Ultraviolet radiation-B-induced cataract in albino rats: maximum tolerable dose and ascorbate consumption.
OBJECTIVE
To investigate the maximum tolerable dose (MTD) for cataract induced by ultraviolet radiation-B (UVB) in 7-week-old albino rats and to study the effect of UVB eye exposure on lens ascorbate content.


METHODS
Fifty 7-week-old albino Sprague Dawley rats were unilaterally exposed in vivo to 300-nm UVB under anaesthesia, receiving 0, 0.25, 3.5, 4.3 and 4.9 kJ/m(2). The MTD was estimated based on lens forward light scattering measurements. Lens ascorbate content was determined in the processed lens using high performance liquid chromatography with UVR detection.


RESULTS
Animals exposed to UVB doses >or=3.5 kJ/m(2) developed cortical cataracts. The MTD for avoidance of UVB-induced cataract was estimated to 3.01 kJ/m(2). UVB exposure decreased lens ascorbate concentration in the exposed lens in line with UVB dose, H(e), according to the models: C = C(NonCo) + C(Co)e(-kH(e) ) for exposed lenses; C = C(NonCo) + C(Co) for non-exposed lenses, and C(d) = C(Co)(e(-kH(e) ) - 1). Parameters for consumable and non-consumable ascorbate were estimated to C(NonCo) = 0.04 and C(Co) = 0.11 micromol/g wet weight of lens. For lens ascorbate difference, tau = 1/k = 0.86 kJ/m(2). A total of 63% of UVB consumable ascorbate has been consumed after only tau = 0.86 kJ/m(2), while MTD(2.3 : 16) = 3.01 kJ/m(2), indicating that ascorbate decrease is in the order of 3.5 times more sensitive to detecting UVR damage in the lens than forward light scattering.


CONCLUSIONS
The MTD for avoidance of UVB-induced cataract in the 7-week-old albino Sprague Dawley rat was estimated to be 3.01 kJ/m(2). In vivo UVB exposure of the rat eye decreases lens ascorbate content following an exponential decline, and suprathreshold doses cause greater effect than subthreshold doses.
Mody
Vino C
VC
St Erik's Eye Hospital, Karolinska Institute, Stockholm, Sweden. vino.mody@ste.ki.se
Kakar
Manoj
M
Elfving
Ase
A
Söderberg
Per G
PG
Löfgren
Stefan
S
D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism*; D002386:Cataract / Q000209:etiology* / Q000378:metabolism / Q000517:prevention & control; D002851:Chromatography, High Pressure Liquid; D004307:Dose-Response Relationship, Radiation; D005260:Female; D007908:Lens, Crystalline / Q000378:metabolism / Q000528:radiation effects*; D020714:Maximum Tolerated Dose; D011833:Radiation Injuries, Experimental / Q000209:etiology* / Q000378:metabolism / Q000517:prevention & control; D051381:Rats; D017207:Rats, Sprague-Dawley; D014466:Ultraviolet Rays / Q000009:adverse effects*
D001205:Ascorbic Acid