Modulation of corticosterone availability to white adipose tissue of lean and obese Zucker rats by corticosteroid-binding globulin

Corticosterone-binding (CB) capacity was determined in periovarian and subc utaneous white adipose tissue (WAT), as well as in plasma of lean and obese Zucker rats. In lean rats, plasma CB was twice the level of obese rats. In lean rat WAT, dexamethasone binding accounted for only 0.05-0.09% of corti costerone binding, and aldosterone bound even less; in the obese rats, dexa methasone accounted for 0.2-0.3% of corticosterone binding. Scatchard plots showed that KD for corticosterone was 3.1 nM (WAT) or 3.4 nM (plasma) in l ean rats and 1.8 nM (WAT) or 1.5 nM (plasma) in obese rats. The total CB ca pacity in WAT was lower in the obese than in lean rats (47-50%). Plasma non -esterified fatty acid levels were higher in obese rats. The results sugges t that CBG may limit the access of glucocorticoids to adipocytes more weakl y in obese rats because of the lower CBG. Fatty acids may increase the affi nity of CBG for corticosterone, which would make WAT cells less accessible to circulating glucocorticoids. The modulation of CBG by fatty acids may pr otect fat reserves by decreasing the sensitivity of WAT to glucocorticoids.