Developmental expression of bovine adrenocortical steroid hydroxylases. Regulation of P-450(17 alpha) expression leads to episodic fetal cortisol production

Plasma steroid dynamics in late- and near-term naturally and artificially conceived bovine pregnancies as elucidated by multihormone high-resolution LC-MS/MS

The plasma levels of corticosteroids and sex steroids during pregnancy are key indicators of mammalian placental function and the onset of parturition. Steroid hormones are believed to be disturbed in pregnancies produced using assisted reproductive technologies (ARTs) due to placental dysfunction and the frequently observed lack of parturition signals. To elucidate the plasma steroid dynamics, a liquid chromatography-tandem mass spectrometry method was developed and used to determine the levels of corticosteroids (corticosterone, 11-deoxycortisol, and cortisol) and their direct precursors (progesterone and 17α-OH-progesterone) as well as sex steroids (androstenedione, estrone, estrone sulfate, testosterone, and 17β-estradiol) in bovine plasma. The levels of these 10 steroids in recipient cows carrying naturally conceived (control), in vitro fertilized (IVF), or cloned (somatic cell nuclear transfer) conceptuses were compared during late-term pregnancy (30 days before parturition), during near-term pregnancy (1 day before parturition), and on the day of parturition (day 0). Significant differences were observed among the corticosteroid levels: higher levels of corticosterone, 11-deoxycortisol, and cortisol were detected in cloned pregnancies at day 30; lower levels of corticosterone were observed in ART-derived pregnancies at days 1 and 0; and estrone and estradiol levels were higher in IVF pregnancies throughout the final development. These results suggested an upregulation of the P450C11 and P450C21 enzymes 30 days before parturition in somatic cell nuclear transfer pregnancies and an overactivation of the aromatase enzyme in IVF pregnancies. Taken together, the monitoring of multiple steroid hormones revealed that the pregnancies obtained using ART exhibited plasma steroid concentration dynamics compatible with the dysregulation of steroidogenic tissues.

Transcriptional regulation of adrenocortical steroidogenic gene expression

By serving as ligands for nuclear and plasma membrane receptors, steroid hormones are key regulators of a diverse array of physiological processes. These hormones are synthesized from cholesterol in tissues such as the adrenal cortex, ovaries, testes, and placenta. Because steroid hormones control the expression of numerous genes, steroidogenic cells utilize multiple mechanisms that ensure tight control of the synthesis of these molecules. This review will give an overview of the molecular mechanisms by which the expression of steroidogenic genes is regulated in the human adrenal cortex.

The human fetal adrenal cortex and the window of sexual differentiation

Understanding normal development is fundamental to appreciating postnatal morphology, physiology and, in some instances, pathophysiology. Developmental biology tends to interrogate models in nonprimate species, for instance the mouse, where genetic manipulation gives privileged insight into the function of particular genes. Some human developmental processes, as occur in the adrenal gland, are not faithfully reproduced in these rodent models, yet have an impact on the pathophysiology and treatment of endocrine disorders, such as congenital adrenal hyperplasia. In this setting, in vitro research of normal human development complements clinical investigation of patients born with congenital disorders.

Reciprocal expression of 17α-hydroxylase-C17,20-lyase and aromatase cytochrome P450 during bovine trophoblast differentiation: a two-cell system drives placental oestrogen synthesis

No definitive information is yet available on the steroidogenic capacity of the two morphologically distinct cell types forming the bovine trophoblast, the uninucleated trophoblast cells (UTCs) and the trophoblast giant cells (TGCs). Hence, in order to localise 17α-hydroxylase-C17,20-lyase (P450c17) on a cellular level and to monitor its expression as a function of gestational age, placentomes from pregnant (days 80–284;n= 19), prepartal (days 273–282; 24–36 h prior to the onset of labour;n= 3) and parturient cows (n= 5) were immunostained for P450c17 using an antiserum against the recombinant bovine enzyme. At all stages investigated, P450c17 was exclusively found in the UTCs of chorionic villi (CV), where staining was ubiquitous between days 80 and 160, but was largely restricted to primary CV and the branching sites of secondary CV between days 160 and 240. Thereafter, a distinct ubiquitous staining reoccurred in the UTCs of all CV in late pregnant, prepartal and parturient animals. Using an antiserum against human aromatase cytochrome P450 (P450arom), specific cytoplasmic staining was observed in TGCs. In placentomes from pregnant cows, staining intensity was higher in mature compared with immature TGCs and was more pronounced in the trophoblast covering big stem villi compared with the trophoblast at other sites of the villous tree. In placentomes of a parturient cow, specific staining was only found in mature TGCs that survived the normal, but substantial, prepartal decline in TGC numbers. These results clearly showed that bovine UTCs and TGCs exhibit different steroidogenic capacities, constituting a ‘two-cell’ organisation for oestrogen synthesis. P450c17 expression appears to be quickly down-regulated and P450arom is up-regulated when UTCs enter the TGC differentiation pathway.

