Gastrin-releasing peptides from Xenopus laevis: Purification, characterization, and myotropic activity

Joseph B. Kim, Ågot Johansson, Susanne Holmgren, J. Michael Conlon

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8 Citations (Scopus)


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 (APTSQQHTEQ10LSRSNINTRG20SHWAVGHLM.NH2) differs from that of GRP-2 by a single amino acid substitution (Asn15→ Thr15). 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 (pD2 = 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 pre-contracted 5 μM carbachol) circular smooth muscle strips from the same region (pD2 = 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.

Original languageEnglish
Pages (from-to)R902-R908
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number3 50-3
Publication statusPublished (in print/issue) - 2001


  • Amphibian
  • Neuromedin C
  • Prostanoid
  • Stomach


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