StAR protein is expressed in both medulla and cortex of the bovine and ratadrenal gland

We have employed polyclonal antibodies to a peptide sequence of bovine ster oidogenic acute regulatory (StAR) protein and human placental 3 beta-hydrox ysteroid dehydrogenase (3 beta-HSD) to determine the localisation and distr ibution of these proteins in rat and bovine adrenal glands. Immunohistochem ical staining demonstrated the presence of StAR protein in the zona glomeru losa (ZG), zona fasciculata (ZF), zona reticularis (ZR) and in the medulla of both species. For 3 beta-HSD, immunostaining was observed in the ZG, ZF and ZR of the rat adrenal and was absent in the medulla. Immunoblotting exp eriments showed intense bands for StAR protein (30 kDa, 37 kDa) in the mito chondria of bovine ZG, ZF and medulla and a less intense band (30 kDa) in t he microsomes. In rat ZG and ZF/R mitochondria only the 30 kDa protein was present. For 3 beta-HSD, an intense band (42 kDa) was found in microsomes a nd mitochondria of rat and bovine ZG and ZFR. A very faint signal for 3 bet a-HSD was seen in adrenal medulla. In conclusion, StAR (or a closely relate d) protein is present throughout the adrenal gland in rat and bovine specie s in contrast to 3 beta-HSD which is confined to the steroidogenic zones. T he possible function of StAR protein in the adrenal medulla merits investig ation.