Weak bases inhibit cleavage and embryogenesis in amphibians and echinoderms.

The action of weak bases was studied on the early embryonic development of a number of species. Gastrulation was disrupted in the frog, Xenopus laevis, the newt, Pleurodeles watlii, the sea urchins, Paracentrotus lividus and Sphaerechinus granularis and the starfish, Asterias rubens. This required only submillimolar amounts of either NH+4 (pH 9.0) or procaine (pH 8.2). At higher concentrations even early cell division was inhibited in all the species with furrow regression particularly noticeable in Xenopus eggs. A similar action of the weak bases on early development, the lack of any action at lower extracellular pH, and the counteracting action of NH+4 on acidity-induced disruption of sea urchin development, all implicate an elevation of intracellular pH. However, a more direct intracellular action of the weak bases cannot be ruled out.