Nitrogen Dioxide Exposure Increases Airway Contractile Response to Histamine by Decreasing Histamine N-Methyltransferase Activity in Guinea Pigs

Hiroki Hoshi, Kohei Yamauchi, Kiyohisa Sekizawa, Yuichi Ohkawara, Hideya Iijima, Eiko Sakurai, Kimito Maeda, Shoji Okinaga, Isao Ohno, Masaaki Honma, Gen Tamura, Yasuo Tanno, Takehiko Watanabe, Hidetada Sasaki, Kunio Shirato

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8 Citations (Scopus)

Abstract

To determine the mechanism responsible for nitrogen dioxide (NO2)-induced airway hyperresponsiveness, we examined the effects of NO2 exposure on the contractile response to histamine and the level of histamine N-methyltransferase (HMT) activity, a histamine-degrading enzyme, in guinea pig trachea in vitro. Guinea pigs were divided into seven groups. Each group received continuous NO2 exposure (2.0 ppm) for either 2, 6, 12, 24, 48, or 96 h. The remaining group did not receive NO2 exposure (control). HMT activity in trachea was decreased from the control value of 70.3 ± 7.7 pmol/min/mg protein to 34.6 ± 6.7 pmol/min/mg protein by 12 h exposures of NO2. However, 24 and 48 h exposures of NO2 did not significantly alter HMT activity. In contrast, HMT activity exceeded the control value by 96 h exposures of NO2 (85.5 ± 5.1 pmol/min/mg protein). Twelve hour exposures of NO2 shifted the concentration-response curves to histamine to lower concentrations and significantly reduced the median effective concentration (EC50) of histamine (log M) from the control value of -5.16 ± 0.09 to -6.15 ± 0.14 (P < 0.01). In contrast, the EC50 concentration of histamine (log M) increased from the control value of -5.20 ± 0.10 to -4.90 ± 0.11 by 96 h exposures of NO2 (P < 0.05). However, NO2 exposure did not alter the contractile response to acetylcholine. Morphologically, tracheal epithelial cells had vacuoles after 12 h exposures of NO2, but denudation of the epithelium did not occur during this experiment. In situ hybridization for HMT mRNA demonstrated that the level of HMT mRNA increased dominantly in tracheal epithelial cells after 96 h exposures of NO2. The present results indicated that the decrease in the level of HMT activity in the trachea was closely associated with the increase in the airway contractile response to histamine, suggesting that NO2-induced transient airway hyperresponsiveness to histamine is due to the decreased capacity of histamine catabolism in airway.

Original languageEnglish
Pages (from-to)76-83
Number of pages8
JournalAmerican journal of respiratory cell and molecular biology
Volume14
Issue number1
DOIs
Publication statusPublished - 1996

ASJC Scopus subject areas

  • Molecular Biology
  • Pulmonary and Respiratory Medicine
  • Clinical Biochemistry
  • Cell Biology

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