Estrogen action in bone: a family plot

In spite of their long described positive effects on bone metabolism, the m olecular mechanisms through which estrogens act are poorly understood, The existence of two estrogen receptors (ERs) might clarify the situation, Two other receptors (ERRs), closely related to the ERs but still awaiting the i dentification of their ligands, interfere with the signalling pathways cont rolled by the ERs. The inteconnexions between the four members of this subf amily of receptors raise new hypotheses concerning the action of estrogens in bone.