Prolactin - Trachte

Question 1

What are the Hypothalamic factors of the Prolactin Endocrine Axis?

Answer 1

Prolactin releasing hormone/factor is a hypothesized primary stimulus

Other positive stimuli are vasoactive intestinal peptide (VIP) and Thyrotropin releasing hormone (TRH)

Prolactin inhibitory factors = Dopamine is primary inhibitor

Question 2

How does Prolactin initiate change on target cells?

Answer 2

interacts through a Janus kinase cell surface receptor (i.e., a Tyrosine kinase JAK/STAT dimer family) to start a cascade of transcription events

Question 3

What are the physiologic effects of Prolactin?

Answer 3

1. Immunity and autoimmunity
2. Breast development during pregnancy:
   prolactin involved in expansion of lobular-alveolar development during pregnancy
3. Milk secretion during lactation:
   prolactin stimulates milk production/lactation
   this is inhibited by high levels of progesterone - no lactation with retained placenta and immediately post-partum

Question 4

How does the hypothalamus regulate the secretion of Prolactin?

Answer 4

Under tonic inhibition by the hypothalamus – through dopamine which is a Prolactin Inhibitory Hormone/Factor (PIH/PIF) –

Acts through Dopamine D2 receptors which reside on pituitary lactorophs

The hypothesized Prolactin releasing hormone is stimulatory.

Question 5

What is the negative feedback from increasing prolactin levels?

Answer 5

There is none!

Question 6

What causes Prolactin Hypersecretion?

Answer 6

Pituitary tumors secreting prolactin.

Tumor that disrupts tonic inhibition

Iatrogenic: Dopaminergic blocking agents (numerous)

Injury, lesion

***NOT associated with pregnancy/lactation.

Question 7

What are the symptoms of Prolactin hypersecretion?

Answer 7

Males => Impotence

Females => amenorrhea, galactorrhea, infertility

Question 8

What are the treatments for a hyperprolactinemia tumor?

Answer 8

dopamine (D2) agonists => Cabergoline (preferred) and Bromocriptine

Question 9

What are the potential adverse side effects of Cabergoline and Bromocriptine?

Answer 9

nausea, vomiting, dizziness (think dopamine antagonists treat N/V, so D2 agonists cause N/V)

orthostatic hypotension may occur (dopamine vasodilates)

discouraged use to prevent post-partum lactation because of increased incidence of strokes and psychiatric manifestations