Showing papers on "Adrenal cortex published in 1997"

Developmental and functional biology of the primate fetal adrenal cortex.

Abstract: I. Introduction II. Development A. Embryonic adrenal development B. Fetal adrenal development C. Neonatal adrenal development D. Growth E. Functional development 1. Ontogeny of steroidogenic activity 2. Functional zonation and ontogeny of steroidogenic enzyme expression 3. Responsiveness to ACTH III. Regulation A. The fetal pituitary and ACTH B. Growth factors 1. Basic fibroblast growth factor (bFGF) 2. Epidermal growth factor (EGF) 3. Insulin-like growth factors I and II (IGF-I and IGF-II) 4. Activin/inhibins 5. TGFβ C. Nuclear receptors/transcription factors D. Placental factors 1. Human CG (hCG) 2. Placental CRH and ACTH 3. Indirect effect of placental glucocorticoid metabolism 4. Placental estrogens IV. Physiology A. Placental estrogen formation B. Timing of parturition and fetal maturation V. Summary

Targeted disruption of the mouse gene encoding steroidogenic acute regulatory protein provides insights into congenital lipoid adrenal hyperplasia

Abstract: An essential component of regulated steroidogenesis is the translocation of cholesterol from the cytoplasm to the inner mitochondrial membrane where the cholesterol side-chain cleavage enzyme carries out the first committed step in steroidogenesis. Recent studies showed that a 30-kDa mitochondrial phosphoprotein, designated steroidogenic acute regulatory protein (StAR), is essential for this translocation. To allow us to explore the roles of StAR in a system amenable to experimental manipulation and to develop an animal model for the human disorder lipoid congenital adrenal hyperplasia (lipoid CAH), we used targeted gene disruption to produce StAR knockout mice. These StAR knockout mice were indistinguishable initially from wild-type littermates, except that males and females had female external genitalia. After birth, they failed to grow normally and died from adrenocortical insufficiency. Hormone assays confirmed severe defects in adrenal steroids—with loss of negative feedback regulation at hypothalamic–pituitary levels—whereas hormones constituting the gonadal axis did not differ significantly from levels in wild-type littermates. Histologically, the adrenal cortex of StAR knockout mice contained florid lipid deposits, with lesser deposits in the steroidogenic compartment of the testis and none in the ovary. The sex-specific differences in gonadal involvement support a two-stage model of the pathogenesis of StAR deficiency, with trophic hormone stimulation inducing progressive accumulation of lipids within the steroidogenic cells and ultimately causing their death. These StAR knockout mice provide a useful model system in which to determine the mechanisms of StAR’s essential roles in adrenocortical and gonadal steroidogenesis.

Scavenger receptor class B, type I (SR-BI) is the major route for the delivery of high density lipoprotein cholesterol to the steroidogenic pathway in cultured mouse adrenocortical cells

Abstract: The class B, type I scavenger receptor, SR-BI, binds high density lipoprotein (HDL) and mediates the selective uptake of HDL cholesteryl ester (CE) by cultured transfected cells. The high levels of SR-BI expression in steroidogenic cells in vivo and its regulation by tropic hormones provides support for the hypothesis that SR-BI is a physiologically relevant HDL receptor that supplies substrate cholesterol for steroid hormone synthesis. This hypothesis was tested by determining the ability of antibody directed against murine (m) SR-BI to inhibit the selective uptake of HDL CE in Y1-BS1 adrenocortical cells. Anti-mSR-BI IgG inhibited HDL CE-selective uptake by 70% and cell association of HDL particles by 50% in a dose-dependent manner. The secretion of [3H]steroids derived from HDL containing [3H]CE was inhibited by 78% by anti-mSR-BI IgG. These results establish mSR-BI as the major route for the selective uptake of HDL CE and the delivery of HDL cholesterol to the steroidogenic pathway in cultured mouse adrenal cells.

Angiotensin II and potassium regulate human CYP11B2 transcription through common cis-elements.

