What is the Origin of Sex Steroid Bioactivity?

This term is fundamental to clinical endocrinology, distinguishing the actual biological effect from the simple laboratory measurement of total hormone concentration. 'Bioactivity' emphasizes the functional outcome, which is a complex product of synthesis, transport, receptor interaction, and metabolism. This concept is vital for accurately assessing hormonal status and guiding replacement therapy.

What is the Mechanism of Sex Steroid Bioactivity?

Only the unbound, or "free," fraction of a sex steroid is generally available to diffuse across cell membranes and bind to intracellular receptors to initiate gene transcription. The bioactivity is therefore inversely proportional to the concentration of SHBG, which tightly binds the majority of these hormones. Furthermore, local tissue enzymes can convert less potent precursors into highly active steroids, such as the conversion of testosterone to dihydrotestosterone, significantly influencing the localized bioactivity.

Sex Steroid Bioactivity ∞ Area

Sex Steroid Bioactivity

Meaning

Sex Steroid Bioactivity refers to the measure of the overall functional impact that sex hormones, such as testosterone, estradiol, and progesterone, exert on their target tissues. This bioactivity is not solely determined by the total circulating hormone level but also by the free, unbound fraction, the concentration of carrier proteins like Sex Hormone Binding Globulin (SHBG), and the local receptor density. It is the true measure of a hormone’s effectiveness at the cellular level.