Cushing's Awareness: Pituitary hormones and disorders

Endocrine disorders usually involve a lot of testing, I thought I would spend some time the next few days talking about some of those tests. With Cushing's Disease, an adenoma can cause hypopituitarism and panyhypopituitarism as well as excess secretion of a hormone or hormones from the adenoma itself. In order to understand what tests are done and why you will first need to know more about the pituitary and disorders associated with it.

Hypopituitarism is a disorder where the pituitary does not secrete enough or any of one or more hormones. The literature varies on this, however. Some define it as "two or more hormones". However, the bottom line is the patient is deficient and this will affect one or more of the bodies functions. Panhypopituitarism, on the other hand, is the deficiency and/or total loss of all hormone production in the pituitary.

The pituitary gland is a bean-shaped (think lima bean) organ that is at the base of the brain. The gland anterior lobe, the intermediate lobe, the posterior lobe. The intermediate lobe is rudimentary in human beings but produces several hormones whose physiologic significance is only now being established.
The pituitary is attached to the hypothalumus (a part of the brain that affects the pituitary gland) by nerve fibers. The pituitary gland itself consists of three sections:

Anterior lobe:

• growth hormone
• prolactin - to stimulate milk production after giving birth
• ACTH (adrenocorticotropic hormone) - to stimulate the adrenal glands
• TSH (thyroid-stimulating hormone) - to stimulate the thyroid gland
• FSH (follicle-stimulating hormone) - to stimulate the ovaries and testes
• LH (luteinizing hormone) - to stimulate the ovaries or testes

Intermediate lobe:

• MSH(melanocyte-stimulating hormone)- to control skin pigmentation

Posterior lobe:

• ADH (antidiuretic hormone) - to increase absorption of water into the bloodby the kidneys
• oxytocin - to contract the uterus during childbirth and stimulate milk production. It is also believed to be important for orgasm

Each of these hormone levels can tell a diagnostician a lot about the state of the pituitary and what may be happening there. The level of each is like a piece of the puzzle, and some need to be measured regularly to get the overall picture.

Not only are these hormone levels important, but the levels of other hormones affected by these are measured. In the thyroid, TSH from the pituitary affects the levels of T3 and T4.

In the adrenal gland, the level of cortisol is affected by the level of ACTH.  It's that feedback loop I'm

always talking about. The level of cortisol at various times of the day (8 a.m., 4 p.m., and midnight) is an important tool for diagnosing Cushing's.  See "When Cortisol is a Night Owl" for more on this.

In post-pubescent females, FSH acts on the ovarian follicles to produce estrogens and LH is instrumental in the production of progesterone. In males, LH is instrumental in the production of testosterone. The hypothalamus secretes gonadotropin-releasing hormone (GnRH) to the pituitary gland in pulses. These, in turn, stimulate the pituitary gland to secrete luteinizing hormone (LH) which then stimulates the Leydig cells of the testes to produce testosterone.

Link

That brings us to the hypothalamus. The hypothalamus is a region of the brain above the pituitary. It contains several types of neurons responsible for secreting different hormones. These are released into the blood in the capillaries and travel to the anterior lobe of the pituitary.

• Corticotropin-releasing hormone (CRH)
• Thyrotropin-releasing hormone (TRH)
• Growth hormone-releasing hormone (GHRH)
• Gonadotropin-releasing hormone (GnRH)
• Dopamine
• Somatostatin

Each of these plays a role in the production of the hormones in the pituitary. Usually, those pituitary hormones are tested rather than the hypothalamic hormones. The hypothalamic hormones are often used to stimulate the pituitary to see if it is producing those anterior lobe hormones, so they are valuable in the testing process.

Altogether, these glands and their hormones comprise the Hypothalamic-Pituitary-Adrenal axis, also known as the HPA-axis. I have not touched on the adrenal hormones, yet, except to mention cortisol.
I will get there.