Gonadotropin- and estrogen-induced increase of peripheral-type benzodiazepine binding sites in the hypophyseal-genital axis of rats.

Peripheral-type benzodiazepine binding sites (PBS) were demonstrated in the cell membranes of various organs (ovary, uterus, oviduct, pituitary and kidney) of mature and immature female rats by using the PBS-specific ligand [3H]PK 11195. The equilibrium dissociation constants of [3H]PK 11195 for PBS in mature rats ranged from 3 to 4 nM. The specific binding of [3H]PK 11195 (2 nM) in the hypophyseal-genital axis of immature (19-27 days old) female rats was found to be significantly increased in the ovary and uterus, concurrently with the increase in age. Administration of pregnant mare serum gonadotropin or diethylstilbestrol to immature rats increased the density of PBS in the ovary and uterus 2- to 3-fold but no change was found in the kidney. The affinity of [3H]PK 11195 to these tissues did not change following hormonal treatment. These results suggest that gonadotropin and estrogen are involved in the induction of PBS in the organs of the hypophyseal-genital axis in female rats.