Endocrine PhysiologyPituitary

Bob Bing-You, MD, MEd, MBA

Medical Director

Maine Center for Endocrinology

Anterior Pituitary

• 1 cm diameter, 0.5-1 gm weight

• Sits in sella turcica

• Connected with hypothalamus via stalk

• The “master gland”

• Six major hormones

Which is not an anterior pituitary hormone?

• A. Prolactin

• B. ACTH

• C. Luteinizing hormone

• D. Vasopressin

• E. Thyrotropin

Growth Hormone

• Promotes growth as child

• Facilitates protein formation, via Insulin-Like Growth Factor 1

• Deficiency = short stature as child

• As adult: poor Quality of Life, osteoporosis, hyperlipidemia

• Excess = acromegaly

IGF-1

• Produced in liver predominantly

• Paracrine effects

• Receptors important for function

• IGF-1 approved as therapy

Adrenocorticotropin

• Stimulated by corticotropin-releasing hormone [CRH]

• Under negative feedback control by cortisol

• Stimulates adrenal cortex to produce glucocorticoids such as cortisol

Thyrotropin [TSH]

• Stimulated by thyrotropin-releasing hormone [TRH]

• Under negative feedback control by T4 and T3

• Stimulates thyroid to increase iodine uptake, produce thyroid hormone

FSH/LH

• Stimulated by gonadotropin-releasing hormone [GnRH]

• Under negative feedback by gonadal steroids [estrogen and testosterone]

• FSH promotes follicle or sperm development

• LH promotes estrogen or testosterone production

Disease deficiency states

• Non-functioning tumors– FSH/LH often first to go

• Head trauma

• Infiltrative diseases

• “Empty sella” syndrome

• Rx underlying cause; replace end hormonal product

Disease excess states

• Acromegaly – rare

• Cushing’s Disease – rare; tumor producing ACTH

• TSH producing tumor – rarer, usually associated with GH - tumor

She has:

• A. Prolactinoma

• B. Cushings Syndrome

• C. Hangover

• D. Hypothyroidism

• E. Acromegaly

Prolactinomas

• Most common secretory pituitary tumor

• 40% of all pituitary tumors

• Most common symptom = hypogonadism– Amenorrhea/galactorrhea– Low libido, erectile dysfunction, gynecomastia

• PRL level and MRI for diagnosis

• Medical Rx almost always 1st choice

Medical Therapy

• Tonically inhibitory dopaminergic fibers from hypothalamus

• Bromocriptine [Parlodel], cabergoline [Dostinex], quinagolide, pergolide

• All effective in reducing tumor size and/or PRL

• ~25% of treated patients have <25% to no decrease size

Bromocriptine vs. cabergoline

• Bromocriptine– Since 1960’s

– Nausea, lightheadedness

– Daily

– 2.5 mg – 10 mg/day

• Cabergoline– Newest

– Once a week

– Little side effects

– 0.5 – 2.0 mg/week

• Both safe in pregnancy

Take-home Points

• Anterior pituitary major player in normal endocrine physiology

• Excess states are surgical problems except for prolactinomas

Questions?

Which is not true?

• A. Too much IGF-1 will cause acromegaly

• B. FSH surge causes ovulation

• C. Most prolactinomas are medically treated

• D. Sarcoidosis can cause adrenal insufficiency

Posterior Pituitary

• Antidiuretic hormone [ADH] aka “vasopressin”

• Formed in supraoptic nuclei in hypothalamus; accumulate in nerve endings in pituitary

• Without ADH, renal collecting tubules totally impermeable to water

ADH

• Minute quantities ADH can cause water reabsorption

• ADH binds to receptors, triggers cAMP, open pores to water

• Under regulation osmoreceptors, sense concentration in extracellular fluid

Diabetes insipidus

• Nephrogenic: renal resistance to ADH– E.g., lithium

• Central D.I.: decreased posterior pituitary secretion of ADH

Diagnosis of Diabetes Insipidus must include:

• A. Copious urine excretion [500 cc/hr]

• B. Low urine specific gravity [e.g., < 1.005]

• C. Hypernatremia

• D. Hypokalemia

Clinical Vignette

• 64 y.o. woman post-op CABG

• Vasopression drip

• Stopping drip, BP drops, Na climbs to 154

• Daughter states mother drinking gallons daily for few years

Treatment of D.I.

• Maintain access to free water

• D5W IV

• DDAVP [desmopressin]– Nasal, oral, IM or IV– Can be given once or twice/day– Resistance rare– Toxic effect is hyponatremia

Key Points

• ADH major hormone of posterior pituitary

• Diabetes insipidus more likely seen post-pituitary surgery

Questions?