Initiation of peristalsis by circumferential stretch of flat sheets of guinea‐pig ileum

Abstract

Segments of isolated guinea‐pig intestine, 12 mm long, were distended slowly by intraluminal fluid infusion or by mechanical stretch as either a tube or flat sheet. In all cases, at a constant threshold length, a sudden, large amplitude contraction of the circular muscle occurred orally, corresponding to the initiation of peristalsis. Circumferential stretch of flat sheet preparations evoked graded contractions of the longitudinal muscle (the ‘preparatory phase’), which were maintained during circular muscle contraction. This suggests that the lengthening reported during the emptying phase of peristalsis is due to mechanical interactions. The threshold for peristalsis was lower with more rapid stretches and was also lower in long preparations (25 mm) compared with short preparations (5‐10 mm), indicating that ascending excitatory pathways play a significant role in triggering peristalsis. Stretching a preparation beyond the threshold for peristalsis evoked contractions of increasing amplitude; thus peristalsis is graded above its threshold. However, during suprathreshold stretch maintained at a constant length, contractions of the circular muscle quickly declined in amplitude and frequency. Circular muscle cells had a resting membrane potential approximately 6 mV more negative than the threshold for action potentials. During slow circumferential stretch, subthreshold graded excitatory motor input to the circular muscle occurred, prior to the initiation of peristalsis. However, peristalsis was initiated by a discrete large excitatory junction potential (12 ± 2 mV) which evoked bursts of smooth muscle action potentials and which probably arose from synchronized firing of ascending excitatory neuronal pathways.

Role of α2‐adrenoceptors in the sympathetic inhibition of motility reflexes of guinea‐pig ileum

“…This contrasts with studies of ascending excitatory reflexes, which have found that such reflexes are graded according to the magnitude of the stimulus (Tonini et al 1996;Spencer et al 1999b). By contrast, the peristaltic reflex evoked in vitro by stretching the intestinal wall is an all-or-nothing phenomenon that is typically not preceded by a graded contraction of the circular muscle (Brookes et al 1999). In both the present study (Fig.…”

“…The output of the intrinsic sensory neurons to local motor neurons also includes slow EPSPs. Thus, motor neurons near the recording balloon will be tonically excited and primed to produce an all-or-nothing propulsive contraction in the same way that the oral end of a slowly distended segment of ileum is primed to produce a similar contraction with no graded pre-contraction (Brookes et al 1999).…”

Smooth Muscle Myosin Heavy Chain Isoform Distribution in the Swine Stomach

“…These neighboring cells could then be activated by any of a number of proposed mechanotransduction mechanisms, including mechanosensitive ion channels, membrane-bound enzymes, or modulation of their cytoskeleton (Hill et al 2001). Evidence for all these mechanisms working in vascular and enteric SM exists (Brookes et al 1999;Farrugia et al 1999;Phillips and Powley 2000). Therefore, selective innervation of SMB MHC-rich cells that shorten quickly could, via stretch-activated mechanotransduction, activate neighboring cells, resulting in more rapid tissue activation.…”

Electromechanical abdominal massage and colonic function in individuals with a spinal cord injury and chronic bowel problems

“…In addition, it is thought that stretch receptors are activated which can reinforce the gastrocolic reflex, causing an increase in motility of the gastrointestinal tract. 21 Also activation of the parasympathetic nervous system, which is highly involved in a Also subjects who did not complete the 10-week period, answered this question.…”