Role of progesterone in the control of female sexual receptivity in Anolis carolinensis.

The synergism of progesterone (P) with estrogen (estradiol benzoate, EB) in the facilitation of receptivity in female green anole lizards (Anolis carolinensis) is independent of time since ovariectomy, but is dependent on the time interval between EB and P administration and on the time of year. There is a brief window of time during which P facilitates receptivity in females primed with a subthreshold dose of EB. Sexual receptivity is induced if the time interval between EB and P is 24 hr but not if it is 48 hr. Furthermore, female A. carolinensis appear to be more sensitive to hormone treatment during different times of the year. Ovariectomized green anole females injected with EB and P during the summer are sexually receptive, but if given the same hormone regimen during the winter, they remain unreceptive.