Abstract: Aldosterone synthase is a mitochondrial enzyme that catalyzes the conversion of 11-deoxycorticosterone to the potent mineralocorticoid aldosterone. The gene encoding aldosterone synthase, CYP11B2, is expressed in the zona glomerulosa of the adrenal cortex. Although the major physiological regulators of aldosterone production are angiotensin II (ANG II) and potassium (K+), the mechanisms by which these compounds regulate CYP11B2 transcription are unknown. Therefore we analyzed the human CYP11B2 5'-flanking region using a transient transfection expression system in the H295R human adrenocortical cell line. ANG II and K+ increased expression of a luciferase reporter construct containing 2015 bp of human CYP11B2 5'-flanking DNA. This response was mimicked by treatment with the calcium channel activator BAYK8644, whereas activation of the protein kinase C pathway with 12-o-tetradecanoylphorbol-13-acetate had no effect. Reporter gene activity was also increased after activation of cAMP-dependent pathways by (Bu)2cAMP. Deletion, mutation, and deoxyribonuclease I footprinting analyses of the CYP11B2 5'-flanking region identified two distinct elements at positions -71/-64 (TGACGTGA) and -129/-114 (CTCCAGCCTTGACCTT) that were both required for full basal reporter gene activity and for maximal induction by either cAMP or calcium-signaling pathways. The -71/-64 element, which resembles a consensus cAMP response element (CRE), bound CRE-binding proteins from H295R cell nuclear extracts as determined by electrophoretic mobility shift analysis. Analysis of the -129/-114 element using electrophoretic mobility shift analysis demonstrated binding of the orphan nuclear receptors steroidogenic factor 1 and chicken ovalbumin upstream promoter transcription factor. These data demonstrate that ANG II, K+, and cAMP-signaling pathways utilize the same SF-1 and CRE-like cis-elements to regulate human CYP11B2 expression.

I. Adrenal Cortex and Steroid 21-Hydroxylase Autoantibodies in Adult Patients with Organ-Specific Autoimmune Diseases: Markers of Low Progression to Clinical Addison’s Disease

Abstract: Adrenal cortex autoantibodies (ACA) were measured by immunofluorescence in 808 children with organ-specific autoimmune diseases without adrenal insufficiency. ACA were found in 14 children (1.7%), mostly in hypoparathyroidism (48%). Ten ACA-positive and 12 ACA-negative children were followed up for a maximum of 10 yr by evaluation of adrenocortical function (ACTH test) and autoantibody status. In all patients steroid-producing cell autoantibodies were assessed by immunofluorescence and autoantibodies to steroid 21-hydroxylase, 17α-hydroxylase, and cytochrome P450 side-chain cleavage enzyme by immunoprecipitation assay. All 10 ACA-positive patients were positive for 21-hydroxylase autoantibodies. Six were positive for steroid-producing cell autoantibodies and 5 also for autoantibodies to 17α-hydroxylase and/or P450 side-chain cleavage enzyme. Overt Addison’s disease developed in 9 (90%) ACA/21-OH-antibody-positive children after 3–121 months, and 1 remaining child had subclinical hypoadrenalism. By contras...

Aging Alters Zonation in the Adrenal Cortex of Men

Abstract: Whereas aging has been shown to be associated with striking reductions in circulating levels of adrenal androgens in humans, the alteration in adrenal function that occurs in aging has not been identified. We sought to determine if there are changes in the zonation of the adrenal in aging men by performing histomorphologic analyses of adrenal specimens that had been obtained at autopsy following sudden death due to trauma. We evaluated adrenals from 21 young men (20-29 yrs) and 12 older men (54-90 yrs); inclusion criteria required the presence of medullary tissue in the specimen and fixation within the first 24 hrs postmortem. Sections stained with H/E were examined microscopically and areas of the cortex that included adjacent medullary tissue were chosen for quantitative evaluation by use of a computerized image analysis system. The average width (arbitrary units, pixels) of the zona reticularis and that of the combined zonae fasciculata/glomerulosa were determined from sections stained for reticulum fibers. The zona reticularis represented 37.1 +/- 1.9% of the total cortical width in the young men, which was significantly greater than that of the older men (27.1 +/- 3.3%, P = 0.0082). The zona fasciculata/glomerulosa to zona reticularis ratio in the young men (1.84 +/- 0.15) was significantly less that that of the older men (3.29 +/- 0.47, P = 0.0011). There was no significant difference in the total width of the cortex in young compared to older men. These data suggest that aging results in alterations within the cortex of the adrenals in men such that there is a reduction in the size of the zona reticularis and a relative increase in the outer cortical zones. A reduced mass of the zona reticularis could be responsible for the diminished production of dehydroepiandrosterone and dehydroepiandrosterone sulfate that occurs during aging.

