Acute regulation of steroid hormone biosynthesis

© 1998 Journals of Reproduction and Fertility 1359-6004/98 $12.50 Steroid hormones play extremely important roles in maintaining bodily homeostasis and reproductive capacity. For example, the adrenal mineralocorticoid aldosterone is essential for maintaining salt balance and, hence, blood pressure, while adrenal glucocorticoids serve to regulate carbohydrate metabolism and also to formulate reactions to stress and other bodily insults. In females, the ovarian and placental steroids, namely oestrogen and progesterone, are requirements for follicular development, ovulation, development and maintenance of secondary sex characteristics and also for sustaining pregnancy should it occur. The most prevalent male hormone, testosterone, and its biologically active androgenic counterpart, dihydrotestosterone, are essential for normal spermatogenesis and for development and maintenance of the secondary sex characteristics in males. Therefore, the steroid hormones play important roles in many species, and maintaining normal concentrations of steroids in the body through their regulated synthesis is important. An equally important consideration is the means by which the synthesis of the steroid hormones are regulated by events occurring in the hypothalamic–pituitary–adrenal/gonadal axis through the actions of trophic hormone releasing hormones and trophic hormones themselves. Briefly, adrenocorticotrophic hormone (ACTH), LH or FSH will be released from specialized cells in the anterior pituitary through the action of corticotrophin-releasing hormone (CRH) or GnRH. After this release, the trophic hormones will interact with specific receptors on the surface of adrenal or gonadal cells and, through the intermediacy of the cAMP or the Ca2+ second messenger system, this will result in the synthesis of the appropriate steroid hormone depending on the tissue and cell type stimulated. This review discusses the events that regulate the acute synthesis of steroid hormones in response to trophic hormone stimulation, demonstrates the role of the steroidogenic acute regulatory (StAR) protein in this process and presents several recent findings pertaining to this protein.