Endocrine Abstracts

Background: Patients taking hydrocortisone replacement for primary or secondary adrenal failure require individual adjustment of their dose. Previous observations in our department suggest that total serum cortisol levels achieved following an afternoon or evening dose of 5 mg hydrocortisone are almost as high as those that result from a 10 mg dose in the early morning; and that the ‘area under the cortisol curve’ (AUC) generated by an evening 5 mg dose is broader than after 10 mg taken early in the morning. One potential explanation for this phenomenon might be a circadian variation in serum CBG concentration, which may, in turn, impact on the interpretation of cortisol profiles and individual dose selection for patients on hydrocortisone replacement therapy. The purpose of this study was to investigate the hypothesis that there is a circadian variation in CBG levels.

Method and results: A total of 34 male patients divided into three groups (ten patients with non-somatotroph structural pituitary disease on HC replacement, 11 patients with treated acromegaly on HC replacement, and 13 patients with treated acromegaly not on HC replacement) and ten healthy volunteers were included. Cortisol and CBG levels were measured at six time points (0800, 1100, 1300, 1500, 1700, and 1900 h). No significant circadian variation in CBG concentration was found in any of the four groups.

Conclusion: Circadian variation in serum cortisol during hydrocortisone replacement is not attributable to changes in cortisol-binding globulin. Alternatively, such changes in serum cortisol may be explained by other factors including 11β-hydroxysteroid dehydrogenase type 1 activity or circadian changes in the binding capacity of CBG.

Disclosure: This study was supported by an unrestricted investigator-initiated grant from Pfizer, Inc.