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 alpha (1)-adrenergic receptors (alpha (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 alpha (1)-AR, agonist phenylephrine (Phe) and oxytocin (OT). 2. Using the reverse transcription-polymerase chain reaction RT-PCR, we detected the alpha (1a)-AR subtype in late pregnant mouse myometrium. We also detected, by immunoblotting studies, PLC beta (1), PLC beta (3) and different alpha -subunits of pertussis toxin-insensitive (Ga alpha (q/II)) and -sensitive G proteins (G alpha (o/i3), G alpha (il/2)). 3. Phenylephrine and NA did not alter the myonietrial 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 muM) recruited PLC beta (1) and PLC beta (3) 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 G alpha (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 muM. 5. The results indicate that OT receptors (OTR) but not alpha (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 alpha (1)-AR subtype expressed in myometrium at this time.