Effect of 17b-estradiol and testosterone treatment on sex steroid binding proteins in the female of the reproductive cycle of the green frog Rana esculenta. Zoological Science 17: 797-803.

In this paper we report the effect of gonadectomy and/or long-term sex steroid (17β-estradiol and testosterone) treatment on binding activity of 17β-estradiol and testosterone binding proteins (EBP and TBP, respectively) in the plasma of the female of the green frog Rana esculenta. Experiments were carried out during different periods of the reproductive cycle when circulating levels of 17β-estradiol and androgens were : 1) low, 2) medium; 3) medium-high; 4) high. This study shows that EBP, but not TBP activity were affected by 17β-estradiol and testosterone treatment. The effect of the hormonal treatment changed according to the period of the reproductive cycle when it was carried out. Both 17β-estradiol and testosterone were ineffective when the circulating levels of 17β-estradiol and androgens were medium-high and high. On the contrary, the maximum effect was registered when circulating 17β-estradiol and androgens were at their minimum levels. Thus, our data indicate that binding activity of EBP apparent changes in response to 17β- estradiol and testosterone treatment varied according to the period of the reproductive cycle, an indication that studies on sex steroid binding proteins regulation should take into consideration the internal endocrine condition before drawing any final conclusion especially in species with a seasonal mode of reproduction.