Objective: To illustrate the existence of bile regurgitation under stress condition, and explore the possible effects and related mechanism of changes of cholecystokinin octapeptide (CCK-8) on stress-induced bile regurgitation in rats.
Methods: (1) Changes in plasma CCK-8 and gastric bile concentration were measured by using radioimmunoassay while simultaneously calculating gastric ulcer index and intragastric pH; (2) Each isolated gastric strips were suspended in a tissue chamber to record the contractile responses by polyphysiograph; (3) The responsiveness of gastric smooth muscle cells (SMCs) to sulfated cholecystokinin octapeptide (CCK-8S) were examined using fura-2-loaded microfluorimetric measurement of intracellular calcium concentration ([Ca(2+)] i); (4) The current of L-type calcium channels (I(CaL)) of SMCs were recorded by patch-clamp techniques.
Results: (1) Compared with the normal control, plasma CCK-8 [from (2.23 +/- 0.88) pmol/L to (10.80 +/- 3.82) pmol/L] and gastric bile concentration [from (37.93 +/- 23.76) micromol/L to (1316.00 +/- 197.36) micromol/L] significantly increased during the stress (P < 0.01) and both simultaneously reached the peak at the time point of 2 h after stress; ulcer index (from 0.62 +/- 0.23 to 32.01 +/- 16.11) and intragastric pH (from 1.06 +/- 1.20 to 5.29 +/- 1.25) apparently increased (P < 0.01); (2) Significant changes to CCK-8S were found in the mean contractile amplitude and frequency of circular muscle and longitudinal muscle of gastric antrum and pylorus; (3) CCK-8S-evoked significant increase in [Ca(2+)] i [from (65.8 +/- 7.4) nmol/L to (472.1 +/- 35.6) nmol/L, P < 0.01] could be suppressed by CCK-A receptor antagonist; whereas a small but significant increases were still elicited by CCK-8S under condition of the removal of extracellular calcium; (4) CCK-8S-intensified calcium current I(Ca-L) [from (-56.42 +/- 6.57) pA to (-88.54 +/- 5.71) pA, P < 0.01)] apparently inhibited by respective administration of nifedipine, Ca(2+)-ATPase inhibitors or calcium dependent chloride channel blocker (P < 0.01).
Conclusions: Gastric mucosal damage induced by bile regurgitation is closely connected with gastric antrum and pylorus dysmotility evoked by CCK-8 during the stress. CCK-8S-evoked [Ca(2+)] i increase in gastric antrum and pylorus SMC depends on the release of intracellular calcium stores which activates L-type voltage-dependent calcium channels through the activation of calcium dependent chloride channels.