The adrenal

During the past 15 years, considerable progress has been made in our understanding of the genetic basis of adrenal development and function. More than 30 single gene disorders have now been identified that can affect the hypothalamic-pituitary-adrenal axis in humans (fig. 1, 2; table 1). This review highlights recent advances in the molecular pathology of: (1) adrenal hypoplasia, (2) adrenal destruction, (3) disorders of adrenal steroidogenesis, (4) adrenal steroid resistance and (5) activation of the adrenal axis/tumorigenesis. Characterizing the molecular basis and natural history of these conditions is providing fascinating insight into adrenal development and function and can help to focus treatment and counselling of patients appropriately. However, ongoing translation of research findings into clinical practice is needed if patient care is to be influenced significantly.     

Molecular pathogenesis of lipoid adrenal hyperplasia and adrenal hypoplasia congenita

Congenital lipoid adrenal hyperplasia (lipoid CAH) is the most severe form of CAH in which the synthesis of all gonadal and adrenal cortical steroids is markedly impaired. Lipoid CAH may be caused by the defect in either the steroidogenic acute regulatory (StAR) protein or the P450scc. More than 34 different mutations in StAR gene have been identified. Clinically, most of the patients manifest adrenal insufficiency from 1 day to 2 months of age, but some patient show delayed onset of adrenal insufficiency. Affected 46, XY subjects do not show pubertal development, whereas affected 46, XX subjects undergo spontaneous feminization, breast development and cyclical vaginal bleeding at the usual age of puberty.

X-linked adrenal hypoplasia congenital (AHC) is a rare congenital adrenal disorder characterized by severe adrenal insufficiency and hypogonadotropic hypogonadism. More than 80 different several intragenic mutations of DAX-1 have been identified. The failure of pubertal development may be caused by either abnormal hypothalamic or pituitary regulation of gonadotropin secretion. In addition, although the testicular steroidogenesis is largely intact, the functional maturity of Sertoli cells and also spermatogenesis are impaired. The type of mutation does not predict clinical phenotype. Thus, unified mechanism how DAX-1 gene defect gives rise to adrenal insufficiency, hypothalamic/pituitary hypogonadism and impaired spermatogenesis remains established.     

Immunohistochemical localization of adrenal ferredoxin in bovine adrenal cortex.

Adrenal ferredoxin, the iron-sulfur protein associated with cytochrome P-450 in adrenocortical mitochondria, has been localized at the light microscopic level in bovine adrenal cortex. Localization was achieved through the use of rabbit antiserum to bovine adrenal ferrodoxin in an unlabeled antibody peroxidase-antiperoxidase method. When sections of bovine adrenal glands were exposed to the adrenal ferredoxin antiserum, intense staining was observed in parenchymal cells of the three cortical zones. Staining for adrenal ferredoxin was not detected in the medullary chromaffin cells. The presence of adrenal ferredoxin in the three cortical zones was verified by electron paramagnetic resonance spectrometry. These determinations also revealed that while the zona fasciculata and the zona reticularis contained approximately equal concentrations of adrenal ferredoxin, the concentration of the iron-sulfur protein in the zona glomerulosa was considerably lower. Similar results were obtained when the levels of cytochrome P-450 were determined in the three cortical zones. These results represent the first immunohistochemical localization within an intact tissue or cell of any component of an NADPH-dependent electron transport sequence which is responsible for the reduction of cytochrome P-450.     

Metabolism of adrenal androgens by human endometrium and adrenal cortex

The enzyme 17 beta-hydroxysteroid dehydrogenase (17OHSD) was studied in human endometrium and adrenal cortex with respect to the metabolism of 5-androstene-3 beta,17 beta-diol (androstenediol) and dehydroepiandrosterone (DHA). The aim was to provide further information concerning the origin and biological significance of these androgens in endometrium, particularly the increased concentrations of the secretory phase and to compare the characteristics of the enzyme in the two tissues. In both endometrium and adrenal cortex the metabolism of androstenediol to DHA was linear with time and increasing enzyme concentration. The preferred cofactor was NAD and the apparent Km values were 3.4 +/- 0.2 (SD) microM (n = 3) for endometrium and 30.5 +/- 6.1 microM (n = 3) for adrenal cortex. In endometrium DHA was not metabolised to androstenediol in the presence of either NADH or NADPH whereas in the adrenal cortex both cofactors were utilised. However, the concentration of NADH required to achieve maximum enzyme activity was 10-fold higher (1 mM) than for NADPH (0.1 mM) and maximum activity with NADH was only 30% of that using NADPH. The apparent Km was 125 microM DHA (n = 2). The study indicates that androstenediol in endometrium does not arise from DHA metabolism but that its presence could be due to a binding protein particularly during the secretory phase. Our findings also suggest that the enzyme of endometrium differs from that of the adrenal cortex and that the kinetic properties may be related to the physiological requirements of the two tissues.     

Capsaicin-sensitive adrenal sensory fibers participate in compensatory adrenal growth in rats

Compensatory adrenal growth, in which one gland undergoes hyperplasia after removal of the other, is mediated by a neural reflex. In the present studies, a method employing capsaicin to selectively remove adrenal sensory fibers was developed and applied to determine whether adrenal capsaicin-sensitive fibers participate in compensatory adrenal growth. The splanchnic nerves of anesthetized male rats were treated with capsaicin or vehicle. Capsaicin treatment selectively removed adrenal calcitonin gene-related peptide-positive fibers. One week after drug treatment, rats underwent left adrenalectomy or sham surgery and recovered for 5 days. Capsaicin treatment bilaterally or to the left splanchnic nerve alone (i.e., the afferent nerve in the reflex) impaired compensatory adrenal growth at 5 days compared with vehicle controls, whereas capsaicin treatment to the right splanchnic nerve alone did not affect growth. Moreover, left adrenalectomy induced c-Fos immunolabeling in ipsilateral dorsal spinal cord that was prevented by capsaicin treatment. These data suggest that adrenal capsaicin-sensitive afferent nerves participate in compensatory adrenal growth and that this effect is primarily on the afferent limb of the reflex.     

