Dr. Robert Gilbert
During a previous project we discovered that progesterone concentration was higher in pregnant than in non-pregnant mares 5 days after ovulation. This novel observation was confirmed recently by an independent group. The discovery is important because it changes current understanding of early pregnancy physiology, and may provide a basis for elucidation of the hitherto unresolved mechanism of recognition of pregnancy in mares. Importantly, it may also allow development of new methods of preventing early pregnancy attrition in horses. In this project, we will investigate the basis for elevated progesterone concentration in pregnant mares in three experiments, addressing three aims, all focused on the hypothesis that the embryo exerts a direct luteotrophic effect on luteal progesterone production.
In the first experiment, we will confirm that increased progesterone concentration is driven by the presence of an embryo rather than the reverse (i.e. that the embryo is more likely to survive in an environment of high progesterone concentration) by testing progesterone concentration in pregnant and non-pregnant bred mares, and in non-bred mares.
In the second experiment we will test the effect of direct co-culture of embryos with luteal tissue, expecting that the embryo will provoke increased progesterone production by cultured luteal tissue in vitro. Control groups will include medium alone,
luteal tissue alone and embryos alone. Progesterone production will be compared with embryo and luteal tissue cultured together.
Finally we will examine the gene expression (mRNA concentration) of genes coding enzymes important for steroidogenesis. RNA will be isolated from corpora lutea of pregnant, non-pregnant and non-bred mares and examined for expression of key steroidogenic enzymes by quantitative (real time) polymerase chain reaction (PCR).
Together these experiments will confirm the presence and illuminate the mechanism of increased progesterone concentration in pregnant mares, inform further studies, and lay the basis for interventions that could improve pregnancy rates in mares.