There is evidence that the free, biologically active fraction of sex steroids in the plasma, is increased in subjects with endocrine-dependent tumours. However, little is known about factors which influence the distribution of these hormones in plasma. In order to investigate this, cortisol (14 μM) was infused, or ACTH (Synacthen, 250 μg, i.v.) was injected into male subjects and this resulted in a significant decrease (up to 38% from basal values) in the fraction of testosterone not bound to sex-hormone binding globulin (non-SHBG bound testosterone). The decrease in the non-SHBG bound testosterone fraction was accompanied by an increase (up to 20% from basal values) in the non-SHBG bound oestradiol fraction after ACTH injection. No significant changes in the unbound concentrations of testosterone or oestradiol were detected.
The addition of cortisol (250 nM) to a plasma pool obtained from male subjects resulted in a similar decrease in the non-SHBG bound testosterone