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  • Title: Dexamethasone effects on ritodrine-induced changes in myometrial contractility and beta-adrenergic receptor function.
    Author: Ward SM, Caritis SN, Chiao JP, Moore JJ.
    Journal: Am J Obstet Gynecol; 1988 Dec; 159(6):1461-6. PubMed ID: 2849880.
    Abstract:
    We have previously demonstrated in pregnant sheep that ritodrine infusion for 24 hours reduces myometrial beta-adrenergic receptor density and isoproterenol-stimulated adenylate cyclase activity. These receptor-associated changes were accompanied by an increasing inability of ritodrine to inhibit uterine contractility induced by a bolus of oxytocin. In the present study, we evaluated whether these ritodrine-induced effects could be altered by dexamethasone. Ten pregnant sheep at gestational ages of 92 to 130 days received ritodrine 2 micrograms/kg/min for 24 hours. Five animals also received dexamethasone 10 mg intravascularly twice during the ritodrine infusion. Before and at 4 and 24 hours of ritodrine infusion, the animals were given an identical dose of oxytocin as a bolus, and the area under the uterine pressure-time curve was quantified. Myometrial biopsy specimens were obtained before and after ritodrine infusion. Dexamethasone treatment prevented ritodrine-induced reductions in beta-adrenergic receptor density and isoproterenol-stimulated adenylate cyclase activity. Despite these receptor-associated effects, dexamethasone did not prevent the loss of tocolytic efficacy associated with prolonged ritodrine infusion.
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