Recent interest has focused on the potential role of amylin in the pathogenesis of non-insulin-dependent diabetes mellitus (NIDDM). This 37-amino acid peptide is found in extracellular amyloid deposits in -5 0 % of pancreatic islets of patients with NIDDM and has been shown to inhibit skeletal muscle glycogen synthesis in vitro. Immunocytochemical studies have colocalized amylin and insulin within p-cell secretory granules in nondiabetic humans, provoking the following questions. Is amylin cosecreted with insulin? Are circulating amylin concentrations higher in patients with NIDDM either before or after food ingestion? To answer these questions, we developed a sensitive and specific immunoassay to measure plasma concentrations of amylin in humans. Use of this assay indicated that, in lean nondiabetic subjects, glucose ingestion resulted in an increase (P < 0.001) in the plasma concentration of amylin (from 2.03 ± 0.22 to 3.78 ± 0.39 pM) and insulin (from 48.3 ± 3.1 to 265 ± 44 pM). There was a significant correlation between the concentrations of insulin and amylin (r = 0.74, P < 0.001) and the increase in insulin and amylin concentration (r = 0.65, P < 0.005). Fasting concentrations of amylin did not differ in diabetic and weight-matched nondiabetic subjects and showed a similar pattern of change after ingestion of a mixed meal. We conclude that amylin is secreted in response to ingestion of either glucose or a mixed meal and circulates at concentrations that do not differ in patients with NIDDM and nondiabetic subjects. It remains to be determined whether amylin at physiological concentrations influences carbohydrate metabolism and if so whether its effects differ in diabetic and nondiabetic humans.

Experimental observations showed that the analogs [D-Trp2]- and [D-Phe2]methionine enkephalin amide were weakly active in releasing GH from rat pituitary in vitro. These observations were used to design more active GH-releasing factors. Conformational energy calculations were carried out, and energetically favored conformations of these polypeptides were found. Structural similarities as well as structural differences between active and inactive analogs were examined, and new sequences were predicted. Progressively more active analogs were designed, then synthesized, and tested. This cycle of steps was repeated, each time using structural and chemical concepts as design guides, until a series of very active analogs resulted. The most active analog to date, Tyr-D-Trp-Ala-Trp-D-Phe-NH2, was shown to release GH in vitro at 10-30 ng/ml medium, which is approximately 10(3) times more active than the two starting enkephalin-based analogs. From the structure-activity data, a mechanism for binding at the receptors is formulated, and a comparison is made between the structural relationships of the GH-releasing peptide analogs and the GH inhibitor, somatostatin.

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The effect of pancreastatin on the release of insulin, glucagon, and somatostatin was studied in the isolated perfused rat pancreas. After an initial equilibration period (-20 to 0 min) with a basal glucose concentration (3.3 mM), the pancreata were perfused with either 16.7 mM glucose (040 min) or with 20 mM arginine (0-20 min). Pancreastatin was introduced 10 min prior to and throughout the administration of the high glucose and arginine and continued during their perfusion. As expected, the glucose and the arginine augmented insulin and somatostatin release. Pancreastatin (1 and 10 nM) markedly suppressed the first phase of insulin release with both insulinogogues used, while the early somatostatin secretion was not significantly decreased. However, the peak incremental somatostatin response to arginine was reduced by 50% (P < 0.05). Conversely, the peptide (10 nM) tended to augment arginine-induced glucagon release. Pancreastatin (100 nM) also suppressed glucose-stimulated insulin release from isolated rat islets. These pancreastatin-mediated alterations in islet hormone release are reminiscent of those known to characterize non-insulin-dependent diabetes. Therefore, the significance of pancreastatin in islet physiology and pathophysiology deserves special consideration.Pancreastatin, a 49-residue peptide with a C-terminal glycine amide, was isolated from porcine pancreatic extracts by using the amide structure as a marker during the isolation procedure (1). It has been shown that pancreastatin inhibited the early phase of glucose-induced insulin release from the isolated perfused rat pancreas (1). This study confirms and extends this finding by demonstrating that pancreastatin significantly suppresses arginine as well as glucose-stimulated insulin release. Furthermore, the peak somatostatin response to arginine decreased while the peptide seemed to augment arginine-induced glucagon release. MATERIALS AND METHODSChemical Synthesis of Pancreastatin. The chemical synthesis of pancreastatin was performed manually by using the stepwise solid-phase synthetic approach as described by Merrifield (2). The 49-residue peptide amide was prepared by using p-methylbenzhydrylamine resin (3) and amino acid derivatives with conventional protection groups. Side-chain protecting groups used were aspartic acid [p- CH2Cl2, and (viii) coupling of the amino acid derivative with dicyclohexylcarbodiimide for 90 min. Each coupling step was monitored by a ninhydrin test (4). In some steps, a double coupling was carried out to improve the yields. The peptide was deprotected and cleaved from the resin by hydrofluoric acid, and the lyophilized crude peptide material obtained was purified by anion-exchange chromatography on a DEAESephadex A-25 column (AB Pharmacia, Uppsala, Sweden) and by preparative HPLC on a uBondapak C18 column (Waters Associates). The synthetic pancreastatin thus obtained was found to be homogenous and to coelute in HPLC with the native peptide. In the experiments described below on the biological effects...