Myron B. Peterson

Role of Thromboxane and Prostacyclin in Pulmonary Vasomotor Changes after Endotoxin in Dogs

Cyclooxygenase inhibitors prevent the pulmonary vasomotor changes in response to low-dose endotoxin. We, therefore, explored the role of two highly vasoactive prostanoids, thromboxane A(2), a vasoconstrictor, and prostacyclin, a vasodilator, in the transient pulmonary vasoconstriction and subsequent loss of alveolar hypoxis vasoconstriction (AHPV) that follows endotoxin. AHPV was tested in the dog with a double-lumened endotracheal tube allowing ventilation of one lung with nitrogen as a hypoxic challenge while the other lung was ventilated with oxygen to maintain systemic oxygenation. Relative distribution of perfusion to the two lungs was assessed with intravenous (133)Xe and external scintillation detectors. The stable metabolites of thromboxane and prostacyclin, i.e., thromboxane B(2) and 6-keto-prostaglandin F(1alpha) were measured in plasma with radioimmunoassay. 15 mug/kg i.v. of endotoxin induced no rise in pulmonary vascular resistance (PVR), but prevented AHPV so that the initial 33% (+/-2 SEM) decrease in perfusion to the hypoxic lung became only a 2% (+/-1) decrease. Circulating levels of thromboxane and prostacyclin concurrently rose (P < 0.01) from nondetectable levels to 380 pg/ml (+/-40) and 360 pg/ml (+/-130). 150 mug/kg of endotoxin induced a transient rise in PVR from 4.09 to 9.00 mm Hg/liter per min in association (r = 0.89, P < 0.01) with a sharp rise in thromboxane levels to 4,460 pg/ml (+/-1,350) whereas prostacyclin levels were elevated less markedly to 550 pg/ml (+/-400). Prostaglandin F(2alpha), another vasoconstrictor, was not elevated. 30 min after endotoxin when PVR was again base line and AHPV lost, thromboxane fell significantly (P < 0.01) to 2,200 pg/ml (+/-1,100) whereas prostacyclin remained elevated at 360 pg/ml (+/-135), a level similar to that seen when 15 mug/kg of endotoxin induced loss of AHPV. Indomethacin prevented the rise in thromboxane and prostacyclin after endotoxin as well as the changes in pulmonary vasomotor tone. Thus, a complex interaction between thromboxane and prostacyclin is involved in the pulmonary vasomotor response to low-dose endotoxin.

Protein Synthesis and Amino Acid Transport in the Isolated Rabbit Right Ventricular Papillary Muscle: EFFECT OF ISOMETRIC TENSION DEVELOPMENT

To investigate the effects of isometric tension development on myocardial protein metabolism, 14C-phenylalanine incorporation into protein was studied in the isolated rabbit right ventricular papillary muscle. Amino acid incorporation was linear for 6 hours in resting muscles and was totally inhibited by 10−3M cycloheximide and 10−3M puromycin. Phenylalanine incorporation into total protein was unaltered by 90 minutes of isometric tension development at peak tension at stimulation rates of 30, 50, or 100/min. Significant increases were noted in muscles stimulated at 50 and 100/min for 180 minutes (P < 0.01). Electrical stimulation, in the absence of isometric tension development, was not responsible for this effect. Passive stretch also appeared to stimulate incorporation, although to a lesser degree than did active tension development. The specific activities of the intracellular phenylalanine pools were identical in control and stimulated muscles. Alpha-aminoisobutyric acid was used to evaluate the effect of tension development on myocardial amino acid transport. Enhanced transport was noted in muscles stimulated isometrically at 30, 50, or 100/min at peak tension. The increased transport ratios could not be solely attributed to active tension development since passive stretch resulted in comparable changes. This study indicates that both passive stretch and tension development are important in regulating myocardial protein synthesis.

Fluorescent/ultraviolet absorbing ester derivative formation and analysis of eicosanoids by high-pressure liquid chromatography☆

Abstract A method is described for the quantitative analysis of eicosanoids (arachidonic acid metabolites, nee, prostaglandins) by reverse-phase high-pressure liquid chromatography following formation of the ester derivative with p -(9-anthroyloxy)phenacyl bromide. The lower limit of detection of the eicosanoid ester is 280 pg (ultraviolet—254 nm) and approximately 50 pg (fluorescence 249 emission, 413-nm cutoff). We separated the esters of seven common eicosanoids by reverse-phase chromatography with acetonitrile and water. Thromboxane B 2 chromatographs as two species and coelutes with PGF 2α . Separation of all others is adequate, including the three metabolites of prostacyclin (6-keto-PGF 1α , 6-keto-PGE 1 , 13,14-dihydro-6,15-diketo-PGF 1α ). We obtained good correlation between radioimmunoassay and derivative analysis of standard 6-keto-PGF 1α extracted from lactated Ringers solution with standard technique, as well as 6-keto-PGF 1α quantitation from tissue culture medium that had contained pulmonary endothelial cells. This method should be applicable to analysis of eicosanoids extracted from biological matrices.

