[Hypothalamic-pituitary-adrenal function in primary hypothyroidism]

Hypothyroidism is known to lead to a certain degree of functional insufficiency of the adrenal gland by affecting both the hypophyseal axis and peripheral metabolism of cortisol. This study was conducted to evaluate hypothalamic, pituitary, and adrenal function in a homogeneous group of patients with long-standing major hypothyroidism.

Forty-five patients (32 females, 13 males; mean age 42.9 +/- 9.6 years; range 20-59) with major primary hypothyroidism known to be long-standing (> 1 year in 1 and for an undetermined duration of several years in all the others) were included. Twenty-nine age-matched subjects served as controls. Insulin-induced hypoglycaemia and oral metyrapone tests were performed before and after treatment had induced euthyroidism. 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 were determined before and 30 min after injection of tetracosactide.

Baseline ACTH and cortisol were not different in patients and controls and were unchanged by treatment. ACTH and cortisol response to hypoglycaemia were weaker in patients with ongoing hypothyroidism (p < 0.05 vs controls) and improved significantly (p < 0.05 vs baseline) after treatment. Adreno-cortical response to exogenous ACTH stimulation was weaker in patients with hypothyroidism (p < 0.05 vs controls) and returned to normal after treatment.

Modifications of the hypothalamic-pituitary-adrenal system resulting from hypothyroidism were minimal and evidenced only by dynamic exploration. Levels returned to normal after adequate treatment and the deficit restricted to the hypothalamus and pituitary might also involve the adrenal gland.