What causes acromegaly?

Acromegaly is caused by the prolonged overproduction of growth hormone (GH) by the pituitary gland. The pituitary produces several important hormones that control body functions such as growth and development, reproduction, and metabolism. But hormones never seem to act simply and directly. They usually cascade or flow in a series, affecting each other's production or release into the bloodstream.

GH 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. The hypothalamus makes hormones that regulate the pituitary. One of the hormones in the GH series, or "axis," is growth hormone-releasing hormone (GHRH), which stimulates the pituitary gland to produce GH.

Secretion of GH by the pituitary into the bloodstream stimulates the liver to produce another hormone called insulin-like growth factor I (IGF-I). IGF-I is what actually causes tissue growth in the body. High levels of IGF-I, in turn, signal the pituitary to reduce GH production.

The hypothalamus makes another hormone called somatostatin that inhibits GH production and release. Normally, GHRH, somatostatin, GH, and IGF-I 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-I continues to rise, leading to bone overgrowth and organ enlargement. High levels of IGF-I also cause changes in glucose (sugar) and lipid (fat) metabolism and can lead to diabetes, high blood pressure (BP), and heart disease.

This answer is based on source information from the National Endocrine and Metabolic Diseases Information Service.