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.
