[Interstitial growth-inhibiting substances in the heart]

Extracts of heart atriums and ventriculi of adult hens and rats were injected in 11-day old chick embryos. The extract of hen heart ventriculi causes a considerable decrease in colchycine mitotic index as well as in the index of labeled nuclei. The ventricular extract prolongs the duration of mitosis (M-phase) to a certain degree. The extract of atriums does not inhibit proliferation activity of heart cells and even stimulated it to some extent. Rat heart extracts act like those of hen. The growth-inhibiting substances (chalones) of heart reveal no species-specificity, though being to a great degree tissue-specific.