AR and thyrotoxicosis: On the other hand, the lower sensitivity of cortical bone to thyrotoxicosis in α2A/C-AR−/−, α2C-AR−/−, and α2A-AR−/− mice (37, 44) suggests that both α2A-AR and α2C-AR signaling pathways contribute to detrimental actions of TH on cortical bone of both femur and vertebra.