Abstract
Both estradiol (ER) and progesterone (PR) receptors have been found in the oviduct of the lizard Podarcis s. sicula. Their concentrations change according to the reproductive cycle and under different hormonal treatment. The estradiol receptor binds DES with high affinity (K~d~ = 4.4 ± 6.9 × 10^−1^ M) and low capacity (7.0 ± 2.1 × 10^−10^ M). The progesterone receptor binds both ^3^H‐progesterone and ^3^H‐R5020 with high affinity (K~d~ = 1.2 ± 2.2 × 10^−9^ M) and low capacity (0.5 ± 2.2 × 10^−10^ M). PR elution profile on DNA‐cellulose shows two peaks eluting at 0.15 M NaCl and 0.27 M NaCl for the cytosol and 0.14 M NaCl and 0.26 M NaCl for the nuclear extract. When analyzed by isoelectrofocusing, PR shows two peaks at pH 7.8–8.0 and 6.8–7.0. During the reproductive cycle, the peak of occupied ER in the nuclei precedes the increase in occupied PR. This pattern suggests a sequential action of estradiol and progesterone on the oviduct. In fact, while estradiol is involved in oviduct growth in early spring, progesterone stimulates glandular activity in the mature oviduct. Long term estradiol treatment up‐regulates nuclear occupied PR, but down‐regulates it when administered in combination with progesterone. On the other hand, progesterone alone or in combination with estradiol, prevents 17β‐estradiol effects on nuclear occupied ER. © 1994 Wiley‐Liss, Inc.