Beta 2-agonist treatment enhances uterine oxytocin receptor mRNA expression in pregnant rats.

The objective of this study was to disclose an interaction between Beta(2)-adrenergic (Beta(2)-ARs) and oxytocin (OT) receptors (OTRs) in the late-pregnant rat uterus. We investigated the level of uterine OTR mRNA expression after the administration of Beta(2)-AR agonists fenoterol and hexoprenaline to rats from day 18 to 22 of pregnancy, and also tested the effect of fenoterol on uterine explants. Hexoprenaline induced a maximum 24% increase of OTR mRNA. Fenoterol in vivo elicited a maximum 125% increase of OTR mRNA, in vitro produced a maximum fourfold increase in OTR mRNA. In fenoterol-treated rats the maximal contractility increasing effect of OT on isolated uterine rings was significantly higher than in intact term pregnant rats, but the EC50 values were not statistically different. It was concluded that the enhanced expression of OTR mRNA induced by Beta(2)-agonists in the late-pregnant rat uterus may be a possible drawback to effective therapy of preterm uterine contractions with Beta(2)-agonists.