ACTH modulation of transcription factors responsible for steroid hydroxylase gene expression in the adrenal cortex

Steroid hormone biosynthesis in the adrenal cortex and gonads involves the coordinated transcription of the genes encoding the steroid hydroxylases, 3beta-hydroxysteroid dehydrogenase (3betaHSD), the steroidogenic acute regulatory protein (StAR), and adrenodoxin (Adx). Transcriptional regulation of steroidogenic genes is multifactorial, entailing developmental, tissue-specific, constitutive, and cAMP-dependent mechanisms. Optimal steroidogenic capacity is achieved by the actions of ACTH which exerts transcriptional pressure on all steroidogenic genes. The actions of ACTH in the adrenal cortex have been studied in great detail and is mediated by cAMP and protein kinase A (PKA) via two temporally distinct pathways. The acute response leads to mobilization of cholesterol, the initial substrate for all steroidogenic pathways, from cellular stores to the inner mitochondrial membrane where cholesterol sidechain cleavage cytochrome P450 (P45011A1) resides. The slower, chronic response of ACTH in the adrenal cortex directs transcription of the genes encoding the steroidogenic enzymes. Although steroidogenic gene transcription in response to ACTH is cAMP-dependent, the consensus cAMP response pathway (CRE/CREB) is not involved. Instead, each steroidogenic gene utilizes unique cAMP-responsive sequences (CRS) found in the promoters of each gene, which bind a diverse array of transcription factors. Moreover, once specific transcription factors are bound to the promoters of the steroidogenic genes, increased gene expression requires posttranslational modification (phosphorylation/dephosphorylation) of the transcription factors and binding of coactivator proteins. This review provides a general view (with emphasis on the human) of the important factors involved in regulating steroidogenic gene expression and ultimately steroid hormone biosynthesis.

Adrenocortical cytochrome b5 expression during fetal development of the rhesus macaque

The developmental expressions of cytochrome b5 (b5), 17 alpha-hydroxylase/17,20-lyase cytochrome P450 (P450c17), and 3 beta-hydroxysteroid dehydrogenase were examined in primate fetal adrenals by immunocytochemistry from 50-160 d gestation. The expression of b5 was evident at 50 d in the developing fetal zone (FZ), but decreased markedly through midgestation, then increased again from 150 d to term. Similar changes in the temporal expression was observed for P450c17. Whereas P450c17 was induced largely in the transitional zone (TZ; outer-most FZ), b5 expression was strongest in FZ cells further from the capsule, although overlap between these regions involved a narrow band of cells beneath the TZ that may represent the developing zona reticularis. Thus, the induction of b5 in the FZ and of P450c17 in the TZ of the fetal adrenal late in gestation coincided temporally with the prepartum rise in dehydroepiandrosterone previously reported. These data are consistent with the proposed role of b5 in supporting 17,20-lyase activity of P450c17. However, the lack of cytochrome b5 and P450c17 expression in the FZ of the developing macaque adrenal cortex for much of the second and third trimesters distinguishes it from the mature zona reticularis seen in adult animals.

