H3 - Pituitary H Fxn

Question 1

How does the Hypothalamus tonically inhibit the secretion of PRL? (3 ways)
Name one drug used.

Answer 1

Via PIH (DA)

1. Reduces synthesis and release of PRL
2. Inhibits lactotroph cell division
3. Increase destruction of PRL containing secretory granules

• give DA agonist (bromocriptine) to reduce excess release of prolactin
• other AP H unaffected

Question 2

Lactotrophs make up how much of the adenohypohysis?

Answer 2

30%

*but 10% of dry weight of Anteriorhypohysis is GH

Question 3

In cases of prolactin secreting tumors, what can get impaired?

Answer 3

Reproduction

High lvls of PRL → inhibits pulsatile secretion of GnRH by hypothalamic neurons

Question 4

GH and PRL share what receptors?

Answer 4

growth hormone/cytokine receptor family (JAK/STAT family of receptors)

Ligand binds → tyrosine kinase (JAK) receptors dimerize/couple → phosphorylation of STATs → activate JAK/STAT pathway

Question 5

After GH is synthesized as a prohormone, where is it stored?

Answer 5

In secretory granules of somatotrophs of the adenohypophysis

*recall that GHRH and somatostatin stimulation of somatotrophs have opposing actions on cAMP lvls and ultimately GH

Question 6

GH and Prolactin are:

peptide, catecholamines, or steroids?

Answer 6

Peptide

• majority circulate in unbound form and has short half life of 20-45 min
• Interacts with receptors in PM

*note: PRL, GH, ADH, and Oxytocin are peptide hormones.

Question 7

Direct target and actions of GH

metabolic effects

Answer 7

1. Adipose tissue
   ↑ lipolysis → mobilization of lipid + ↑ FFA
   Antagonize insulin
2. Muscle
   ↑ AA transport + protein synthesis
3. Liver
   ↑ RNA, protein, and glucose synthesis
   Secretes IGF-1 (mediates indirect effect)
   ↑ gluconeogenesis

*in addition to metabolic effects, GH also has effects on muscle and skeletal growth which is mediated by IGF (indirect)

Question 8

Indirect actions of GH

Answer 8

Indirect actions of GH is on muscle and skeletal growth mediated by IGF

1. Bone/cartilage:
   IGF-1 stim. proliferation of epiphyseal cartilage (long bone growth)
2. Muscle:
   stim prolif, differentiation, and protein synthesis
3. Adipose tissue:
   Stim uptake of glucose, inhibits lipolysis (GH directly ↑ lipolysis)
   - recall action of IGF is insulin like and antagonizes GH

*recall that direct effect is on adipose, muscle, and liver

Question 9

Production of IGF requires what?

Answer 9

GH AND Insulin

Question 10

Insulin like Growth Factor (IGF-1)

Answer 10

Insulin like actions (shocker)

Powerful Mitogen and growth promoting agent

Slowly increases from birth → puberty

GH promotes IGF-1 secretion

Question 11

Stimuli of GH secretion

Answer 11

1. Hypoglycemia
2. AAs (arginine)
3. ↓ FFAs
4. a-adrenergic agonist (clonidine)
5. b-adrenergic ANTAGONIST (propanolol)
6. estrogens

Question 12

Inibitors of GH secretion

Answer 12

1. Hyperglycemia
2. ↑ FFA
3. Obesity
4. a-adrenergic ANTAGONIST
5. b-adrenergic agonist
6. pharmacological doses of corticosteroids