The Effect of PGF2α on the Expression of Sodium Dependent Vitamin C Transporters in Early vs. Mid-Cycle Corpora Lutea of Sheep

The corpus luteum (CL) is an ovarian structure responsible for progesterone secretion and the maintenance of early pregnancy. In the absence of pregnancy, the CL regresses in response to uterine prostaglandin PGF2α. Vitamin C is an antioxidant that scavenges free radicals generated during normal metabolic functions. Sodium dependent vitamin C transporters (SVCT) are responsible for maintaining high concentrations of vitamin C within the cell. Release of vitamin C from the CL is one of the first events to occur prior to luteolysis (regression). Exogenous PGF2 causes a transient (less than 24h) depletion of vitamin C from CL in the early luteal phase (day 1-4 after estrus), and these CL do not regress. Exogenous PGF2 in mid-luteal phase CL (day 10) causes an irreversible depletion of vitamin C, which is followed by luteal regression. Thus, the day 10 CL has acquired luteolytic capacity. The objectives of this research were to determine if exogenous PGF2α affected the concentrations of mRNA for SVCT 1 & 2 in sheep corpora lutea, and to determine if the effect was dependent upon the luteolytic capacity of the CL. We also examined if there was an acute (2h) or sustained (24h) effect of PGF2α on concentrations of SVCT mRNA. Mature ewes were randomly separated into two groups: early luteal phase (day 3) and mid luteal phase (day 10). Each group was further divided into two treatments, saline treated (control) or PGF2α treated. From each animal, two CL were harvested, one at 2h and the other 24h after treatment. Using real time polymerase chain reaction (RT-PCR) we were able to estimate relative concentrations of SVCT mRNA within the cells. We found that SVCT1 did not amplify to measureable levels during standard curve validation while SVCT2 did. As such, only SVCT2 mRNA concentrations were analyzed in this study. We found that in early cycle CL, treatment with PGF2α did not alter SVCT2 mRNA concentrations at 2 or 24hrs post treatment. As the CL aged from the early cycle to the mid luteal cycle, SVCT2 mRNA concentrations increased significantly within the corpus luteum. Finally, in mid cycle CL, SVCT2 mRNA concentrations did not change 2hrs after treatment with PGF2α, but decreased sharply 24hrs after treatment. Maintenance of SVCT2 mRNA concentrations in early cycle CL is likely critical in enabling those cells to recover their initial vitamin C concentrations 24hrs after treatment with PGF2α. The significant increase in vitamin C concentrations as the CL ages from the early cycle to the mid cycle, corresponds to an increase in transporter mRNA. With the increase in membrane transporters, the cell is able to take in more vitamin C which would account for the increased vitamin C concentrations seen in the mid cycle corpora lutea. The inability of mid cycle CL to recover their vitamin C concentrations 24hrs after treatment with PGF2α, is also related to the decrease in SVCT2 mRNA seen in these cells, because there were fewer transporters available with which to replenish cellular vitamin C concentrations. As we continue to increase our knowledge of the mechanisms involved in luteal function, we come closer to developing new reproductive techniques that can benefit both animals and humans in the future.Agriculture Honors ProgramWill C. Hauk Endowment FundNo embarg