Adrenocorticotropin inhibits compensatory adrenal growth after unilateral adrenalectomy

Effect of chronic corticosterone treatment on expression and distribution of serotonin 5-HT7 receptors in rat adrenal glands

Sensitized stress-induced corticosterone (CORT) secretion in chronically stressed rats involves 5-HT7 receptor activation. The effect of 14-day chronic CORT and vehicle (VEH) administration on 5-HT7 receptor expression in adrenal glands, adrenal 5-HT content, and adrenocorticotropic hormone and CORT secretion was analysed. On day 15, VEH- and CORT-treated animals were perfused or decapitated without stress exposure (0 min) or after 10 and 30 min of restraint for collection of trunk blood and tissues. 5-HT7 receptor-like immunoreactivity (5-HT7R-LI), 5-HT7 receptor protein, and mRNA levels were determined by immunohistochemistry, Western blot, and reverse transcription polymerase chain reaction assays, respectively; 5-HT levels and hormones were quantified using HPLC and ELISA kits, respectively. An undisturbed control group was included for most experimental comparisons. Chronic CORT strongly increased 5-HT7R-LI in the outer adrenal cortex, as well as 5-HT7 receptor protein and mRNA in whole adrenal glands; adrenal 5-HT content also increased in these animals. Decreased adrenocorticotropic hormone and CORT secretion at 30 min of restraint occurred in CORT-treated rats. The results support the notion that chronic stress-induced increase of adrenocortical 5-HT7 receptors and adrenal 5-HT content is a glucocorticoid-dependent phenomenon; the development of magnified stress-induced 5-HT7 receptor-mediated CORT responses in chronically stressed animals nevertheless likely involves additional mechanisms.

ACTH signalling and adrenal development: lessons from mouse models

The melanocortin-2-receptor (MC2R), also known as the ACTH receptor, is a critical component of the hypothalamic-pituitary-adrenal axis. The importance of MC2R in adrenal physiology is exemplified by the condition familial glucocorticoid deficiency (FGD), a potentially fatal disease characterised by isolated cortisol deficiency. MC2R mutations cause ~25% of cases. The discovery of a MC2R accessory protein MRAP, mutations of which account for ~20% of FGD, has provided insight into MC2R trafficking and signalling. MRAP is a single transmembrane domain accessory protein highly expressed in the adrenal gland and essential for MC2R expression and function. Mouse models helped elucidate the action of ACTH. The Mc2r-knockout (Mc2r - / - ) mice was the first mouse model developed to have adrenal insufficiency with deficiencies in glucocorticoid, mineralocorticoid and catecholamines. We recently reported the generation of the Mrap - / - mice which better mimics the human FGD phenotype with isolated glucocorticoid deficiency alone. The adrenal glands of adult Mrap - / - mice were grossly dysmorphic with a thickened capsule, deranged zonation and deranged WNT4/beta-catenin and sonic hedgehog (SHH) pathway signalling. Collectively, these mouse models of FGD highlight the importance of ACTH and MRAP in adrenal progenitor cell regulation, cortex maintenance and zonation.

Transcriptome Profile in Unilateral Adrenalectomy-Induced Compensatory Adrenal Growth in the Rat

Compensatory adrenal growth evoked by unilateral adrenalectomy (hemiadrenalectomy) constitutes one of the most frequently studied in vivo models of adrenocortical enlargement. This type of growth has been quite well characterized for its morphological, biochemical, and morphometric parameters. However, the molecular basis of compensatory adrenal growth is poorly understood. Therefore, the aim of this study was to investigate the rat adrenal transcriptome profile during the time of two previously described adrenocortical proliferation waves at 24 and 72 h after unilateral adrenalectomy. Surgical removal of the left adrenal or a sham operation was accomplished via the classic dorsal approach. As expected, the weight of the remaining right adrenal glands collected at 24 and 72 h after hemiadrenalectomy increased significantly. The transcriptome profile was identified by means of Affymetrix^® Rat Gene 2.1 ST Array. The general profiles of differentially expressed genes were visualized as volcano plots and heatmaps. Detailed analyzes consisted of identifying significantly enriched gene ontological groups relevant to adrenal physiology, by means of DAVID and GOplot bioinformatics tools. The results of our studies showed that compensatory adrenal growth induced by unilateral adrenalectomy exerts a limited influence on the global transcriptome profile of the rat adrenal gland; nevertheless, it leads to significant changes in the expression of key genes regulating the circadian rhythm. Our results confirm also that regulation of compensatory adrenal growth is under complex and multifactorial control with a pivotal role of neural regulatory mechanisms and a supportive role of other components.

