Interspecies variations of corticosteroid-binding globulin parameters |
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| Institution: | 1. Ecole Nationale Vétérinaire de Toulouse Unité associée INRA de Physiopathologie et Toxicologie expérimentales 23 chemin des Capelles, 31 076 Toulouse, France;2. INRA, Station de Pharmacologie 180 chemin de Tournefeuille, 31 300 Toulouse, France;1. Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot, Israel;2. Mastitis Reference Center, The Veterinary Institute, Bet Dagan, Israel;3. Cattle Breeders Association, Caesarea, Israel;4. Institute of Animal Science, Agricultural Research Organization, Bet-Dagan, Israel;1. Collaborative Innovation Center of Yangtze River Delta Region Green Pharmaceuticals, Zhejiang University of Technology, Hangzhou, Zhejiang, 310014, China;2. Institute of Drug Metabolism and Pharmaceutical Analysis, Zhejiang University, Hangzhou, Zhejiang, 310058, China;1. Fertility and Research Centre, School of Women’s and Children’s Health, University of New South Wales Sydney, New South Wales, Australia;2. Stats Central, Mark Wainwright Analytical Centre, University of New South Wales Sydney, New South Wales, Australia;3. Department of Academic Family Medicine, West Winds Primary Health Center, Saskatchewan, Canada;4. College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada;5. Department of Anatomy, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand;1. Division of Cardiology, Department of Medicine, University of Florida College of Medicine–Jacksonville, Jacksonville, Florida, USA;2. Division of Foot and Ankle, Department of Orthopaedic Surgery and Rehabilitation, University of Florida College of Medicine–Jacksonville, Jacksonville, Florida, USA;3. CirQuest Labs, Memphis, Tennessee, USA;1. Department of Obstetrics and Gynaecology, Child & Family Research Institute, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada;2. Department of Human Reproductive Medicine, Beijing Obstetrics and Gynaecology Hospital, Capital Medical University, Beijing 100026, China;3. Department of Obstetrics and Gynaecology, E-DA Hospital, Kaohsiung 82445, Taiwan |
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| Abstract: | In mammalian plasma, cortisol binds to a specific α1-glycoprotein: corticosteroid-binding globulin (CBG). In this study, we measured the protein binding of cortisol by equilibrium dialysis in seven species in which plasma cortisol concentrations varied from 0.02 to 0.05 (ewe, dog, cow) to 0.1 to 0.6 (horse, human, cynomolgus monkey) to reach 1.6 μM (squirrel monkey). No binding of cortisol to CBG was discernible in plasma from squirrel monkey. In all other species examined, we showed that the CBG maximal capacity (Bmax) was 3 (1.7 to 5.2) times more than the plasma cortisol levels, with cow, dog, ewe exhibiting the lowest and cynomolgus monkey exhibiting the highest values. We also noted the existence of a linear relationship between Bmax and the corresponding dissociation constant (Kd), Bmax being systematically 10 (8.5 to 11.8) times more than Kd. The low binding affinity of cortisol assigned to albumin did not differ between species. The free (6 to 14%), CBG-bound (67 to 87%), and albumin-bound (7 to 19%) cortisol fractions calculated from the estimated binding parameters and measured plasma cortisol concentrations were similar within species, except for squirrel monkey, in which half of the cortisol was albumin bound, and the other half remained protein free. Our most appealing finding was that in most species, as much as 68% of plasma CBG remained free of cortisol under physiologic conditions. These results are discussed with respect to the theories concerning the role of CBG in plasma transport and the local delivery of cortisol and free CBG as a proper hormone. |
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