What is the Origin of Bioavailability across BBB?

The term combines the pharmacological concept of "bioavailability," which describes drug absorption and systemic circulation, with the physiological reality of the "Blood-Brain Barrier," a specialized structure discovered in the late 19th century. Clinical pharmacology adapted this composite term to address the unique challenge of drug delivery to the brain, especially for neuroactive hormones.

What is the Mechanism of Bioavailability across BBB?

Passage across the BBB is governed by several physicochemical properties of the molecule, including lipophilicity, molecular weight, and the presence of specific transport mechanisms. Small, lipid-soluble molecules often diffuse passively across the barrier. Larger or less lipid-soluble substances rely on carrier-mediated transport or receptor-mediated transcytosis to gain access. Hormones, being lipophilic steroids, typically cross via passive diffusion, whereas peptides often require specific transport systems to gain access to the brain's regulatory centers.

Bioavailability across BBB ∞ Area

Bioavailability across BBB

Meaning

Bioavailability across the Blood-Brain Barrier defines the fraction of an administered substance, such as a hormone, peptide, or therapeutic compound, that successfully traverses the endothelial cells of the cerebral capillaries to reach its target tissue in the central nervous system. This metric is a crucial determinant of efficacy for any compound intended to influence neuroendocrine function or cognitive processes. High permeability is essential for achieving therapeutic concentrations in the brain parenchyma.