Plasma ACTH and Cortisol Responses to TRF, Vasopressin or Hypoglycemia in Cushing's Disease and Nelson′s Syndrome

Abstract

The response of plasma ACTH and/or cortisol concentrations to thyrotropin-releasing-factor (TRF), vasopressin, and insulin administration was determined in 5 patients with Nelson′s syndrome and 12 patients with untreated Cushing′s disease. TRF administration was associated with a mean increment of 267 pg/ml in plasma ACTH concentrations in patients with Nelson′s syndrome, and of 42 pg/ml in patients with Cushing′s disease. The increment in plasma cortisol concentrations in the latter group was 12 /Ltg%. No ACTH or cortisol response was observed in normal subjects. Patients with Cushing′s disease or Nelson′s syndrome exhibited significantly greater increments in plasma ACTH concentrations in response to vasopressin administration (P < .05, P< .02 respectively) than did normal subjects; the increment in cortisol concentration was also greater, (P < .05), in patients with Cushing′s disease than in normal subjects. No significant difference was present between patients with Cushing′s disease and Nelson′s syndrome with regard to the magnitude of the ACTH response to vasopressin administration. In contrast, the increment in plasma cortisol and plasma ACTH concentrations following insulin induced hypoglycemia was significantly less in patients with Cushing′s disease than seen in normal subjects, (P <.001, P < .05 respectively); while this stimulus was associated with a significantly greater increment in plasma ACTH concentrations in patients with Nelson′s syndrome as compared to that seen in normal subjects, (P < .01) and in patients with Cushing′s disease (P <.01). These findings indicate that pituitary function in patients with Nelson′s syndrome is not autonomous and suggest the possibility that altered central nervous regulatory mechanisms might play a role in the etiology of the pituitary tumors which are frequently associated with this syndrome. The TRF induced rise in plasma cortisol and ACTH concentrations in patients with Cushing′s disease and Nelson′s syndrome suggests the possibility of altered hypothalamic or pituitary receptors in such patients.