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Putative steroid-binding receptors and nonreceptor components and testicular activity in the lizard Podarcis sicula sicula

Summary. Labelled testosterone- and oestradiol-binding molecules have been found in the cytosol and nuclei of lizard testes. DNA–cellulose affinity chromatography was used to separate putative sex-steroid-binding receptors (adhering molecules) and nonreceptor components (nonadhering molecules). A putative androgen receptor (K_d:10^–10 mol l^–1; 3–9 fmol g^–1 tissue) was found mainly in the nuclei of testicular cells when actively undergoing spermatogenesis. This suggests that, as in higher vertebrates, testosterone is implicated in spermatogenetic step regulation (meiosis and spermiogenesis) in lizard testis. In the cytosol, testosterone-binding molecules (K_d; 10^–9 mol l^–1; 384–784 fmol g^–1 tissue) with several properties of androgen-binding proteins are present from autumn to spring. The behaviour of these molecules is consistent with the role assigned to androgen-binding proteins as androgen reservoir.

A putative oestrogen receptor is present throughout the sexual cycle, except during the culmination phase (breeding). The putative oestrogen receptor may be involved in the regulation of the first spermatogenetic step (spermatogonia multiplication) and in the induction of post-reproductive refractoriness. This phase is present in temperate-zone lizards.

These studies show that the evaluation of sex-steroid-binding molecules is useful in considering the relationships between sex hormones and spermatogenetic activity in the testes of lizards.

Keywords: sex-steroid-binding molecules; testis; reproductive cycle; lizard