Abstract
Purpose: :
To determine the 24-hour pattern of aqueous humor protein concentration in rats and explore whether it is driven endogenously and/or affected by ambient light.
Methods: :
Sprague-Dawley rats 10-12 weeks of age were entrained to a standard light-dark cycle (lights turned on at 6am and off at 6pm). On the day of the experiment, the rats were divided into 2 groups: (1) standard light-dark condition with aqueous humor samples collected every 4 hours at 6 time points (8am, noon, 4pm, 8pm, midnight, and 4am) and (2) acute constant dark condition (lights not turned on at 6am, but instead remained off) with aqueous humor samples collected every 4 hours at 3 time points (8am, noon, and 4pm) during the subjective light-phase. Protein concentrations of aqueous humor samples collected from 10-14 rats at each time point were determined using the Bradford method.
Results: :
Average aqueous humor protein concentrations ranged from a minimum of 0.305±0.115 mg/ml (mean±SD, N=10) at midnight to a maximum of 1.505±0.342 mg/ml (N=14) at noon under standard light-dark condition. Under standard light-dark condition the 3 light-phase aqueous humor protein concentration values were each higher than all the dark-phase values (One-way ANOVA and post-hoc Bonferroni tests, P<0.05), demonstrating a consistent pattern of 24-hour aqueous humor protein concentration. Under acute constant dark condition, the 3 subjective light-phase aqueous humor concentration values each remained higher than all the subjective dark-phase values (One-way ANOVA and post-hoc Bonferroni tests, P<0.05), demonstrating an endogenously regulated pattern of aqueous humor protein concentration in the absence of light. At 8am, noon, and 4pm, aqueous humor protein concentrations were higher under standard light-dark condition than under acute constant dark condition (Student’s t-test, P<0.01), demonstrating that exposure to light increases aqueous humor protein concentration.
Conclusions: :
We observed an endogenously driven 24-hour pattern of aqueous humor protein concentration that was accentuated by a physiological effect of ambient light, with higher concentrations of protein during the subjective light-phase than during the subjective dark-phase. This pattern is inversely related to the intraocular pressure pattern previously demonstrated in the Sprague-Dawley rat. This experiment shows a physiological effect of light on aqueous humor protein concentration in rats.
Keywords: aqueous • circadian rhythms • anterior chamber