What is the Origin of Bio-Available Hormone Fractions?

This term is a fundamental concept in clinical endocrinology and pharmacology, stemming from the biophysical understanding of hormone transport and protein binding dynamics within the plasma. 'Bio-available' emphasizes the capacity for biological utilization, while 'fractions' refers to the distinct binding states of the hormone in the bloodstream.

What is the Mechanism of Bio-Available Hormone Fractions?

Steroid and thyroid hormones primarily circulate bound to specific proteins like Sex Hormone-Binding Globulin (SHBG) or Thyroid-Binding Globulin (TBG), which act as inactive reservoirs. The small, unbound fraction and the easily dissociable albumin-bound fraction constitute the bio-available pool. This dynamic equilibrium ensures a constant, regulated supply of active hormone to target cells, where it engages intracellular receptors to modulate gene transcription or trigger non-genomic actions.

Bio-Available Hormone Fractions

Meaning

Bio-Available Hormone Fractions represent the circulating portion of a hormone that is not tightly bound to high-affinity carrier proteins, rendering it immediately accessible to diffuse into tissues and exert biological effects. This free and loosely-bound fraction is the physiologically active component responsible for initiating cellular responses via receptor interaction. Clinical measurement of these fractions provides a more accurate assessment of functional endocrine status than total hormone levels alone.