1. Mechanism of Hormonal Action
22/02/2019
Dr. Omary Chillo (MD, PhD)

2. What are the general mechanisms of hormonal action?
22/02/2019
Dr. Omary Chillo (MD, PhD)

3. Dr. Omary Chillo (MD, PhD)
Hormone
Signaling Cascade
Surface Receptors
Cytoplasmic Receptors
Nuclear
Receptors
Biological Action
22/02/2019
Dr. Omary Chillo (MD, PhD)

4. Down Regulations of Receptors
Decreased in the number of receptors
Receptors destroyed or deactivated
Decreases Responsiveness of the target tissue to the hormone
22/02/2019
Dr. Omary Chillo (MD, PhD)

5. Up Regulations of Receptors
Increase in the number of receptors
Receptors activated or manufactured
Increases responsiveness of the target tissue to the hormone
22/02/2019
Dr. Omary Chillo (MD, PhD)

6. Intracellular Signaling
Hormone-receptor complex
Activated Receptor initiates hormonal effects by:-
Changing the membrane potential
Activating intracellular enzymes
Activating genes
22/02/2019
Dr. Omary Chillo (MD, PhD)

7. Intracellular Signaling
Changing the membrane potential
Na+
Hormone-receptor complex
Activated Receptor
Open or close Na+, K+, Ca2+
Eg. Epinephrine and norepinephrine
22/02/2019
Dr. Omary Chillo (MD, PhD)

8. Intracellular Signaling
Activating Intracellular Enzymes
Hormone-receptor complex
Enzyme A
Activated Kinase
Molecule P
Second Messenger
Eg. Insulin
22/02/2019
Dr. Omary Chillo (MD, PhD)

9. Intracellular Signaling
Activating genes
Hormone-receptor complex
Genetic Transcription
e.g. Thyroxine
22/02/2019
Dr. Omary Chillo (MD, PhD)

10. Second Messenger Mechanisms
Enzyme A
Second Messengers
cyclic AMP/cyclic GMP
Calcium-Calmodulin complex
Phospholipase C
22/02/2019
Dr. Omary Chillo (MD, PhD)

11. Adenyl Cyclase-cAMP Mechanisms
Gs Protein
Enzyme
Adenyl Cyclase
Examples:-
FSH
TRH
Angiotensin II
Glucagon
HCG
TSH
PTH LH
ATP
Activated cAMP
Protein P
ADP
ATP
22/02/2019
Dr. Omary Chillo (MD, PhD)

12. Phospholipase C Mechanisms
Examples:-
Oxytocin
GnRH
TRH
Vasopression
Angiotensin II
Gs Protein
PIP2
IP3
DAG
Ca2+
Cell Response
22/02/2019
Dr. Omary Chillo (MD, PhD)

13. Activated Receptor Calcium-Calmodulin Mechanisms Ca2+
Hormone-receptor complex
Activated Receptor
Ca2+ binds to Pr-calmodulin
Activation of Protein Kinases
Eg. Smooth muscle contraction is brought by activation of myosin kinase
22/02/2019
Dr. Omary Chillo (MD, PhD)

14. Dr. Omary Chillo (MD, PhD)
Properties of the hormone effect
1. Specificity
The special feature of the target cells is the presence of receptors which can “attract” and interact with the hormone.
22/02/2019
Dr. Omary Chillo (MD, PhD)

15. Dr. Omary Chillo (MD, PhD)
2. Signal Transmission
The role of the hormones is to transit the regulatory signals from the control (endocrine) system to the target cells (organs or glands).
It could enhance or inhibit some function of the target.
22/02/2019
Dr. Omary Chillo (MD, PhD)

16. Dr. Omary Chillo (MD, PhD)
3. High Biological Efficiency
Low plasma concentration (nmol – pmol/L) great regulatory function
22/02/2019
Dr. Omary Chillo (MD, PhD)

17. Dr. Omary Chillo (MD, PhD)
4. Interaction Between the Hormones
(1) Synergistic effects. When two or more hormones work together to produce particular result their effect are said to be synergistic.
These effects may be additive or complementary.
Additive: Same effect of the hormones on one target organ, for example, epinephrine and norepinephrine on the heart rate
Complementary: Work on different stages of a physiological procedure, for example, FSH (initiation) and testosterone (maintenance) on spermatogenesis
22/02/2019
Dr. Omary Chillo (MD, PhD)

18. Dr. Omary Chillo (MD, PhD)
22/02/2019
Dr. Omary Chillo (MD, PhD)

19. Dr. Omary Chillo (MD, PhD)
(2) Permissive effect. A hormone is said to have a permissive effect on the action of a second hormone when it enhances the responsiveness of a target organ to the second hormone or when it increases the activity of the second hormone.
Estrogen – Expression of progesterone receptors on uterus – progesterone effect on the uterus.
Glucocorticoids – effects of catecholamines on cardiovascular system
22/02/2019
Dr. Omary Chillo (MD, PhD)

20. Dr. Omary Chillo (MD, PhD)
(3) Antagonist Effects. In some situations the actions of one hormone antagonize the effects of another.
Lactation during pregnancy is prevented because the high concentration of estrogen in the blood inhibits the milk secretion and action of prolactin.
22/02/2019
Dr. Omary Chillo (MD, PhD)

21. Dr. Omary Chillo (MD, PhD)
Thanks
22/02/2019
Dr. Omary Chillo (MD, PhD)