A 63-yrs-old woman has surgery for pancreatico cutaneous fistula develops after a distal pancreatectomy and drainage of a pseudocyst. Somatostatin is prescribed. Somatostatin contributes to which of the following processes?
|A||Inhibition of adrenocortical cells|
|B||Inhibition of pancreatic D cells|
|C||Stimulation of antral gastrin cells|
|D||Stimulation of secretin-producing cells in the duodenum|
a. Two forms of somatostatin are synthesized. They are referred to as SS-14 and SS-28, reflecting their amino acid chain length.
b. Both forms of somatostatin are generated by proteolytic cleavage of prosomatostatin, which itself is derived from preprosomatostatin.
c. Two cysteine residules in SS-14 allow the peptide to form an internal disulfide bond.
d. Five stomatostatin receptors have been identified and characterized, all of which are members of the G protein-coupled receptor superfamily.
Each of the receptors activates distinct signalling mechanisms within cells, although all inhibit adenylyl cyclase. Four of the five receptors do not differentiate SS-14 from SS-28.
e. Cells within pancreatic islets secrete insulin, glucagon and somatostatin. Somatostatin appears to act primarily in a paracrine manner to inhibit the secretion of both insulin and glucagon.
f. It also has the effect in suppressing pancreatic exocrine secretions, by inhibitingcholecystokinin-stimulated enzyme secretion and secretin-stimulated bicarbonate secretion.
g. Somatostatin is secreted by scattered cells in the GI epithelium, and by neurons in theenteric nervous system. It has been shown to inhibit secretion of many of the other GI hormones, including gastrin, cholecystokinin, secretin and vasoactive intestinal peptide.
h. In addition to the direct effects of inhibiting secretion of other GI hormones, somatostatin has a variety of other inhibitory effects on the GI tract, which may reflect its effects on other hormones, plus some additional direct effects.
i. Somatostatin suppresses secretion ofgastric acid and pepsin, lowers the rate of gastric emptying, and reduces smooth muscle contractions and blood flow within the intestine. Collectively, these activities seem to have the overall effect of decreasing the rate of nutrient absorption