cholecystokinin-39 and gastrin-17

A new specific method for determination of cholecystokinin, CCK-8, and CCK-33, 39 in rat plasma is described. Plasma CCK radioimmunoassay (RIA) is difficult, because of cross-reactivity with gastrin. In the rat, problems because of difficulties in separating gastrin from CCK by high performance liquid chromatography (HPLC) exist. These were solved by enzyme digestion of gastrin before HPLC separation of molecular variants of CCK from gastrin fragments. Cholecystokinin immunoreactive forms in the HPLC fractions were determined by an antibody, which recognises the carboxyl terminus of CCK and gastrin. Fasting concentrations of small (CCK-8) and large (CCK-33, 39) molecular forms of CCK averaged 1.9 (0.3) pM and were raised to 13.4 (3.8) pM in rats fed ad libitum. Cholecystokinin in lactating rats rose two-fold after suckling, compared with 2.8 fold in response to feeding. The basal ratio between CCK-8 and CCK-33, 39 was approximately 1:1, but increased in favour of CCK-8 after feeding and in response to suckling. Gastrin like immunoreactivity measured in unextracted plasma was found to rise after feeding, but was unchanged in response to suckling.

Topics: Animals; Cholecystokinin; Chromatography, High Pressure Liquid; Eating; Female; Gastric Mucosa; Gastrins; Intestinal Mucosa; Lactation; Methods; Pregnancy; Protein Precursors; Radioimmunoassay; Rats; Rats, Inbred Strains; Serine Endopeptidases; Sincalide

Molecular heterogeneity between cholecystokinin (CCK) present in humans and that present in the pig has been proposed. We recently demonstrated that CCK-8 exists in humans in form identical to the porcine peptide. The aims of this work were to evaluate the presence in human plasma of CCK forms larger than CCK-8 and to compare them with the well-characterized porcine forms. Antiserum (no. 4899) was raised in a New Zealand white rabbit immunized with porcine CCK-33 that had specificity for the 7 to 21 region of that peptide and that recognized molecules present in human plasma. To characterize these, postprandial human plasma was applied to an immunoaffinity column generated with this antiserum. Adsorbed peptides were eluted, concentrated on an octadecylsilane cartridge, separated by reversed-phase HPLC and gel filtration chromatography, and screened by cross-reacting and specific CCK and gastrin radioimmunoassays and CCK bioassay by quantification of amylase release by rat pancreatic acini. Two peptides were consistently identified that possessed CCK-like but not gastrin-specific immunoreactivity and CCK-like biological activity. These appeared to be similar in size to CCK-33 and intermediate in size between CCK-33 and CCK-8. Though analogous to porcine CCK based on antibody cross-reactivity and biological activity, the human peptides were heterogeneous from the porcine peptides based on differing chromatographic behavior.

Topics: Amylases; Animals; Antibody Specificity; Cholecystokinin; Chromatography, Gel; Chromatography, High Pressure Liquid; Eating; Female; Gastrins; Humans; Male; Molecular Weight; Peptide Fragments; Radioimmunoassay; Rats; Receptors, Cholecystokinin; Sincalide; Swine

Histamine accumulated in the ligated vagus nerve of the rat, both above and below the ligature; maximum accumulation was after 4 h. The finding is suggestive of axonal flow. Further evidence for histamine in peripheral nerves was obtained in experiments showing that the guinea-pig gut wall could be labelled with [3H]histamine. The experiments were carried out with isolated strips of stomach wall and taenia coli. Electrical stimulation released [3H]histamine from these specimens. The release could be blocked by Ca2+-free medium or by tetrodotoxin. The release was unaffected by vagal denervation or chemical sympathectomy (6-hydroxydopamine) but prevented by reserpinization. Gastrin-17 and cholecystokinin-39 released radioactivity by a tetrodotoxin-sensitive mechanism. The possible existence of a gastrin/cholecystokinin-sensitive neuronal pool of histamine in the gut wall offers a new perspective on the postulated role of histamine as a physiological stimulant of gastric acid secretion and might explain why H2-receptor antagonists block gastrin-stimulated acid secretion.

Topics: Animals; Cholecystokinin; Colon; Electric Stimulation; Gastrins; Guinea Pigs; Histamine; Neurons; Peptide Fragments; Stomach; Synaptic Transmission; Vagus Nerve