Hooc

Octreotide

Octreotide

FIGURE 8-10 (A) Structures of preprosomatostatin, somatostatin 28 (SS-28), and somatostatin 14 (SS-14). The preprosomatostatin has 116 amino acids; it is cleaved to SS-28 and then, under some circumstances, to SS-14. However, both SS-14 and SS-28 are biologically active. B illustrates the disulfide structure of SS-14 and the synthetic, long-acting SS-14 analog octreotide; this drug is used to suppress SS-14 secretion in acromegaly and in gut endocrine tumors. [Information abstracted from Weiss, J. A. H. (1995). Somatostatin. In "Endocrinology" (L. J. DeGroot, M. Besser, H. G. Burger, J. L. Jameson, D. L. Loriaux, J. C. Marshall, W. D. Odell, J. T. Potts, Jr., and A. H. Rubenstein, eds.), Vol 1, Chapter 17, pp. 266-279. W. B. Saunders, Philadelphia PA.]

FIGURE 8-10 (A) Structures of preprosomatostatin, somatostatin 28 (SS-28), and somatostatin 14 (SS-14). The preprosomatostatin has 116 amino acids; it is cleaved to SS-28 and then, under some circumstances, to SS-14. However, both SS-14 and SS-28 are biologically active. B illustrates the disulfide structure of SS-14 and the synthetic, long-acting SS-14 analog octreotide; this drug is used to suppress SS-14 secretion in acromegaly and in gut endocrine tumors. [Information abstracted from Weiss, J. A. H. (1995). Somatostatin. In "Endocrinology" (L. J. DeGroot, M. Besser, H. G. Burger, J. L. Jameson, D. L. Loriaux, J. C. Marshall, W. D. Odell, J. T. Potts, Jr., and A. H. Rubenstein, eds.), Vol 1, Chapter 17, pp. 266-279. W. B. Saunders, Philadelphia PA.]

14, and 15-15). Endothelins are produced by a variety of cells in the GI tract, including plexus nerves and mucosal cells. The precise biological role of the endothelins in the GI tract remains to be elucidated.

O. Galanin

Human galanin is a 30-amino-acid peptide (see Figure 8-12) derived from a prepro form of 201 amino acids. Galanin does not have any structural homology to other GI hormones. Galanin is found in neurons associated with the submucosa. As yet, the physiologi cal role of galanin is not clearly defined. There is some evidence that it can inhibit the release of somatostatin, insulin, pancreatic polypeptide, and neurotensin.

P. Vasoactive Intestinal Peptide (VIP)

Vasoactive intestinal peptide (VIP) is a straight chain 28-amino-acid intestinal peptide. VIP has extensive structural homology with both glucagon and secretin, as well as some homology with GIP (see Figure 8-6). VIP occurs widely in both the intestinal and nervous systems of many mammals and lower animals.

TABLE 8-7 Properties of Somatostatin 28 (SS-28) and Somatostatin 14 (SS-14)"

Relative amounts (%)

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