Angiotensin II Stimulates Secretion of Endogenous Ouabain From Bovine Adrenocortical Cells via Angiotensin Type 2 Receptors

Abstract: Angiotensin II stimulates secretion of corticosteroids and ouabain-like activity from adrenocortical cells. Distinct adrenocortical angiotensin II receptor subtypes (AT1, AT2) have been described, ...

The ontogenesis of the steroidogenic tissues

Abstract: Based on the common function of steroid hormone-producing tissues and homologous regulation by the hypothalamo-pituitary axis, the adrenal cortex and the gonads have been suggested to have an intimate ontogenic relationship This assumption is also supported by the findings of common transcription factors implicated in the differentiation of both types of tissue and further supported by concomitant defects in such tissues due to the disruption of a single gene Similarly, simultaneous anomalies in those tissues are also observed in some diseases caused by mutations of the genes encoding those transcription factors A recent immunohistochemical study with one of the transcription factors, Ad4BP/SF-1, definitely demonstrated the presence of a particular cell population designated the 'adreno-genital primordium (AGP)' which gives rise to both the adrenal cortex and the gonads In the process of differentiation from the AGP to the mature adrenal cortex and the gonads of the two sexes, several interesting issues can be raised as to the next targets for the study To address these issues it is important to elucidate the upstream regulatory mechanisms and downstream target genes of such transcription factors as WT1, SRY, SOX9 and DAX1, in addition to Ad4BP/SF-1, all of which are implicated in steroidogenic tissue differentiation

Insulin-like growth factors augment steroid production and expression of steroidogenic enzymes in human fetal adrenal cortical cells: implications for adrenal androgen regulation.

