Summary
Docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid found in fish oil, has been attracting considerable attention as a health food constituent. The long-term intake of DHA has been reported to improve bronchial asthma by inhibiting the production of inflammatory substances.
To date, however, the immediate effects on the contractile response of tracheal smooth muscle have yet to be studied.
To clarify the immediate effects of DHA on the contractile response of tracheal smooth muscle, a research group led by Professor Yoshio Tanaka, Lecturer Keisuke Obara, and Assistant Professor Kento Yoshioka at the Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toho University, examined the effect of DHA on the contractile response of tracheal smooth muscle isolated from guinea pigs.
Their findings revealed that DHA potently and immediately inhibits the contractile response of tracheal smooth muscle induced by U46619, a stable derivative of thromboxane A₂ (TXA₂), and prostaglandin F_2α (PGF_2α), without affecting the contractile response induced by acetylcholine, histamine, or leukotriene D₄ (LTD₄).
These findings indicate that DHA may ameliorate the bronchial asthma associated with increased levels of TXA₂ and PGF_2α by immediately inhibiting TXA2- and PGF2α-induced hypercontraction of tracheal/bronchial smooth muscle (Fig. 1) in addition to its anti-inflammatory effects.

Terminology
(*1) Prostanoid TP receptor
A receptor that shows high affinity for thromboxane A2. Antagonists of the prostanoid TP receptor are clinically indicated for the treatment of asthma.,br>
(*2) Thromboxane A₂ (TXA₂) and prostaglandin F_2α (PGF_2α)
Prostanoids that produce during inflammation. Their production is reported to be increased in patients with bronchial asthma and during asthma attacks.