Lecture 17 (hormone signaling and feedback control)

What are the 6 steps of hormone signaling?

1. Synthesis

2. Release

3. Transport

4. Recognition by specific receptor

5. Signal transduction

6. Removal of hormone signal

Peptide hormone synthesis

-Fast

-Peptide binds to receptor on membrane that causes transcription/translation

-Stored in secretory vesicles and degraded in blood

Steroid hormone synthesis

-Slow

-Enzymes convert cholesterol into steroids inside the cell

-Produced on demand and transported by carrier proteins

-Regulates gene expression

What are two major types of membrane receptors?

1. G protein coupled receptors

2. Tyrosine kinase protein receptors

G-protein coupled receptor

Uses a secondary messenger (cAMP or PIP2) to cause an action

What two enzymes use a tyrosine kinase receptor?

IGF-1 and insulin

Tyrosine kinase receptor pathway

Uses several second messengers to elicit transcription and translation of enzymes

How are most hormones regulated?

Negative feedback loop

Desensitization/adaptation

Receptor activation either shuts off the receptor or removes it from the membrane

Up-regulation

Receptor activation increases number or affinity for receptors

Hormone agonist

-Binds to a receptor and mimics the actions of a natural hormone

-Will either establish a full or partial response (depends on binding)

Hormone antagonist

-Binds to a receptor and interrupts natural hormone action

-Either competitive or noncompetitive inhibition

Hormone therapy

Use of hormone or analog (agonist or antagonist) as treatment for a hormone related disease

GnRH agonists

-Stimulate pituitary and causes pituitary desensitization (too much)

-May be effective for sterilization in males and some disease conditions in both genders

ADH antagonists

-Inhibit ADH action

-Increase urine output

-Decrease water reabsorption by the kidney