DIFFERENTIAL PROCESSING OF PROVASOTOCIN - RELATIVE INCREASE OF HYDRIN-2 (VASOTOCINYL-GLY) IN AMPHIBIANS ABLE TO ADAPT TO AN ARID ENVIRONMENT

Hydrin 2 (vasotocinyl-Gly) is an intermediate in pro-vasotocin process ing found, along with vasotocin, only in the neurohypophysis of anuran amphibians. It increases cutaneous water permeability in the frog and is likely involved in neuroendocrine control of osmoregulation. The r elative amounts of vasotocin and hydrin 2 stored in neurohypophysis ha ve been measured on the one hand in amphibian species known not to ada pt in dry areas, on the other hand in two species, Bufo regularis (Afr ica) and Bufo viridis (Near-East) able to survive in an arid environme nt. In the first group, the proportions of the two peptides are approx imately equal whereas in the two toads the molar ratio hydrin 2 to vas otocin reaches 2. The ratio does not appear to vary significantly when these toads are either submitted to dehydration or placed in saline s olutions. Predominance of hydrin 2 suggests an adaptive decrease of th e activity of the alpha-amidating enzymatic system involved in the con version of vasotocinyl-Gly into mature amidated vasotocin.