PURPOSE. TO determine the effect of moderate zinc deficiency on antioxidant
defenses and measures of oxidative stress in the retina and retinal pigmen
t epithelium (RPE) of Brown Norway Rats.
METHODS. Twenty-four rats were housed individually and divided into three g
roups of 8 rats each. Group 1 was fed ad libitum a semipurified control die
t formulated to contain 50 parts per million [ppm] total zinc; group 2 was
fed ad libitum an identical diet but containing 5 ppm total zinc; and group
3 was pair-fed the control diet but restricted in amount to that consumed
by group 2. Food intake was measured daily and the rats weighed weekly. Aft
er 6 weeks, the rats were killed and the following measurements were made:
serum zinc, serum alkaline phosphatase, retinal zinc, RPE choroid zinc, RPE
-choroid catalase, liver metallothionein (MT), retinal MT, RPE-choroid MT,
retinal catalase. and retinal thiobarbituric reactive substances (TBARS).
RESULTS. The following showed statistically significant differences between
groups 2 and 3, respectively: serum Zn (1216 mu g/l versus 1555 mu g/l, P
less than or equal to 0.01), serum alkaline phosphatase (3.75 U/mg versus 5
.10 U/mg, P less than or equal to 0.05), liver MT (4.3 mu g/mg protein vers
us 16.7 mu g/mg, P less than or equal to 0.0001), RPE-choroid MT (1.3 mu g/
mg protein versus 2.2 mu g/mg, P less than or equal to 0.02), retinal MT (0
.85 mu g/mg protein versus 2.8 mu g/mg, P less than or equal to 0.05), and
retinal TEARS (6.2 nM/mg protein versus 2.2 nM/mg, P less than or equal to
0.05).
CONCLUSIONS. The results show that retinal MT and RPE MT concentrations are
very sensitive to intake of dietary zinc. The increase in retinal TBARS in
group 2 indicates that moderate zinc deficiency increases oxidative stress
to the retina. The results also suggest that MT is protective against lipi
d peroxidation of retinal membranes.