Search Results

You are looking at 1 - 3 of 3 items for

  • Author: C. Legrand x
  • All content x
Clear All Modify Search
Free access

C. Legrand and J. P. Maltier

Summary. 6-Hydroxydopamine, when injected at 14:00 h on Days 21 and 22 of pregnancy in the rat (2 × 50 mg/kg), markedly decreased plasma and uterine noradrenaline concentrations ( − 60% and −82% respectively; P < 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 × 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 α-adrenoceptors located post-synaptically to improve the overall excitability of the myometrium at the onset of labour.

Free access

C. Legrand, A. Banuelos-Nevarez, C. Rigolot, and J. P. Maltier

Summary. Sympathetic nerve terminals were destroyed by administration of 6-hydroxydopamine (2 × 50 mg/kg) at 10:00 h on Days 4 and 5 of pregnancy in the rat. In the myometrium, this treatment markedly decreased noradrenaline concentrations (by 99%, P < 0.001), demonstrating that myometrial noradrenaline is mainly originated from sympathetic nerves; therefore after 6-hydroxydopamine, the distribution and spacing of blastocysts remain unaffected throughout the uterus. Administration of phenoxybenzamine (2 × 6 mg/kg) in the morning of Days 4 and 5, or prazosin (4 × 3 mg/kg) from 12:00 h on Day 4 until 12:00 h on Day 5 disorganized the even distribution of blastocysts from the tubal end to the cervical end of the uterine horns. These results provide evidence that a noradrenergic transmission via action on myometrial post-synaptic α1-adrenoceptors is involved as a regulatory mechanism of uterine motility for distribution and spacing of blastocysts in the rat uterus.

Free access

C. Legrand, A. Banuelos-Nevarez, and J. P. Maltier

Summary. In the early pregnant rat, electrical activity of the myometrium consisted of regular bursts of spike potential, which appeared well propagated on Day 2 of pregnancy. During Day 3, there was a gradual disappearance of propagated activity. Concomitantly, there was a 7-fold increase (P < 0·001) of uterine progesterone concentrations. At this stage, mean duration of bursts was 15·2 ± 0·9 sec and intervals of complete quiescence between bursts were 84·2 ± 7·0 sec. At 10:00 h on Day 4, there were peaks in the uterine concentrations of oestradiol and progesterone, + 36% and + 654%, respectively, compared with values on Day 2 (P < 0·05). Between 10:00 and 20:00 h on Day 4, EMG activity exhibited a rapid and transient rise: bursts were of longer duration at the utero-tubal end of the horn (+ 60%, P < 0·05) with an increased amplitude of spike potentials (+67% and +90% respectively at the tubal and cervical ends of the uterus, P < 0·05). The administration of prazosin depressed EMG activity reversibly in a dose-dependent manner with maximal inhibition at about 2–3 h later. It is concluded that the changes observed during EMG recordings are relevant to the intrauterine distribution of blastocysts and related to changes in the steroidal environment and/or to catecholamine effects via α1-adrenoceptors.

Keywords: myometrial activity; blastocyst distribution; prazosin; rat