Quadruple injection of hypothalamic peptides to evaluate pituitary function in normal subjects.

A single intravenous injection of four hypothalamic releasing hormones-corticotropin-, growth hormone-, gonadotropin- and thyrotropin-releasing hormones-was administered to normal subjects. Except for the plasma adrenocorticotropic hormone (ACTH) level, a statistically significant increase in all anterior pituitary hormone levels occurred. Transient flushing was the only consistent side effect. In the same persons, results were compared with those obtained with insulin-induced hypoglycemia and a single-dose overnight metyrapone test. Growth hormone and cortisol responses to insulin-induced hypoglycemia were similar but prolactin increment was less than that obtained by the peptide injection. ACTH increments from both tests were substantially less than those obtained by the overnight metyrapone test. We conclude that pituitary function can be effectively studied in normal subjects by the combination of a metyrapone test with a triple bolus of growth hormone-, thytropin- and gonadotropin-releasing hormones, but not by a quadruple bolus of the hypothalamic peptides. Compared with insulin-induced hypoglycemia, this approach yields more information with fewer side effects.