Role of substance P nerves in longitudinal smooth muscle contractions of the esophagus

Abstract

Longitudinal muscle strips from different sites along the opossum esophagus were stimulated transmurally so as to produce neurally mediated contractions. Low-frequency transmural stimulation produced contractions after termination of the stimulus ("off" contractions), whereas high-frequency stimuli produced contractions beginning during the stimulus and extending beyond termination of the stimulus (extended-duration contractions). The intrastimulus portion of the extended-duration contraction was partially antagonized by atropine or substance P desensitization, whereas the poststimulus portion of the contraction was selectively and fully antagonized by desensitization with substance P. A combination of atropine and substance P desensitization abolished the extended-duration contraction. The amplitude of contraction was greater in the proximal than in the distal strips, irrespective of the mode of stimulation. The poststimulus portion of the extended-duration contraction was significantly longer in muscle strips taken from more distal than proximal portions of the esophagus. This gradient in duration of contractions was abolished by substance P desensitization but was not affected by atropine. Exogenously applied substance P (10 microM) produced equally sustained long-duration contractions at all sites along the esophagus. These observations suggest that a) both acetylcholine- and substance P-containing nerves are responsible for the extended-duration contraction of longitudinal muscle, and b) transmural stimulation causes an aborally directed increase in the duration of contractions; this gradient of increasing duration of contraction appears to be due to a more prolonged neural release of substance P at more distal sites.