Abstract: The fetal zone is a unique adrenal cortical compartment that exists only during fetal life in humans and higher primates and produces large amounts of the adrenal androgen dehydroepiandrosterone sulfate (DHEA-S). Growth of the fetal zone is primarily regulated by ACTH, the actions of which are mediated in part by locally produced autocrine/paracrine growth factors. We previously demonstrated that one of these growth factors, insulin-like growth factor II (IGF-II), is mitogenic for cultured fetal zone cells and is produced in high abundance by these cells in response to ACTH. In the present study, we determined whether IGF-II also modulates the differentiated function of fetal zone cells. We examined the effects of recombinant human IGF-II and the closely related peptide, IGF-I, on 1) basal and agonist-stimulated [ACTH-(1-24), forskolin, or 8-bromo-cAMP] cortisol and DHEA-S production, 2) basal and ACTH-stimulated steady state abundance of messenger ribonucleic acids (mRNAs) encoding the steroidogenic enzymes cytochrome P450 side-chain cleavage (P450scc) and cytochrome P450 17alpha-hydroxylase/17,20-lyase (P450c17), and 3) basal and ACTH-stimulated steady state abundance of mRNA encoding the ACTH receptor. Basal cortisol (23.93 +/- 1.20 pmol/10(5) cells x 24 h) and DHEA-S (548.87 +/- 43.17 pmol/10(5) cells x 24 h) productions were significantly (P < 0.05) increased by IGF-I (2.3- and 1.8-fold, respectively) and IGF-II (2.8- and 1.8-fold, respectively). As expected, ACTH, forskolin, and cAMP markedly increased the production of cortisol by 26-, 10-, and 13-fold, respectively, and that of DHEA-S by 5.4-, 4.6-, and 5.5-fold, respectively, compared with basal levels. IGF-II (100 ng/mL) significantly (P < 0.001) increased ACTH-, forskolin-, and cAMP-stimulated production of cortisol by 2.4-, 4.3-, and 3.2-fold, respectively, and that of DHEA-S by 1.4, 1.6-, and 1.4-fold, respectively. IGF-I (100 ng/mL) had similar effects as IGF-II and significantly (P < 0.001) increased ACTH-, forskolin-, and cAMP-stimulated production of cortisol by 2.8-, 3.9-, and 3.1-fold, respectively, and that of DHEA-S by 1.3-, 1.6-, and 1.4-fold, respectively. The similar potencies of IGF-I and IGF-II suggest that the actions of these factors were mediated via a common receptor, most likely the type I IGF receptor. The effects of IGF-II on ACTH-stimulated steroid production were dose-dependent (EC50, 0.5-1.0 nmol/L), and IGF-II markedly increased the steroidogenic responsiveness of fetal zone cells to ACTH. With respect to cortisol production, IGF-II shifted the ACTH dose-response curve to the left by 1 log10 order of magnitude. IGF-II also increased ACTH-stimulated abundance of mRNA encoding P450scc (1.9-fold) and P450c17 (2.2-fold). Basal expression of P450scc was not affected by IGF-II. In contrast, basal expression of P450c17 was increased 2.2-fold by IGF-II and IGF-I in a dose-responsive fashion. Neither IGF-I nor IGF-II affected basal or ACTH-stimulated abundance of mRNA encoding the ACTH receptor, suggesting that the increase in ACTH responsiveness was not mediated by an increase in ACTH-binding capacity. Taken together, these data indicate that activation of the type I IGF receptor increases ACTH responsiveness in fetal zone cells by modulating ACTH signal transduction at some point distal to ACTH receptor activation. These data also indicate that locally produced IGF-II modulates fetal adrenal cortical cell function by increasing responsiveness to ACTH and possibly (based on its direct stimulation of P450c17 expression) augmenting the potential for adrenal androgen synthesis. Thus, activation of the type I IGF receptor on adrenal cortical cells may play a pivotal role in adrenal androgen production, both physiologically in utero and at adrenarche, and in pathophysiological conditions ofhyperandrogenemia, such as the polycystic ovary syndrome.

Impaired diurnal adrenal rhythmicity restored by constant infusion of corticotropin-releasing hormone in corticotropin-releasing hormone-deficient mice.

Abstract: The normal pattern of daily glucocorticoid production in mammals requires circadian modulation of hypothalamicpituitary-adrenal axis activity. To assess both the factors responsible for imparting this diurnal profile and its physiologic importance, we have exploited corticotropin-releasing hormone (CRH)-deficient mice generated by homologous recombination in embryonic stem cells. CRH-deficient mice have lost normal circadian variations in plasma ACTH and glucocorticoid while maintaining normal circadian locomotor activity. Constant peripheral infusion of CRH produced marked diurnal excursions of plasma glucocorticoid, indicating that CRH acts in part as a permissive factor for other circadian modulators of adrenocortical activity. The presence of atrophic adrenals in CRH-deficient mice without an overt deficit in basal plasma ACTH concentration suggests that the diurnal increase in ACTH is essential to maintain normal adrenal function.

Steroidogenic factor 1 messenger ribonucleic acid expression in steroidogenic and nonsteroidogenic human tissues: Northern blot and in situ hybridization studies.

Abstract: Steroidogenic factor-1 (SF-1), a tissue-specific orphan nuclear receptor, regulates the genes of several steroidogenic enzymes, Mullerian inhibiting substance, and the gonadotrophins. Also, this transcription factor is crucial for hypothalamic, adrenal, and gonadal organogenesis in the mouse. We recently cloned the human SF-1 (hSF-1) complementary DNA (cDNA) and now report the distribution of this factor’s messenger RNA (mRNA) in human tissues. Northern blot analyses of peripheral tissues revealed high hSF-1 mRNA expression in the adrenal cortex and the gonads, but no hSF-1 mRNA was detected in the placenta. High hSF-1 mRNA expression also was seen in the spleen. In this tissue, in addition to the main transcript of 3.5–4 kb seen in the adrenal and gonads, two additional transcripts of 4.4 kb and 8 kb were noted. The additional 4.4-kb transcript also was seen in several peripheral tissues and various components of the brain. However, adult liver and heart showed only the 4.4-kb transcript. In the human br...

