Restricted accessResearch articleFirst published online 2001-7
Chloride Channel Blockers 5-nitro-2-(3-phenlpropyamino) Benzoic Acid and Anthracene-9-Carboxylic Acid Inhibit Contractions of Pregnant Rat Myometrium in Vitro
Objective:We compared in vitro relaxant effect of chloride channel modulators, such as 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and anthracene-9-carboxylate (9-AC), and β2-adrenergic agonists, such as ritodrine, in pregnant rat myometrium.
Methods:Isolated myometrial strips were obtained from eight pregnant rats, and the strips were mounted in organ baths for recording isometric tension. The effects of 10-8-10-4 M ritodrine, 10-6-3 × 10-4 M NPPB, and 10-6-10-3 M 9-AC on spontaneous contractions were recorded.
Results:Ritodrine (10-8-10-5 M) completely inhibited the amplitude and frequency of spontaneous contrations in myometrial strips isolated from pregnant rats in a concentration-dependent manner, but the relaxant effect of ritodrine at 10-4 M concentration resulted in tachyphylaxis. The chloride channel blocker NPPB (10-6-3 × 10-4 M) and the chloride transport inhibitor 9-AC (10-5-10-3 M) decreased the amplitude of spontaneous myometrial contractions in a concentration-dependent manner; the maximum inhibition produced by the highest tested concentration of each drug was 43.8% and 42.1% of the original degree of spontaneous contractions, respectively. The frequency of myometrial contractions was significantly inhibited by NPPB and 9-AC beginning with the concentration of 10-4 M.
Conclusion:NPPB and 9-AC appear to be effective relaxants of pregnant rat myometrium. These effects of NPPB and 9-AC might be therapeutically advantageous in clinical management of preterm labor.
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