Plasma Protein Binding of Endogenous Glucocorticosteroids and Its Influence on Hair and Saliva Concentrations

The study investigated the role of plasma protein binding (PPB) in the concentration shifts of glucocorticosteroids (GCs) like cortisol and cortison in blood, saliva, and hair. It found that cortisol binds more strongly to transport proteins than cortison, leading to a shift in concentration ratios from 3:1 in plasma to 1:1 in free concentrations. This affects their incorporation into hair and diffusion into saliva, with cortisol transitioning less proportionally and cortison more so. The study also highlighted that PPB accounts for about 50% of the observed concentration shifts, challenging previous beliefs that enzymatic inactivation was the main factor. Additionally, hair analysis showed continuous GC incorporation during chronic stress, with older hair showing reduced concentrations due to washing effects. The findings suggest that PPB is a significant factor in GC concentration variations across different matrices.