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In Vitro Estrogen-like Effects of 7,12-Dimethylbenz(a)anthracene on Anterior Pituitary Dopamine Receptors of Rats

Unité de Neurobiologie de la Reproduction, CNRS-INRA, 78350 Jouy-en-Josas, France

The ability of 7,12-dimethylbenz(a)anthracene (DMBA), a potent inducer of mammary tumors, to mimic short term effects of estradiol (17ß-E₂) on the anterior pituitary, was tested in vitro. Incubation of anterior pituitaries from ovariectomized rats with DMBA resulted in a marked depletion of membrane dopamine receptors (labeled with [³H] spiperone) and a parallel stimulation of prolactin (PRL) release. Maximal receptor depletion and PRL release were obtained after 15–30 min of incubation with 10^-8 M DMBA. These effects were reversible and already significant after a 5-min incubation. Their magnitude, dose dependency, and time course were identical to those reported for 17ß-E₂. A structurally related noncarcinogenic polycyclic aromatic hydrocarbon, phenanthrene, had no effect on [³H]spiperone binding or PRL release. When DMBA and 17ß-E₂, at suboptimal concentrations, were simultaneously added to the culture medium, no synergistic effect could be observed. When 10^-8 M of both compounds were introduced simultaneously, the decrease in dopamine receptors and the increase in PRL release were not greater than those observed in the presence of 10^-8 M of only one compound, indicating that the same mechanism(s) can be involved. These data suggest that DMBA in desensitizing lactotrophs to dopamine and in releasing PRL, by direct estrogen-like actions on anterior pituitary, may provide a hormonal state conducive to tumor development.

¹ To whom requests for reprints should be addressed.

Received 7/14/87. Revised 2/22/88. Revised 7/12/88. Accepted 8/ 3/88.