Effects of Various Selective Phosphodiesterase Inhibitors on Relaxation and Cyclic Nucleotide Contents in Porcine Iris Sphincter
FULL PAPER Pharmacology Effects of Various Selective Phosphodiesterase Inhibitors on Relaxation and Cyclic Nucleotide Contents in Porcine Iris Sphincter Takuya YOGO1), Takeharu KANEDA2), Yoshinori NEZU1), Yasuji HARADA1), Yasushi HARA1), Masahiro TAGAWA1), Norimoto URAKAWA2) and Kazumasa SHIMIZU2) 1)Laboratories of Veterinary Surgery and 2)Veterinary Pharmacology, Nippon Veterinary and Life Science University, 7–1 Kyonan-cho 1– chome, Musashino, Tokyo 180–8602, Japan (Received 26 March 2009/Accepted 1 July 2009) ABSTRACT. The effects of various selective phosphodiesterase (PDE) inhibitors on muscle contractility and cyclic nucleotide contents in porcine iris sphincter were investigated. Forskolin and sodium nitroprusside inhibited carbachol (CCh)-induced contraction in a concen- tration-dependent manner. Various selective PDE inhibitors, vinpocetine (type 1), erythro -9-(2-hydroxy-3-nonyl)adenine (EHNA, type 2), milrinone (type 3), Ro20–1724 (type 4) and zaprinast (type 5), also inhibited CCh-induced contraction in a concentration-dependent manner. The rank order of potency of IC50 was zaprinast > Ro20–1724 > EHNA milrinone > vinpocetine. In the presence of CCh (0.3 M), vinpocetine, milrinone and Ro20–1724 increased cAMP, but not cGMP, contents. In contrast, zaprinast and EHNA both increased cGMP, but not cAMP, contents. This indicates that vinpocetine-, milrinone- and Ro20–1724-induced relaxation is correlated with cAMP, while EHNA- and zaprinast- induced relaxation is correlated with cGMP in porcine iris sphincter. KEY WORDS: cAMP, cGMP, iris sphincter, PDE inhibitor, smooth muscle. J. Vet. Med. Sci. 71(11): 1449–1453, 2009 Cyclic nucleotides are important secondary messengers, chol (CCh)-induced contraction of porcine iris sphincter and are associated with smooth muscle relaxation [7]. induced by selective PDE (type1–5) inhibitors.
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