Regulation of dopamine receptors in the MtT/W15 transplantable pituitary tumor by estrogen.
We investigated the effects of estrogens on the regulation of dopamine receptors in the MtT/W15 transplantable rat pituitary tumor. Diethylstilbestrol (DES) and 17beta-estradiol treatment in female rats significantly decreased the number of dopamine binding sites (B max) from 85 +/- 3.9 fmol/mg protein in untreated rats to 9.2 +/- 1.2 and 8.2 +/- 2.8 fmol/mg protein in DES and 17beta-estradiol-treated rats, respectively, while the binding affinities (Kd) did not change significantly. Testosterone treatment did not change the B max, while ovariectomy resulted in a significant increase in the B max (146.3 +/- 6.7 fmol/mg protein). The effects of DES on the B max were reversible, since removal of the DES for one week before sacrificing the animals led to a marked increase in the B max (54.9 +/- 3.1 fmol/mg protein). Pituitaries from normal female rats treated with DES for 6 and 9 weeks had a significant decrease in the B max. These results show that the number of dopamine binding sites in the membranes of MtT/W15 tumors is decreased by estrogen treatment and that this effect is reversible after removal of the estrogenic stimulus.
D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line; D004054:Diethylstilbestrol / Q000494:pharmacology*; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007700:Kinetics; D010052:Ovariectomy; D010911:Pituitary Neoplasms / Q000378:metabolism*; D051381:Rats; D011920:Rats, Inbred WF; D011954:Receptors, Dopamine / Q000187:drug effects / Q000378:metabolism*; D013134:Spiperone / Q000378:metabolism; D013739:Testosterone / Q000494:pharmacology
D011954:Receptors, Dopamine; D013739:Testosterone; D004958:Estradiol; D013134:Spiperone; D004054:Diethylstilbestrol