Enhanced pulmonary inflammatory response to inhaled endotoxin in pregnant rats.

Evidence suggests that pregnant animals are more sensitive than nonpregnant animals to the systemic administration of endotoxin. Studies were undertaken to assess whether an enhanced sensitivity of the pulmonary system to aerosolized endotoxin might exist during pregnancy. Pregnant Sprague-Dawley female rats (17 d of gestation) or age-matched virgin female rats were exposed to air or endotoxin (lipopolysaccharide) by inhalation for 3 h. At 18 h following exposure to endotoxin, lactate dehydrogenase activity levels in bronchoalveolar lavage (BAL) fluid samples from pregnant rats were 1.5-fold greater than those from endotoxin-exposed virgin rats. BAL polymorphonuclear leukocyte (PMN) numbers were also approximately twofold greater in pregnant rats than in virgins following the inhalation of endotoxin. The increases in BAL PMNs in pregnant rats following endotoxin exposure were observed just following exposure to endotoxin as well as at 18 h following exposure. These results indicate that an increased pulmonary inflammatory response to inhaled endotoxin occurs during pregnancy in rats. Additional findings suggest that these pregnancy-linked pulmonary responses to endotoxin cannot be explained by the following potential mechanisms: changes in the inhaled dose of endotoxin, or alterations in the responsiveness of alveolar macrophages to endotoxin. To our knowledge this is the first study that has evaluated pulmonary responses to inhaled endotoxin during pregnancy. Our finding that pregnancy is associated with an increased lung inflammatory response to aerosolized endotoxin raises the possibility that there may be a generalized enhancement of pulmonary responses to inhaled toxic agents during pregnancy.

Nitric oxide production by rat bronchoalveolar macrophages or polymorphonuclear leukocytes following intratracheal instillation of lipopolysaccharide or silica.

Exposure of the lung to lipopolysaccharide (LPS) or silica results in an activation of alveolar macrophages (AMs), recruitment of polymorphonuclear leukocytes (PMNs) into bronchoalveolar spaces, and the production of free radicals. Nitric oxide (NO) is one of the free radicals generated by bronchoalveolar lavage (BAL) cell populations following either LPS or silica exposure. The purpose of the present study was to assess the relative contributions of AMs and PMNs to the amounts of NO produced by BAL cells following intratracheal (IT) instillation of either LPS or silica. Male Sprague Dawley rats (265-340 g body wt.) were given LPS (10 mg/100 g body wt.) or silica (5 mg/100 g body wt.). BAL cells were harvested 18-24 h post-IT and enriched for AMs or PMNs using density gradient centrifugation. Media levels of nitrate and nitrite (NOx; the stable decomposition products of NO) were then measured 18 h after ex vivo culture of these cells. Following IT exposure to either LPS or silica, BAL cell populations were approximately 20% AMs and approximately 80% PMNs. After density gradient centrifugation of BAL cells from LPS- or silica-treated rats, cell fractions were obtained which were relatively enriched for AMs (approximately 60%) or PMNs (approximately 90%). The amounts of NOx produced by the AM-enriched fractions from LPS- or silica-treated rats were approximately 2-4-fold greater than that produced by the PMN-enriched fractions. Estimations of the relative contribution of AMs or PMNs to the NOx produced indicated that: (i) following LPS treatment, 75%-89% of the NOx was derived from AMs and 11%-25% from PMNs; and (ii) following silica treatment, 76%-100% of the NOx was derived from AMs and 0-24% from PMNs. Immunohistochemistry for inducible NO synthase on lung tissue sections supported these findings. We conclude that AMs are the major source of the NO produced by BAL cells during acute pulmonary inflammatory responses to LPS or silica.

Influence of hyperthyroidism on rat lung cytokine production and nuclear factor-kappaB activation following ozone exposure.

Results from previous studies indicate that hyperthyroidism increases the risk of ozone-induced lung toxicity. To better understand the processes that might contribute to the increased pulmonary inflammatory response to ozone in hyperthyroidism, we evaluated bronchoalveolar lavage fluid levels of selected cytokines in control and hyperthyroid rats after exposure to air or ozone. In addition, we assessed whether there is a relative increase in nuclear factor-kappa B (NF-kappaB) binding activity in cells harvested by bronchoalveolar lavage from hyperthyroid rats following the inhalation of ozone. A hyperthyroid condition was induced by the administration of thyroxine (0.5 mg/kg body weight) for 7 days. Control rats received vehicle injections. The animals were then exposed by inhalation to air or ozone (2 ppm for 3 h) and studied 18 h following the exposure. Bronchoalveolar lavage levels of MIP-2 and MCP-1 were increased in both control and hyperthyroid rats by ozone exposure. However, the increases in hyperthyroid rats were much greater, MIP-2 1.5-fold and MCP-1 11-fold, when compared to levels in controls following ozone. These changes appeared to be relatively specific; bronchoalveolar lavage fluid levels of interleukin (IL)-6, IL-4, and IL-10 were generally low or nondetectable across all of the studied groups at the 18-h postexposure time point. We also found that NF-kappaB binding activity was increased at both 4 and 18 h following ozone exposure in bronchoalveolar lavage cell extracts from hyperthyroid rats relative to the activity in control samples. Collectively, these results suggest that mechanisms contributing to the enhanced pulmonary inflammatory response to ozone in a hyperthyroid state include an increase in NF-kappaB activation and an upregulation of chemokine production.