Eserine-induced hypertone of guinea pig distal colon in vivo: a new pharmacological procedure for testing smooth muscle relaxants.

A new in vivo procedure suitable for testing the smooth muscle relaxant properties of a test substance is described. Topical eserine produced a long-lasting steady increase in tone of guinea pig distal colon and enhanced the atropine-sensitive phasic activity. Intravenously administered atropine, pirenzepine, and dicyclomine (which possess competitive antimuscarinic properties) produced a dose-related inhibition of eserine-induced muscle tone and suppressed phasic contractions. On the other hand, verapamil and octylonium bromide (which produce smooth muscle relaxation by interfering with Ca++ availability for contraction) did not suppress phasic contraction although they were fully effective in inhibiting eserine-induced tone. The eserine-induced contraction of guinea pig distal colon appears to be a suitable, quick, and inexpensive test for evaluating the effects of potential smooth muscle relaxants against background hypermotility produced by amplifying the neurogenic drive to the target organ.