PAF antagonists inhibit pulmonary vascular remodeling induced by hypobaric hypoxia in rats.

Chronic hypoxia causes pulmonary hypertension and pulmonary vascular remodeling in rats. Because platelet-activating factor (PAF) levels increase in lung lavage fluid and in plasma from chronically hypoxic rats, we examined the effect of two specific, structurally unrelated PAF antagonists, WEB 2170 and BN 50739, on hypoxia-induced pulmonary vascular remodeling. Treatment with either agent reduced hypoxia-induced pulmonary hypertension and right ventricular hypertrophy at 3 wk of hypoxic exposure (simulated altitude 5,100 m) but did not affect cobalt (CoCl2)-induced pulmonary hypertension. The PAF antagonists had no effect on the hematocrit of normoxic or chronically hypoxic rats or CoCl2-treated rats. Hypoxia-induced pulmonary hypertension was associated with an increase in the vessel wall thickness of the muscular arteries and reduction in the number of peripheral arterioles. In WEB 2170-treated rats, these changes were significantly less severe than those observed in untreated chronically hypoxic rats. PAF receptor blockade had no acute hemodynamic effects; i.e., it did not affect pulmonary arterial pressure or cardiac output nor did it affect the magnitude of acute hypoxic pulmonary vasoconstriction in awake normoxic or chronically hypoxic rats. Isolated lungs from chronically hypoxic rats showed a pressor response to the chemotactic tripeptide N-formyl-Met-Leu-Phe (fMLP) and an increase in the number of leukocytes lavaged from the pulmonary circulation. In vivo treatment with WEB 2170 significantly reduced the fMLP-induced pressor response compared with that observed in isolated lungs from untreated chronically hypoxic rats. These results suggest that PAF contributes to the development of chronic pulmonary hypertension induced by chronic hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular evolution of cytochrome c oxidase: rate variation among subunit VIa isoforms

Cytochrome c oxidase (COX) consists of 13 subunits, 3 encoded in the mitochondrial genome and 10 in the nucleus. Little is known of the role of the nuclear-encoded subunits, some of which exhibit tissue-specific isoforms. Subunit VIa is unique in having tissue-specific isoforms in all mammalian species examined. We examined relative evolutionary rates for the COX6A heart (H) and liver (L) isoform genes along the length of the molecule, specifically in relation to the tissue-specific function(s) of the two isoforms. Nonsynonymous (amino acid replacement) substitutions in the COX6AH gene occurred more frequently than in the ubiquitously expressed COX6AL gene. Maximum-parsimony analysis and sequence divergences from reconstructed ancestral sequences revealed that after the ancestral COX6A gene duplicated to yield the genes for the H and L isoforms, the sequences encoding the mitochondrial matrix region of the COX VIa protein experienced an elevated rate of nonsynonymous substitutions relative to synonymous substitutions. This is expected for relaxed selective constraints after gene duplication followed by purifying selection to preserve the replacements with tissue-specific functions.      

Leukotriene E4 causes pulmonary vasoconstriction, not inhibited by meclofenamate

Leukotriene E4 (LTE4) appears to be a rather stable product of the lipoxygenase pathway. Its action in the pulmonary circulation is unknown. Therefore we investigated its effect on the circulation of isolated rat lungs perfused with a cell- and plasma-free solution. Synthetic LTE4 in doses from .15 micrograms to 5 micrograms/.25 ml .9% NaCl injected as a bolus in the pulmonary artery during normoxia caused a fast, transient perfusion pressure increase within seconds. This was followed by a slow rise in baseline perfusion pressure (normoxia) over 25 min. In addition, 5 micrograms LTE4 caused edematogenic lung damage. Injection of 1.5 micrograms LTE4 during hypoxic vasoconstriction caused fast, transient pressure rises, similar to normoxic conditions. 6-keto-PGF1 alpha and TXB2 were measured in the lung effluent before and after LTE4 injection. Neither 6-keto-PGF1 alpha nor TXB2 production changed after LTE4 injection. Meclofenamate (.5 micrograms/ml) increased the fast, transient and the slow, sustained pressure rise. We conclude that LTE4 caused direct pulmonary vasoconstriction unrelated to cyclooxygenase products.     

PAF antagonists inhibit monocrotaline-induced lung injury and pulmonary hypertension.

