Drugs affecting pituitary, thyroid, parathyroid, and hypothalamic function

• A combination of neural and endocrine systems, originating in the hypothalamus, regulates CNS, autonomic nervous system, and endocrine functions. • The hypothalamus produces two hormones-oxytocin and vasopressin-that are stored in and released from the posterior lobe of the pituitary gland. The hypothalamus releases a series of stimulating and inhibiting factors to promote the release of stimulating hormones from the anterior pituitary gland. These stimulating hormones affect several other endocrine glands. • The anterior lobe of the pituitary gland produces growth hormone (GH), a hormone important for the regulation of growth and development. Release of GH is determined by inhibiting and releasing factors and by chemical signals for growing tissue. • The thyroid gland is a bilobar gland located in the neck around the trachea. This vascular gland uses dietary iodine to produce two thyroid hormones (T3 and T4). These hormones affect the way many body cells utilize energy and maintain metabolism. These hormones are regulated by a balance between TRH, TSH, and the thyroid hormone levels. • The parathyroid glands are four very small groups of tissue located on the back of the thyroid gland. These cells produce parathyroid hormone (PTH), the most important regulator of serum calcium levels in the body. PTH stimulates osteoclasts to release calcium from the bone, increases intestinal absorption of calcium, and increases calcium resorption from the kidneys. It also stimulates cells in the kidney to produce calcitriol, the active form of vitamin D, which stimulates intestinal transport of calcium into the blood. Calcium is a vital anion that is used in many of the body's metabolic processes, including membrane transport processes, conduction of nerve impulses, muscle contraction, and blood clotting. To be effective, the serum levels of calcium must be maintained between 9 and 11 mg/dL. • The GH somatropin is an example of a drug used to replace a pituitary hormone. It is given by injection to children with GH defi ciency, to some adults with GH defi - ciency, and to girls with Turner syndrome. • Release of GH is blocked by octreotide, bromocriptine, and GH-inhibiting factor (somatostatin). These drugs can be used to treat acromegaly and must be given by injection. • Vasopressin (or ADH) is administered by injection or intranasally in order to regulate water loss when levels of ADH are low or absent. Vasopressin blocks the release of water in the nephron and increases vascular volume while decreasing osmolarity. The dosage of this drug is determined by patient response and water balance. • Thyroid hormone is given to replace low levels of thyroid hormone resulting from surgery, radiation, autoimmune disorders, inadequate iodine in the diet, malignancies, or pituitary-hypothalamic disorders. Levothyroxine (T4) is the most commonly used thyroid hormone because of its predictability and reliability. • Patients treated with thyroid hormone need lifelong therapy. They should be monitored for nutritional balance related to changes in metabolism and should be evaluated periodically for the effectiveness of other maintenance drugs as the patient reaches normal thyroid function and metabolism changes. • Drugs used to block thyroid function include the thionamides-methimazole (MMI) and propylthiouracil (PTU)-and iodine preparations. The thionamides block the coupling of iodine to the thyroid hormone, whereas the iodine preparations prevent formation of thyroid hormone by blocking iodine uptake. I-131 is used in diagnostic imaging to isolate areas of increased thyroid gland activity or in one large dose to cause thyroid gland destruction by beta ray emission. Patients effectively treated with antithyroid drugs will need to be monitored for hypothyroidism and the need for thyroid hormone replacement. • Hypercalcemia is treated with calcitonin (a thyroid hormone that counters the action of PTH), the bisphosphonates, and gallium. These drugs are used to treat any condition characterized by increased calcium levels or bone resorption, such as postmenopausal osteoporosis, Paget disease, and hypercalcemia associated with malignancy. • Hypocalcemia is treated with vitamin D derivatives. Vitamin D compounds regulate the following processes: absorption of calcium and phosphate from the small intestine, mineral resorption in bone, and reabsorption of phosphate from the renal tubules. Working with PTH and calcitonin to regulate calcium homeostasis, vitamin D actually functions as a hormone. Patients receiving vitamin D products need to be cautioned about using OTC multiple-vitamin preparations and should be encouraged to increase dietary intake of calcium.