Smooth Muscle (pt 4/4) Nitric Oxide

Question 1

What is the difference between N2O and NO2?

Answer 1

N2O = Nitrous Oxide (anesthetic gas)
NO2 = Toxic Pulmonary Irritant

Question 2

What is Nitric Oxide?

Answer 2

-A highly reactive gaseous signaling molecule
-Readily diffuses across cell membranes
-Endogenous to the human body
-Potent Vasodilator
-Platelet Inhibitor
-Immune Regulator
-Neurotransmitter
-Exogenous NO and NO-releasing compounds used in pharmacology (Nitrates, nitrites, nitroprusside, nitroglycerin)
-A naturally occurring environmental pollutant
-The major bioactive component of Endothelial-Derived Relaxing Factor (EDRF)
-Acts on vascular smooth muscle → relaxation

Question 3

A gas that can diffuse through cell membranes.
-Triggers biochemical reactions
-Dissipates rapidly
-Synthesized & released by normal endothelium
-Regulated by endothelial ICF Ca++
↑ cytosol Ca++ ⇒ NO production
-Synthesis induced by increased stress

Answer 3

Nitric Oxide

Question 4

Increased cytosol Ca++ causes what?

Answer 4

Nitric Oxide Production

Question 5

What substances lead to increased cytosol Ca++ (leading to increased Nitric Oxide)?

Answer 5

Ach
Bradykinin
Catecholamines
Substance P
ADP

Question 6

What is the MOA of Nitric Oxide?

Answer 6

-Vasodilation via guanylyl cyclase activation (↑cGMP)
-Inhibits platelet aggregation (Anti-thrombotic effect)
-Inhibits platelet derived vasoconstrictive substances
-Produced in leukocytes, fibroblasts, & vascular smooth muscle

Question 7

The synthesis of Nitric Oxide is made by 1 of 3 enzymes that are expressed in a wide variety of cell types. What are the 3 enzymes?

Answer 7

nNOS (NOS-1)
iNOS (NOS-2)
eNOS (NOS-3)

Question 8

What is nNOS (NOS-1)?

Answer 8

nNOS (NOS-1) – neuronal
Triggered by ↑ intracellular Ca2+

Question 9

What is iNOS (NOS-2)?

Answer 9

-inducible or macrophage
-Triggered by inflammatory mediators
-Has constitutive activity

Question 10

What is eNOS (NOS-3)?

Answer 10

eNOS (NOS-3) – endothelial
Triggered by ↑ intracellular Ca2+

Question 11

NO mediates its effects by ______ modification of proteins.

Answer 11

covalent

Question 12

How does Nitric Oxide interact with metals (Metalloproteins)?

Answer 12

-NO interacts with metals especially Heme
-NO binds to the heme of sGC (primary target)
-Synthesizes GTP to cGMP to activate Protein Kinase G (PKG)
-Reduce Ca2+ levels in blood vessels
-Decreases vascular tone
-Decreases vascular smooth muscle contraction
-Mechanism contributes to cytotoxic effects r/t NO overproduction
-NO inhibits the heme of heme-containing CYP450 enzymes
-Major cause of inflammatory liver disease

Question 13

How does Nitric Oxide overproduction contribute to inflammatory liver disease?

Answer 13

Nitric Oxide binds to heme, synthesizing GTP to cGMP and activating Protein Kinase G (PKG).
-NO Inhibits the heme of heme-containing CYP450 enzymes
-Major cause of inflammatory liver dz

Question 14

How does Nitric Oxide interact with Thiols?

Answer 14

-Compounds containing a carbon bonded sulfur + hydrogen group
-NO + (-SH) = nitrosothiol
-Found endogenously in the amino acid cysteine
-Unknown physiologic role

Question 15

What is Tyrosine Nitration?

Answer 15

-NO undergoes both oxidation and reduction reactions
-NO reacts very efficiently to superoxide
-Superoxide = O2- (a free radical; Synthesized by many cellular enzymes)
-NO + (O2-) = OONO- (Peroxynitrite – highly reactive oxidizing agent that causes DNA damage, Nitration of tyrosine, and Oxidation of cysteine to disulfides or sulfur oxides)
-Reaction is mitigated by glutathion
-NO synthesis is increased in many inflammatory and degenerative diseases (Shown by Increasing Peroxynitrite levels and Increased tyrosine nitration = irreversible protein modification (Activate or inhibit protein function) )
-(+) Detection of tyrosine in tissues is a sign of oxidative stress
-Accumulation of toxins, peroxides and free radicals

Question 16

What is Superoxide (O2-)?

Answer 16

A free radical synthesized by many cellular enzymes.

Question 17

Nitric Oxide + Superoxide (O2-) = ?

Answer 17

Peroxynitrite (OONO-): a very highly reactive oxidizing agent.

Question 18

What are the effects of Peroxynitrite (OONO-)?

Answer 18

-DNA damage
-Nitration of tyrosine
-Oxidation of cysteine to disulfides or sulfur oxides

Question 19

What mitigates the reaction of Nitric Oxide + Superoxide to Peroxynitrite?

Answer 19

Glutathione

Question 20

NO synthesis is ________ in many inflammatory and degenerative diseases.

