Evidence for a noradrenergic transmission in the control of parturition in the rat.
6-Hydroxydopamine, when injected at 14:00 h on Days 21 and 22 of pregnancy in the rat (2 X 50 mg/kg), markedly decreased plasma and uterine noradrenaline concentrations (-60% and -82% respectively; P less than 0.001). As a consequence of this treatment, there was severe disturbance in the distribution pattern of parturitions: 61% of rats had suppressed parturition and 31% of rats displayed a lengthened or interrupted labour. A bolus dose of prazosin (3 mg/kg) administered at 12:00 h on Day 22 completely blocked the normal process of parturition throughout the next 6 h, a result which is compatible with the half-life of the drug (2.9 +/- 0.8 h). Administration of phentolamine (3 mg/kg) at term induced a significant decrease of uterine activity (frequency X duration of bursts of spike potentials) as revealed by electromyographic recordings in vivo. These results suggest that noradrenaline released from sympathetic nerve terminals interacts with alpha-adrenoceptors located post-synaptically to improve the overall excitability of the myometrium at the onset of labour.
Legrand
C
C
Maltier
J P
JP
D000818:Animals; D004576:Electromyography; D005260:Female; D006892:Hydroxydopamines / Q000494:pharmacology; D007743:Labor, Obstetric / Q000187:drug effects; D009638:Norepinephrine / Q000097:blood / Q000502:physiology*; D016627:Oxidopamine; D010646:Phentolamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D014590:Uterine Contraction / Q000187:drug effects*
D006892:Hydroxydopamines; D016627:Oxidopamine; D009638:Norepinephrine; D011224:Prazosin; D010646:Phentolamine