Lack of Cyclic Nucleotide Regulation of MBCQ-induced Relaxation of Rat Ileal Smooth Muscle

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The effects of the type V phosphodiesterase (PDE V) inhibitors, MBCQ, zaprinast and dipyridamole, on the relationship between relaxation and cyclic nucleotide content were investigated in rat ileal smooth muscle. Each of MBCQ (0.01-10μM), zaprinast (0.1-100μM) and dipyridamole (0.01-10μM) inhibited carbachol (CCH; 10μM)-induced contractions in a concentration-dependent manner. When compared with the concentration of these agents prodecing 50% relaxation (IC_<50>) of CCH-induced contraction, MBCQ was 14-20 fold more potent than the other agents. The ingibitory potency of these agents against high K^+ (65mM KCI)-induced contractions were similar to that for CCH. MBCQ (1, 10μM) did not significantly increase the cGMP content above control levels in the presence of CCh (10μM), Both Zaprinast (1-100μM) and dipyridamole (1-100μM) increased the cGMP content of smooth muscle preparations in a concentration-dependent manner. There was a positive correlation between the inhibition of the CCh-induced contraction and the increase in cGMP content elicited by zaprinast and dipyridamole (zaprinast; r=0.72, P<0.05, dipyridamole; r=0.92, P<0.05). However, MBCQ at a concentration which induced a medium-sized relaxation did not significantly increase the cGMP content. Neither MBCQ, zaprinast nor dipyridamole significantly increased the cAMP content of the preparations above control. In summary, it is suggested that the inhibition of CCh-induced contractions by zaprinast and dipyridamole of involves increases in cGMP content via inhibition of PDE V. However the inhibition of CCh-induced contraction by MBCQ may not involve cyclic nucleotides in rat ileal smooth muscle.
日本平滑筋学会の論文

Lack of Cyclic Nucleotide Regulation of MBCQ-induced Relaxation of Rat Ileal Smooth Muscle

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