Tumor-promoting phorbol esters and mezerien induce contraction in hydra

12-O-tetradecanoyl phorbol-13-acetate (TPA, 1-100 ng/ml) induced a reversible contraction in the hydra, Hydra japonica. Another tumor-promoting phorbol ester, phorbol-12, 13-didecanoate (PDD), and mezerein also induced contraction, but non-tumor-promoting derivatives such as 4alpha-PDD and phorbol did not.