Nitric Oxide

Question 1

Viagra inhibits ____, which breaks down nitric oxide.

Answer 1

Phosphodiesterase 5, which breaks down nitric oxide.

Question 2

Why is the choroid just like the penis

Answer 2

Both are innervated by the same types of sympathetic/parasympathetic nerves, both are vascular, and both react the same way with Viagra.

Question 3

How can viagra like drugs cause improvement in glaucoma patients

Answer 3

By increasing blood flow

Question 4

What first messenger and enzyme is required for the choroid cells to release NO into the smooth muscle to cause relaxation?

Answer 4

Acetylcholine

Nitric oxide synthase (NOS)

Question 5

Nitric oxide binds to which receptors?

Answer 5

G proteins

Question 6

What does NO cause when released?

Answer 6

Relaxation, dilation

Can also cause oxygen free radicals and hydrogen peroxide, which can lead to DNA fragmentation and cell death.

Question 7

In the vasculature, NO reacts with ___, stimulating it to produce the intercellular mediator ____, which does what?

Answer 7

Iron
cyclic GMP.
cGMP, in turn, enhances the release of neurotransmitters, resulting in smooth muscle relaxation and vasodilation.

Question 8

nNOS

• Found where?
• Acts like what?
• Responsible for?

Answer 8

Neuronal nitric oxide synthase.

Found in the choroid and retina
Acts like a neurotransmitter
Also found in the brain and involved with learning and memory
Responsible for vasodilation

Question 9

_____ nervous system regulates blood flow constantly to the eye to keep it steady during systemic BP changes

Answer 9

Parasympathetic

Question 10

eNOS

• Found where
• Regulates what
• May be involved with what

Answer 10

Endothelial nitric oxide synthase.

• Found in the endothelium (corneal endothelium)
• Regulates basal choroidal blood flow and ciliary blood flow, therefore aqueous humor production.
• May be involved in decrease blood flow in ARMD or glaucoma. (both have lower baseline blood flow)

Question 11

iNOS

• Found where?
• Role

Answer 11

Inducible nitric oxide synthase.

Found in RPE.
Should only be used for a short time in order to help during periods of stress. Can cause oxidative damage to RPE, creating H2O2 and oxygen free radicals, which will damage the tissues and cause apoptosis.

Also made by neutrophils.

Question 12

4 examples of second messengers that can affect blood flow on a regional basis

Answer 12

1. Adenosine from ATP
2. Carbon monoxide (has a higher affinity for hemoglobin that Co2)
3. Carbon dioxide
4. AA, which synthesizes leukotrienes, thromboxanes, and prostaglandins.

Question 13

How does the production of NO change with age?

Answer 13

An uneven distribution of NO synthesizing mechanism occurs, which results in the build up of iNOS. iNOS can cause oxidative damage by creating H2O2 and oxygen free radicals, leading to apoptosis.

Question 14

VEGF

Answer 14

Vascular endothelial growth factor. Keeps blood vessels happy, but can cause neo-vascularization.

Can affect NO, which affects smooth muscles by relaxing it, decreasing proliferation of cells, or decreasing fibrotic activity.

Question 15

Nitroglycerin (GTN) is used to make

• What can it treat?
• Main role?

Answer 15

Bombs and dynamite. Also used in medication as a vasodilator. Can be used to treat heart failure, high blood pressure, and/or angina (chest pain when heart muscles don’t get enough oxygen rich blood).

180th most prescribed medication

Question 16

NO impact on BBB and BRB

Answer 16

eNOS and iNOS keep tight junctions between endothelial cells closed. Uses G proteins.