Urologists should be aware of the links between hypogonadism and other serious health issues, as androgen deficiency may be the first clinically apparent sign of additional, future medical problems.
Together, the free testosterone and albumin-bound testosterone comprise the "bioavailable" fraction. Bioavailable testosterone is readily available for diffusion through the cell membrane into the cytoplasm, where it binds to the androgen receptor. This complex then travels to the cell nucleus, where it drives RNA transcription. In contrast to bioavailable testosterone, testosterone bound to SHBG is not readily available to transit the cell membrane, bind to the nuclear androgen receptor, or drive transcription. The testosterone-SHBG complex does interact with cell surface SHBG receptors, mediating specific cytoplasmic cyclic AMP-dependent signal cascades. However, the role and importance of these pathways in stimulating androgen effects is not clear (Clin Biochem 2003; 36:591-6).