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Gastrointestinal hormones are peptides released to circulation from endocrine cells as well as neurons in the gastrointestinal tract. More than 30 hormone genes are currently known to be expressed in the stomach and intestines, which makes the gut the largest endocrine organ in the body. Moreover, cell and molecular biology now makes it feasible to conceive gastrointestinal endocrinology under five general headings: 1) The structural homology groups the hormones into eight families, each of which is assumed to originate from a common ancestral gene; 2) the individual hormone gene often have multiple phenotypes due to alternative splicing of the primary transcript, tandem organization of the translational product or differentiated maturation of the prohormone. By a combination of these mechanisms, more than 100 different hormonally active peptides are released from the gastrointestinal tract; 3) in addition, gut hormone genes are also widely expressed outside the gut, some only in neurons and/or in endocrine cells, but others also in other extraintestinal cell-types; 4) the different cell types may express different hormonally active fragments of the same prohormone by variation in the cell-specific posttranslational processing. Finally, 5) endocrine cells, neurons, and spermatozoa display different cell-specific release of gut peptides, so the same peptide may act as a metabolic blood-borne hormone, as a neurotransmitter, as a long-acting growth factor, and as an acute fertility factor.

Publisher Summary This chapter discusses the tumor biology of gastrin and cholecystokinin (CCK) by giving a description of the normal biology of the gastrin and CCK systems followed by a discussion of the expression and growth stimulation of gastrin and CCK peptides in carcinomas, sarcomas, and benign tumors. The novel methods for the measurement of gastrin and CCK expression in experimental and clinical oncology have been mentioned. The single most important aspect in gastrin and CCK tumor biology is the possible involvement of gastrin in the development of several common carcinomas. Expression of the gastrin gene has been found not only in colorectal carcinomas, but also in bronchial, ovarian, pancreatic, and apparently some gastric carcinomas. Specific aspects of the association between gastrin or CCK, and cancer have been reviewed. However, because the emphasis has been on clinical correlations, a more comprehensive review including the basic aspects is needed.

The basal concentrations of sulfated and non-sulfated gastrins in serum were measured radioimmunochemically in healthy subjects and in normo- and hyper-gastrinemic diseases. The degree of sulfation in patients with duodenal and gastric ulcer, chronic pancreatitis, gallstone disease, and chronic renal failure were similar to that of healthy controls, in whom 37.7 +/- 1.9% (mean +/- SEM) of serum gastrins were sulfated. In eight patients with the Zollinger-Ellison syndrome 57 +/- 5.4% of the gastrins were sulfated (p less than 0.005, compared with controls). In patients with pernicious anemia (no. = 20) only 24.4 +/- 2.0% of the gastrins were sulfated (p less than 0.005, compared with controls). An inverse correlation (r = -0.63, p less than 0.01) was found between the degree of sulfation and the total gastrin concentration in pernicious anemia but not in gastrinoma patients. The results indicate that diseases with increased synthesis of gastrin are accompanied by an abnormal degree of sulfation.

Gastrin 17 (G17) is a potent stimulant of gastric acid secretion in vivo. In this study, the effects of G17 and some related peptides on intracellular free Ca2+ in isolated pig parietal cells were studied. Both G17 and the synthetic peptide pentagastrin increased intracellular free Ca2+ in a dose-dependent manner over the concentration range 10(-9) to 10(-6) M, suggesting a specific action. The EC50 values were 3 X 10(-8) M for G17 and 8 X 10(-8) M for pentagastrin. The N-terminal tridecapeptide of G17 [(1-13)G17] did not have any effect on intracellular free Ca2+, nor was it able to inhibit the action of G17. A glycine-extended gastrin [(5-17)G17-Gly)] elicited a small but significant increase in intracellular free Ca2+ although only at 10(-6) M. This increase was approximately 20% of that obtained with a similar concentration of G17. Sequential incubations with (5-17)G17-Gly and G17 showed that both peptides increased the intracellular free Ca2+ through the same mechanisms.