Developmental gonadal expression of the transcription factor SET and its target gene, P450c17 (17alpha-hydroxylase/c17,20 lyase)

Cytochrome P450c17 catalyzes the 17alpha-hydroxylase/17,20 lyase activity needed for sex steroid synthesis. We recently characterized the nuclear phosphoprotein SET as a novel transcriptional regulator that binds to the -447/-399 region of the rat P450c17 gene, along with the transcription factors COUP-TF II, NGF-IB, and SF-1. Gel shift studies localized SET binding to nucleotides -410/-402. We have shown that SET activates transcription of the rat P450c17 gene in neuronal precursor cells and now show that it also activates transcription from the -418/-399 region of the rat P450c17 gene in mouse Leydig MA-10 cells. Studying the ontogenic expression of SET and P450c17 in the rodent gonad, we found that SET expression preceded P450c17 expression in the embryonic genital ridge, suggesting that SET may be important for initiating P450c17 expression in this region. Expression of SET also preceded P450c17 expression in the testis and ovary, and its expression was much greater during embryogenesis than in the adult gonad. In the adult rat testis, P450c17 was expressed only in Leydig cells, while SET was expressed in Leydig cells and in spermatocytes. In the adult rat ovary, P450c17 was expressed only in theca cells, while SET was expressed in theca cells and also in oocytes. Because SET is expressed early in development in the genital ridge and in the testis and ovary, and because SET has many functions in addition to its activity as a transcription factor, we determined whether SET acts a transcription factor in oocytes. The SET protein was detected by Western blots in Xenopus oocytes from stages II through VI and in mature oocytes. Using extracts of Xenopus oocytes in gel shift assays, we detected a protein that bound to the -418/-399 region of the rat P450c17 gene, to which SET binds. Nuclear injection of either a -418/-399TK32LUC wildtype reporter construct or a construct containing a mutant SET site into Xenopus oocytes from stages III through VI resulted in activation of luciferase activity with the wildtype but not the mutant construct in all stages. These data suggest that Xenopus SET is able to bind to specific DNA sequences to activate transcription at all stages of Xenopus oogenesis. These data indicate that SET is an evolutionarily conserved transcription factor that participates in the early ontogenesis of the gonadal system, regulates P450c17 gene transcription in Leydig cells, and may also activate other genes expressed in immature oocytes, thus playing a role in oocyte development.

Developmental expression and regulation of adrenocortical cytochrome P4501B1 in the rat

A 57-kDa protein whose expression in rat adrenocortical microsomes is increased after weaning has been identified as cytochrome P4501B1 (CYP1B1). Levels of CYP1B1 protein were moderately expressed in late gestation fetuses and on postnatal day 1 (pdl), but were nearly undetectable on pd6 and pd1O. CYP1B1 expression initially increased in the late preweaning period (pd17-19) and again immediately postweaning (pd21-24). The temporal coincidence of CYP1B1 expression and weaning was not due to transition from suckling to solid food, as neonates that were prematurely weaned showed no increase in adrenal CYP1B1 compared with normally weaned littermates. The pattern of CYP1B1 expression paralleled changes in microsomal metabolism of 7,12-dimethylbenz[a]anthracene (DMBA), a marker of CYP1B1 activity. Twice daily injections of ACTH to rat pups (pd3-10) failed to significantly increase the expression of CYP1B1 in pd 10 adrenals, although the injections weakly stimulated steroidogenesis. Adrenocortical cells from pd17 neonates and adult cells, when cultured for 3 days, responded similarly to ACTH induction, although neonates showed more than 4-fold less basal activity. It is concluded that rat adrenal CYP1B1 may be developmentally suppressed, and its expression is independent of diet or the presence of a dam. This suppression is retained in cell culture, but is not due to deficient ACTH signaling. These results may explain the reported resistance of neonatal rat adrenals to the toxic effects of polycyclic aromatic hydrocarbons, which are metabolized by CYP1B1 into mutagenic by-products.

A putative binding site for Sp1 is involved in transcriptional regulation of CYP17 gene expression in bovine ovary

