Interaction of thromboxane A2 and tissue pathology during graded bacteremia

Platelet activating factor mediates cardiopulmonary dysfunction during graded bacteremic shock

OBJECTIVE

To determine whether or not platelet activating factor (PAF) is a necessary mediator of cardiovascular dysfunction during graded bacteremia, and to identify PAF interactions with eicosanoids and tumor necrosis factor-alpha (TNF-alpha).

METHODS

Seventeen anesthetized, hemodynamically monitored adult swine were studied for 4 hours in three groups. Group 1 (ANES, n = 5) were anesthesia controls; group 2 (septic control, SC, n = 6) received intravenous Aeromonas hydrophila (109/mL) at rates incrementally increased from 0.2 to 4.0 mL/ kg/h; group 3 (WEB, n = 6) received the PAF receptor antagonist WEB 2086, 3.0 mg/kg intravenously, then A. hydrophila. Cardiopulmonary parameters and plasma thromboxane B2 (TXB2), prostaglandin 6-keto F1 alpha (PGI2), leukotriene B4 (LTB4), leukotrienes C4D4E4 (LTC4D4E4), and TNF-alpha were measured hourly. Statistical analysis was carried out using two-way analysis of variance (ANOVA) for repeated measurements, Dunnett's t test, and Student's t test, where appropriate. Statistical significance was determined at the 95% confidence interval. Values are presented as the mean +/- SEM.

RESULTS

Pulmonary arterial pressure, pulmonary capillary wedge pressure, central venous pressure heart rate, VO2 and O2ER decreased significantly after WEB 2086 infusion, compared with SC, and mean arterial pressure, systemic vascular resistance index, stroke volume index, and left ventricular stroke work index increased. Arterial pH decreased significantly in SC animals, but was maintained at normal levels during bacteremia in the WEB group. Differences between WEB and SC for cardiac index, pulmonary vascular resistance index, right ventricular stroke work index, PaO2, SaO2, and PcO2, were not significant. The addition of WEB 2086 significantly decreased plasma levels of TXB2, PGI2, LTB4, and TNF-alpha compared with the SC group. LTC4D4E4 was decreased in WEB compared with SC animals, in which LTC4D4E4 increased during graded bacteremia.

CONCLUSIONS

PAF is necessary to the development of systemic vasodilation and hypotension, pulmonary hypertension, decreased stroke volume, metabolic acidosis, and increased oxygen uptake during graded bacteremia. PAF-induced eicosanoid and cytokine release may be involved.

Cecal ligation and puncture is associated with pulmonary injury in the rat: role of cyclooxygenase pathway products

The present studies evaluated the role cyclooxygenase products play in bacterial sepsis induced pulmonary injury in the rat. Lung injury was assessed by determining the pulmonary capillary filtration coefficient (Kf) and the lung lavage protein concentration four and 18 hours after cecal ligation and puncture. Four hours after cecal ligation, the Kf was unchanged from control, however, by 18 hours, the Kf was increased 171% (p < .05). Similarly, lung lavage protein levels were unchanged four hours after cecal ligation but were significantly (p < .05) elevated at 18 hours. On the other hand, pulmonary lavage immunoreactive thromboxane B2 (iTXB2) levels were increased both four and 18 hours after the initiation of sepsis. In order to determine if cyclooxygenase products played a role in the sepsis associated lung injury, ibuprofen was administered prior to cecal ligation. Ibuprofen pretreatment prevented the sepsis associated increase in both Kf and lung lavage protein concentration. These studies suggest that bacterial sepsis in the rat is associated with pulmonary injury and that early administration of ibuprofen ameliorates this damage.

The effect of thromboxane on contraction of canine mesenteric and lingual arteries

Thromboxane A2 (TXA2), a potent vasoconstrictor agent, is released from platelets and smooth muscle during inflammation and trauma. TXA2 may cause lingual artery (LA) contraction, leading to lingual paresthesia. The effects of U-46619, a TxA2 mimetic, on isolated rings of canine LA and mesenteric artery (MA) were examined. U-46619 (1 nmol/L to 1 mumol/L) caused a triphasic contraction of LA and MA; a rapid, phasic contraction; a slow, sustained contraction; and, upon washout of U-46619, a maintained contraction. The MA relaxed slowly, but the LA remained contracted for at least three h after washout. Decreasing extracellular calcium ion (Ca2+o) to less than 0.1 mumol/L with 2 mmol/L EGTA relaxed MA, but not LA. EGTA (4 mmol/L) partially relaxed the maintained contraction of LA. Inhibition of protein kinase C with amphotericin B or staurosporine inhibited the phasic and sustained contractions of LA, but did not affect the maintained contraction in the presence or absence of EGTA. Thus, CA2+o was required for the initial contraction of the LA by U-46619, but did not appear to be required for the maintained contraction following washout of U-46619. The data support the conclusion that following a brief exposure to U-46619, maintained contraction of LA persists by a unique mechanism that may be independent of Ca2+ and protein kinase C. Sustained LA contraction after exposure to endogenous TXA2 during inflammation and trauma may contribute to impaired lingual blood flow and orofacial tissue injury.

Thromboxane-induced neutrophil adhesion to pulmonary microvascular and aortic endothelium is regulated by CD18

Thromboxane (Tx) A2 generation and subsequent selective pulmonary sequestration of neutrophils (PMNs) is characteristic of several forms of the adult respiratory distress syndrome (ARDS). Therefore, we examined PMN-dependent adhesion to cultured pulmonary microvessel and aortic endothelium (EC) in response to U46,619 (Tx mimic). Nonstimulated PMNs were two fold more adherent to pulmonary microvessel EC than to aortic EC (P less than 0.01). PMN pretreatment with Tx mimic (10(-6) M) increased adhesion to both types of EC (P less than 0.01). The Tx mimic-induced adhesion was blocked by receptor antagonists to Tx (SQ29,548) and to leukotrienes (FPL55,712), and by the anti-CD18 mAb TS1/18 (P less than 0.01, all cases). Baseline PMN adhesion also was modulated by Tx, leukotrienes, and CD18, for both EC types. These results indicate pulmonary microvessel EC is intrinsically more adhesive for both nonstimulated and stimulated PMNs than aortic EC and that Tx mediates PMN-dependent adhesion by coupled interaction of Tx and LT receptors via CD18 activation.