ATP-sensitive potassium channels modulate in vitro tocolytic effects of β₂-adrenergic receptor agonists on uterine muscle rings in rats in early but not in late pregnancy.

Aim: To investigate whether ATP-sensitive potassium (K(ATP)) channels modulate the tocolytic effect of β2-adrenergic receptor (β2-AR) agonists (ritodrine and salmeterol) in early-pregnant (day 6) and late-pregnant (day 22) rat uterus in vitro, in order to examine the relation between the K(ATP) channel sulphonylurea-binding regulatory subunit (SUR) expression and pharmacological reactivity of β2-AR agonists.

Methods: The tocolytic effects of ritodrine and salmeterol (10(-10)-10(-5) M) on spontaneous rhythmic contractions were investigated cumulatively, alone, or in the presence of the K(ATP) channel blocker glibenclamide (10(-6) M) and the K(ATP) channel opener pinacidil (10(-9)-10(-7) M) after 5-min preincubation.

Results: β2-AR agonist induced myometrial relaxation was inhibited by glibenclamide and enhanced by pinacidil on day 6, when SUR1 expression levels were high.