Cortisol response to arginine-vasopressin does not compare with cortisol response to insulin-hypoglycemia in pituitary tumors.

ABSTRACT

Timed cortisol responses to insulin-hypoglycemia (IH) and arginine-vasopressin (AVP) were compared in 16 patients with pituitary tumors and six healthy controls. Serum cortisol was estimated by a specific and sensitive radioimmunoassay as per the WHO protocol. The basal cortisol (AM) was normal (> 290 nmol/l) in 9 patients and low in seven. With IH peak cortisol response was normal (> 550 nmol/l) in 10 patients, 8 of whom had normal and 2 had low basal (AM) cortisol. In contrast AVP evoked normal cortisol responses in only 5 of these patients, all of whom had normal basal (AM) cortisol and none had low basal (AM) cortisol. The data indicate lower sensitivity for AVP stimulation test (50%) and favour IH as the standard cortisol stimulation test in patients with pituitary tumors awaiting surgery.