Thromboxane and Stable Prostaglandin Endoperoxide Analogs Stimulate Water Permeability in the Toad Urinary Bladder

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Abstract
The effects of thromboxane B2 and the stable prostaglandin endoperoxide analogs (15Z)-hydroxy - 9α - 11α - (epoxymethano)prosta - 5Z,13E - dienoic acid (U44069) and (15Z)-hydroxy -11α,9α-(epoxymethano) prosta-5Z,13E-dienoic acid (U46619) were tested on water flow across the toad urinary bladder. In the presence of indomethacin or meclofenamic acid, inhibitors of prostaglandin and thromboxane A2 synthesis, thromboxane B2 stimulated water flow in a dose-dependent manner. U44069 (1 μM) stimulated water flow from 3.6±0.8 to 12.4±1.2 mg/min per 10 cm2 hemibladder surface area, while U46619 (1 μM) stimulated water flow from 2.8±1.0 to 21.8±2.0 mg/min per 10 cm2. The prostaglandin endoperoxide/thromboxane A2 antagonist trans- 13-azaprostanoic acid, an inhibitor of vasopressin-stimulated water flow, inhibited thromboxane B2- and U46619-stimulated water flow in a dose-dependent manner. The inactive cis-13-azaprostanoic acid did not inhibit vasopressin-stimulated water flow in untreated hemibladders and had no effect on U46619-stimulated water flow in indomethacin or meclofenamic acid pretreated hemibladders. U46619 (1 μM) enhanced vasopressin-stimulated water flow in indomethacin pretreated hemibladders, producing a significant parallel shift (P < 0.001) in the dose-response relationship to submaximal concentrations of vasopressin (0.1-0.6 mU/ml), while not affecting water flow stimulated by supramaximal concentrations of vasopressin (10 mU/ml). trans-13-Azaprostanoic acid abolished the potentiating effects of U46619 on vasopressin-stimulated water flow. These results show that thromboxane A2-like compounds stimulate water flow in the toad urinary bladder.