Cytochrome P450 1A2 is a hepatic autoantigen in autoimmune polyglandular syndrome type 1.

Abstract: Autoantibodies directed against proteins of the adrenal cortex and the liver were studied in 88 subjects of Sardinian descent, namely six patients with autoimmune polyendocrine syndrome type 1 (APS1), 22 relatives of APS1 patients, 40 controls with other autoimmune diseases, and 20 healthy controls. Indirect immunofluorescence, using tissue sections of the adrenal cortex, revealed a cytoplasmatic staining pattern in 4 of 6 patients with APS1. Western blotting with adrenal mitochondria identified autoantigens of 54 kDa and 57 kDa, Western blotting with placental mitochondria revealed a 54-kDa autoantigen. The 54-kDa protein was recognized by 4 of 6 patients with APS1 both in placental and adrenal tissue, whereas the 57-kDa protein was detected only by one serum. Using recombinant preparations of cytochrome P450 proteins, the autoantigens were identified as P450 scc and P450 c17. One of six APS1 patients suffered from chronic hepatitis. In this patient, immunofluorescence revealed a centrolobular liver and ...

Effects of Adrenomedullin on the Human Adrenal Glands: An in Vitro Study

Abstract: Numerous lines of evidence indicate that adrenal medulla exerts a paracrine control on the secretory activity of the cortex by releasing catecholamines and several regulatory peptides. Adrenomedullin (ADM) is contained in adrenal medulla of several mammalian species, including humans. Thus, we investigated whether human ADM1–52 exerts a modulatory action on steroid secretion of human adrenal cortex in vitro. Dispersed adrenocortical cells (obtained from the gland tail deprived of chromaffin cells) and adrenal slices (including both capsule and medulla) were employed. ADM specifically inhibited angiotensin II-stimulated aldosterone secretion of dispersed cells and enhanced basal aldosterone production by adrenal slices, minimal effective concentrations being 10−7 and 10−9 mol/L, respectively. These effects of ADM were suppressed by the CGRP1 receptor antagonist CGRP8–37 (10−5 mol/L). Neither basal and ACTH-stimulated aldosterone secretion of dispersed cells nor agonist-enhanced aldosterone production by ad...

Modulation of Hypothalamic–Pituitary–Adrenal Function by Transgenic Expression of Interleukin-6 in the CNS of Mice

Abstract: Interleukin-6 (IL-6) and IL-6 receptor mRNA and protein have been reported in different brain regions under normal and pathophysiological conditions. Although much is known about the hypothalamic–pituitary–adrenal (HPA) axis stimulation after acute administration, less is known about the chronic effects of IL-6 on the function of the HPA axis. In the present study, we examined the function of the HPA axis in transgenic mice in which constitutive expression of IL-6 under the control of the glial fibrillary acidic protein (GFAP) promoter was targeted to astrocytes in the CNS. GFAP-IL6 mice heterozygous or homozygous for the IL-6 transgene had normal basal plasma corticosterone levels but, after restraint stress, showed abnormally increased levels in a gene dose-dependent manner. The increased plasma corticosterone levels in the IL-6 transgenic mice were associated with increased adrenal corticosterone content and hyperplasia of both adrenal cortex and medulla. Notably, plasma adrenocorticotrophic hormone (ACTH) levels and pituitary ACTH content were either not changed or decreased in these mice, whereas plasma arginine vasopressin (AVP) was increased, supporting a role for AVP in response to acute immobilization stress. The reduced ACTH response together with the adrenal hyperplasia in the IL-6 transgenic mice suggests direct activation at the level of the adrenal gland that may be directly activated by AVP or sensitized to ACTH. A similar mechanism may play a role in the blunted ACTH response and elevated corticosterone levels under pathophysiological conditions observed in humans with high brain levels of IL-6.

