S. Mhaouty-kodja et al., Catecholamines are not linked to myometrial phospholipase C and uterine contraction in late pregnant and parturient mouse, J PHYSL LON, 536(1), 2001, pp. 123-131
1. We investigated whether catecholamines through activation of alpha (1)-a
drenergic receptors (alpha (1)-AR) are involved in mouse uterine contractio
n at parturition. Myometrial phospholipase C (PLC) activity and uterine con
traction were measured in response to noradrenaline (NA), the specific alph
a (1)-AR, agonist phenylephrine (Phe) and oxytocin (OT).
2. Using the reverse transcription-polymerase chain reaction RT-PCR, we det
ected the alpha (1a)-AR subtype in late pregnant mouse myometrium. We also
detected, by immunoblotting studies, PLC beta (1), PLC beta (3) and differe
nt alpha -subunits of pertussis toxin-insensitive (Ga alpha (q/II)) and -se
nsitive G proteins (G alpha (o/i3), G alpha (il/2)).
3. Phenylephrine and NA did not alter the myonietrial inositol phosphate (I
nsP) 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 b
y pertussis toxin (300 ng ml(-1), 2 h pretreatment), suggesting the involve
ment of a member of the G alpha (q) family.
4. Noradrenaline and Phe failed to increase uterine contraction at late Pre
gnancy 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 li
nked to myometrial PLC activation and uterine contraction in late pregnant
and parturient mouse. This discrepancy between mouse and other mammals coul
d be attributed to the alpha (1)-AR subtype expressed in myometrium at this
time.