The effect of somatostatin analogs on secretion of growth, pancreatic, and gastrointestinal hormones in man

The potency and specificity of somatostatin (SS) and four of its analogs were compared in seven patients with pancreatic endocrine tumors. The analogs tested were [D-Trp⁸]-SS, [D-Trp⁸, D-Cys¹⁴]-SS, Des-Asn⁵-[D-Trp⁸, D-Ser¹³]-SS, and Des-(AA)^{1, 2, 4, 5, 12, 13}, [D-Trp⁸]-SS, and they did not show selective effects on the suppression of basal concentrations of GH, insulin, glucagon, pancreatic polypeptide, gastrin, gastric inhibitory peptide, motilin, enteroglucagon, or neurotensin. The observation that the potency of these analogs is similar to that of the parent molecule throws considerable light on the structure/activity relationship of the somatostatin molecule. Des-AA^{1, 2, 4, 5, 12, 13}, [D-Trp⁸]-SS has been reported to have a prolonged action when administered sc. When administered iv, however, this octapeptide analog was not long acting, suggesting that the prolonged action seen in the previous study was a result of delayed uptake from the injection site. An increment in plasma SS concentrations of 19 ± 3 pmol/liter suppressed basal concentrations of GH, insulin, glucagon, and several gastrointestinal hormones by more than 50%, suggesting that even small changes in plasma SS levels may be physiologically important.