The response of the cat anococcygeus muscle to nerve or drug stimulation and a comparison with the rat anococcygeus.

1 The cat anococcygeus muscle is shown to possess a dual innervation similar to the rat anococcygeus, with a motor adrenergic innervation and an inhibitory innervation whose transmitter is unknown. The pharmacological properties of the cat muscle were investigated and compared with those of the rat muscle.2 The cat muscle contracts to noradrenaline, 5-hydroxytryptamine, tyramine, amphetamine, guanethidine, cocaine and lysergic acid diethylamide (LSD). The effects of noradrenaline and 5-hydroxytryptamine are blocked by phentolamine and methysergide respectively.3 The cat anococcygeus is relaxed by acetylcholine, carbachol, isoprenaline, ATP, prostaglandins E(1), E(2) and F(2alpha) and vasopressin, all of which contract the rat muscle. The effects of acetylcholine and carbachol are blocked by atropine and those of isoprenaline by propranolol.4 Field stimulation produces contraction of the cat anococcygeus, which is blocked by phentolamine and guanethidine but unaffected by hexamethonium, atropine or neostigmine.5 In the presence of guanethidine (10(-5)M), the tone of the muscle is raised and field stimulation produces relaxation of the muscle. These inhibitory responses are unaffected by phentolamine, hexamethonium, atropine or neostigmine.6 Neostigmine potentiates the effects of acetylcholine, but not of carbachol in relaxing the cat anococcygeus and in contracting the rat anococcygeus, but has no effect on either motor or inhibitory responses to field stimulation.7 Cold storage for up to eight days had little effect on either the motor response to noradrenaline or the motor or inhibitory response to field stimulation of the cat anococcygeus. Beyond eight days, the response to field stimulation diminishes more rapidly than the response to noradrenaline.