plasma cathepsin D was not significantly altered with L-655,240 administration during traumatic shock. L-655,240 at 20 micrograms/ml markedly attenuated minced rat lung fragments from producing LTC4 and LTD4.L-655,240 exhibited significant anti-proteolytic activity in pancreatic homogenates. Therefore, L-655,2340 does not stabilize lysosomal membranes directly, but exerts an anti-proteolytic action which appears to curtail the production of a myocardial depressant factor by the ischemic pancreas, thus protecting during traumatic shock. A combination anti-eicosanoid drug such as L-655,240 may therefore prove to be an important therapeutic agent in acute ischemic disorders including traumatic shock.

Protective effects f CG-4203, a novel stable prostacyclin analog, in traumatic shock

We studied the effects of CG-4203, a novel stable prostacyclin analog, in a severe model of traumatic shock in rats. Traumatic shock was produced by Noble Collip drum trauma and was characterized by marked hypotension, a 4- to 5-fold increase in plasma cathepsin D and myocardial depressant factor activities, and survival time of 95 +/- 15 minutes. Treatment with CG-4203 (100 ng/kg/min) significantly prolonged survival time to 194 +/- 20 min (p less than 0.002). Traumatized rats treated with CG-4203 exhibited significantly lower plasma activities of the lysosomal hydrolase cathepsin D (p less than 0.05). Furthermore, the plasma accumulation of myocardial depressant factor (MDF) activity was also significantly blunted in traumatized CG-4203 treated rats when compared with traumatized rats receiving only the vehicle (p less than 0.01). Our results suggest that a combination of membrane stabilizing and anti-proteolytic effects and inhibition of platelet aggregation may mediate the protective effects of CG-4203 in traumatic shock.