Understanding Growth HormoneGrowth hormone is part of a cascade of hormones that, as the name implies, regulates the physical growth of the body. This cascade begins in a part of the brain called the hypothalamus, which makes hormones that regulate the pituitary gland. One of these, growth hormone-releasing hormone (GHRH), stimulates the pituitary gland to produce GH. Another hypothalamic hormone, somatostatin, inhibits GH production and release. Secretion of GH by the pituitary gland into the bloodstream causes the production of another hormone, called insulin-like growth factor 1 (IGF-1), in the liver. IGF-1 is the factor that actually causes the growth of bones and other tissues of the body. IGF-1, in turn, signals the pituitary to reduce GH production.
GHRH, somatostatin, GH, and IGF-1 levels in the body are tightly regulated by each other and by sleep, exercise, stress, food intake, and blood sugar levels. If the pituitary continues to make GH independent of the normal regulatory mechanisms, the level of IGF-1 continues to rise, leading to bone growth and organ enlargement. The excess GH also causes changes in sugar and lipid metabolism, and can cause diabetes.
Causes of AcromegalyAcromegaly is caused by prolonged overproduction of growth hormone (GH) by the pituitary gland. Common acromegaly causes include:
In over 90% of acromegaly patients, the acromegaly is caused by a benign (not cancerous) tumor of the pituitary gland called a pituitary adenoma (or growth hormone-secreting adenoma).
In a few patients, acromegaly is caused not by pituitary tumors, but by tumors of the pancreas, lungs, and adrenal glands. These tumors also lead to an excess of GH, either because they produce GH themselves or, more frequently, because they produce GHRH, the hormone that stimulates the pituitary to make GH.
(Click Acromegaly Causes for more information.)