title: Gastrin-releasing peptides from Xenopus laevis: purification, characterization, and myotropic activity.
abstract: Two molecular forms of gastrin-releasing peptide (GRP) were isolated from an extract of the intestine of the tetraploid frog Xenopus laevis. The primary structure of GRP-1 (APTSQQHTEQ(10)LSRSNINTRG(20) SHWAVGHLM.NH(2)) differs from that of GRP-2 by a single amino acid substitution (Asn(15)--> Thr(15)). GRP-(20-29) peptide (neuromedin C) was also isolated from the extract. Synthetic GRP-1 produced concentration-dependent contractions of longitudinal smooth muscle strips from Xenopus cardiac stomach (pD(2) = 8.93 +/- 0.32; n = 6). The responses were unaffected by tetrodotoxin, atropine, and methysergide, indicating a direct action of the peptide on smooth muscle cells. GRP-1 elicited concentration-dependent relaxations of precontracted (5 microM carbachol) circular smooth muscle strips from the same region (pD(2) = 8.96 +/- 0.21; n = 8). The responses were significantly (P < 0.05) attenuated (71 +/- 24% decrease in maximum response; n = 6) by indomethacin, indicating mediation, at least in part, by prostanoids. Despite the fact that Xenopus GRP-1 differs from pig GRP at 15 amino acid sites, both peptides are equipotent and equally effective for both contractile and relaxant responses, demonstrating that selective evolutionary pressure has acted to conserve the functional COOH-terminal domain in the peptide. The data suggest a physiologically important role for GRP in the regulation of gastric motility in X. laevis.
authors.affiliation: Regulatory Peptide Center, Department of Biomedical Sciences, Creighton University Medical School, Omaha, NE 68178-0405, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Kim
authors.lastname: Johansson A
authors.forename: S
authors.initials: S
authors.lastname: Holmgren
authors.forename: J M
authors.initials: JM
authors.lastname: Conlon
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001839:Bombesin / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019886:Gastrin-Releasing Peptide / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D005755:Gastrins / Q000378:metabolism*; D005768:Gastrointestinal Hormones / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000494:pharmacology; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008969:Molecular Sequence Data; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D013270:Stomach / Q000187:drug effects / Q000502:physiology; D013552:Swine; D014982:Xenopus laevis
chemical_list: D005755:Gastrins; D005768:Gastrointestinal Hormones; D010446:Peptide Fragments; C434742:gastrin-releasing peptide 1; C434743:gastrin-releasing peptide 2; D019886:Gastrin-Releasing Peptide; C040794:neuromedin C; D001839:Bombesin; D007213:Indomethacin