In the bovine ovary, thecal cells are the only cell type capable of expressing the CYP17 gene in response to LH. With the onset of ovulation and luteinization in the cow, there is complete loss of P450c17alpha expression. To characterize the molecular mechanisms involved in tissue-specific regulation of the CYP17 gene in the bovine ovary, deletion mutations of the bovine CYP17 promoter were ligated into a promoterless luciferase expression vector, and reporter constructs were transiently transfected into primary cultures of bovine thecal and luteal cells. Deletion of the promoter sequences between -191 and 101 bp dramatically decreased the levels of reporter gene activity in both thecal and luteal cells. Computer-assisted analysis revealed the presence of a putative inverted Sp1-like binding site at -188/-180 bp. Deletion or mutation of this sequence caused a decrease in both basal and forskolin-stimulated reporter gene activity. In addition, mutation or deletion of this sequence also decreased reporter gene expression induced by overexpression of the protein kinase A catalytic subunit. Electrophoretic mobility shift assays showed that this sequence binds to a nuclear protein(s) from both thecal and luteal cells that is related to Sp1, as suggested by the results of gel mobility supershift assay employing an antibody raised against Sp1. DNA-binding activity was not increased by the addition of forskolin to thecal or luteal cells. We conclude that this inverted Sp1-like binding sequence is involved in constitutive as well as cAMP-dependent expression of the CYP17 gene in the bovine ovary.

cAMP-dependent transactivation involving the homeodomain protein Pbx1

Pbx1 is a DNA-binding homeodomain protein originally discovered in the t(1;19) chromosomal translocation associated with pediatric pre-B acute lymphoblastic leukemia. Previously we reported a cAMP-regulatory sequence (CRS1) in the promoter region of the bovine CYP17 gene encoding steroid 17alpha-hydroxylase cytochrome P450 (P450c17) to be the first endogenous Pbx1 binding site and that overexpression of Pbx1 in mouse adrenal Y1 tumor cells enhances cAMP-dependent transcription mediated by this element. Here we report further characterization of Pbx1 binding site in CRS1 and role of Pbx1 in cAMP-dependent, CRS1-mediated transcription. By gel shift analysis utilizing nuclear extracts from Y1 cells, a high-affinity Pbx-binding sequence has been determined to be TTGAT(T/G)GA(T/C)A which represents the 5' portion of CRS1. An artificial Pbx-binding sequence (PRS), previously determined by random PCR analysis, is similar to the Pbx1-binding sequence in CRS1 and by both gel shift analysis and transfection studies shows characteristics very similar to CRS1. Upon overexpression, Pbx1 is found capable of enhancing CRS1-mediated transcription in both steroidogenic (Y1, JEG3) and nonsteroidogenic (HepG2 and S194) cells when coexpressed with the catalytic subunit of cAMP-dependent protein kinase A. Thus even though Pbx1 has been found to be involved only in cAMP-dependent transcription of a gene involved in steroidogenesis (CYP17), Pbx1 is capable of participating in cAMP-dependent transcription of target genes without complex formation with steroidogenic tissue-specific nuclear factors.

Ontogeny of immunoreactive and bioactive microsomal steroidogenic enzymes during adrenocortical development in rats

The functional development of the neonatal rat adrenal cortex is characterized by a triphasic response to adrenocorticotropic hormone (ACTH), with a nadir in responsiveness around neonatal day 10 (d10). In this study, the hypothesis was tested that hyporesponsiveness to ACTH partly results from deficiencies in steroidogenic enzyme content. Immunoreactive (ir) levels of mitochondrial cytochrome P450 enzymes (side chain cleavage (P450scc) and 11 beta-hydroxylase (P450c11)) did not change during neonatal development. Immunoreactive levels of microsomal 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD), however, were significantly and comparably lower in both day 1 (d1) and d10 neonates compared to adult rats. Activity of 3 beta-HSD did not parallel changes in ir 3 beta-HSD content. Enzyme activity was low on d1 (approximately 39% of adult activity), but by d10 was statistically equivalent to that of microsomes from adult adrenal glands. Immunoreactive levels of microsomal cytochrome P450 21 alpha-hydroxylase (P450c21) were significantly lower in d1 glands than in adult glands (by approximately 50%), but by d10 were statistically indistinguishable from adults. On the other hand, P450c21 activity was equivalent on d1 and d10 and both were significantly lower compared to adults (approximately 62% of adult activity). ACTH injections from d3-d10 facilitated the adrenocortical steroidogenic response to ACTH on d10. This treatment increased levels of ir 3 beta-HSD, but not ir P450c21. The results suggest that rat adrenocortical 3 beta-HSD and P450c21 are developmentally and differentially regulated, and that ir levels of the proteins are not correlated with enzyme activity during the neonatal period. One possible explanation for these observations is that multiple isoforms of the two enzymes, with different antigenic and enzymatic properties, may be expressed during development at different times. In addition, the combined decreased activities of these two enzymes can almost entirely account for the decreased steroidogenic output of rat adrenocortical cells on d1, but not during the later neonatal period.

