THE RAT ANOCOCCYGEUS MUSCLE AND ITS RESPONSE TO NERVE-STIMULATION ANDTO SOME DRUGS (REPRINTED FROM BRIT J PHARMACOL, VOL 45, PG 404-416, 1972)

1. A new smooth muscle preparation, the rat anococcygeus muscle, is de scribed. The muscle is paired, thin, consists of smooth muscle only an d the muscle cells are organized in parallel bundles. It has a dense a drenergic innervation distributed throughout the muscle but apparently no cholinergic innervation. The muscles are easily isolated. 2. The m uscle contracts to noradrenaline, acetylcholine, furmethide, 5-hydroxy tryptamine, but not to histamine. Isoprenaline produces contraction at high concentrations. The effects of noradrenaline and acetylcholine a re blocked by phentolamine and atropine respectively. The response to isoprenaline is little affected by propranolol. 3. The muscle contract s in response to field stimulation or stimulation of extrinsic nerves. This response is completely blocked by phentolamine but unaffected by hexamethonium or atropine. 4. Guanethidine 10(-6)-5 x 10(-6)M blocks the motor response to nerve stimulation and potentiates that to noradr enaline. Higher concentrations of guanethidine raise tone. In the pres ence of raised tone, field stimulation produces an inhibitory response insensitive to hexamethonium but abolished by tetrodotoxin 2 x 10(-7) g/ml. This inhibitory response to stimulation can also be shown after other drugs which raise tone. 5. The inhibitory response to nerve sti mulation is not mimicked by acetylcholine, isoprenaline or ATP, nor bl ocked by atropine, phentolamine, phenoxybenzamine, propranolol, hexame thonium or lysergic acid diethylamide.