Stimulation of intestinal smooth muscle by atropine, procaine, and tetrodotoxin

Abstract

In order to determine whether or not atropine, procaine, and tetrodotoxin (TTX) can stimulate intestinal smooth muscle directly, we examined the effects of these drugs on the mechanical and electrical activities of several types of cat intestinal smooth muscle preparations. The preparations consisted of isolated rings of 1) intact intestinal wall, 2) intact longitudinal and circular muscle, 3) ganglion-free circular muscle, and 4) ganglion-free circular muscle devoid of its dense layer and plexus muscularis profundus. Atropine and procaine (greater than 10(-4) M) stimulated all four types of preparation. On the other hand, TTX (up to 5 X 10(-6) M) stimulated only preparations 1 and 2. It is concluded that whereas atropine and procaine can directly stimulate intestinal smooth muscle, the excitatory effect of TTX is neurally mediated.

Sodium Channel Blockers Alter Slow-Wave Frequency of the Rat Stomach in vivo

“…In contrast, sodium chan nel blockers tended to increase jejunal spik ing as indicated by a prolongation of phase II and phase III of the MMC compared to con trol, when given intragastrically. Our results in vivo do not confirm previously published data showing an increase in spontaneous contractions of both in vivo and in vitro after sodium channel blockade with tetrodotoxin, lidocaine, or procaine [7][8][9][10]. It has been speculated that the small and large in testine receive continuous inhibitory input that can be suppressed by sodium channel blockers [7][8][9][10].…”

“…In vitro, the local anesthetics procaine and lidocaine increase contractile activity of gastrointestinal smooth muscle [7][8][9][10], So dium channel blockers might exert similar effects in vivo resulting in disturbances of gastrointestinal motility. Possible secondary motility disorders could at least partly ex plain side effects in patients chronically treated with these drugs.…”

Spontaneous electromechanical activity in the rat duodenumin vitro

“…This finding is strengthened by the observation that in the duodenal segment TTX causes an increase in the pressure wave amplitude but it fails to affect the force of contraction. The presence of tonic inhibitory intramural neurons supplying the circular layer of small intestine is well known (BORTOFF & MULLER, 1975;WOOD, 1972). Moreover the effects induced by TTX are still present after atropine and guanethidine indicating that the tonic inhibitory neurons are non-adrenergic, non-cholinergic (NANC) in nature.…”

Intrinsic Neural Control of Intestinal Motility

“…Excitatory motor neurons cannot control the spread of excitation within the muscular syncytium, and observations that excitability of the muscle is greatly increased when neuronal activity is experimentally abolished (3,58) indicate that excitatory nerves do not control the responsiveness of the muscle to the pacemaker. Control of both the responsiveness of the muscle to the pacemaker and of spread of excita tion within the syncytium require modulation of continuously active inhibi tory innervation of the muscle.…”