Cholecystokinin in pig plasma: release of components devoid of a bioactive COOH-terminus.

Using radioimmunoassays specific for different sequences of cholecystokinin (CCK), we studied the intestinal release of CCK in pigs. After stimulation by intraduodenal infusion of HCl, plasma CCK concentrations, measured with an antiserum specific for the sulfated, bioactive sequence of CCK, increased from 1.4 +/- 0.7 to 42.7 +/- 11.7 pM in portal plasma and from 0.5 +/- 0.3 to 12.3 +/- 1.5 pM in peripheral plasma. The concentrations measured with an antiserum specific for the NH2-terminal sequence 5-10 of CCK-33 were considerably higher, increasing from 64 +/- 17 to 139 +/- 14 pM in portal plasma and from 69 +/- 7 to 102 +/- 9 pM in peripheral plasma. Chromatography suggested that the NH2-terminal immunoreactivity consisted of large CCK fragments devoid of the bioactive COOH-terminal octapeptide, i.e., desocta and/or desnona CCK-58, CCK-39, and CCK-33. The bioactive forms in both portal and peripheral plasma comprised CCK-58-, CCK-33-, CCK-22-, CCK-12-, and CCK-8-like forms. Generally, the CCK-22-like component predominanated, but although CCK-8 was more abundant than CCK-33 in portal plasma, these forms occurred in equal amounts in peripheral plasma. Large amounts of NH2-terminal immunoreactivity were also found in the venous effluent of the isolated perfused duodenum after stimulation with gastrin-releasing peptide; the venous perfusate contained mainly CCK-22- and CCK-8-like material, which together constituted greater than 80% of the bioactive CCK components. Both duodenal and jejunal mucosa contained components resembling NH2-terminal fragments as well as large amounts of intact CCK-58 and CCK-33.(ABSTRACT TRUNCATED AT 250 WORDS)