Follicles in pregnant rat ovary are incapable of steroidogenesis

Antral follicles are present in the ovaries throughout gestation. These follicles are “physically immature” and cannot ovulate under the induction of LH/hCG. The purpose of the present study is to examine whether follicles in pregnant rat ovaries are capable of steroidogenesis. StAR is believed to be the key regulator of steroid hormone biosynthesis. Antisense StAR probe and anti-StAR rabbit serum have been used to detect the StAR expression in ovarian follicles at various stages of pregnant rats. The results indicate that theca-interstitial cells and the membrane granulosa cells at the stages from the estrous or pre-estrous in the normal cycling rat ovary express StAR mRNA and its protein, whereas neither granulosa cells nor the theca cells in pregnant ovary throughout gestation express StAR. These results indicate that the pregnant follicles throughout gestation are incapable of steroidogenesis.