Seminal fluid signaling in the female reproductive tract: lessons from rodents and pigs

¹ Research Centre for Reproductive Health, Department of Obstetrics and Gynaecology, University of Adelaide, SA 5005, Australia.

^* To whom correspondence should be addressed. E-mail: sarah.robertson{at}adelaide.edu.au.

	Abstract

Seminal fluid contains potent signaling agents that influence female reproductive physiology to improve the chances of conception and pregnancy success. Cytokines and prostaglandins synthesized in the male accessory glands are transferred to the female at insemination, where they bind to receptors on target cells in the cervix and uterus, activating changes in gene expression leading to modifications in structure and function of the female tissues. The consequences are increased sperm survival and fertilization rates, conditioning of the female immune response to tolerate semen and the conceptus, and molecular and cellular changes in the endometrium that facilitate embryo development and implantation. Male-female tract signaling occurs in rodents, livestock animals, and all other mammals examined thus far, including humans. In mice, the key signaling moieties in seminal plasma are identified as members of the transforming growth factor- family. Recent studies indicate a similar signaling function for boar factors in the pig, whereby both the sperm and plasma fractions of seminal fluid appear to synergize in activating an inflammatory response and downstream changes in the female tract after insemination. Seminal plasma elicits endometrial changes with induction of pro-inflammatory cytokines and cyclo-oxygenase-2, causing recruitment of macrophages and dendritic cells. Sperm contribute by interacting with seminal plasma factors to modulate neutrophil influx into the luminal cavity. The cascade of changes in local leukocyte populations and cytokine synthesis persists through the pre-implantation period. Exposure to seminal fluid alters the dynamics in pre-implantation embryo development with an increase in the number of fertilized oocytes attaining viable blastocyst stage. There is also evidence that seminal factors influence the timing of ovulation, corpus luteum development and progesterone synthesis. Insight into the molecular basis of seminal fluid signaling in the female reproductive tract may inform new interventions and management practices to ensure maximal fertility and reduce embryo mortality in pigs and, potentially, other livestock animals.

Key Words: Pig, seminal fluid, Pregnancy, Reproduction, Rodent, Uterus

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