Secretion of Gastrin

The most recently discovered means of secretion is autocrine release (C3, H9, S8), by which cells stimulate their own growth. Trophic peptides bind to specific receptors in the membranes of their own cells (Fig. 4, last box). Autocrine secretion is supposed to play a decisive role in tumor and cancer development. The first 

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The answer is d. (Hardman 7 pp 907—909J The main action of omeprazole is the inhibition of secretion of gastric acid Because it is a specific inhibitor of the proton pump (H+,K+,ATPase), other actions are secondary to the marked decline of acid secretion. As a result of the reduction of gastric acidity, there is increased secretion of gastrin leading to hyper-gastrinemia. 

NaHCOs and CaCOs can neutralize HCl rapidly, depending on particle size and crystal structure, and effectively. NaHCOs acts rapidly but absorption of unneutralized NaHCOs produces risks for alkalosis and sodium retention which may lead to edema, hypertension or heart failure. Also neutralized antacids may cause alkalosis by permitting the absorption of endogenous NaHCOs. Ca + may stimulate the secretion of gastrin and HCl and calcium-containing antacids have been associated with rebound acid hypersecretion. 

Gastric acid secretion is inhibited in the presence of acid itself. A negative feedback occurs when the pH approaches 2.5 such that further secretion of gastrin is inhibited until the pH rises. Ingested carbohydrates and fat also inhibit acid secretion after they reach the intestines several hormonal mediators for this effect have been proposed. The secretion of pepsinogen appears to parallel the secretion of H+, while the patterns of secretion of mucus and bicarbonate have not been well characterized. 

Bombesin 54 120,121), isolated from frog skin, is thought to have antidiuretic and antihypertensive properties. It stimulates the secretion of gastrin, pancreatic and gastric secretion, and causes contraction of the gallbladder. 

Nerve endings in the stomach secrete two stimulatory neurotransmitters acetylcholine and gastrin-releasing peptide. Their action is both direct on parietal cells and mediated through the secretion of gastrin from G cells and histamine from ECL cells. Gastrin acts on parietal cells directly and indirectly too, by stimulating the release of histamine. 

Maximal secretion of gastrin occurs at an antral pH of 5 to 7. At pH 2,5, secretion is reduced by about 80% maximal... 

C signal transduction pathway. Secretion of calcitonin is stimulated by hypercalcemia but the effect of the hormone on calcium transport appears to be secondary to increased phosphate uptake by target cells. The number and activity of osteoclasts are decreased, and urinary excretion of hy-droxyproline is decreased, Calcitonin may also inhibit release of calcium from the extracellular fluid calcium pool, but it increases calcium and phosphate excretion by renal tubules. Some tubular cells respond to calcitonin, PTH, and vasopressin, while others respond only to one or two of these hormones. In general, the actions of calcitonin in kidney and in bone are antagonistic to those of PTH. Calcitonin decreases secretion of gastrin and of gastric acid, and inhibits bile flow. 

Fig. 4. Four routes of cellular secretion of gastrin. Several other regulatory systems, wherein the same peptide acts as hormone, neurotransmitter, and growth factor, are also released as they occur in these four cell types. Autocrine and paracrine secretion are assumed to play decisive roles for the growth of malignantly transformed cells.

MEN type I is characterized by hyperparathyroidism, together with pituitary and pancreatic tumours. Hyper-calcaemia caused by excess PTH. secretion is the dominant feature in this syn-drt)me. The most common pituitary tumour is a non-functioning chromophobe adenoma which, although it dws not secrete a hormone itself, may have effects on the secretion of other anterior pituitary hormones. The most common pancreatic tumour in MEN type 1 is an islet cell tumour secreting gastrin. The secretion of gastrin may lead to gastric ulceration. 

Ciccotosto GD, McLeish A, Hardy KJ, Shulkes A (1995) Expression, processing and secretion of gastrin in patients with colorectal carcinoma. Gastroenterology 109 1142-1153... 

Gastric and pancreatic secretions Low levels of alcohol can stimulate the secretion of gastrin and histamine within the gut, hut higher levels above 20% tend to inhibit secretion and spirits can irritate gastric mucosa. Alcohol has been used as an appetite stimulant, but this is contraindicated in patients suffering from gastric ulceration or hyperacidity. Pancreatic secretions are also increased by ethanol, and chronic oversecretion can lead to pancreatitis. 

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