Effects of daily melatonin injections on the photoperiodic gonadal response of the female frog Rana ridibunda.

The effects of daily melatonin injections on female gonads in Rana ridibunda were examined. Melatonin-treated R. ridibunda maintained on a long photoperiod (18L:6D) had significantly smaller gonads than control animals. Thus, frogs injected daily with melatonin exhibited a substantial decrease in ovary weight when compared to saline-injected animals. Our findings suggest that melatonin exerts antigonadal effects in female Rana ridibunda.