Expression of adrenocorticotrophic hormone receptor mRNA in human adrenocortical neoplasms: correlation with P450scc expression

Abstract: OBJECTIVEAdrenocorticotrophin (ACTH) is the main hormone-regulating steroid secretion from the adrenal cortex. The ACTH receptor (ACTH-R) has recently been cloned, allowing systematic evaluation of its expression and function in adrenal tumorigenesis. We investigated ACTH-R and P450 side-chain cleavage enzyme (P450scc) mRNA expression in a variety of neoplastic adrenocortical tissues by Northern blot and reverse-transcriptase-PCR (RT-PCR). PATIENTS AND MEASUREMENTSWe studied tissue from eight normal adrenals, six diffuse adrenocortical hyperplasias in patients with ACTH-dependent Cushing's syndrome, 22 adrenal adenomas, six carcinomas and two carcinoma cell lines. Poly A mRNA was electrophoresed, immobilized on a nylon membrane and hybridized using α32P-CTP labelled human ACTH-R and P450scc cDNAs. RESULTSMean ACTH-R mRNA expression showed significant differences between groups (P=0.0001), but appeared to be independent of plasma ACTH concentrations. Compared to normal adrenal =100±12%), expression was low in non-functional adenomas (23±11%) and carcinomas (19±12%), intermediate in adrenocortical hyperplasias (88±6%) and cortisol-producing adenomas (81±15%) and high in aldosteronomas (175±29%). In adenomas, ACTH-R mRNA expression correlated closely with the expression of P450scc mRNA r=0.8, P=0.0001) suggesting regulation by similar factors. However, carcinomas and cancer cell lines did not show a positive correlation between these two parameters r=−0.44, P=0.2). CONCLUSIONSWe have demonstrated that plasma ACTH is not the major factor influencing ACTH-receptor mRNA expression in neoplastic adrenal tissue. In benign tumours of the adrenal cortex there was a close positive correlation between ACTH-receptor mRNA and P450scc mRNA which was missing in adrenocortical carcinomas, probably as a result of tumour dedifferentiation.

Leptin receptors in the adrenal medulla of the rat.

Abstract: Leptin is the protein product of the recently cloned obesity gene. Leptin receptor mRNA is found in a number of central and peripheral locations. The hypothalamus is a presumed site of action. However, little is known about the specific locations of the receptor in peripheral organs. Epinephrine has potent anorectic effects and can cause weight loss by a variety of mechanisms. Excretion of epinephrine is reduced in the ob/ob mouse, which lacks leptin, suggesting an effect by leptin on the adrenal medulla. In the current study, the presence of the leptin receptor was identified on epinephrine-secreting cells in the adrenal medulla. Immunohistochemical studies found dense leptin receptor-like immunoreactivity in the adrenal medulla with no labeling in the adrenal cortex. Double immunofluorescent labeling confirmed that the leptin receptor was present on cells that were phenylethanolamine N-methyltransferase-like immunoreactive and therefore were epinephrine-secreting cells. Leptin receptor mRNA in the adrenal medulla was detected by reverse transcriptase-polymerase chain reaction, with the majority of the mRNA coding for the short isoform (Ob-Ra) of the receptor. Finally, autoradiography was performed using 125I-labeled leptin; specific binding was found in the adrenal medulla, with no specific binding in the adrenal cortex. These results suggest that leptin may have a direct effect on epinephrine-secreting cells in the adrenal medulla. Epinephrine may play a role in mediating the effects of leptin to reduce body weight.

