UV absorption by uric acid in diurnal bird aqueous humor.
OBJECTIVE
To analyze the components responsible for the UV absorbance in diurnal bird aqueous humor.


METHODS
The absorbance studies were carried out using a Hitachi spectrophotometer (U 2000). Uric acid was determined by high-performance liquid chromatography (LC-10 system; Shimadzu, Kyoto, Japan). Chicken and turkey eyes were examined.


RESULTS
The UV absorbance in chicken aqueous was largely accounted for by the presence of protein, tryptophan, tyrosine, ascorbic acid, and uric acid. Ascorbic acid was low (23 micromol/l). Uric acid was, on the other hand, remarkably high (151 micromol/l) compared with that in mammals (cattle, 16 micromol/l). Principally the same results were obtained in chicken and turkey.


CONCLUSIONS
Uric acid is a significant UV-absorbing substance in the aqueous humor of diurnal birds with its peak absorbance at 292 nm. The hypothesis that the aqueous humor acts as a UV filter seems to be valid also for the avian eye. However, in these eyes uric acid fulfills the role that ascorbic acid does in mammals.
Ringvold
A
A
Eye Department, National Hospital, Oslo, Norway. a.d.ringvold@klinmed.uio.no
Anderssen
E
E
Kjønniksen
I
I
D000042:Absorption; D000818:Animals; D001082:Aqueous Humor / Q000378:metabolism*; D001205:Ascorbic Acid / Q000378:metabolism; D002417:Cattle; D002645:Chickens; D002851:Chromatography, High Pressure Liquid; D005136:Eye Proteins / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D014364:Tryptophan / Q000378:metabolism; D014422:Turkeys; D014443:Tyrosine / Q000378:metabolism; D014466:Ultraviolet Rays; D014527:Uric Acid / Q000378:metabolism* / Q000528:radiation effects*
D005136:Eye Proteins; D014527:Uric Acid; D014443:Tyrosine; D014364:Tryptophan; D001205:Ascorbic Acid