Ontogeny of StAR and ACTH-R genes in ovine placenta

It has been demonstrated that the ovine placenta secretes estrogen, progesterone and cortisol, and that plasma concentrations of estrogen and cortisol increase before birth. Among the elements important for steroid production is steroidogenic acute regulatory protein (StAR) which acutely delivers cholesterol from the outer to the inner mitochondrial membrane for rapid steroidogenesis. This study was designed to determine if StAR is present in ovine placenta, and if its expression changes during fetal development. In addition, because cortisol is secreted by the placenta, we also examined the expression of adrenocorticotropic hormone receptor (ACTH-R) to determine if it was present and if the pattern of expression changed as gestation proceeded. The mRNA levels for StAR and ACTH-R were assessed by RNase protection assay (RPA) and protein levels were measured by Western blot in placentas from pregnant ewes (100-105 days of gestation, n = 8; 120 days of gestation, n = 5; 135-142 days of gestation, n = 8). The data show that the ovine placenta expresses StAR and ACTH-R. There was a significant increase in the StAR mRNA and protein between 100 and 142 days of gestation, but there were no significant age-related changes in ACTH-R mRNA and protein levels. The data suggest that the increased steroid production by the placenta in late gestation may be related to the increased expression of StAR.