PHYSIOLOGICAL FACTORS IN THE CIRCADIAN-RHYTHM OF PROTEIN-CONCENTRATION IN AQUEOUS-HUMOR

PURPOSE. The authors addressed three questions concerning the circadia n rhythm of aqueous humor protein concentration in rabbits. First, is there an endogenous oscillator for this circadian rhythm? Second, does a circadian rhythm occur for individual aqueous humor protein compone nts? Third, what is the role of ocular sympathetic nerves, which are m ore active in the dark phase, in this circadian rhythm? METHODS. Adult New Zealand albino rabbits were entrained to a daily 12-hour light/12 -hour dark cycle. Under a constant dark environment for 24 hours, rabb its were killed at 4-hour intervals, beginning at 2 hours before the o nset of the subjective light phase. Eight rabbits were used for each o f the six time points. Aqueous humor and vitreous humor were collected , and their protein concentrations were determined. Major aqueous humo r protein components were resolved by polyacrylamide gel electrophores is (PAGE), stained with silver reagent, and analyzed using densitometr y. Another group of eight light-dark-entrained rabbits underwent unila teral transection of the cervical sympathetic trunk. Three weeks after the operation, the circadian elevation of intraocular pressure (IOP) at 2 hours into the dark phase was determined for both eyes. Rabbits w ere later killed at this time point, and total protein concentrations in aqueous humor and vitreous humor were determined in both eyes. Majo r aqueous humor protein components in both eyes were resolved by PAGE and were compared. RESULTS. In light-dark-entrained rabbits, a circadi an rhythm of protein concentration appeared in the aqueous humor under a constant dark environment. Total protein concentration in aqueous h umor increased sharply in the early subjective light phase, remained r elatively high during the remainder of the subjective Light phase, and decreased in the subjective dark phase. Analyses of albumin and other abundant proteins in the aqueous humor showed that all of them varied similarly in a circadian pattern. In contrast, total protein concentr ation in the vitreous humor remained unchanged. In rabbits with unilat erally decentralized ocular sympathetic nerves, total protein concentr ations in the aqueous humor and the vitreous humor in the early dark p hase showed no difference between the two eyes. In addition, there was no difference in individual aqueous humor protein concentration betwe en the two eyes. However, the nocturnal IOP elevation in the decentral ized eye was less than that in the contralateral, intact eye. CONCLUSI ONS. The circadian rhythm of aqueous humor protein concentration in ra bbits can continue without an external signal of dark-light change, in dicating the existence of an endogenous oscillator. A similar circadia n rhythm occurs for various major aqueous humor protein components. Th e nocturnal increase in ocular sympathetic activities plays a limited role in the circadian rhythm of aqueous humor protein concentration.