Lung platelet-activating factor (PAF) levels increased in some rats at 1-3 wk after subcutaneous injection of monocrotaline (MCT). We tested the effect of specific PAF antagonists, WEB 2086 and WEB 2170, on MCT-induced lung injury and subsequent pulmonary hypertension and right ventricular hypertrophy. Treatment with either agent decreased MCT-induced pulmonary hypertension and right ventricular hypertrophy at 3 wk after injection. Treatment with WEB 2170 reduced MCT-induced pulmonary vascular leak at 1 wk after injection, and WEB 2086-treatment exclusively during the early leak phase also decreased MCT-induced right ventricular hypertrophy at 3 wk. Treatment with WEB 2170 between the 3rd and 4th wk after MCT injection inhibited the progression of right ventricular hypertrophy at 4 wk. These results suggest that PAF contributes to the early pulmonary vascular leak, and this leak phase is important for the development of pulmonary hypertension and right ventricular hypertrophy in MCT-treated rats. Furthermore, it appears that PAF action contributes to the maintenance of a chronic inflammatory process that involves the synthesis of other lipid mediators (prostaglandins and leukotrienes) and leads to pulmonary hypertension. We conclude that PAF has a role in the MCT-induced inflammatory lung injury and pulmonary hypertension.     

Severe pulmonary hypertension and arterial adventitial changes in newborn calves at 4,300 m

Some human newborns have a syndrome characterized by irreversible pulmonary hypertension and severe hypoxemia and by medial hypertrophy and adventitial thickening of pulmonary arteries. We considered that newborn calves made severely hypoxic might reproduce features of the human disease. When 2-day-old calves were placed at 4,300 m simulated altitude, pulmonary arterial pressure was increased and could be reversed by 100% O2. However, after 2 wk at 4,300 m, pulmonary arterial pressures were suprasystemic and there was right-to-left shunting probably through the foramen ovale and a patent but restrictive ductus arteriosus. Suprasystemic pulmonary pressure and hypoxemia persisted with 100% O2 breathing. Morphometrical examination of the lung arteries showed a markedly thickened adventitia with cellular proliferation and collagen and elastin deposition. There was increased medial thickness and distal muscularization of the pulmonary arteries associated with decreased luminal diameter. The rapid development of severe pulmonary hypertension and poor responsiveness to O2 was associated with increased arterial wall thickness, particularly involving the adventitia. Thus the pulmonary arterial circulation in these calves, which were placed at high altitude for 2 wk, exhibited features resembling persistent pulmonary hypertension in newborn infants.     

Measurement of peptidoleukotrienes in biological fluids

Samples of human bronchoalveolar lavage fluid (BALF) and urine were utilized to demonstrate methods for quantitation and validation of leukotrienes (LTs). These methods utilize an enzyme immunoassay (EIA) that uses commercially available reagents, the antibody recognizing LTC4, LTD4, LTE4, and N-acetyl LTE4. BALF containing epithelial lining fluid was collected from atopic asthmatics both before and 5 min after the subjects had been challenged with a local instillation of allergen into the airways. BALF samples collected without allergen challenge had low levels of immunoreactive LTs, whereas samples collected after allergen were markedly elevated. After high-performance liquid chromatography (HPLC) separation of LTs, EIA revealed the presence of LTC4. The identity was validated by incubating LTC4 with a bovine gamma-glutamyl transpeptidase with dipeptidase activity that converted added [3H]-LTC4 as well as LTC4 immunoreactivity to LTE4. Urine samples collected from six healthy volunteers, one patient with adult respiratory distress syndrome (ARDS), and three patients in status asthmaticus were also analyzed for LTs. After HPLC separation of LTs and quantitation by EIA, urine samples from healthy subjects were found to have low but measurable LTE4. In contrast, the urine samples from the patients in status asthmaticus and from the ARDS patient had large elevations of LTE4 levels compared with healthy subjects. When the HPLC fractions containing [3H]LTE4 and LT immunoreactivity in the ARDS sample were treated with acetic anhydride, HPLC analysis indicated that both radiolabel and immunoreactivity now eluted at the retention time of N-acetyl LTE4, the derivatized product of LTE4. The methods described are relatively easy and can be used to measure and validate the existence of peptidoleukotrienes in biological samples.