Bromocriptine and sulpiride competitively inhibit estrogen binding to its receptor in the adrenal gland

Bromocriptine and sulpiride incubated simultaneously with [3H]-estradiol in the cytosol from adrenal glands of adult male rats, yielded curves typical of competitive inhibition as analyzed by Lineweaver-Burk plots. The inhibition constant for both drugs was approximately 10(8) M-1, only 10 times lower than the association constant for estradiol.