Prolactin-secreting pituitary tumors

Published on 02/03/2015 by admin

Filed under Endocrinology, Diabetes and Metabolism

Last modified 02/03/2015

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CHAPTER 20

Prolactin-secreting pituitary tumors

1. Describe the normal control of prolactin secretion. How is it altered in prolactin-secreting tumors?

Multiple factors affect prolactin secretion (Fig. 20-1). However, the principal influence on prolactin secretion is tonic inhibition by dopamine input from the hypothalamus. Dopamine interaction with receptors of the D2 subtype on pituitary lactotroph membranes activates the inhibitory G-protein, leading to decreased adenylate cyclase activity and decreased levels of cyclic adenosine monophosphate (cAMP). In prolactin-secreting pituitary adenomas, a monoclonal population of prolactin-producing cells escapes the normal physiologic input of dopamine from the hypothalamus, apparently by acquiring a peripheral blood supply. In almost all cases, responsiveness to a pharmacologic dose of dopamine is maintained.

2. What are the normal levels of serum prolactin? Are they different in men and women? What levels are seen in patients with prolactin-secreting tumors?

3. What are the physiologic causes of an elevated prolactin level that must be considered in the differential diagnosis of prolactin-secreting tumors? What levels can be reached under these circumstances?

4. List the abnormal causes of an elevated serum prolactin value other than a prolactin-secreting tumor, and state the mechanisms underlying the abnormal prolactin production.

See Table 20-1.

TABLE 20-1.

ABNORMAL CAUSES OF ELEVATED SERUM PROLACTIN LEVEL OTHER THAN PROLACTIN-SECRETING TUMORS AND UNDERLYING MECHANISM OF ABNORMAL PROLACTIN PRODUCTION

CAUSES MECHANISM
Pituitary stalk interruption
Trauma
Surgery
Pituitary, hypothalamic, or parasellar tumor
Infiltrative disorders of the hypothalamus
Interference with the hypothalamic-pituitary pathways: Prolactin production increases because the tonic inhibition of prolactin secretion is interrupted; often accompanied by hypopituitarism
Pharmacologic agents:
 Phenothiazines
 Tricyclic antidepressants
 Alpha-methyldopa
 Metoclopramide
 Cimetidine
 Estrogens
Specific interference with dopaminergic input to the pituitary gland
Hypothyroidism Increased thyrotropin-releasing hormone that stimulates prolactin release
Renal failure and liver cirrhosis Decreased metabolic clearance of prolactin; also, increased production in chronic renal failure
Intercostal nerve stimulationChest wall lesions
Herpes zoster
Mimicking of the stimulation caused by suckling

5. What are the typical levels of serum prolactin associated with these causes?

6. How does prolactin elevation result in gonadal dysfunction? What are the symptoms associated with gonadal dysfunction?

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