GLP-1 and related peptides cause concentration-dependent relaxation of rat aorta through a pathway involving KATP and cAMP

increasing evidence from both clinical and experimental studies indicates that the insulin-releasing hormone, glucagon-like peptide-1 (GLP-1) may exert additional protective/reparative effects on the cardiovascular system. The aim of this study was to examine vasorelaxant effects of GLP-1(7-36)amide, three structurally-related peptides and a non-peptide GLP-1 agonist in rat aorta. Interestingly, all GLP-1 compounds, including the established GLP-1 receptor antagonist, exendin (9-39) caused concentration-dependent relaxation. Mechanistic studies employing hyperpolarising concentrations of potassium or glybenclamide revealed that these relaxant effects are mediated via specific activation of ATP-sensitive potassium channels. Further experiments using a specific membrane-permeable cyclic AMP (cAMP) antagonist, and demonstration of increased cAMP production in response to GLP-1 illustrated the critical importance of this pathway. These data significantly extend previous observations suggesting that GLP-1 may modulate vascular function, and indicate that this effect may be mediated by the GLP-1 receptor. However, further studies are required in order to establish whether GLP-1 related agents may confer additional cardiovascular benefits to diabetic patients. (c) 2008 Elsevier Inc. All rights reserved.

Amolopkinins W1 and W2 – novel bradykinin-related peptides (BRPs) from the skin of the Chinese torrent frog, Amolops wuyiensis: antagonists of bradykinin-induced smooth muscle contraction of the rat ileum.

Bradykinin-related peptides (BRPs) represent one of the most widespread and closely studied families of amphibian defensive skin secretion peptides. Apart from canonical bradykinin (RPPGFSPFR) that was first reported in skin extracts of the European brown frog, Rana temporaria, many additional site-substituted, N- and/or C-terminally extended peptides have been isolated from skin extracts and secretions from representative species of the families Ranidae, Hylidae, Bombinatoridae and Leiopelmatidae. The most diverse range of BRPs has been found in ranid frog skin secretions and this probably reflects the diversity and number of species studied and their associated life histories within this taxon. Amolops (torrent or cascade frogs) is a genus within the Ranidae that has been poorly studied. Here we report the presence of two novel BRPs in the skin secretions of the Chinese Wuyi Mountain torrent frog (Amolops wuyiensis). Amolopkinins W1 and W2 are dodecapeptides differing in only one amino acid residue at position 2 (Val/Ala) that are essentially (Leu1, Thr6)-bradykinins extended at the N-terminus by either RVAL (W1) or RAAL (W2). Amolopkinins W1 and W2 are structurally similar to amolopkinin L1 from Amolops loloensis and the major BRP (Leu1, Thr6, Trp8)-bradykinin from the skin of the Japanese frog, Rana sakuraii. A. wuyiensis amolopkinins were separately encoded as single copies within discrete precursors of 61 amino acid residues as deduced from cloned skin cDNA. Synthetic replicates of both peptides were found to potently antagonize the contractile effects of canonical bradykinin on isolated rat ileum smooth muscle preparations. Amolopkinins thus appear to represent a novel sub-family of ranid frog skin secretion BRPs.

Kassina senegalensis skin tachykinins: Molecular cloning of kassinin and (Thr2, Ile9)-kassinin biosynthetic precursor cDNAs and comparative bioactivity of mature tachykinins on the smooth muscle of rat urinary bladder

Tachykinins are among the most widely-studied families of regulatory peptides characterized by a highly-conserved C-terminal -Phe-X-Gly-Leu-Met.amide motif, which also constitutes the essential bioactive core. The amphibian skin has proved to be a rich source of these peptides with physalaemin from the skin of Physalaemus fuscomaculatus representing the archetypal aromatic tachykinin (X = Tyr or Phe) and kassinin from the skin of Kassina senegalensis representing the archetypal aliphatic tachykinin in which X = Val or Ile. Despite the primary structures of both mature peptides having been known for at least 30 years, neither the structures nor organizations of their biosynthetic precursors have been reported. Here we report the structure and organization of the biosynthetic precursor of kassinin deduced from cDNA cloned from a skin secretion library. In addition, a second precursor cDNA encoding the novel kassinin analog (Thr2, Ile9)-kassinin was identified as was the predicted mature peptide in skin secretion. Both transcripts exhibited a high degree of nucleotide sequence similarity and of open-reading frame translated amino acid sequences of putative precursor proteins. The translated preprotachykinins each consisted of 80 amino acid residues encoding single copies of either kassinin or its site-substituted analog. Synthetic replicates of each kassinin were found to be active on rat urinary bladder smooth muscle at nanomolar concentrations. The structural organization of both preprotachykinins differs from that previously reported for those of Odorrana grahami skin indicating a spectrum of diversity akin to that established for amphibian skin preprobradykinins.