OBJECTIVES: I. Determine whether release of endogenous growth hormone (GH)-releasing hormone is involved in GH responses to clonidine, pyridostigmine, levodopa, arginine, GH-releasing peptide, insulin-induced hypoglycemia, and exercise in patients with acromegaly. II. Determine whether endogenous GH-releasing hormone influences the maintenance of GH hypersecretion.

PROTOCOL OUTLINE: Growth hormone-releasing hormone antagonist (GHRH-A) is administered to volunteers and followed with 1 of these challenges: insulin, clonidine, pyridostigmine, arginine, levodopa, growth hormone-releasing peptide, or exercise. Tests are repeated with normal saline as the control; the order of administration (control vs. pharmacologic stimulation) is randomly assigned. Patients receive GHRH-A (dose determined in volunteer study), thyrotropin-releasing hormone, and growth-releasing hormone. All stimulation tests follow an overnight fast.