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Summary
Diurnal rhythm of plasma cortisol was determined using a fluaorometric method to measure the levels of 11-hydroxycorticosteroids in venous blood samples collected at 8.00 a.m. and 10.00p.m. in 68 patients with definite rheumatoid arthritis. Thirty-four of these patients were receiving long-term oral corticosteroid therapy. The remaining 34 age and sex-matched patients, who had never previously received corticosteroid drugs, served as controls and helped to provide the normal range of diurnal rhythm of plasma cortisol. Using this normal range, 16 of the 34 corticosteroid-treated rheumatoid patients were found to have abnormal diurnal rhythm. Three of these 16 patients had normal hypothalmo-pituitary-adrenal function as tested by tetracosactrin, lysine 8-vasopressin, insulin hypoglycaemia and metyrapone. Of 18 patients receiving corticosteroid therapy and with normal diurnal rhythm of plasma cortisol, 8 had normal responses to tetracosactrin, lysine8-vasopressin, insulin hypoglycaemia and metyrapone testing. The data, therefore, indicate that diurnal rhythm of plasma cortisol is not a reliable guide to the presence of corticosteroid-induced suppression of the hypothalamo-pituitary-adrenal axis in patients receiving low-dosage long-term oral corticosteroid therapy.
Abnormal diurnal rhythm appeared to be related to the total dose of corticosteroid givenandto the duration of therapy but not to the mean daily dose, nor the daily regimen of therapy. Patients receiving triamcinolone, dexamethasone and betamethasone as a group had a higher prevalence of abnormal diurnal rhythm of plasma cortisol when compared with patients receiving prednisone or prednisolone, or methylprednisolone: these patients had, however, received a larger total dose of corticosteroid and had had their therapy for a longer time.