Cortisol binding

Estrogens are bound to SHBG and progestins to CBG. SHBG binds estradiol about five times less avidly than it binds testosterone or DHT, while progesterone and cortisol have little affinity for this protein (Table 42-8). In contrast, progesterone and cortisol bind with nearly equal affinity to CBG, which in turn has little avidity for estradiol and even less for testosterone, DHT, or estrone. 

B28. Bladon, P. T., Rowlands, T. E., Whittaker, J. A., and Oakey, R. E., Serum cortisol binding capacity measured with concanavalin A-Sepharose in patients with a recent inflammatory response. Clin. Chim. Acta 253,9-20 (1996). 

Adrenal Tumours The assay-method is entirely based on the Schwartz-Mann Kit. According to this method, cortisol is first extracted from the plasma using CH2C12 (methylene chloride). In the actual radioimmunoassay the cortisol present in the extract competes with Cortisol-H3 i.e., the radioactive tracer) for the common binding sites on transcortin, which is incidently not an antibody but a cortisol-binding protein. Now, the free cortisol is quantitatively removed by adsorption on dextran-coated charcoal from the one bound to the transcortin. Finally, the bound radioactivity (due to Cortisol-H3) is measured which is then employed to calculate exactly the amount of cortisol present in the sample by the help of a Standard Curve (or Calibration Curve). 

Cortisol-binding protein is also lost in the urine and plasma concentrations of cortisol may be also reduced. 

Possible consequences of the loss of binding proteins (e.g., ceruloplasmin, transferrin, vitamin D-binding protein, thyroxin-binding globulin, and cortisol-binding protein) have been already mentioned. 

The glucocorticoid cortisol is secreted from the adrenal cortex as a stress response under the control of adrenocorticotropic hormone (ACTH, corticotropin) produced by the anterior pituitary. Cortisol promotes catabolism by inducing synthesis of specific proteins. Cortisol binds to a cytosolic cortisol receptor which then translocates to the nucleus and switches on the expression of specific genes, notably that for PEP carboxykinase (PEPCK). Cortisol-induced expression of the key gluconeogenesis enzyme PEPCK increases levels of the enzyme and hence increases gluconeogenesis and available blood glucose. The cAMP-and cortisol-mediated pathways for induction of PEPCK expression are further linked by CREB-dependent expression of a coactivator protein PGC-1 that promotes cortisol-dependent expression of PEPCK. 

CAT-REL, vesicular catecholamine release CB-R, cannabinoid receptor CB1-R, CB2-R, cannabinoid receptors CBD, chitin-binding domain CBG, cortisol-binding globulin CBZ-R, central benzodiazepine receptor CCK-R, cholecystokinin receptor CDC, chrysanthemum dicarboxylic acid CDK, cell division kinase, cyclin-dependent protein kinase... 

ACE-I angiotensin-converting enzyme inhibitor CBG cortisol binding globulin... 

Steroid hormones (e.g., cortisol and estrogen) are hydro-phobic and insoluble in water. These hormones circulate in plasma, reversibly bound to transport proteins (e.g., cortisol-binding globulin and sex-hormone binding globulin) with only a small fraction free or unbound available to exert physiological action.The half-life of steroid hormones is 30 to 90 minutes. Free steroid hormones, being hydrophobic, enter the cell by passive diffusion and bind with intracellular receptors either in the cytoplasm or the nucleus. ... 

Pottinger, T.G., F.R. Knudsen and J. Wilson. Stress-induced changes in the affinity and abundance of cytosolic cortisol-binding sites in the liver of rainbow trout, Oncorhynchus mykiss (Walbaum), are not accompanied by changes in measurable nuclear binding. Fish Physiol. Biochem 12 499-511, 1994. 

Cortisol Hydrocortisone a glucocorticoid steroid hormone synthesized by the adrenal gland in response to binding of ACTH. Cortisol binds to cytosolic or nnclear receptors that act as transcription factors for glucocorticoid-responsive genes. In general, cortisol is a catabolic hormone that promotes the breakdown of proteins. 

Transport to tissues Cortisol is secreted into the blood stream where it is 90% bound to cortisol-binding globulin (CBG) and albumin. Active cortisol (remaining 10%) freely diffuses into cells where it exerts its actions via intracellular receptors. CBG plays an important role in regulating cortisol delivery and clearance. Dexamethasone has low affinity for CBG. It... 

In the serum, progesterone is bound to either cortisol binding globulin or albumin, with only a small fraction being freely available. The metabolic clearance rate for progesterone is 2,100 to 2,500 L/day, for which protein binding has no role. 

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