Blood pressure control, even in a healthy individual, is a complicated process because it results from a combination of cardiac output and peripheral vascular resistance (PVR), each of which can be influenced by a variety of factors.
Abnormal increase in blood pressure can be caused by increase in volume of the blood, electrolyte disturbances, kidney problems, metabolic syndrome, eclampsia (common condition in pregnancy), and pheochromocytoma, a tumor that secretes the hormone epinepherine. The control of blood pressure through the adrenal glands (which lie above the kidneys) is influenced, in turn, by a hormone called ACTH, which comes form the pituitary gland in the brain.
Essential Hypertension Resulting from a Tumor in the Brain
There are many types of tumors that can occur in the pituitary gland in the brain. A common type of tumors occurring in any gland is known as an adenoma. An adenoma occuring in the pituitary gland can involve various hormones. The pituitary hormone that affects blood pressure via the adrenal gland is ACTH.
Cushing's Disease results from an adenoma in the pituitary gland. Normally, ACTH is released from the pituitary gland only when needed and in amounts appropriate to maintain blood pressure at a healthy level, but when cells in the pituitary that produce ACTH grow out of control, a tumor results. Not only does this produce pressure on the surrounding tissue, but the cells within the tumor produce too much ACTH, which in turn causes the adrenal glands to produce too much ephinepherine, resulting in hypertension.
Differential Diagnosis of Cushing's Disease
The effects on the level of epinepherine and blood pressure in Cushing's Disease is are the same as when a tumor is present not on the pituitary but in the adrenal glands. In the latter case, when a tumor (pheochromocytoma) develops in the adrenal glands, excessive epinepherine is produced. Since one result of hypertension is headache, based on symptoms alone it can be difficult to distinguish between pheochromocytoma and Cushing's Disease; this can be resolved by way of brain imaging, using MRI or CT scnanning.