Two Sp1-binding sites mediate cAMP-induced transcription of the bovine CYP11A gene through the protein kinase A signaling pathway

Two sequence elements located at -111 to -100 base pairs and -70 to -50 base pairs in the 5'-flanking region of the bovine CYP11A gene and in closely related positions in CYP11A of other species contain G-rich regions that are similar to the consensus Sp1-binding site. These sequences bind the purified transcription factor Sp1 as well as nuclear proteins from mouse Y1 adrenal cells that interact with an antibody specific for Sp1. Both of these CYP11A sequences support basal and cAMP-dependent transcription of reporter gene plasmids transfected into Y1 cells, and mutations within the G-rich -111/-100-base pair sequence that reduce or eliminate the binding of Sp1-related Y1 nuclear proteins also markedly reduce cAMP-induced transcription. cAMP-dependent transcription supported by both CYP11A sequence elements is mediated by protein kinase A at levels comparable to that promoted by different cAMP-response sequences and transcription factors in other genes involved in steroidogenesis. These results indicate that ACTH-dependent regulation of cholesterol side chain cleavage cytochrome P450 levels in the adrenal cortex which is mediated through cAMP involves the ubiquitous transcription factor Sp1.

Immunohistochemical evaluation of the cellular localization and ontogeny of 3 beta-hydroxysteroid dehydrogenase/delta 5-4 isomerase in the human fetal adrenal gland

The enzyme, 3 beta-hydroxysteroid dehydrogenase/delta 5-4 isomerase (3 beta-HSD) is an essential element in the biosynthetic pathway for potent adrenal steroid hormones that appear to regulate maturation of many tissues in utero and are critical for homeostasis after birth. The results of prior studies are suggestive that 3 beta-HSD activity in the human fetal adrenal (HFA) is very low and restricted to the outer zone of cortical cells, the neocortex (NC), during mid-gestation. Near the time of birth, however, there must be enhanced expression of this enzyme to allow for adaptation to extrauterine life. In the present study, we sought to characterize, by use of immunohistochemical methods, the cellular localization and developmental changes of 3 beta-HSD in the HFA during the interval of 11-41 wks gestation. Early in gestation, 11-15 wks, we noted considerable 3 beta-HSD in NC and in occasional fetal zone (FZ) cells as well. Thereafter until 24-25 wks, 3 beta-HSD was very low in NC cells and virtually absent from the FZ. Throughout the third trimester, the outer 1/2-2/3 of the NC was increasingly immunostained and clusters of immunoreactive cells also appeared near the central medullary vein of the adrenal. The NC cells and those located in the cortical cuff region that expressed 3 beta-HSD resembled zona glomerulosa cells. Among many other fetal tissues studied, only testicular Leydig cells (18,19 wks) and hilar cells of the ovary (26 wks) were found to contain 3 beta-HSD in quantities sufficient to be detected by immunohistochemistry. These results are suggestive of a heretofore undocumented stimulus to 3 beta-HSD in the HFA in early gestation followed by a suppression of the adrenal concentration of this enzyme during mid-gestation. High levels of 3 beta-HSD in early development may facilitate cortisol production, which is believed to play a role in differentiation of the medullary precursors during this developmental period. The control of adrenal 3 beta-HSD during human fetal development may be more complex than initially envisioned and requires further study.

Regulation of steroid hydroxylase gene expression in the ovine fetal adrenal gland at 0.4 gestation

This study was designed to test the hypothesis that ACTH from the fetal pituitary is a major regulator of adrenocortical steroid hydroxylase gene expression in the ovine fetus at 0.4 (60-70 days) of gestation. Pregnant ewes at 0.4 gestation received intravenous infusions of dexamethasone (0.76 mg/h, n = 13) for 48 h. The rationale for this regime was that some of the infused dexamethasone would cross the placenta and act on the fetal pituitary to suppress ACTH release. Control animals received infusions of saline (0.38 ml/h, n = 12) for 48 h. At the end of the infusion period, the animals were killed, umbilical vessel blood taken for ACTH and cortisol analyses, and the fetal adrenal glands taken for assessment of P-450scc, P-450(17 alpha) and P-450c21 levels using the techniques of hybridization histochemistry and RNase protection assay. Dexamethasone treatment decreased maternal and fetal concentrations of ACTH to 29 +/- 10 and < 20 pg/ml, respectively and cortisol concentrations to 3.5 +/- 0.6 and 3.2 +/- 0.8 nmol/l respectively. The adrenal glands from the dexamethasone-treated fetuses exhibited significantly lower levels of mRNA for P-450scc (11% of control) and P-450(17 alpha) (2% of control). These results suggest that ACTH is a major regulator of steroid hydroxylase gene expression and subsequent cortisol biosynthesis in vivo in the ovine fetus at 0.4 gestation.

