A cardioactive factor in human plasma with positive inotropic and positive chronotropic activities.

A cardioactive factor with a molecular weight of about 100,000 and that exhibits positive inotropic and positive chronotropic activity on isolated guinea pig atria has been found in human plasma. The positive inotropic activity is less stable than the positive chronotropic activity. The two activities move together in cation- and anion-exchange chromatography, gelfiltration chromatography, and polyethylene glycol precipitation. They may be associated with a single large polypeptide or with different subunits of a complex protein.