Comparaison de l’activité réflexe de l’utérus au cours de l’insémination artificielle et de l’accouplement chez la brebis

Abstract

To identify and to compare the reflex mechanisms involved in the activation of the uterine motility following artificial insemination (AI) and mating in the ewe. The contractile activity of the uterus was monitored in presence and absence of adrenergic (phentolamine) and cholinergic (atropine) antagonists, using an implantable telemetric device equipped with a sensor catheter inserted into the uterine lumen, and connected to a radio-telemetric transmitter. During AI, a uterine contraction (UC) of short duration (<20 seconds) appeared in direct response to animal restraint, to the speculum introduction, then when the speculum was opened. Both the UC evoked by restraint of the ewe and insertion of the speculum were abolished in presence of phentolamine, while atropine inhibited the UC in response to opening of the speculum only. After AI, the uterine activity increased sharply and was all the more intense and extended with higher vaginal wall pressure. Phentolamine or atropine did not inhibit this motor response, whereas a similar pattern of uterine hyperactivity occurred following i.v. injection of oxytocin (100 and 200 mIU; Syntocinon). After mating, an increase in uterine activity was never observed. Only penis intromission evoked a UC of short duration (about 20 seconds), abolished in presence of phentolamine only. Artificial insemination in the ewe increases uterine motility, resulting from the reflex activation of adrenergic and cholinergic nerve fibres of the autonomic nervous system, following by a reflex release of oxytocin from the pituitary gland (also called "Ferguson reflex"). This secretion of OT was elicited by the excessive dilation of the vaginal wall with the speculum. By comparison, mating did not evoke a period of uterine hyperactivity and respects the physiological post-coital resting period.