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

1 We investigated whether catecholamines through activation of α 1 ‐adrenergic receptors (α 1 ‐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 α 1 ‐AR agonist phenylephrine (Phe) and oxytocin (OT). 2 Using the reverse transcription‐polymerase chain reaction RT‐PCR, we detected the α 1a ‐AR subtype in late pregnant mouse myometrium. We also detected, by immunoblotting studies, PLCβ 1 , PLCβ 3 and different α‐subunits of pertussis toxin‐insensitive (Gα q/11 ) and ‐sensitive G proteins (Gα o/i3 , Gα i1/2 ). 3 Phenylephrine and NA did not alter the myometrial inositol phosphate (Ins P ) production of late pregnant or parturient mouse. In similar conditions, OT increased Ins P production in a dose‐dependent manner. Consistent with these results, only OT (10 μ m ) recruited PLCβ 1 and PLCβ 3 to myometrial plasma membranes. The OT‐induced Ins P response was not altered by pertussis toxin (300 ng ml −1 , 2 h pretreatment), suggesting the involvement of a member of the Gα q 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 μ m . 5 The results indicate that OT receptors (OTR) but not α 1 ‐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 α 1 ‐AR subtype expressed in myometrium at this time.