The manner in which gastrin causes an increase in the activity of the smooth muscles of the stomach is rather unknown. However, recent studies have demonstrated that the smooth muscle cells of the stomach and the intestine are affected with the gastrin secretion (Bowen, 2003). The parietal cells in dog contain about 44, 000 receptors. It has been demonstrated that the acid secretion is blocked following immuno-neutralization of gastrin.
This occurs after peptides are given intragastrically (Bowen, 2003). Gastrin may play a role in the development of duodenal ulcers, as it is fount that such patients have a higher gastrin level for a long period of time (Ganong, 2005). In two conditions, namely, Zolinger-Ellison syndrome and Hypergastrinemia, the secretions of gastrin are higher than normal.
In these conditions, certain gastrin-producing tumors are produced, known as ‘gastrinomas’, which cause the release of excessive quantity of gastrin, in the pancreas and the duodenum. Due to this excessive amount of secretion, tumors are formed in the stomach and the duodenum (Sargret, 2007, & Bowen, 2003). CCK or ‘Cholecystokinin’ is one of the hormones that get attached to the gastrin receptors. These receptors are also known as CCK-B receptors, and belong to the G-protein coupled receptor family.
When gastrin binds to the receptors, it encourages an increase in the levels of calcium ions within the cells, synthesis of inositol phosphate and activation of protein kinase – C (Bowen, 2003, Ganong, 2005 & Feldman, 2006). Cholecystokinin-pancreozymin is primary known as ‘cholescytokinin’ (CCK). It was earlier thought that cholecytokinin helped to increase the contraction of the gall bladder. On the other hand, the pancreozymin hormone (PZ) was thought to increase the production of the enzymes present in pancreatic juice.
However, recent studies have demonstrated that CCK-PZ is emitted from the upper portion of the small intestine (especially the duodenum), by certain specialized epithelium cells, known as ‘I-cells’. CCK has activity of both the earlier thought CCK-PZ. Both gastrin and CCK-PZ have microheterogeneity (occur in variety of tissues and fluids of peptides that may be of different lengths) and macroheterogeneity (it refers to the variation of the single amino acids of different molecular structures) properties (Ganong, 2005).