Abstract
The binding of corticosterone, dexamethasone and aldosterone was investigated in plasma
and in homogenates of liver, kidney, brain, brown adipose tissue and visceral (periovaric)
and subcutaneous white adipose tissues of Zucker lean and obese rats: intact controls,
adrenalectomized and sham-operated. Corticosterone-binding globulin (CBG) accounted
for most of the binding, whereas that of glucocorticoid and mineralocorticoid receptors
was much lower. Plasma corticosterone levels increased in sham-operated and obviously
decreased in the adrenalectomized animals. Sham-operated and adrenalectomized lean
rats showed decreased plasma CBG; in the obese, CBG levels were lower than in controls
and were not affected by either surgery. No variation with obesity or surgery was
observed either in dexamethasone or aldosterone binding, the latter being practically
zero in most samples. When expressed per unit of tissue protein, CBG activity was
maximal in adipose tissues, with lowest values in brain and liver. In lean rats, tissue
CBG activity decreased with either surgical treatment; no changes were observed in
the obese, which also had lower CBG tissue levels. The relative lack of changes in
CBG of obese rats suggests that they have lost - at least in part - the ability to
counter-modulate the changes in glucocorticoid levels through CBG modulation, thus
relying only on the control of corticosterone levels. This interpretation agrees with
the postulated role of CBG modulating the availability of glucocorticoids to target
cells.
Key words
Glucocorticoid Receptor - Corticosterone-binding Globulin - Obesity - Glucocorticoids
- CBG