60 YEARS OF POMC: N-terminal POMC peptides and adrenal growth

The peptide hormones contained within the sequence of proopiomelanocortin (POMC) have diverse roles ranging from pigmentation to regulation of adrenal function to control of our appetite. It is generally acknowledged to be the archetypal hormone precursor, and as its biology has been unravelled, so too have many of the basic principles of hormone biosynthesis and processing. This short review focuses on one group of its peptide products, namely, those derived from the N-terminal of POMC and their role in the regulation of adrenal growth. From a historical and a personal perspective, it describes how their role in regulating proliferation of the adrenal cortex was identified and also highlights the key questions that remain to be answered.

Enucleation-induced rat adrenal gland regeneration: expression profile of selected genes involved in control of adrenocortical cell proliferation

Enucleation-induced adrenal regeneration is a highly controlled process; however, only some elements involved in this process have been recognized. Therefore, we performed studies on regenerating rat adrenals. Microarray RNA analysis and QPCR revealed that enucleation resulted in a rapid elevation of expression of genes involved in response to wounding, defense response, and in immunological processes. Factors encoded by these genes obscure possible priming effects of various cytokines on initiation of regeneration. In regenerating adrenals we identified over 100 up- or downregulated genes involved in adrenocortical cell proliferation. The changes were most significant at days 2-3 after enucleation and their number decreased during regeneration. For example, expression analysis revealed a notable upregulation of the growth arrest gene, Gadd45, only 24 hours after surgery while expression of cyclin B1 and Cdk1 genes was notably elevated between days 1-8 of regeneration. These changes were accompanied by changes in expression levels of numerous growth factors and immediate-early transcription factors genes. Despite notable differences in mechanisms of adrenal and liver regeneration, in regenerating adrenals we identified genes, the expression of which is well recognized in regenerating liver. Thus, it seems legitimate to suggest that, in the rat, the general model of liver and adrenal regeneration demonstrate some degree of similarity.

Neuromedin-U inhibits unilateral adrenalectomy-induced compensatory adrenal growth in the rat

Neuromedin-U (NMU) is a brain-gut peptide, which has been previously found to stimulate hypothalamic-pituitary-adrenal axis in the rat and to control the growth of the rat adrenal cortex. The present study aimed to investigate the possible involvement of NMU in the regulation of unilateral adrenalectomy-induced compensatory adrenal growth, a phenomenon known to be neurally mediated. The right adrenal gland of mature female rats was removed, the contralateral gland was then analyzed at 24 and 72h following surgery. Groups of rats were given 3 subcutaneous injections (24, 16 and 8h before decapitation) of NMU8 (1.5 or 3.0 nmol/100g/per injection). Three hours before sacrifice all rats received an intraperitoneal injection of 0.1mg/100g body weight of vincristin. By means of RT-PCR the presence of NMUR1 mRNA was detected in adrenal cortex of both intact and hemiadrenalectomized rats. As expected, unilateral adrenalectomy-induced an increase in adrenal weight, associated with increased plasma ACTH, aldosterone and corticosterone levels. The administration of NMU to hemiadrenalectomized rats did not significantly affect these parameters. NMU administration, however, notably inhibited the unilateral adrenalectomy-induced adrenocortical cell proliferation in both zona glomerulosa and zona fasciculata, as assessed by the metaphase index and the number of parenchymal cell nuclei per unit area of the tissue. When compared to hemiadrenalectomized animals receiving saline, a significant decrease of blood corticosterone levels was observed after 24h in rats treated with the highest dose of NMU. Since these effects were independent on changes in blood ACTH, they could reflect an interaction of NMU with the neural system innervating the adrenal gland.

