The production of the hormone progesterone is important for the maintenance of pregnancy in the mammalian system. There are two groups of granulosa cells found in the ovary prior to ovulation that may possibly be involved in the maintenance of pregnancy. The PI wants to determine the function of one group, namely the cumulus granulosa cells during pregnancy since these cells disappear right after ovulation and their role remains a mystery. It is already known that the other group, the mural granulosa cells, become part of the corpus luteum following ovulation and produce progesterone. An attempt will be made here to compare the relative abilities of these two cell populations to secrete progesterone under simulated in vivo conditions using a newly developed technique known as the kidney transplantation procedure. The cells will be placed under the kidney capsule of a pregnant rat and observed for secretion of progesterone. This SGER proposal is considered high risk because of the uncertainty that this unique technique will provide the feasibility of assessing the in vivo function of the cumulus granulosa cells.