Amniotic fluid steroid levels and fetal adrenal weight in congenital adrenal hyperplasia

The concentration of 17-OH-progesterone was determined in second trimester amniotic fluid collected from 58 pregnancies at risk for fetal 21-hydroxylase deficiency. The prediction was incorrect in 1 male nonsalt-loser who had an increased plasma 17-OH-progesterone concentration at 3 months of age. All 11 infants predicted to be affected were salt-losers. The adrenals from 2 affected fetuses available for study were significantly enlarged in comparison with adrenal size in 84 normal fetuses from 15 to 26 weeks' gestation. Amniotic fluid steroid analysis reliably predicts the fetus with 21-hydroxylase deficiency most at risk in early infancy. There is no evidence from this study to indicate that ACTH is not the main trophic factor for fetal adrenal growth and steroidogenesis.     

Dynorphin and enkephalins in adrenal paraneurones. Opiates in the adrenal medulla

Immunoreactive dynorphin (ir-Dyn), immunoreactive leucine-enkephalin (ir-Leu-Enk) and various other neuropeptides were measured in acid extracts of bovine adrenal medulla and isolated adrenal chromaffin cells. Their respective levels ranged as follows: Leu-Enk greater than Dyn greater than bombesin greater than vasoactive intestinal peptide (VIP) greater than neurotensin greater than substance P. Comparisons of the total catecholamine levels with the levels of Leu-Enk in both extracts gave ratios in the same order of magnitude (2600, tissue extract and 5000, cell extract). However, the catecholamine/Dyn ratio in the tissue extract (138 000) was much higher than that found in the cell extract (20 180), suggesting a possible selective degradation of Dyn in tissue extract as compared with cell extract or an induction of Dyn biosynthesis in cells which have been isolated from their natural microenvironment. Immunofluorescence staining of isolated chromaffin cell sections revealed the presence of ir-Dyn in 5 to 10% of the total cell population. To localize ir-Dyn in regard to Leu-Enk and catecholamines, adrenal chromaffin cells were separated into three populations (I, II, and III) on a stepwise bovine serum albumin (BSA) gradient. Relative high levels of ir-Dyn were measured in cell layer I (4 pmol/10(6) cells), a cell population enriched in noradrenaline. However, ir-Leu-Enk was more concentrated in cell layers II and III (5.3 and 8.3 pmol/10(6) cells), two populations enriched in adrenaline. Isolation and high pressure liquid chromatography (HPLC) analysis of adrenomedullary Dyn indicated the presence of at least five molecular forms corresponding to Dyn-(1-11), Dyn-(1-12), Dyn-(1-13), Ala-containing-Dyn-(1-13) and a nonidentified molecule eluting closely to Dyn-(1-13). These data indicate that adrenal ir-Dyn and ir-Leu-Enk have distinct cellular distributions. In addition, the identification of Dyn fragments in bovine adrenal medulla indicates that these short peptides may be considered as natural active forms of Dyn.     

Stress and adrenal function

The natural environment is composed of various potentially hostile stressors. It is a basic requirement of life that the cells of an organism must be maintained within closely defined physiological limits. The maintenance of a constant interior mileu results from physiological and behavioural homeostatic adaptations. The physiological regulation of homeostatis is achieved by complex endocrine interactions, principally by the hormones secreted from the adrenal glands. In this brief review the responses of the avian adrenal glands to stressful stimuli, the mechanism of adrenal activation, and the function of the adrenal responses will be considered.     

Immunohistochemical localization of adrenal ferredoxin and distribution of adrenal ferredoxin and cytochrome P-450 in the rat adrenal

Adrenal ferredoxin, the iron-sulfur protein associated with cytochromes P-450 in adrenocortical mitochondria, has been localized immunohistochemically at the light microscopic level in rat adrenals by employing rabbit antiserum to bovine adrenal ferredoxin in both an unlabeled antibody peroxidase-antiperoxidase method and an indirect fluorescent antibody method. When sections of rat adrenals were exposed to the adrenal ferredoxin antiserum in both procedures, positive staining for adrenal ferredoxin was observed in parenchymal cells of the three cortical zones but not in medullary chromaffin cells. Marked differences in the intensity of staining, however, where observed among the three cortical zones: the most intense staining being found in the zona fasciculata, less in the zona reticularis, and least in the zona glomerulosa. Furthermore, differences in staining intensity were also observed among cells within both the zona fasciculata and the zona reticularis. In agreement with these immunohistochemical observations, determinations of adrenal ferredoxin contents by electron paramagnetic resonance (EPR) spectrometry in homogenates prepared from capsular and decapsulated rat adrenals revealed that the concentration of adrenal ferredoxin in the zona glomerulosa was lower than that in the zona fasciculata-reticularis. Similar results were obtained when the contents of cytochrome P-450 were determined in capsular adn decapsulated rat adrenal homogenates. These observations indicate that adrenal ferrodoxin and cytochrome P-450 are not distributed uniformly throughout the rat adrenal cortex.     

Enlightening the adrenal gland

The secretion of glucocorticoid hormones is tightly regulated by the circadian clock and by negative humoral feedback loops, both acting on the hypothalamic-pituitary gland-adrenal axis. However, a new study Ishida et al., 2005 [this issue of Cell Metabolism) shows that light can influence the adrenal's glucocorticoid output by a more direct pathway.