Abstract
Among the effects of clonidine [St 155, 2-(2, 6-dichlorophenylamino)-2-imidazoline hydrochloride], those on the cardiovascular system have received considerable attention. Clonidine induces a biphasic change in blood pressure, consisting of initial brief hypertension and subsequent long-lasting hypotension (1). The initial hypertension has been explained by a sympathomimetic action of this drug and the subsequent hypotension by some centrallymediated repression of the sympathetic tone (2-5).
The isolated preparation of taenia coil is an excellent material to study sympathomimetic and parasympathomimetic actions of drugs, responding to the former with inhibition and to the latter with excitation (6, 7). The present paper reports the effects of clonidine on the excitation and contraction of taenia coll. The knowledge obtained with this material will be useful to interpret the drug actions on smooth muscle in general.
