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Abstract
PURPOSE: This study was performed to determine if the circadian rhythm of aqueous humor formation and the aqueous humor suppressing effect of beta-adrenergic antagonists can occur in the absence of adrenally derived epinephrine. METHODS: Twenty-one human subjects who had undergone bilateral adrenalectomy were studied during a 28-hour period. The study was divided into four time periods as follows: morning 1 (8 AM to noon), afternoon (noon to 4 PM), night (midnight to 6 AM), and morning 2 (8 AM to noon). At 6:45 AM before the morning 2 measurements, one drop of 0.5% timolol was applied to one eye and one drop of placebo (artificial tears) was applied to the other eye. Topical fluorescein and a scanning fluorophotometer were used to measure the rate of aqueous humor flow. Twenty normal controls were studied in a similar fashion but did not undergo the morning 2 measurement. RESULTS: In the subjects lacking adrenals, the daytime rates of aqueous flow were 3.17 +/- 0.78 microliters/min (mean +/- SD) and 3.16 +/- 0.67 microliters/min for the morning 1 and afternoon periods, respectively. The rates in daytime periods were not significantly different from each other (P = 0.699). The rate of aqueous flow for the night period was 1.37 +/- 0.37 microliters/min, a 57% reduction from both morning 1 and afternoon periods (P < 0.001). The morning, afternoon, and night rates of flow in normal controls were not significantly different from the rates in subjects lacking adrenals. For the morning 2 period, the aqueous flow was 2.74 +/- 0.54 microliters/min for the placebo-treated eye and 1.77 +/- 0.38 microliters/min for the timolol-treated eye. The rate of aqueous flow was reduced (35%) in the timolol-treated eye when compared to the fellow placebo-treated eye (P < 0.001). The timolol-treated eye also showed a 26% reduction in intraocular pressure when compared to the fellow placebo-treated eye (P < 0.001). CONCLUSION: The study demonstrates that both the circadian rhythm of aqueous flow and the daytime response to timolol persist in the absence of the adrenal glands.