Progesterone receptor in the liver and oviduct of the lizard Podarcis sicula Marina Paolucci * , Carlo Di Cristo Deparment of Biological and Environmental Sciences, University of Sannio, Via Port’Arsa, 11, 82100 Benevento, Italy Received 3 January 2002; accepted 15 March 2002 Abstract In this paper we report the presence of a 3 H-Progesterone ( 3 H-P) binding moiety, which has the characteristics of a true receptor, in the liver of the female of the lizard Podarcis sicula. 3 H-P binding studies show the presence of one type of binding site with an average Kd value of 6.2 F 2.0 nM in the cytoplasm and 6.3 F 1.1 nM in the nucleus. Competition experiments showed that progesterone (P) was the best competitor, while testosterone, deoxycorti- costerone (DOC), corticosterone, 17a-hydroxyprogesterone; R5020; RU486 and RU26988-5 were poor competitors. We have also investigated the immunological characteristics of progesterone receptor (PR) in both the liver and the oviduct of Podarcis sicula, by Western blotting using the monoclonal antibody PR22 raised against the PR isoforms A and B of chicken. One imunoreactive band of about 70 kDa was detected in cytoplasmic and nuclear extracts of both the liver and the oviduct. PR immunoreactivity was present in the liver during the quiescent phase. In the oviduct PR immunoreactivity increased from the recovery to the full grown phase. P treatment of estrogen-primed females did not affect the presence of PR in the liver, while brought about a PR increase in the oviduct. This study suggests that PR is expressed differently in the liver and the oviduct of Podarcis sicula throughout the reproductive cycle. PR might fulfill different requirements in relation to the different physiological functions of the tissue during the reproductive cycle. D 2002 Elsevier Science Inc. All rights reserved. Keywords: Progesterone receptor; Reptiles; Reproduction; Liver; Oviduct Introduction Progesterone (P) is a versatile hormone involved in pregnancy and uterine maintenance in mammals. In oviparous species its role is well exemplified by the chicken oviduct. P is essential for 0024-3205/02/$ - see front matter D 2002 Elsevier Science Inc. All rights reserved. PII:S0024-3205(02)01857-X * Corresponding author. Tel.: +39-0824-305133; fax: +39-0824-23013. E-mail address: paolucci@unisannio.it (M. Paolucci). www.elsevier.com/locate/lifescie Life Sciences 71 (2002) 1417 – 1427