Adrenocorticotropin and cortisol responsiveness to thyrotropin-releasing hormone and luteinizing hormone-releasing hormone discloses two subsets of patients with Cushing's disease.

In 23 consecutive patients with Cushing's disease and 52 control subjects, the responses of ACTH and cortisol to TRH and LRH were investigated. From the pattern of cortisol levels after the administration of the releasing hormone in the controls, a criterion for paradoxical responsiveness could be derived (maximum cortisol increase, greater than 6.0 micrograms/100 ml). According to this criterion, 9 patients with Cushing's disease showed a paradoxical responsiveness to one or both releasing hormones (3 to both TRH and LRH, 3 to TRH alone, and 3 to LRH alone; group I). In all patients tested, paradoxical responses of cortisol were preceded by paradoxical increments in ACTH. The remaining 15 patients showed no paradoxical increments in ACTH or cortisol after TRH or LRH (group II). ACTH levels in group I (89 +/- 28 pg/ml) were significantly lower than those in group II (185 +/- 164 pg/ml; P less than 0.02). Nevertheless, in both groups, a similar plasma cortisol level was found, suggesting a relatively higher bioactivity of ACTH in group I. A second difference between both groups was a lower amplitude of cortisol variability during the day in group I. The 2 groups did not differ in clinical data, such as age, sex distribution, sellar volume, and duration of disease, or dexamethasone suppressibility, bromocriptine sensitivity, and basal PRL levels. These latter findings do not favor an intermediate lobe origin of Cushing's disease in patients with paradoxical responses to TRH/LRH. To conclude, TRH/LRH responsiveness of ACTH/cortisol discloses two subsets of patients with Cushing's disease.