Adrenal hyperplasia. Light micrograph of a section through an adrenal gland with nodular hyperplasia, a proliferation of cells that cause it to become enlarged. The adrenal glands are found on top of the kidneys. They are part of the endocrine system, releasing hormones such as adrenaline into the bloodstream. An increase in the number of cells can lead to the overproduction of adrenal hormones that can cause Cushing's syndrome. Symptoms of Cushing's syndrome include weight gain, muscle weakness, high blood pressure and psychological disturbances.