Synergistic Effect of Partially Inactivating Mutations in Steroid 21-Hydroxylase Deficiency

Abstract: Lesions in the gene encoding steroid 21-hydroxylase result in congenital adrenal hyperplasia, with impaired secretion of cortisol and aldosterone from the adrenal cortex and overproduction of androgens. Mild forms of the disease cause late-onset symptoms of hyperandrogenism and are thought to be largely underdiagnosed. A limited number of mutations account for the majority of mutated alleles, but additional rare mutations are responsible for the symptoms in some patients. We previously reported a rare allele in two siblings with late-onset disease. This allele contained three sequence alterations, a C to T transition 4 bases upstream of translation initiation, a CCG to CTG change at codon 105 (P105L), and a CCC to TCC transition at codon 453 (P453S). The latter mutation has been found in other ethnic groups, whereas P105L seems to be unique to this family. We have now analyzed the functional consequences of the -4, P105L, and P453S sequence alterations by in vitro translation and after expression of mutant enzyme in cultured cells. As expected, the base substitution at position-4 had no measurable effect on gene expression. The P105L mutation reduced enzyme activity to 62% for 17-hydroxyprogesterone and 64% for progesterone, and the P453S mutation reduced activity to 68% and 46%, respectively. When present in combination, the two mutations caused a reduction of enzyme activity to 10% for 17-hydroxyprogesterone and 7% for progesterone. These results indicate that P105L and P453S can be expected to result in a very subtle disease manifestation when not found in combination, motivating their inclusion when genotyping to ascertain undiagnosed patients with the mildest forms of 21-hydroxylase deficiency.

The Role of Endothelins in the Paracrine Control of the Secretion and Growth of the Adrenal Cortex

Abstract: Endothelins (ETs) are a family of vasoactive peptides (ET-1, ET-2, and ET-3) mainly secreted by vascular endothelium and widely distributed in the various body systems, where they play major autocrine/paracrine regulatory functions, acting via two subtypes of receptors (ET A and ET B ). Adrenal cortex synthesizes and releases ETs and expresses both ET A and ET B . Zona glomerulosa possesses both ET A and ET B , whereas zona fasciculata/reticularis is almost exclusively provided with ET B . ET S exert a strong mineralocorticoid and a less intense glucocorticoid secretagogue action, mainly via ET B receptors. ETs also appear to enhance the growth and steroidogenic capacity of zona glomerulosa and to stimulate its proliferative activity. This trophic action of ETs is likely to be mediated mainly by ET A receptors. The intraadrenal release of ETs undergoes a multiple regulation, with the rise in blood flow rate and the local release of nitric oxide being the main stimulatory factors. Data are also available that indicate that ETs may also have a role in the pathophysiology of primary aldosteronism caused by adrenal adenomas and carcinomas.

Splanchnicotomy increases adrenal sensitivity to ACTH in nonstressed rats.

Abstract: Awake rats demonstrate an ultradian rhythm in adrenal secretion of corticosterone Splanchnic denervation in unstressed rats increases the frequency of corticosterone pulses, revealing an inhibitory function of adrenal innervation In contrast, one day after surgical stress, adrenal denervation reduces adrenal pulsatility, suggesting a stimulatory function of adrenal innervation To test whether neural modulation of pulsatile secretion was due to a direct effect of the splanchnic nerve on adrenal sensitivity to adrenocorticotropic hormone (ACTH), rats treated with dexamethasone were administered repetitive pulses of ACTH, and the amplitude of corticosterone responses was determined Intact or control (C) and splanchnicotomized (SPLNX) rats were tested at 2 or 5 days after surgery Five days after surgery, adrenal responsiveness in C animals was reduced compared with SPLNX animals However, no differences were seen 2 days after surgery To determine whether the reduction in adrenal responsiveness involved a cellular or organ level mechanism, dispersed adrenal cortical cells isolated from intact or denervated adrenal glands were stimulated with ACTH, and corticosterone secretion was determined Consistent with in vivo results, denervation increased the responsiveness of adrenal cells obtained 5, but not 1 or 2, days after surgery These findings support a neurally mediated inhibition of adrenal sensitivity to ACTH in unstressed rats

Vascularization of the adrenal cortex: its possible involvement in the regulation of steroid hormone release.

