The effect of diterpenoidic diacylglycerols on tentacle regeneration in Hydra vulgaris.

1. The effect of two ichthyotoxic diterpenoid diacylglycerols, verrucosins A and B, previously isolated from the mantle of a marine nudibranch mollusc, were studied on Hydra vulgaris tentacle regeneration. 2. A potent effect was found for both verrucosins in the low nanomolar range; the rank of potency observed was analogous to that reported for diglycerid activation of protein kinase C and to that found for verrucosin activation of this enzyme. 3. In the high nanomolar range, the two verrucosins were found to be toxic to Hydra vulgaris. 4. Verrucosin B-induced toxicity and tentacle regeneration were found to be dependent on [Ca2+] in the assay medium.