Isolation and structure of a new active peptide xenopsin on rat stomach strip and some biogenic amines in the skin of Xenopus laevis.

Abstract

A new active peptide xenopsin was obtained from the skin of X. laevis, possessing a potent contractile activity on rat stomach strip in vitro. The amino acid sequence of xenopsin is pyrGlu-Gly-Lys-Arg-Pro-Trp-Ile-Leu-OH. The contractile responses on a rat stomach strip were proportional to the peptide doses. This peptide also had a moderate contractile activity on guinea-pig ileum but the response was not reproducible. I.v. injection of this peptide lowered arterial blood pressure of the anesthetized rat but a prompt and intense tachyphylaxis was observed. Xenopsin and several of its analogous peptides were synthesized and their biological activities were determined. Essential sequence that displayed the activity was Arg-Pro-Trp-Ile-Leu-OH. In addition to xenopsin and caerulein, the skin of X. laevis contained biological active amines, serotonin, bufotenidine and N-methylserotonin.