Abstract: This review examines the morphology of the adrenal gland with particular reference to the adrenal vasculature. It examines the possibility that variability in adrenal gland responsiveness may be attributable to neural or hormonal modulation of adrenal blood flow. Changes in the rate of blood flow through the adrenal cortex would be expected to play an important role in the regulation of steroid hormone release. It would affect both the delivery of the major stimulant (ACTH) and the removal of the end product from the steroidogenic cells (the glucocorticoids). In the past, interest in this area has concentrated on the regulation of arterial blood flow, rather than the regulation of venous drainage. The current review examines the concept of vascular damming, and attempts to link the morphological features of the gland with experimental data associated with glucocorticoid release. It is postulated that regulation of venous drainage, via the vascular dam, plays an important role in the storage of the secretory product during the animals' inactive phase, and in the initial rapid rise in plasma levels of the glucocorticoids seen in response to stress or injection of ACTH.

Endothelins Stimulate Deoxyribonucleic Acid Synthesis and Cell Proliferation in Rat Adrenal Zona Glomerulosa, Acting through an Endothelin A Receptor Coupled with Protein Kinase C- and Tyrosine Kinase-Dependent Signaling Pathways

Abstract: The effects of endothelins (ET) on the proliferative activity of the rat adrenal cortex have been investigated in vivo, using an in situ perfusion technique of the intact left gland. The chemicals were dissolved in the perfusion medium, and the perfusion continued for 120 min. ET-1 concentration dependently increased the mitotic index and [3H]thymidine incorporation into DNA in the zona glomerulosa (ZG; 6- and 3-fold increases, respectively, at a 10(-8) M concentration), but not in the inner adrenocortical layers, where the basal proliferative activity was negligible. The effect of 10(-8) M ET-1 was blocked by the ETA receptor antagonist BQ-123, whereas the ETB receptor antagonist BQ-788 was ineffective. ET-2 and ET-3 (10(-8) M) enhanced DNA synthesis in the ZG, but their effects were less intense than that of 10(-8) M ET-1 and were directly related to their binding potency for the ETA receptor subtype (ET-1 > ET-2 >> ET-3). The selective ETB receptor agonists BQ-3020, IRL-1620, and sarafotoxin-6B were ineffective. The ZG proliferogenic action of 10(-8) M ET-1 was reversed by both the protein kinase C inhibitor Ro31-8220 and the tyrosine kinase inhibitor tyrphostin-23; a complete blockade was obtained at a 10(-6)-M concentration of each inhibitor. In contrast, neither the protein kinase A inhibitor H-89 (10(-5) M) nor the cyclooxygenase and lipoxygenase inhibitors indomethacin and phenidone (10(-5) M) affected ET-1 action. Collectively, our findings indicate that ETs stimulate the proliferation of rat adrenal ZG cells, acting through ETA receptors coupled with protein kinase C- and tyrosine kinase-dependent signaling pathways. The results of the present study are in keeping with the view that in mammals, ZG is the proliferative layer involved in the maintenance of growth of the entire adrenal cortex and with the previous autoradiographic demonstration that ZG is the only adrenocortical layer provided with ETA receptors.

Endothelin-1 stimulates steroid secretion of human adrenocortical cells ex vivo via both ETA and ETB receptor subtypes.

Abstract: The role played by endothelins (ETs) and their receptor subtypes (ETA and ETB) in the regulation of steroid hormone secretion in human adrenal gland remains unclear. Therefore, we investigated the gene expression of ET-1 and its receptors in highly pure preparations of human adrenocortical cells and the effect of ET-1 on their secretory activity. Reverse transcription-PCR with primers specific for prepro-ET-1, ET-converting enzyme-1, ETA, and ETB complementary DNAs demonstrated the expression of all of these genes in human adrenocortical cells. ET-1 increased the secretion of aldosterone and cortisol by enhancing both earlier and late steps of their synthesis. The secretory response to ET-1 was partially (60%) inhibited by BQ-123 and BQ-788, which are selective antagonists of the ETA and ETB receptors, respectively. When added together, the two antagonists suppressed the secretagogue effect of ET-1. Collectively, these findings suggest that ET-1, acting via both ETA and ETB receptors, may exert an autocri...