Regulation of expression of the 3 beta-hydroxysteroid dehydrogenases of human placenta and fetal adrenal

The appropriate expression of 3 beta-hydroxysteroid dehydrogenase/delta 5-->4-isomerase (3 beta-HSD) is vital for mammalian reproduction, fetal growth and life maintenance. Several isoforms of 3 beta-HSD, the products of separate genes, have been identified in various species including man. Current investigations are targeted toward defining the processes that regulate the levels of specific isoforms in various steroidogenic tissues of man. High levels of expression of 3 beta-HSD were observed in placental tissues. It has been generally considered that the multinucleated syncytiotrophoblastic cells are the principal sites of 3 beta-HSD expression and, moreover, that 3 beta-HSD expression is intimately associated with cyclic AMP-promoted formation of syncytia. Herein we report the presence of 3 beta-HSD immunoreactive and mRNA species in uninucleate cytotrophoblasts in the chorion laeve, similar to that in syncytia but not cytotrophoblast placenta. In vitro, 3 beta-HSD levels in chorion laeve cytotrophoblasts were not increased with time nor after treatment with adenylate cyclase activators, whereas villous cytotrophoblasts spontaneously demonstrated progressive, increased 3 beta-HSD expression. Moreover, 3 beta-HSD synthesis appeared to precede morphologic syncytial formation. Thus high steroidogenic enzyme expression in placenta is not necessarily closely linked to formation of syncytia. Both Western immunoblot and enzymic activity analyses also indicated that the 3 beta-HSD expressed in these cytotrophoblastic populations was the 3 beta-HSD type I gene product (M(r), 45K) and not 3 beta-HSD type II (M(r), 44K) expressed in fetal testis. In cultures of fetal zone and definitive zone cell of human fetal adrenal, 3 beta-HSD expression was not detected until ACTH was added. ACTH, likely acting in a cyclic AMP-dependent process, induced 3 beta-HSD type II activity and mRNA expression. The higher level of 3 beta-HSD mRNA in definitive zone compared with fetal zone cells was associated with parallel increases in cortisol secretion relative to dehydroepiandrosterone sulfate formation.

Regulation of steroid hydroxylase gene expression: importance to physiology and disease

Steroid hydroxylase gene expression is multifactorial in nature, being regulated by tissue-specific, developmental, constitutive and signal transduction systems. The biochemistry of this complex pattern of regulation is not yet clearly elucidated, but studies in several laboratories have led to an understanding of specific aspects of regulation, particularly that involving signal transduction. The complexity of regulation appears to be necessary for normal human physiology because of the wide variety of steroid hormones produced by these enzymes. Genetic diseases associated with the steroid hydroxylases provide examples of how aberrant physiology can result from alterations in the multifactorial regulation of steroid hydroxylase gene expression.

