Date Published: August 3, 2006
Publisher: BioMed Central
Author(s): Dagmar Waberski, Anke Döhring, Florencia Ardón, Nadine Ritter, Holm Zerbe, Hans-Joachim Schuberth, Marion Hewicker-Trautwein, Karl Fritz Weitze, Ronald HF Hunter.
Whole boar semen or seminal plasma has been demonstrated to advance the time of ovulation in gilts. As a means of clarifying this influence, the contribution of uterine lymphatics and their white cell populations has been examined. After duct visualisation with Evan’s blue, lymph was sampled from a mesometrial vessel in eight pre-ovulatory gilts whose uterine lumen was infused simultaneously with whole semen in one ligated horn and saline in the contralateral ligated horn. Lymph was collected from cannulated vessels for periods of up to four hours under general anaesthesia. Thereafter, mesometrial lymph nodes, utero-tubal junction and uterine wall tissues were sampled. The proportion of nucleated cells in the sampled lymph increased towards the end of the collection period, but erythrocytes were found in all instances preventing a meaningful differentiation and identification of leukocytes. Prominent uterine lymph nodes were present in the mesometrium on both sides of the reproductive tract in 7 of 10 gilts. Differences in cellular contents were demonstrated between the side of the tract infused with semen and that infused with saline control. Two of 4 gilts had lower values for CD4 (Cluster Differentiation) and 3 of 6 gilts higher values for MHC II (Major Histocompatibility Complex) markers on the side challenged with semen. In contrast, values remained constant for CD8 but ranged widely for CD18. Immunohistochemical analysis of uterine tissue samples for MHC II+ cells revealed significant differences (P < 0.05) between the control and semen-treated ligated portions of the horns, as well as between the tissue sample of uterine wall and that from the utero-tubal junction, but there were no significant differences for CD4+ cells. It therefore remains plausible that semen-induced cytokines in the uterine lymph undergo counter-current transfer to the ipsilateral ovary and accelerate the final maturation of pre-ovulatory Graafian follicles.
The process of ovulation has continued to attract attention since the appreciation that it is triggered by a surge of gonadotrophic hormones detectable in the systemic circulation [1-4]. This surge is known to be prompted by either a positive feedback influence of oestradiol from the maturing follicle(s) in so-called spontaneous ovulators or coital stimulation in reflex ovulators . Elevated levels of hypophyseal gonadotrophins in the systemic circulation bind to ovarian tissues during the pre-ovulatory interval , but the full spectrum of changes consequent upon such binding remains to be described. Classical features include an increase in bloodflow, a progressive shift in steroid hormone synthesis from oestradiol to progesterone representing the onset of luteinisation, a morphological reorganisation of the granulosa cell layers and dissolution of the basement membrane enabling vascularisation of the granulosa, and a resumption of meiosis in the oocyte(s) destined to be shed into the Fallopian tube(s) (reviewed by Hunter ).
Ten animals underwent the above procedures and samples of lymph were collected in eight of them.
In terms of clarifying the phenomenon of precocious ovulation in pigs as a response to infusion of whole semen into the uterus, this preliminary study has not provided specific data as to underlying physiological mechanisms. Nonetheless, it has offered one line of guidance which can be developed in future studies when the technical problem of obtaining lymph samples free of blood contamination in acute experiments has been resolved. The relevant observations concern populations of leukocytes and short-term responses to treatments as monitored in uterine tissues and mesometrial lymph nodes.
It remains plausible that semen-induced cytokines in the uterine lymph undergo counter-current transfer to the ipsilateral ovary and accelerate the final maturation of pre-ovulatory Graafian follicles.
The author(s) declare that they have no competing interests.