Gastric digestion

CCK is found in the digestive tract and the central and peripheral nervous systems. In the brain, CCK coexists with DA. In the peripheral nervous system, the two principal physiological actions of CCK are stimulation of gaU. bladder contraction and pancreatic enzyme secretion. CCK also stimulates glucose and amino acid transport, protein and DNA synthesis, and pancreatic hormone secretion. In the CNS, CCK induces hypothermia, analgesia, hyperglycemia, stimulation of pituitary hormone release, and a decrease in exploratory behavior. The CCK family of neuropeptides has been impHcated in anxiety and panic disorders, psychoses, satiety, and gastric acid and pancreatic enzyme secretions. 

Ketoconazole. For treatment of systemic mycoses with amphotericin B or miconazole, the patient must be admitted to a hospital. This is not always possible, particularly in areas where systemic mycoses occur frequently, nor is it always desirable, because of the expense. For these reasons, it was desirable to find an antimycotic that combined safety and broad-spectmm activity with oral adraiinistration. Ketoconazole (10), which is orally active, met most of these requirements. This inhibitor of the ergosterol biosynthesis is an A/-substituted imidazole, that differs from its precursors by the presence of a dioxolane ring (6,7). Ketoconazole is rapidly absorbed in the digestive system after oral adrninistration. Sufficient gastric acid is required to dissolve the compound and for absorption. Therefore, medication that affects gastric acidity (for example, cimetidine and antacids) should not be combined with ketoconazole. 

Agricultural Use. Citric acid and its ammonium salts are used to form soluble chelates of iron, copper, magnesium, manganese, and zinc micronutrients in Hquid fertilizers (97—103). Citric acid and citrate salts are used in animal feeds to form soluble, easily digestible chelates of essential metal nutrients, enhance feed flavor to increase food uptake, control gastric pH and improve feed efficiency. 

FIGURE 2.16 pH versus enzymatic activity. The activity of enzymes is very sensitive to pH. The pH optimum of an enzyme is one of its most important characteristics. Pepsin is a protein-digesting enzyme active in the gastric fluid. Trypsin is also a proteolytic enzyme, but it acts in the more alkaline milieu of the small intestine. Lysozyme digests the cell walls of bacteria it is found in tears. 

There are two main classes of proteolytic digestive enzymes (proteases), with different specificities for the amino acids forming the peptide bond to be hydrolyzed. Endopeptidases hydrolyze peptide bonds between specific amino acids throughout the molecule. They are the first enzymes to act, yielding a larger number of smaller fragments, eg, pepsin in the gastric juice and trypsin, chymotrypsin, and elastase secreted into the small intestine by the pancreas. Exopeptidases catalyze the hydrolysis of peptide bonds, one at a time, fi"om the ends of polypeptides. Carboxypeptidases, secreted in the pancreatic juice, release amino acids from rhe free carboxyl terminal, and aminopeptidases, secreted by the intestinal mucosal cells, release amino acids from the amino terminal. Dipeptides, which are not substrates for exopeptidases, are hydrolyzed in the brush border of intestinal mucosal cells by dipeptidases. 

It will be appreciated that the delivery of nutrients from foods is attenuated by the structure of the food and the way in which it is digested. Thus, delivery from the food structure occurs over the same timescale as gastric emptying. Carotenoids, and other compounds, isolated from the food structure are generally emptied from the stomach and absorbed more rapidly. These different rates of delivery may have profound effects on subsequent metabolism. 

Phytochemicals influence other digestive secretions. Several traditional herbal medicines stimulate gastric mucous secretion, providing protection (Sairam et al., 2001). The secretion and recycling of bile are also responsive to phytochemicals. The way in which certain polysaccharides increase fecal concentrations of bile acids (DalT Angelo and Lino van Poser, 2000) and thereby influence recycling and synthesis is particularly noteworthy. 

Carotenoids and urino-digestive cancers — On the whole, findings from epidemiological studies did not demonstrate a protective role of carotenoids against colorectal, gastric, and bladder cancers. Indeed, most prospective and case-control studies of colorectal cancer showed no association with dietary intake or plasma level of most carotenoids. - Only lycopene and lutein were shown to be protective against colorectal cancer. Otherwise, findings from the ATBC study s showed no effect of P-carotene supplementation on colorectal cancer. 

Takeuchi, K., Ueshima, K., Hironaka, Y., Fujioka, Y., May-sumoto, J. and Okabe, S. (1991a). Oxygen free radicals and lipid peroxidation in the pathc nesis of gastric mucosal lesions induced by indomethadn in rats. Relation to gastric hypermotility. Digestion 49, 175-184. 

Gastric Retention of Enzyme-Digestible Hydrogels in the Canine Stomach under Fasted and Fed Conditions... 

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