Kinetics of in vitro binding of oestradiol in subcellular fractions of testicular and uterine tissue: Characterization of oestradiol binding in testicular nuclei

Abstract

1. 1. Oestradiol in rat testicular and uterine tissue is specifically bound to nuclear receptor sites, which can be separated in KCl-extractable nuclear and nuclear residual (a nuclear fraction which resists KC1 extraction) receptor sites. 2. 2. The amount of “extractable” nuclear binding sites for oestradiol in testis could be increased by mild trypsin treatment. Treatment of testicular nuclei with deoxycholate or DNAse resulted in a decrease of residual receptor sites and a concomitant increase of unbound oestradiol in the “extractable” nuclear fraction. 3. 3. The presence of KCN in vitro resulted in a relative increase in the number of oestradiol binding sites in the nuclear residual fraction in both uterine and testicular tissue; the number of binding sites in the KCl-extractable fraction was not affected by KCN. 4. 4. During in vitro incubations of testicular tissue the number of oestradiol binding sites in the KCl-extractable nuclear fraction reached a maximum and remained constant after 30min of incubation; the number of binding sites in the nuclear residual fraction decreased after incubation periods longer than 30 min. 5. 5. During in vitro incubations of uterine tissue the number of oestradiol binding sites in the KCl-extractable nuclear fraction and the nuclear residual fraction after an initial increase decreased to 50% of the maximal value between 30 and 60 min of incubation. 6. 6. It is concluded, that the testicular oestradiol receptor shows certain characteristics comparable with those of the uterine receptor. However, regarding the differences in retention time of steroids in the nucleus, it seems very unlikely that the oestradiol effect in uterus and the oestradiol effect in testis, if present, are mediated by identical receptor mechanisms.