Functional protection of photoreceptors from light-induced damage by dimethylthiourea and Ginkgo biloba extract.
OBJECTIVE
To investigate the functional protective effect of a synthetic (dimethylthiourea, DMTU) and a natural antioxidant (Ginkgo biloba extract, EGb 761) against light-induced retinal degeneration.


METHODS
Wistar rats were exposed for 24 hours to 1700-lux light after treatment with DMTU or EGb 761. Electroretinograms were recorded before and on day (D)1, D3, D8, D15, D22, and D29 after light exposure. The b-wave amplitude was plotted against log L (ganzfeld luminance), providing the b-wave sensitivity curve. The Naka-Rushton function fitted to the sensitivity curve enabled derivation of the parameters Bmax (saturated amplitude) and K (luminance-inducing Bmax/2). In addition, rats from each group were killed for retinal morphometric analyses.


RESULTS
In the untreated group, light exposure caused collapse of the b-wave sensitivity curves. Bmax was reduced by 51% at D1 without subsequent recovery. K increased temporarily, reverting to normal values 8 days later. The outer nuclear layer thicknesses decreased markedly in the superior retina. In the treated groups, light exposure had a weaker effect on sensitivity curves. The values of Bmax were not significantly different from those in the unexposed-untreated group, although K increased temporarily. Retinal morphometry was preserved.


CONCLUSIONS
Dimethylthiourea and EGb 761 afford functional protection against light-induced retinal damage.
Ranchon
I
I
Laboratory of Biophysics, School of Pharmacy, University of Auvergne, Clermont-Ferrand, France.
Gorrand
J M
JM
Cluzel
J
J
Droy-Lefaix
M T
MT
Doly
M
M
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D004596:Electroretinography; D005419:Flavonoids / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000494:pharmacology*; D020441:Ginkgo biloba; D008297:Male; D020419:Photoreceptor Cells, Vertebrate / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects*; D010936:Plant Extracts; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D012160:Retina / Q000187:drug effects / Q000473:pathology / Q000528:radiation effects; D012162:Retinal Degeneration / Q000517:prevention & control*; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology; D000096983:Ginkgo Extract
D000975:Antioxidants; D005419:Flavonoids; D016166:Free Radical Scavengers; D010936:Plant Extracts; D013890:Thiourea; C063170:Ginkgo biloba extract; D000096983:Ginkgo Extract; C038983:1,3-dimethylthiourea