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      Prenatal and Early, but Not Late, Postnatal Exposure of Mice to Sidestream Tobacco Smoke Increases Airway Hyperresponsiveness Later in Life

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          Abstract

          Background

          Cigarette smoke exposure in utero and during early postnatal development increases the incidence of asthma and airway hyperresponsiveness (AHR) later in life, suggesting that a possible critical period of developmental sensitivity exists in the prenatal and early postnatal periods.

          Objective

          We investigated mechanisms of susceptibility during critical developmental periods to sidestream smoke (SS) exposure and evaluated the possible effects of SS on neural responses.

          Methods

          We exposed three different age groups of mice to either SS or filtered air (FA) for 10 consecutive days beginning on gestation day (GD) 7 by maternal exposure or beginning on postnatal day (PND) 2 or PND21 by direct inhalation. Lung function, airway substance P (SP) innervation, and nerve growth factor (NGF) levels in broncho alveolar lavage fluid were measured after a single SS exposure on PND59.

          Results

          Methacholine (MCh) dose response for lung resistance (R L) was significantly elevated, and dynamic pulmonary compliance (C dyn) was significantly decreased, in the GD7 and PND2 SS exposure groups compared with the FA groups after SS exposure on PND59. At the same time points, the percent area of SP nerve fibers in tracheal smooth muscle and the levels of NGF were significantly elevated. MCh dose–response curves for R L and C dyn, SP nerve fiber density, and the level of NGF were not significantly changed in the PND21 exposure group after SS exposure on PND59.

          Conclusions

          These results suggest that a critical period of susceptibility to SS exposure exists in the prenatal and early postnatal period of development in mice that results in increased SP innervation, increased NGF levels in the airway, and enhanced MCh AHR later in life.

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          Most cited references 74

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          The nerve growth factor 35 years later.

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            Association between exposure to environmental tobacco smoke and exacerbations of asthma in children.

            Exposure to environmental tobacco smoke, as reported by parents, has been linked to diminished pulmonary function and more frequent exacerbations of asthma in children with the disease. Further insight into this association might be gained by using urine cotinine levels to measure actual exposure. We measured urine cotinine levels in 199 children with asthma; 145 also underwent pulmonary-function studies. A parent answered questions about each child's exposure to environmental tobacco smoke. Acute exacerbations of asthma during the preceding year were documented through blinded review of medical records. Possible confounding factors were accounted for by the use of multivariate analysis and by comparisons of serum theophylline levels in exposed and unexposed children. The median urine cotinine levels were 5.6 ng per milliliter in the 116 children reported not to have been exposed to tobacco smoke, 13.1 ng per milliliter in the 53 children exposed to cigarette smoking by the mother or other persons, and 55.8 ng per milliliter in the 30 children exposed to cigarette smoking by the mother and other persons. Acute exacerbations of asthma increased with exposure, whether such exposure was reported by a parent or identified on the basis of the cotinine level; the relative risks for the highest as compared with the lowest exposure category were 1.8 (95 percent confidence interval, 1.4 to 2.2) for reported exposure and 1.7 (95 percent confidence interval, 1.4 to 2.1) for exposure indicated by cotinine levels. The forced expiratory volume in one second (FEV1), the forced expiratory flow between 25 and 75 percent of vital capacity, and the ratio of FEV1 to forced vital capacity also decreased with increases in both measures of exposure. Measurement of urine cotinine levels provides further evidence of an association between exposure to environmental tobacco smoke and pulmonary morbidity in children with asthma. These data emphasize the need for systematic, persistent efforts to stop the exposure of children with asthma to environmental tobacco smoke.
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              Maternal and grandmaternal smoking patterns are associated with early childhood asthma.

              To investigate the associations of maternal and grandmaternal smoking before, during, and after pregnancy with childhood asthma. We conducted a case-control study nested within the Children's Health Study in southern California. The case patients consisted of 338 children with asthma that had been diagnosed in the first 5 years of life, and 570 control subjects were countermatched on in utero exposure to maternal smoking within grade, sex, and community of residence. Detailed maternal and household smoking histories and other asthma risk factor information was obtained by telephone interview. The participation rates were 72.3% and 82.5%, respectively, for control subjects and case patients. In utero exposure to maternal smoking was associated with increased risk for asthma diagnosed in the first 5 years of life (odds ratio [OR], 1.5; 95% confidence interval [CI], 1.0 to 2.3), and for persistent asthma (OR, 1.5; 95% CI, 1.0 to 2.3). The associations did not differ in children with early transient asthma compared to those with early persistent asthma. Relative to never-smokers, children whose mothers smoked throughout the pregnancy had an elevated risk of asthma in the first 5 years of life (OR, 1.6; 95% CI, 1.0 to 2.6). Children of mothers who quit smoking prior to the pregnancy showed no increased risk (OR, 0.9; 95% CI, 0.5 to 1.5). We were unable to assess the association of smoking cessation during pregnancy because very few mothers were reported to have done so (15%). Asthma risk did not increase in a monotonic pattern with smoking intensity during pregnancy. Postnatal secondhand smoke exposure was not independently associated with asthma. Grandmaternal smoking during the mother's fetal period was associated with increased asthma risk in her grandchildren (OR, 2.1; 95% CI, 1.4 to 3.2). Maternal and grandmaternal smoking during pregnancy may increase the risk of childhood asthma.
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                Author and article information

                Journal
                Environ Health Perspect
                Environmental Health Perspectives
                National Institute of Environmental Health Sciences
                0091-6765
                1552-9924
                September 2009
                22 May 2009
                : 117
                : 9
                : 1434-1440
                Affiliations
                [1 ] Department of Neurobiology and Anatomy and
                [2 ] Department of Orthopedics, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA
                Author notes
                Address correspondence to Z.-X. Wu, Department of Neurobiology and Anatomy, P.O. Box 9128, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506 USA. Telephone: (304) 293-7222. Fax: (304) 293-8159. E-mail: zwu@ 123456hsc.wvu.edu

                The authors declare they have no competing financial interests.

                Article
                ehp-117-1434
                10.1289/ehp.0800511
                2737022
                19750110
                This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.
                Categories
                Research

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