MEDICAL HYPOTHESES AND RESEARCH
VOL. 2, No. 4, October 2005


Y. Chiba, et al. [2005] Med Hypotheses Res 2: 597-603.


Difference in the Effects of Cigarette Smoke Exposure in
vivo on Bronchial Smooth Muscle Contractility in vitro
in Three Strains of Rats



Yoshihiko Chiba*, Masahiko Murata, Yuji Yoshikawa, Akiyoshi
Saitoh, Hiroyasu Sakai, Junzo Kamei and Miwa Misawa


Abstract. Cigarette smoking is a risk factor for development of airway
hyperresponsiveness and chronic obstructive pulmonary disease (COPD). However, little is
known concerning the effect of cigarette smoking on the contractility of airway smooth
muscle. The current study was carried out to determine the responsiveness of bronchial
smooth muscles isolated from rats that were chronically exposed to mainstream cigarette
smoke (CS) in vivo. The bronchial smooth muscle responsiveness was compared in three
strains of rats. Male Wistar, Brown-Norway (BN) and Sprague-Dawley (SD) rats were
exposed to diluted mainstream CS for 2 hours/day, every day for 2 weeks. Twenty-four hours
after the last CS exposure, the smooth muscle responsiveness of isolated left main bronchus
was measured. The concentration-response curve to acetylcholine (ACh) of bronchial smooth
muscle isolated from the CS-exposed group was significantly shifted upward as compared
with that from the air-exposed control in Wistar rats, but not in BN and SD strains. In none
of the strains of rats, significant change in response to high K+-depolarization of bronchial
smooth muscle was observed after the chronic CS exposure. In conclusion, in vivo exposure
to CS caused a significant bronchial smooth muscle hyperresponsiveness to ACh in Wistar
rats, but not in BN and SD strains. The Wistar strain of rats might be useful for studying and
understanding the mechanism of bronchial hyperresponsiveness induced by cigarette
smoking.


*Address all correspondence to: Dr. Y. Chiba, Department of Pharmacology,
School of Pharmacy, Hoshi University, 2-4-41 Ebara, Shinagawa-ku, Tokyo 142-8501,
Japan.  Phone: 81-3-5498-5786. Fax: 81-3-5498-5787.
E-Mail:
chiba@hoshi.ac.jp



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