Synergistic effects of pre-treatment and a cocktail of steroids upon induction of ovulation. Frogs were pre-treated with or without (Ethanol alone) steroids, or at the indicated concentrations, for one day before ovulation induction by a mixture of steroids. Frogs were then treated with a mixture of estradiol and progesterone at the indicated concentrations. After 24 to 30 hr incubation, the numbers of ovulated eggs were counted as described in the Materials and Methods. Annotations underneath each column indicate substance and concentration for both pre-treatment and the induction of ovulation. For example, Et0-P20E10 represents pre-treatment with 0% ethanol for one day followed by induction by a mixture of 20 μM progesterone and 10 μM estradiol the following day. The left column represents the induction results in response to PMSG-hCG injection. Each value represents the mean of data from more than three different females. The number of ovulated frogs per number treated is indicated over each column. Vertical lines indicate standard deviation.