Influence of Melatonin on the Rate of Rana pipiens Tadpole Metamorphosis In Vivo and Regression of Thyroxine-Treated Tail Tips In Vitro: (tadpole/metamorphosis/thyroxine/melatonin/tissue culture).

Metamorphosis of Rana pipiens tadpoles may be retarded when the light phase of the light/dark (LD) cycle is shortened or when thyroxine (T ) is given in the dark because melatonin peaks during the dark. Injection of premetamorphic tadpoles in spontaneous metamorphosis with melatonin (15 μg) retarded tail growth and hindlimb development on 18L:6D but had no significant effect on 6L:18D. During induced metamorphosis (30 μg/liter T ), melatonin injections retarded tail resorption on 18L:6D and accelerated it on 6L:18D, but did not affect the hindlimb.