HYPOTHALAMIC-PITUITARY-ADRENAL FUNCTION I N PRIMARY HYPOTHYROIDISM

Objectives: Hypothyroidism is known to lead to a certain degree of fun ctional insufficiency of the adrenal gland by affecting both the hypop hyseal axis and peripheral metabolism of cortisol. This study was cond ucted to evaluate hypothalamic, pituitary, and adrenal function in a h omogeneous group of patients with longstanding major hypothyroidism. M ethods: Forty-five patients (32 females, 13 males; mean age 42.9 +/-9. 6 years; range 20 -59) with major primary hypothyroidism known to be l ong-standing (>1 year in 1 and for an undetermined duration of several years in all the others) were included. Twenty-nine age-matched subje cts served as controls. Insulin-induced hypoglycaemia and oral metyrap one tests were performed before and after tratment had induced euthyro idism. Plasma ACTH and cortisol were measured every 20 min for 2 hours during the hypoglycaemia test and ACTH before and after the last dose of metyrapone. Plasma cortisol levels mere determined before and 30 m in after injection of tetracosactide. Results: Baseline ACTH and corti sol were not different in patients and controls and mere unchanged by treatment. ACTH and cortisol response to hypoglycaemia mere weaker in patients with ongoing hypothgroidism (p<0.05 vs controls) and improved significantly (p<0.05 vs baseline) after treatment. Adreno-cortical r esponse to exogenous ACTH stimulation was weaker in patients with hypo thyroidism (p<0.05 vs controls) and returned to normal after treatment . Conclusions: Modifications of the hypothalamic-pituitary-adrenal sys tem resulting from hypothyroidism were minimal and evidenced only by d ynamic exploration. Levels returned to normal after adequate treatment and the deficit restricted to the hypothalamus and pituitary might al so involve the adrenal gland.