Effect of 17 beta-estradiol and testosterone treatment on sex steroid binding proteins in the female of the green frog Rana esculenta.

In this paper we report the effect of gonadectomy and/or long-term sex ster oid (17 beta-estradiol and testosterone) treatment on binding activity of 1 7 beta-estradiol and testosterone binding proteins (EBP and TBP, respective ly) in the plasma of the female of the green frog Rana esculenta. Experimen ts were carried out during different periods of the reproductive cycle when circulating levels of 17 beta-estradiol and androgens were : 1) low, 2) me dium; 3) medium-high; 4) high. This study shows that EBP, but not TBP activ ity were affected by 17 beta-estradiol and testosterone treatment. The effe ct of the hormonal treatment changed according to the period of the reprodu ctive cycle when it was carried out. Both 17 beta-estradiol and testosteron e were ineffective when the circulating levels of 17 beta-estradiol and and rogens were medium-high and high. On the contrary, the maximum effect was r egistered when circulating 17 beta-estradiol and androgens were at their mi nimum levels. Thus, our data indicate that binding activity of EBP apparent changes in response to 17 beta-estradiol and testosterone treatment varied according to the period of the reproductive cycle, an indication that stud ies on sex steroid binding proteins regulation should take into considerati on the internal endocrine condition before drawing any final conclusion esp ecially in species with a seasonal mode of reproduction.