The effect of hydrocortisone on limb regeneration in the bullfrog tadpole, Rana catesbeiana.

Tadpoles of the bullfrog Rana catesbeiana lose the ability to regenerate limbs amputated through the femur at a very early stage in development. Well-differentiated limbs which in other species can regenerate if amputated through the ankle, cannot in this species. Nonregenerating tadpole limbs either show rapid healing of the cut surface by connective tissue with no breakdown of skeletal structures, or the beginning of dedifferentiation in the cartilage. However, the cells of the rudimentary blastema that forms do not undergo proliferation; instead they become separated from the epidermis by the regrowth of the connective tissue layer which acts as a block to regeneration. This condition, termed the critical stage, is reached more often by animals that received injections of hydrocortisone than by control animals. Experimental animals furthermore, produced larger blastemata. No advanced regeneration could be obtained however.