Reptile (Podarcis sicula) brain progesterone receptor: relationship to plasma steroids and vitellogenic cycle during Gonadal recrudescence

We identified and partial characterized a seasonal brain PR in a lower vertebrate, the reptile, Podarcis sicula. [³H]-P binding detect the presence of one type of binding site with high affinity and specificity and low capacity The levels in the nuclear and cytosolic extract change according to the reproductive cycle and under different steroids treatments. Brain PR nuclear extract level results high in early recrudescence period when vitellogenin synthesis is kept at its minimum and they decrease when E₂ and P levels rise. The decrease of brain PR levels could depend on the increase of E₂ and P and can be related to the augmentation of the vitellogenin synthesis as demonstrated in turtle liver of Chrysemys picta. The progesterone receptor levels in the nuclear brain extract result significantly higher in ovariectomized females than in intact females sacrificed soon after capture and in sham operated. Treatment with E₂ and/or P significantly reduce the PR brain levels providing the only evidence that PR in the lizard brain down-regulated by ovarian steroids and indirectly suggesting that P in Podarcis sicula brain as in Rana esculenta brain and liver may be involved, by its receptor, in the vitellogenin modulation.