Inotropic responses of the isolated frog ventricle to serum

A study has been made of the effects of newborn calf-serum on the isolated frog ventricle. Preparations were superfused with solutions containing different concentrations of serum and the changes in contractility measured. Ordinary calf-serum evoked a dose-dependent increase in contractile force which was unaffected by adrenergic receptor antagonists (propranolol and phentolamine). Serum which was either used in growing HeLa cells or incubated with chymotrypsin failed to elicit a positive inotropic response. However, if prostaglandin-like materials were extracted from the serum then its ability to potentiate the twitch remained unaltered. These results suggest that the cardioactive-factor present in calf-serum is most probably related to a polypeptide, and possibly a growth factor.