title: Increased plasma protein binding and lower metabolic clearance rate of aldosterone in plasma of low cortisol concentration.
abstract: During ACTH or cortisol infusion in ten recumbent normal men taking dexamethasone, the metabolic clearance rate of aldosterone increased by 50% as plasma cortisol was raised from low (2 mug/dl) to high concentration (50 mug/dl). Since splanchnic blood flow did not change, a greater efficiency of removal of aldosterone must have occurred, by means of displacement of aldosterone from high-affinity sites on plasma protein. At 37 C, equilibrium dialysis of low-cortisol plasma showed one-third of plasma aldosterone bound to albumin, and 24 to 28% bound to higher-affinity sites on other protein. As plasma cortisol increased, a progressively smaller fraction was tightly bound, approaching zero as transcortin was saturated with cortisol. The addition of large amounts of aldosterone to low-cortisol plasma displaced 14C-cortisol from transcortin binding sites. The results support earlier evidence that a significant fraction of plasma aldosterone is bound to transcortin, from which it is readily displaced by cortisol, resulting in an increased metabolic clearance rate of aldosterone by making a larger fraction available for removal from plasma.
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000494:pharmacology; D000328:Adult; D000450:Aldosterone / Q000097:blood / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism*; D003956:Dialysis; D006801:Humans; D006854:Hydrocortisone / Q000097:blood* / Q000494:pharmacology; D007263:Infusions, Parenteral; D008297:Male; D008657:Metabolic Clearance Rate; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism; D013997:Time Factors; D014156:Transcortin / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D012709:Serum Albumin; D000450:Aldosterone; D000324:Adrenocorticotropic Hormone; D014156:Transcortin; D006854:Hydrocortisone