Retinal Metabolism Flashcards
Sources of metabolites for retina
Glycogen stores (retina) Glucose (aqueous) Amino acids (aqueous) A variety of saturated and unsaturated fatty acids (aqueous)
Delivery of glucose into the retina
Derived from the serum
Simple diffusion into aqueous
Glucose in the aqueous
Due to the open system nature of glucose metabolism, there is a constant flux of glucose from the plasma into the aqueous, and utilization by the retinal tissues
-aqueous glucose levels is ~80% of serum glucose level
Glucose metabolism of the retina, ciliary epithelium, lens and cornea contribute to the production of _________ even with aerobic conditions
Lactic acid
Trafficking of lactic acid in the eye
Lactic acid, although produced in significant quantities, does not accumulate in the aqueous of the posterior chamber to levels much above serum levels. Suggesting a mechanism for trafficking of lactic acid away from the aqueous
Accumulation of lactic acid in the aqueous
Does not accumulate, has a mechanisms for quick trafficking of lactic acid away from the aqueous
Although lactic acid is always produced by the tissues listed above (lens, cornea, ciliary epithelium, retina), when is lactic acid produced in the largest quantities?
During sleep or conditions that block atmospheric O2 from being absorbed by the eye. Aqueous O2 levels decreases significantly during sleep, resulting in less aerobic metabolism, thus production of more lactic acid
What effect of topical epinephrine to the eye would you expect on the metabolism?
Vasoconstriction, reduction in oxygen flow, increase in lactic acid
What supports the retinal tissue metabolism
Vitreous
Where does the retina get O2 from
In addition to the aqueous providing O2 derived directly from the atmosphere, the retina also abstains O2 from the vitreous.
O2 concentrations across the vitreous increase int he ______ direction in areas furthest away from the _____ of the eye
Posterior
Anterior
Evidence for O2 support by the vitreous for the retina
Retinal tears dramatically increase the level of O2 int he vitreous near the tear site
Other than O2, what does the vitreous do for the retina
Serves as a metabolic reservoir for the retina providing short-term nutrients during emergencies
Vitreous’ role in retinal ischemia
After 1 hour:
- retinal glycogen decreased 35%
- vitreous glucose decreased to 60% and lactic acid increased slightly
- vitreous glycogen decreased
Ascorbic acid in the vitreous
- High levels
- Vitreous to serum ratio 9:1
- Concentrated by active transport in ciliary body epithelium
- supplied by the diet
Reason for high ascorbic acid in the vitreous
Can absorb UV light
Serves as a free radical scavenger
Benefits of ascorbic acid in the vitreous
To protect the retina (and lens) from metabolic and light induced production of singlet oxygen
Evidence of the benefits of ascorbic acid in the vitreous
Supplements are shown to reduce the irreversible type I form of light damage to dark-reared rats and shift light damage to the reversible type II form of damage in cycle-light-reared animals
What can protect against oxidative damage due to inflammation
Ascorbic acid
Evidence that ascorbic acid protects against inflammation
Endotoxins induced ocular inflammation in rabbit resulted in an increased ascorbic acid concentration in the vitreous that was not derived from the aqueous
-it was likely that ascorbic acid synthesis was up regulated in response to inflammatory mediators such as histamine
What would be the significance of inflammation and ascorbic acid in humans
If you are having an inflammatory response, you should supplement with vitamin C to get more ascorbic acid since we don’t synthesize our own
What transporter used for glucose in retina?
GLUT3
Which of the following is insulin depending and would not be found in the retina?
GLUT 4
What si the major energy metabolism pathways in the retina?
Glycolysis
TCA and electron transport
When is lactic acid produced int he largest quantities in the retina
When eyes are closed, sleeping
What are the important things that ascorbic acid do to protect the lens and the retina?
Protects against UV light damage and protects against radical damage and inflammatory damage
When the eye is subject to endotoxins that cause an inflammatory response, which of the following would likely protect the eye?
Ascorbic acid
