Intrauterine seminal plasma increases ovarian steroidogenesis in the pig

Abstract

Previous studies have shown that intrauterine infusion of seminal plasma (SP) increases litter size in gilts, an effect attributed to beneficial effects on early preimplantation embryo development mediated via cytokines secreted by endometrial cells. More recently SP treatment has been reported to advance ovulation in sows, indicating a role of SP in ovarian regulation. In vitro studies have suggested a mechanism whereby SP treatment of gilts increases progesterone secretion by cultured granulosa cells and thecal tissue. The present study investigates the effect of SP treatment on ovarian function in vivo in gilts during early luteal development. Ten Large White X Landrace gilts were given transcervical infusion of either seminal plasma (SP) or saline (PBS) prior to artificial insemination with extended semen. Venous blood samples were collected daily during the first 9 days post-insemination by means of chronic indwelling venous catheters inserted before ovulation. Serum progesterone levels were measured using radioimmunoassay (DSL). Ovarian tissues were collected at autopsy on day 9 for determining ovulation rate and corpora lutea (CL) weights. Seminal plasma induced a marked increase in serum progesterone levels (p<0.006) and CL weight (p=0.042) compared to the PBS-treated controls, without a change in ovulation rate. This result suggests that SP treatment of gilts enhances ovarian function by increasing steroidogenic activity of luteal cells during early pregnancy. The increase in the production of progesterone in the pre-implantation period may enhance embryo survival, thereby contributing to increased littersize. Transforming growth factor beta (TGF) has been identified as the active moiety in human and murine seminal plasma in initiating the post-mating inflammatory response in the uterus. Similar high concentrations of this cytokine have also been measured in pig seminal plasma (unpublished data). Further studies will investigate whether TGF is the agent responsible for enhancement of luteal function in the pig, and whether increased progesterone secretion during the preimplantation period contributes to the fertility enhancement previously reported. (Supported in part by Pig Research & Development Corporation, Australia).