An uncommon inotropically active peptide from dog blood plasma

An octapeptide possessing inotropic activity has been isolated from heparinised dog blood plasma. It was found to be composed of seven isoleucine and one glycine residues and an as yet unidentified compound (X). The aminoacid sequence of its peptide chain was elucidated as iLeu. iLeu. iLeu, iLeu. Gly. iLeu. iLeu. The effect of this peculiar peptide compound on the dog heart papillary muscle was found to parallel that of adrenaline calculated on a Mole/Mole basis. The activity of the peptide compound was destroyed by mineral acid hydrolysis.