Thromboxane and pulmonary hypertension following E. coli endotoxin infusion in sheep: Effect of an imidazole derivative

We assessed the effect of a specific thromboxane synthetase inhibitor (an imidazole derivative) on pulmonary hemodynamics and the concentrations of TxB2 (TxA2), 6-keto-PGF1 alpha (PGI2), and PGF2 in pulmonary lymph and transpulmonary blood samples following intravenous administration of E. coli endotoxin (1 microgram/kg) in sheep. In control animals the rise in pulmonary artery pressure correlated with increases in plasma and lymph TxB2 concentrations and large transpulmonary concentration gradients of this metabolite were measured. In imidazole treated animals both pulmonary hypertension as well as increases in plasma and lymph TxB2 concentrations were substantially reduced. In contrast, peak concentrations of 6-keto-PGF1 alpha (PGI2) and PGF2 alpha were severalfold higher than those measured in control animals. This suggests a shunting of endoperoxide metabolism towards prostacyclin and primary prostaglandins and documents the specificity of the thromboxane synthetase inhibitor. Our study provides evidence that endotoxin-induced pulmonary hypertension is mediated by pulmonary synthesis of TxA2.

Thromboxane release during percutaneous transluminal coronary angioplasty

The reason for coronary artery occlusion following percutaneous transluminal angioplasty (PTCA) remains an enigma. We postulated that alterations in arachidonic acid metabolism might contribute to coronary artery occlusion, particularly if platelets are perturbed and release thromboxane because of mechanical stimuli during PTCA. We serially monitored coronary sinus and peripheral arterial plasma thromboxane (TX) and prostacyclin (by standard radioimmunoassay of the metabolites TXB2 and 6-keto-PFG1 alpha) during PTCA in 10 patients. TX and prostacyclin were unchanged from control in seven uncomplicated procedures. In one patient with vasospasm, no changes were found. In two patients with occlusion, marked increases were measured in coronary sinus plasma TX. Patient No. 1 increased from 390 to 1375 pg/ml. Patient No. 2 increased from 155 to 1425 pg/ml. Both required emergency bypass grafting. No change in 6-keto-PGF1 alpha was found. Uncomplicated PTCA does not alter arachidonic acid metabolism through cyclooxygenase. Vasospasm need not be associated with TX release, but coronary artery occlusion is. TX may play a role in coronary artery occlusion during PTCA because of (1) increased release and (2) unopposed physiologic effects because increases were not found in the physiologic antagonist prostacyclin.

Studies on the reversibility of anoxic damage to the myocardial protein synthetic mechanism: Effects of glucose

Abstract The ability of glucose to prevent anoxic injury to myocardial protein synthesis was evaluated with the isolated rabbit papillary muscle serving as an in vitro model system. Papillary muscles were incubated under anoxic conditions (95% N2 and 5% CO2) for 1 to 4 h and then reoxygenated (95% O2 and 5% CO2) for 2 h with 14C phenylalanine present during the final hour of incubation. The protein synthetic rate (amino acid incorporation into protein) measured in this manner was defined as residual protein synthetic capacity. The effect of alterations in glucose concentration during anoxia on residual protein synthetic capacity was evaluated. Glucose concentrations ranged from 5 to 30 m m during anoxia and were set at 5 m m for the reoxygenation and incorporation periods. Control muscles were treated in an identical manner, but were oxygenated for the entire period. Residual protein synthesis was reduced by 73%, 45%, 4%, and 2% after exposure to 2 h of anoxia in the presence of 5, 10, 15, and 30 m m glucose respectively. These differences were not due to alterations in the tissue phenylalanine pool since identical relative specific activities were found in experimental and control muscles. Polyacrylamide disc gel electrophoresis demonstrated the banding pattern and the pattern of tracer amino acid incorporation to be the same in control muscles and muscles exposed to anoxia and 15 m m glucose before reoxygenation and labeling. Residual protein synthesis following incubation with 12.5 m m sugar (fructose, sucrose, galactose, or mannitol) plus 5 m m glucose during anoxia approximated that with 5 m m glucose. The addition of glucose and insulin was no more effective than glucose at concentrations of 5 or 15 m m . Glucose (15 m m ) preserved residual protein synthesis in muscles stimulated under isometric conditions throughout anoxia and reoxygenation. Improved mechanical activity was noted during reoxygenation in muscles incubated with 15 m m glucose. Studies with inhibitors of glucose transport and glucose metabolism indicated that the protective effect of glucose was due to the intracellular metabolism of glucose. Exposure of cardiac muscle to high levels of glucose during anoxia appears to retard damage to myocardial protein synthesis and may prolong cellular viability.

Prostaglandin response to intravenous nitroglycerin

Abstract Recent studies suggest that nitroglycerin (TNG)-induced vascular and myocardial effects may be mediated by arachidonic acid metabolites. We examined the correlation between prostacyclin (PGI2) and thromboxane (TXA2) release in the coronary sinus (CS) and intravenous administration of TNG. Concentrations of PGI2 and TXA2 were derived indirectly by measuring their stable metabolites, 6-ketoprostaglandin F1α (6KF1α) and thromboxane B2 (TXB2), respectively. Fifteen dogs were studied in three equal groups. Group I received 2 μg/kg/min TNG followed by 10 μg/kg/min. Group II received the same concentrations in reverse order. Group III received 10 μg/kg/min after pretreatment with 10 mg/kg ibuprofen. After 90 min stabilization blood samples drawn from the pulmonary artery (PA), left atrium (LA), inferior vena cava (IVC), and CS before and during TNG infusion were analyzed for TXB2 and 6KF1α. No 6KF1α was generated in any groups. Groups I and II showed significant TXB2 production exclusively in the CS during the first TNG infusion but not during the second. This response was prevented by pretreating with ibuprofen. We were unable to correlate the hemodynamic effects of TNG with the presence of increased TXA2 in the coronary sinus blood. These data demonstrate that the action of TNG is not mediated by prostacyclin. TNG infusion does result in an initial significant thromboxane release in the myocardial circulation which can be blocked by ibuprofen.