Role of altered responsiveness of hypertrophic smooth muscle in manometric abnormalities of the obstructed opossum oesophagus

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Abstract
The movements of the obstructed oesophagus are abnormal, but whether this relates to the disease causing the obstruction, to the altered load conditions or to abnormal neuromuscular functions in hypertrophic smooth muscle is unclear. In an opossum model of chronic oesophageal obstruction, we compared the mechanical responsiveness of hypertrophic smooth muscle in vitro to in vivo manometric function. Related to their greater thickness, strips of hypertrophic muscle generated greater force in response to electrical stimulation and to stretch than control strips. Hypertrophic muscle often generated repetitive contractions; spread of contractions orad from the stimulus site was common in hypertrophic oesophageal bands. On manometry, the obstructed oesophagus generated abnormally high pressures proximally, and highly variable pressure amplitudes in the middle and distally; pressure waves often occurred simultaneously throughout the oesophagus, were repetitive or multi-peaked and led to a lasting rise of oesophageal pressure. Alterations in the intrinsic neuromuscular functions of hypertrophic smooth muscle including generation of greater force, repetitive or spontaneous contractions, and retrograde spread of contractions explain many, but not all, of the manometric abnormalities seen in the chronically obstructed oesophagus.