Steroidogenesis in isolated adrenocortical cells during development in rats

After postnatal day 1 (d1), the hypothalamo-pituitary-adrenal axis of neonatal rats becomes less responsive to certain stimuli for up to 2 weeks. The present study was designed to quantify the development of adrenocortical cell responsiveness to its normal secretagogue, adrenocorticotropic hormone (ACTH), and to better localize intracellular sites of adrenal cell hyporesponsivity. Maximum steroidogenic responses of collagenase-dispersed adrenocortical cells (using two isolation methods) to ACTH varied significantly in the order adult > d1 > d10. The response pattern to dibutyryl cAMP ((Bu)2cAMP) was identical to that observed for ACTH (adult > d1 > d10), suggesting that neonatal adrenal responsiveness is limited by a site distal to cAMP formation. Sensitivity (EC50) of adult cells to ACTH was approximately 3-fold greater than in neonatal cells, but there was no age-dependent shift in sensitivity to (Bu)2cAMP. 20 alpha-Hydroxycholesterol (20 alpha-OHCHOL), a membrane permeable analog of cholesterol, also failed to normalize the d10 adrenal response to ACTH. This result indicates that one site of refractoriness is apparently distal to cholesterol transport, and strongly suggests possible differential cytochrome P450 enzyme expression or activity in neonatal rat adrenal cells. Finally, although stimulated secretion was lower in neonatal cells, basal corticosterone secretion was significantly greater in neonatal adrenals, suggesting that constitutive activity of neonatal adrenal cells is high compared to that of adult cells.

The time-course of ACTH stimulation of cortisol synthesis by the immature ovine foetal adrenal gland

The aim of this study was to establish the time-course of foetal adrenal gland activation by ACTH at a period of intra-uterine development during which adrenal function is minimal (100-120 days of gestation). Blood samples for cortisol analysis were collected at 6-h intervals during the 24 h ACTH (0.05, 0.5 and 5.0 micrograms/h) infusion and during the subsequent 24-h period following cessation of the infusion. Plasma cortisol concentrations were measured using a newly developed radioimmunoassay, whose sensitivity was found to be comparable to that of the validated double-isotope dilution derivative method. There was a significant increase in foetal plasma cortisol concentration, from 3.9 +/- 1 to 17.8 +/- 1.9 nmol/l, within 12 h of commencement of the 2 higher doses of ACTH. Values are mean +/- SEM; n = 5. Following termination of the infusion, cortisol levels fell significantly by the first 6 h, returning to basal levels thereafter. An increase in plasma ACTH from 4.6 +/- 0.6 to 8.4 +/- 1.0 pmol/l was sufficient to initiate a significant increase in cortisol production. The results suggest that the normal low values of cortisol at this period of gestation result from inadequate endogenous ACTH production at this stage.

Morphological evidence for a close interaction of chromaffin cells with cortical cells within the adrenal gland

The adrenal medulla appears to exert a regulatory influence on adrenocortical steroidogenesis. We have therefore studied the morphology of rat, porcine and bovine adrenals in order to characterize the contact zones of adrenomedullary and adrenocortical tissues. The distribution of chromaffin cells located within the adrenal cortex and of cortical cells located within the adrenal medulla was investigated. Chromaffin cells were characterized by immunostaining for synaptophysin and chromogranin A, both being considered specific for neuroendocrine cells. Cortical cells were characterized by immunostaining for 17 alpha-hydroxylase, an enzyme of the steroid pathway. Cellular contacts of chromaffin cells and cortical cells were examined at the electron microscopical level. In rat and porcine adrenals, rays of chromaffin cells, small cell clusters and single chromaffin cells or small invaginations from the medulla could be detected in all three zones of the cortex. Chromaffin cells often spread in the subcapsular space of the zona glomerulosa. In porcine and bovine adrenals, 17 alpha-hydroxylase immunoreactive cells were localized within the medulla. Single cortical cells and small accumulations of cells were spread throughout this region. At the ultrastructural level, the chromaffin cells located within the cortex in pig and rat adrenals formed close cellular contacts with cortical cells in all three zones. Our morphological data provide evidence for a possible paracrine role of chromaffin cells; this may be important for the neuroregulation of the adrenal cortex.

Cortisol and cortisone production in rat and mouse adrenal incubations

The presence of 17 alpha-hydroxylase in rodent adrenals is debated. The presence in blood of mice of 11-deoxycortisol together with the absence of cortisol is well known. We demonstrated here the in vitro synthesis of 17 alpha-hydroxyprogesterone and cortisol from [3H]progesterone in rat and mouse adrenals. We have shown that these syntheses represented 45 and 28% of those of 11-deoxycorticosterone and corticosterone, respectively, from progesterone. These data clearly suggest the presence of a 17 alpha-hydroxylase activity in vitro in these rodents adrenals. In addition, a noticeable synthesis of cortisol (0.87-1.57% per mg tissue, i.e. 52-64% per incubation flask) from 11-deoxycortisol was also observed and was inhibited by 0.1-0.3 mumol of Metyrapone and SKF 12185. These results allow to underline that the adrenals of rat and mouse, two species commonly used in laboratory experiments, may be used for in vitro investigations on cortisol metabolism from exogenous radioactive precursors.

