NIP-121 and cromakalim, potassium channel openers, preferentially suppress prostanoid-induced contraction of the guinea-pig isolated trachea.

We have investigated the relaxant effect of the potassium channel openers, NIP-121 and cromakalim, on spontaneous and spasmogen-induced tone in the isolated guinea-pig trachea. NIP-121 and cromakalim fully suppressed the spontaneous tone in a concentration-dependent manner and the maximal response was 89 and 97% of that to 1 mM aminophylline. The suppressant effect of NIP-121 (pD2 7.39) was 5 times stronger than that of cromakalim (pD2 6.69). Spontaneous tone was completely inhibited by the cyclooxygenase inhibitor, indomethacin, and partially inhibited by the thromboxane A2 (TXA2) antagonist, BM13177. In the presence of indomethacin, the contraction induced by prostaglandin (PG) F2 alpha and PGD2 was reversed by BM13177 to the same extent. NIP-121 and cromakalim reversed the contraction induced by PGF2 alpha, PGD2 and the TXA2 mimetic, U46619, and the effects were more potent than those observed on the contraction induced by leukotriene (LT) D4, LTC4, histamine and acetylcholine. The maximal relaxant responses (%) induced by NIP-121 and cromakalim were 97 and 96 for PGF2 alpha, 94 and 87 for PGD2, 94 and 93 for U46619, 69 and 69 for LTD4, 75 and 58 for LTC4, 73 and 61 for histamine and 1 and 16 for acetylcholine, respectively. The relaxant effect of NIP-121 on responses to these spasmogens (pD2 7.35 for PGF2 alpha, 7.40 for PGD2, 7.31 for U46619, 7.28 for LTD4, 7.09 for LTC4, and 7.15 for histamine) was about 10-20 times stronger than the effect of cromakalim (pD2 6.23 for PGF2 alpha, 6.04 for PGD2, 6.20 for U46619, 6.01 for LTD4, 5.82 for LTC4 and 5.88 for histamine).(ABSTRACT TRUNCATED AT 250 WORDS)