In order to gain further knowledge about the possible oestrogen-like activities of clenbuterol (a beta 2-adrenergic drug illegally used as partitioning agent in food producing animals), we treated a hormone dependent human breast cancer cell line (CG-5) with different concentrations of the drug (10(-3) M to 10(-8) M). The effects of clenbuterol and oestradiol on cell proliferation were compared. Both oestradiol and clenbuterol, at low concentrations (10(-7) M and 10(-8) M) stimulated cell proliferation, but the effects of clenbuterol were less marked and significant. Probably clenbuterol elicited cell proliferation through a different mechanism, since it did not affect the cellular oestrogen receptor concentration. Clenbuterol failed in binding to the high affinity oestrogen receptors present in the CG-5 cells. As the beta-adrenergic receptors and the susceptibility to their stimulation have been recently demonstrated in vivo and in vitro in many tumour and normal cells, it is reasonable to suppose that clenbuterol may induce cell proliferation through beta-adrenergic stimulation.
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