Reduced epinephrine reserve in response to insulin-induced hypoglycemia in patients with pituitary adenoma.

OBJECTIVE Hypoglycemia induces rapid secretion of counterregulatory hormones such as catecholamine, glucagon, cortisol, and GH. Insulin-induced hypoglycemia is used for evaluating GH-IGF-I and ACTH-adrenal axes in patients with pituitary disorders. The aim of this study was to determine whether the response of catecholamine secretion to hypoglycemia is disrupted in patients with pituitary adenoma. METHODS The study population comprised 23 patients with pituitary adenoma (non-functioning adenoma or prolactinoma). An insulin tolerance test was performed and serum catecholamines as well as plasma GH and serum cortisol were measured. RESULTS The study patients showed diminished response of plasma epinephrine to insulin-induced hypoglycemia. With the cutoff level of peak epinephrine for defining severe impairment set at 400 pg/ml, more patients with secondary adrenal insufficiency showed severe impairment of the epinephrine response than did those without it. Peak epinephrine levels to insulin-induced hypoglycemia were significantly correlated with peak cortisol levels. In patients with secondary hypothyroidism, secondary hypogonadism, GH deficiency, or diabetes insipidus, the prevalence of severe impairment of the epinephrine response was similar to that in patients without these deficiencies. CONCLUSIONS Impaired epinephrine secretion in response to insulin-induced hypoglycemia was frequently observed in patients with pituitary adenoma. This disorder was especially severe in patients with secondary adrenal insufficiency.