Answer 20

Increased

Question 21

Increased Nitric Oxide synthesis in inflammatory and degenerative diseases leads to ?

Answer 21

-Increasing Peroxynitrite levels
-Increased tyrosine nitration = irreversible protein modification (Activate or inhibit protein function).

Question 22

What is a sign of oxidative stress?

Answer 22

(+) Detection of tyrosine in tissues
Accumulation of toxins, peroxides and free radicals

Question 23

Endogenous vasodilators (Acetylcholine or bradykinen) activate NO synthesis in the luminal endothelial cells, leading to ?

Answer 23

Endogenous vasodilators (Acetylcholine or bradykinen) activate NO synthesis in the luminal endothelial cells, leading to calcium efflux from the endoplasmic reticulum into the cytoplasm

Question 24

Increased Calcium into the cytoplasm causes Ca to bind to _____, which activates _______, resulting in ____ synthesis from _______.

Answer 24

Calcium binds to calmodulin (CaM), which activates NO synthase (eNOS), resulting in NO synthesis from L-arginine.

Question 25

NO diffuses into smooth muscle cells, where it activates ________ and _____ synthesis from ______.

Answer 25

NO diffuses into smooth muscle cells where it activates soluble guanylyl cyclase and cGMP synthesis from guanosine triphosphate (GTP).

Question 26

cGMP binds to and activates ______, resulting in an overall reduction in calcium influx and _______ of calcium-dependent muscle contraction.

Answer 26

cGMP binds to and activates protein kinase G (PKG), resulting in an overall reduction in calcium influx and inhibition of calcium-dependent muscle contraction.

Question 27

PKG can also block _____ that lead to muscle contraction.

Answer 27

PKG can also block other pathways that lead to muscle contraction.

Question 28

cGMP signaling is terminated by ______, which convert cGMP to ______.

Answer 28

cGMP signaling is terminated by phosphodiesterases, which convert cGMP to GMP.

Question 29

What is the primary approach to decreasing Nitric Oxide generation in cells?

Answer 29

NOS Inhibitors.

Question 30

What is the structure of NOS Inhibitors?

Answer 30

Structure = Arginine analogues Bind to the NOS arginine-binding site

Question 31

NOS's are structurally _____, so most meds are non-selective.

Answer 31

NOS’s are structurally similar so most meds are non-selective

Question 32

nNOS Inhibition is useful in what disorders?

Answer 32

nNOS Inhibition – useful in neurodegenerative disorders

Question 33

iNOS inhibition is useful in what disorders?

Answer 33

iNOS Inhibition – useful in sepsis and inflammatory disorders

Question 34

Concurrent eNOS inhibition impairs what?

Answer 34

Concurrent eNOS inhibition impairs hemostatic signaling. -Vasoconstriction -Ischemic damage

Question 35

NOS selective drugs are ?

Answer 35

Under investigation.

Question 36

What is the MOA of Nitric Oxide donors?

Answer 36

Metabolized to release Nitric Oxide and elicit smooth muscle relaxation.

Question 37

Explain the effects of Organic Nitrates.

Answer 37

-Ex: Nitroglycerin is metabolized to NO, promoting venous dilation. Arterial & venous dilation with less effects on platelet aggregation. -Exhibit tolerance during continuous administration

Question 38

Explain the effects of Organic Nitrites.

Answer 38

Arterial vasodilators but abused for euphoric effects. -Require metabolic activation to elicit vasorelaxation -Arterial vasodilators -Do not exhibit tolerance

Question 39

What is the example drug of the Organic Nitrites?

Answer 39

Ex: Inhaled Amyl Nitrite

Question 40

What are the effects of Sodium Nitroprusside (Nipride)?

Answer 40

Arterial & venous dilation and used to rapidly reduce arterial HTN. -Dilates arterioles and venules -Used for rapid pressure reduction in arterial hypertension -Breaks down to cyanide and NO in the presence of light and via chemical/enzymatic mechanisms

Question 41

What are the effects of NO Inhalation?

Answer 41

Reduces PA pressures & improves perfusion of ventilated lung areas. -Used in the Tx of: Pulmonary HTN, Acute Hypoxia, and CPR. -Ex: Compressed Gas

Question 42

What reaction can occur with the use of Compressed Gas for NO Inhalation?

Answer 42

-Can react with O2=NO2 -Pulmonary irritant = decreased lung function -Can induce the formation of methemoglobin

Question 43

What is the example drug of the PDE Inhibitors?

Answer 43

Sildenafil

Question 44

What are the effects of the PDE Inhibitors?

Answer 44

Slows the degradation of cGMP & prolong NO effects. -Risk for Hypotension, blindness with surgery & anesthesia (ischemic optic neuropathy)

Question 45

Why should you give Newborns with hypoxic respiratory failure due to pulmonary hypertension Inhaled Nitric Oxide?

Answer 45

Because it dilates the pulmonary vessels. ↓ Peripheral Vascular Resistance ↓ PA Pressures ↓ V/Q Mismatch due to dilation of lung tissue with better ventilation

Question 46

Does Extracorporeal membrane oxygenation (ECMO) effect pulmonary pressures?

Answer 46

No