Adipocyte alpha 2A-adrenoceptor is the only alpha 2-adrenoceptor regulated by testosterone.

The effects of chronic administration of testosterone on alpha 2-adrenoceptor expression in male hamsters were investigated in order to explore the selectivity of testosterone regulation towards the alpha 2-adrenoceptor subtypes. A homogeneous population of alpha 2-adrenoceptors was identified with [3H]RX821002 binding in adipocytes, colocytes and liver, whereas the alpha 2-adrenoceptor sites identified in kidney and brain were heterogeneous. Competition studies with alpha 2-adrenoceptor ligands characterized the presence of the alpha 2A-adrenoceptor subtype in adipocytes, colocytes, kidney and brain homogenates and of the alpha 2B-adrenoceptor subtype in kidney and liver. RNase protection assay with a selective hamster alpha 2A-adrenoceptor cRNA probe confirmed the expression of alpha 2A-adrenoceptor mRNA in adipocytes, colocytes, kidney and brain. Testosterone treatment did not modify the alpha 2-adrenoceptor densities whatever the subtype, except for the adipocyte alpha 2A-adrenoceptor, which was significantly increased. These results demonstrate that testosterone only up-regulates the adipocyte alpha 2A-adrenoceptor.