The release of rat intestinal cholecystokinin after oral trypsin inhibitor measured by bio‐assay.

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Abstract
The distribution, molecular form and release of cholecystokinin (CCK)-like activity in extracts of rat small intestine was studied with an in vitro gallbladder bioassay. In contrast to the reported heterogeneity of CCK-like immunoreactivity in the intestine, only a single molecular form of CCK-like activity was detected using the bioassay. This CCK-like activity eluted from Sephadex G50 after the triacontriapeptide of cholecystokinin (CCK33) and before cholecystokinin octapeptide (CCK8). This CCK-like actiity, which corresponded to an approximate MW of 2500, may represent the 22 amino acid peptide of CCK (CCK22). The bioassay peak of CCK-like activity had pancreozymin activity and CCK/gastrin C terminal immunoreactivity. The CCK-like activity was readily extracted from the small intestine at neutral pH, but subsequent treatment with cold 0.5 M-acetic acid extracted further CCK-like activity of the same molecular form as that recovered under neutral conditions. The bioassay detected no CCK-like activity, nor was pancreozymin-like activity found in fractions corresponding to CCK33 or CCK8 after Sephadex G50 chromatography of rat intestinal extracts. Oral trypsin inhibitor was a potent stimulus for the release of CCK-like activity from the upper small intestine of the rat. After oral trypsin inhibitor release, CCK-like activity was rapidly resynthesized.