Acclimation of the euryhaline toad Bufo viridis to hyperosmotic solution (NaCl, urea and mannitol)

Bufo viridis were acclimated to hyperosmotic solutions of NaCl, urea or mannitol. The toads could not be acclimated to mannitol solutions of osmotic strength higher than 300 mosmol kg-1 H2O, but could be acclimated easily to NaCl and urea higher than 500 mosmol kg-1 H2O. Water uptake diminished under mannitol acclimation while the apparent osmotic permeability under NaCl and urea acclimation increased. Urea and sodium influx across the isolated skin changed inversely upon hyperosmotic acclimation, but they did not seem to depend on one another. The adaptational advantages of the observed changes are discussed.