The protective action of zinc against the deleterious effects of cadmium in the regenerating forelimb of the adult newt, Notophthalmus viridescens.

Forelimbs of adult male newts (Notophthalmus viridescens) were amputated and immediately dipped in cadmium nitrate for 2 minutes; in addition, some of the newts were injected with zinc chloride 24 hours prior to, or 24 hours after amputation. Dipping the amputated forelimb of a newt in a solution of 0.4 M cadmium nitrate completely inhibited or retarded regeneration throughout the 65 days of observation. Other effects of cadmium administration included erythema of the limb, an extensive protrusion of the humerus, and in some cases atypical differentiation of regenerates. When zinc chloride was injected (0.04 mg/g of body weight) intraperitoneally into the newt 24 hours prior to limb amputation and cadmium dipping, the deleterious effects of cadmium treatment were prevented and normal regeneration occurred. When zinc chloride was administered 24 hours after amputation and cadmium dipping, it gave no protection against the cadmium. It is suggested that cadmium might inhibit regeneration through the inactivation of zinc metalloenzymes as a result of an exchange of cadmium for zinc. Zinc chloride administered to newts prior to cadmium treatment may prevent the replacement of zinc by cadmium.