Progesterone decreases the relaxing effect of the β3-adrenergic receptor agonist BRL 37344 in the pregnant rat myometrium

Abstract

Although the published results regarding the function of the β3-adrenergic receptors (β3-ARs) in the regulation of smooth muscle activity are very promising, the question of the mechanism of β3-ARs' action in the pregnant myometrium cannot be fully answered by human investigations. To assess whether it possesses an essential role in the regulation of uterine contractility in pregnant rats, as in humans, we performed functional, western blotting and molecular biology experiments on the late-pregnant rat myometrium. The influence of progesterone on the function of the β3-ARs was also investigated. We demonstrated the presence and the functional activity of the β3-ARs in the late-pregnant rat myometrium. The maximum dose-dependent uterus-relaxing effect of the selective β3-agonist BRL 37344 was recorded at the end of pregnancy in rats, similarly as in humans. The extent of its relaxing action was regarded as moderate. The expression of β3-AR protein and mRNA remained unchanged during the investigated period. The administration of progesterone had no effect on the β3-AR mRNA and protein expression or the maximum relaxation effect of BRL 37344, but shifted the dose–response curve to the right and decreased the synthesis of the second messenger, cAMP. It can be concluded that the β3-ARs play an additional role in the regulation of the contractile activity of the pregnant rat uterus. The inhibitory effect of progesterone on the functional activity of the β3-ARs may have important consequences in the case of human application if this effect is also demonstrated in pregnant human myometrial tissue.