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Effects of Ethacrynic Acid on Intraocular Pressure of Anesthetized Rats

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Abstract:

Ethacrynic acid (ECA) lowers intraocular pressure (IOP) by an effect usually ascribed to increased drainage of aqueous humor by the trabecular meshwork. Here, we describe the effects of a continuous 2-hr intracameral infusion of balanced salt solution (BSS), with or without 2 mM ECA (sodium salt), on IOP of pentobarbital anesthetized rats. The infusion was divided into a constant (0.05 μl/min) and a periodic (0.25 μl/min) component that cycled 4 min on then 4 min off. This permitted the calculation of dynamic changes in resistive (trabecular and uveoslceral drainage) and nonresistive (aqueous synthesis, episcleral venous pressure) components of IOP by fitting a second-order transfer function to the responses. ECA markedly blunted the BSS-induced rise in IOP (P < 0.01). The rise in resistive mechanisms (ocular impedance) was transiently blunted by ECA (P < 0.05) during the third and fourth 8-min cycles, and nonresistive mechanisms were reduced by ECA from cycles 3–10 (P < 0.05). Then, at the end of the infusion, the control and ECA dynamic values were similar (P > 0.05), although IOP of ECA-treated rats was still slightly reduced (P < 0.05). The most likely explanation is a summation of small changes in both resistive and nonresistive components of IOP dynamics. Systemic blood pressure was unchanged within either group. The well-known effects of ECA on the trabecular meshwork, alone, are insufficient to explain the dynamic changes in IOP observed in this model.

Document Type: Research Article

Affiliations: 1: Department of Pharmacology, College of Medicine, The Pennsylvania State University, Hershey, Pennsylvania 17033 2: Department of Otolaryngology, Eye & Ear Institute of Pittsburgh, Pittsburgh, Pennsylvania 15213

Publication date: 1999-03-01

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