What's new in the localization of sex steroids in the human ovary and its tumors?

It is important to understand the distribution of steroidogenesis in steroid producing tissues in order to obtain a better understanding of steroid metabolism. Recent advances in purification and subsequent generation of antibodies against cytochromes P-450 specific for steroid hormone biosynthesis have made it possible to localize the sites of steroidogenesis immunohistochemically. This review provides the localization of sex-steroid hormone biosynthesis in normal and pathological human ovaries including sex-cord stromal tumors, hyperthecosis and Brenner tumor, as determined by the tissue distribution of immunoreactivity of individual enzymes specific for different stages of the biosynthetic process.

Brenner tumor of the ovary: immunoanalysis of steroidogenic enzymes in 23 cases

Immunohistochemical analysis of cytochromes P-450 aromatase and P-450 17 alpha-hydroxylase, which catalyze the production of estrogens and androgens, respectively, was performed for 23 cases of ovarian Brenner tumor. Immunoreactivity for P-450 aromatase was observed in the epithelial cells of the tumor distinctly in two cases and faintly in four cases, while immunoreactivity for P-450 17 alpha-hydroxylase was seen in two cases. No immunoreactivity was observed in the stromal cells of the tumors, nor were luteinized cells observed in the cases examined. No correlation was observed between the immunoreactivity of cytochromes P-450 in the epithelial cells of the tumor and endometrial abnormalities. These findings, together with a review of the literature, suggest that the usual Brenner tumor is not associated with specific steroidogenesis. Rare massive Brenner tumors may, however, be capable of androgenic or estrogenic activity.

Complexity of steroid hydroxylase gent expression in the adrenal cortex A microcosm of regulated transcription

Regulation of the expression of steroid hydroxylase genes in the adrenal cortex involves mechanisms required for maintenance of optimal steroidogenesis, tissue specificity, and ontogeny of the steroidogenic pathway. Evaluation of the molecular basis of this complexity promises to unfold new aspects of regulated eukaryotic gene expression.

Structural characterization of the bovine CYP17 (17 alpha-hydroxylase) gene

The complete exonic and partial intronic sequence of the bovine CYP17 (P45017 alpha) gene has been determined. The gene contains eight exons with exon/intron boundaries which are identical to those determined previously for the human CYP17 gene. The site of initiation of transcription of this gene is located within a 6-base sequence 52 bp from the initiation of translation. Considerable sequence homology (58.7%) is found when approximately 500 bp of the 5'-flanking sequences of the bovine and human CYP17 genes are compared. A computer-based search of this region of bovine CYP17 for consensus sequences associated with binding of transcription factors (i.e., GR, PR, CREB/ATF, AP1, AP2, AP3, AP4, AP5, OTF, CTF/NF1, SP1) shows only the consensus CREB/ATF sequence TGACGT which is also found to be at approximately the same position in the human CYP17 gene. In bovine adrenal cortex, transcription of the CYP17 gene is regulated by the peptide hormone adrenocorticotropin via cAMP. Whether the consensus CREB/ATF sequence is associated with the cAMP-mediated transcription of the CYP17 gene remains to be elucidated.

Regulation of steroid hydroxylase gene expression is multifactorial in nature

In summary, regulation of steroid hydroxylase gene expression is complex and multifactorial, involving cAMP-dependent and -independent mechanisms required for maintenance of optimal steroidogenic capacity, tissue-specific mechanisms which lead to different steroidogenic pathways in different tissues, and developmental mechanisms which lead to fetal imprinting of steroid hydroxylase expression and which probably overlap with both maintenance and tissue-specific mechanisms. Future studies will involve identification of the trans-acting factors associated with each of these aspects of the multifactorial regulation and characterization of the cis-regulatory elements to which they bind. Such studies will inevitably lead to the identification of genes encoding these trans-acting factors and investigation of their regulation. In this way, it will be possible to work outward from the steroid hydroxylase genes toward the cell surface receptors in order to elucidate the series of events which lead to cAMP-dependent and -independent regulation of steroid hydroxylase gene expression.