Catecholamines are not linked to myometrial phospholipase C and uterine contraction in late pregnant and parturient mouse

Abstract

1. We investigated whether catecholamines through activation of α1-adrenergic receptors (α1-AR) are involved in mouse uterine contraction at parturition. Myometrial phospholipase C (PLC) activity and uterine contraction were measured in response to noradrenaline (NA), the specific α1-AR agonist phenylephrine (Phe) and oxytocin (OT). 2. Using the reverse transcription-polymerase chain reaction RT-PCR, we detected the α1a-AR subtype in late pregnant mouse myometrium. We also detected, by immunoblotting studies, PLCβ1, PLCβ3 and different α-subunits of pertussis toxin-insensitive (Gαq/11) and -sensitive G proteins (Gαo/i3, Gαi1/2). 3. Phenylephrine and NA did not alter the myometrial inositol phosphate (InsP) production of late pregnant or parturient mouse. In similar conditions, OT increased InsP production in a dose-dependent manner. Consistent with these results, only OT (10 μM) recruited PLCβ1 and PLCβ3 to myometrial plasma membranes. The OT-induced InsP response was not altered by pertussis toxin (300 ng ml-1, 2 h pretreatment), suggesting the involvement of a member of the Gαq family. 4. Noradrenaline and Phe failed to increase uterine contraction at late pregnancy and at parturition. In contrast, OT induced uterine contraction in a dose-dependent manner with maximal increase (400%) at a concentration of 1 μM. 5. The results indicate that OT receptors (OTR) but not α1-AR are linked to myometrial PLC activation and uterine contraction in late pregnant and parturient mouse. This discrepancy between mouse and other mammals could be attributed to the α1-AR subtype expressed in myometrium at this time.