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Cortisol Binding by Dog Plasma1

1963; Oxford University Press; Volume: 73; Issue: 3 Linguagem: Inglês

10.1210/endo-73-3-353

1945-7170

John E. Plager, Robert H. Knopp, W. Roy Slaunwhite, Avery A. Sandberg,

Hormonal Regulation and Hypertension

Cortisol binding by dog plasma was studied by ultrafiltration and equilibrium dialysis techniques and was compared to human plasma using 3 criteria: 1) the binding curve; 2) the sensitivity of the binding proteins to heat inactivation; and 3) the effect of estrogen administration on the cortisol-binding properties of the plasma. The resting plasma cortisol level in the dog is below 2 μg/ 100 ml, and at this level, by ultrafiltration analysis, about 88% of the cortisol is bound. At a plasma level of 10 μg/100 ml, 67% of the cortisol is bound and at 100 μg/100 ml, 56% is bound. A 4% dog albumin solution binds about 50% of the cortisol. Human transcortin is inactivated by heating the plasma at 60 C for 20 min; dog plasma shows little change in binding characteristics following this period of heating. Human transcortin increases in concentration during estrogen administration. Estrogen treatment of 4 dogs did not change their plasma cortisol-binding properties. Dog plasma, therefore, contains a protein (s) similar to human transcortin, with high affinity for cortisol. The concentration of this protein in dog plasma, however, provides much less cortisol-binding capacity than does transcortin, and, unlike transcortin, this protein does not increase in concentration with estrogen treatment and does not show similar heat lability.