1. The actions on the taenia of 4-(m-chlorophenylcarbamoyloxy)-2-butynyl-trimethylammonium
chloride (McN-A-343), N-benzyl-3-pyrrolidyl
acetate methobromide (AHR-602),
tetramethylammonium (TMA) and
choline phenyl ether have been examined and compared with the actions of
acetylcholine,
nicotine and 1,1-dimethyl-4-phenylpiperazinium (
DMPP).2. Responses of the taenia to these agonists are quantitatively and often qualitatively dependent on the tone of the preparation. A method is described which makes allowance for the effect of tone on heights of contractions.3.
Acetylcholine,
McN-A-343 and
AHR-602 produced only contractions; TMA produced contractions or biphasic responses; and
choline phenyl ether,
nicotine and
DMPP produced contractions, relaxations or biphasic responses.4. The mode of action of these compounds has been analysed by means of
hyoscine,
ganglion-blocking drugs,
tetrodotoxin and local anaesthetics.5. It is concluded that
acetylcholine,
McN-A-343,
AHR-602, TMA and
choline phenyl ether act on
muscarinic receptors in the smooth muscle.
Choline phenyl ether has an additional action on
nicotinic receptors of
cholinergic neurones.
Nicotine and
DMPP act on
nicotinic receptors of
cholinergic neurones and of inhibitory neurones. An action on the latter is sometimes also seen with TMA and
choline phenyl ether.6. With
nicotine or
DMPP, and TMA or
choline phenyl ether in the presence of
hyoscine, part of the contraction phase of biphasic responses (in which a contraction follows relaxation) is best explained as being triggered by the initial relaxation-that is, as a "rebound contraction".7. None of the compounds tested appeared to exert an
atropine-sensitive action on neurones.8. In the presence of
hyoscine high concentrations of agonists can act on sites not involved with lower concentrations.