Planimetry of the radiographic image of the gallbladder was used to study the response of the gallbladder to cholecystokinin (CCK). A new observation was that the resting size of the gallbladder in each dog was variable during the six observations made. Despite the resting size difference, good dose response curves were obtained using 1/4, 1/2. 1, 2, and 4 units of CCK/kg. The relative reduction of gallbladder size from the resting state was considered the response. After truncal vagotomy, there was an increase in the mean resting size of each gallbladder which ranged from 22percnt; to 87percnt;. Progressive increase in gallbladder she did not occur when measurements at 3 weeks post-vagotomy were compared with those made at 7 months. After truncal vagotomy, the response to CCK was not altered. Endogenous CCK release secondary to exogenous CCK stimulation of gastric acid secretion was also studied and found not to be a significant factor in gallbladder contraction. It was thus felt that the secondary effect of gastric achlorhydria produced by truncal vagotomy did not invalidate the CCK dose response data.
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