Cooperation of aquaporin 5 and the adrenergic system in the initiation of birth in rat model

Aquaporins (AQPs) are involved in the process of implantation, regulate myometrial contractions and cervical ripening, and maintain appropriate placental functioning. The molecular mechanism of these functions is not fully understood. Our study aimed to investigate the physiological significance of AQP5 during pregnancy and to determine the cooperation between the adrenergic system and the AQP5 in uterine contraction in the late-pregnant rat uterus. After administering AQP5 siRNA intraperitoneally to Sprague-Dawley rats, the length of the gestational period was determined and the changes in uterine contractions were measured in an isolated organ bath system. Pharmacological influence on AQP5 expression and uterine contraction was investigated by treatment with terbutaline (10 mg/kg, subcutaneously) and doxazosin (5 mg/kg, orally) <i>in vivo</i>; and mercuric chloride (HgCl₂), <i>in vitro</i>. Moreover, the levels of cAMP response element binding protein (CREB) were measured in the uterus by an ELISA kit. The gestational period became shorter, AQP5 expression significantly decreased and rat uterus contraction increased after AQP5 siRNA treatment compared to the control. Treatment with terbutaline significantly increased AQP5 mRNA and protein expression after 30 min and continuously reduced it until 90 min, whereas doxazosin treatment did not significantly alter AQP5 expression. Treatment with the AQP5 antagonist HgCl₂ increased spontaneous uterus contraction and decreased norepinephrine-induced uterus contraction with decreasing AQP5 expression in pregnant rat uterus. Moreover, the tocolytic effect through the adrenergic system was amplified in the presence of an AQP5 antagonist, presumably via the changes in cAMP level. In conclusion, our findings elucidate the collaborative role of aquaporin 5 (AQP5) and adrenergic systems in the regulation of uterine contractions in late-pregnant rats. Our findings suggest this may be a good starting point for developing a new tocolytic therapy.