Contractile effect of endothelin on isolated iris sphincter muscle of the pig

Porcine endothelin (1 nM-0.3 microM) produced a concentration-dependent contraction of the isolated sphincter muscle of the pig iris. Neither atropine (1 microM) nor tetrodotoxin (1 microM) nor pre-exposure of the preparation to 10 microM capsaicin for 15 min affected the endothelin-induced response. We propose that the endothelin-induced contraction of the iris sphincter muscle of the pig is largely due to a direct action on smooth muscle cells and is unrelated to neurogenic myotic mechanisms.