Chronic stress induces adrenal hyperplasia and hypertrophy in a subregion-specific manner

The adrenal gland is an essential stress-responsive organ that is part of both the hypothalamic-pituitary-adrenal axis and the sympatho-adrenomedullary system. Chronic stress exposure commonly increases adrenal weight, but it is not known to what extent this growth is due to cellular hyperplasia or hypertrophy and whether it is subregion specific. Moreover, it is not clear whether increased production of adrenal glucocorticoid after chronic stress is due to increased sensitivity to adrenocorticotropic hormone (ACTH) vs. increased maximal output. The present studies use a 14-day chronic variable stress (CVS) paradigm in adult male rats to assess the effects of chronic stress on adrenal growth and corticosterone steroidogenesis. Exogenous ACTH administration (0-895 ng/100 g body wt) to dexamethasone-blocked rats demonstrated that CVS increased maximal plasma and adrenal corticosterone responses to ACTH without affecting sensitivity. This enhanced function was associated with increased adrenal weight, DNA and RNA content, and RNA/DNA ratio after CVS, suggesting that both cellular hyperplasia and hypertrophy occurred. Unbiased stereological counting of cells labeled for Ki67 (cell division marker) or 4,6-diamidino-2-phenylindole (nuclear marker), combined with zone specific markers, showed that CVS induced hyperplasia in the outer zona fasciculata, hypertrophy in the inner zona fasciculata and medulla, and reduced cell size in the zona glomerulosa. Collectively, these results demonstrate that increased adrenal weight after CVS is due to hyperplasia and hypertrophy that occur in specific adrenal subregions and is associated with increased maximal corticosterone responses to ACTH. These chronic stress-induced changes in adrenal growth and function may have implications for patients with stress-related disorders.

Infusion of ACTH stimulates expression of adrenal ACTH receptor and steroidogenic acute regulatory protein mRNA in fetal sheep

The late-gestation plasma cortisol surge in the sheep fetus is critical for stimulating organ development and parturition. Increased adrenal responsiveness is one of the key reasons for the surge; however, the underlying mechanisms are not fully understood. Our recent studies suggest that ACTH-mediated increased expression of ACTH receptor (ACTH-R) and steroid acute regulatory protein (StAR) may play a role in enhancing responsiveness. Hence, we examined effects of ACTH infusion in fetal sheep on mRNA expression of these two mediators of adrenal responsiveness and assessed the functional consequences of this treatment in vitro. Fetuses of approximately 118 and 138 days of gestational age (dGA) were infused with ACTH-(1-24) for 24 h. Controls received saline infusion. Arterial blood was sampled throughout the infusion. Adrenals were isolated and analyzed for ACTH-R and StAR mRNA, or cells were cultured for 48 h. Cells were stimulated with ACTH, and medium was collected for cortisol measurement. Fetal plasma ACTH and cortisol concentrations increased over the infusion period in both groups. ACTH-R mRNA levels were significantly higher in ACTH-infused fetuses in both the 118 and 138 dGA groups. StAR mRNA increased significantly in both the 118 and 138 dGA groups. Adrenal cells from ACTH-infused fetuses were significantly more responsive to ACTH stimulation in terms of cortisol secretion than those from saline-infused controls. These findings demonstrate that increases in circulating ACTH levels promote increased expression of ACTH-R and StAR mRNA and are coupled to heightened adrenal responsiveness.

Zone-specific cell proliferation during compensatory adrenal growth in rats

Compensatory adrenal growth after unilateral adrenalectomy (ULA) leads to adrenocortical hyperplasia. Because zonal growth contributions are not clear, we characterized the phenotype of cortical cells that proliferate using immunofluorescence histochemistry and zone-specific cell counting. Rats underwent ULA, sham adrenalectomy (sham), or no surgery and were killed at 2 or 5 days. Adrenals were weighed and sections immunostained for Ki67 (proliferation), cytochrome P-450 aldosterone synthase (P450aldo, glomerulosa), and cytochrome P-450 11beta-hydroxylase (P45011beta, fasciculata). Unbiased stereology was used to count proliferating glomerulosa and fasciculata cells. Adrenal weight increased after ULA compared with sham and no surgery at both time points, and there was no difference between sham and no surgery. However, either ULA or sham increased Ki67-positive cells in the outer fasciculata at both time points compared with no surgery. Outer fasciculata-restricted proliferation is thus associated with adrenal weight gain in ULA but not sham. Experiment repetition using proliferating cell nuclear antigen and bromodeoxyuridine showed similar results. After ULA, adrenal DNA, RNA, and protein increased at both time points, whereas after sham, only adrenal DNA increased at 2 days. Compensatory growth thus results from hyperplasia and hypertrophy, whereas sham induces only a transient adrenal hyperplasia. Dexamethasone pretreatment prevented the increase in adrenal weight after ULA and blocked Ki67 labeling in the outer fasciculata but not zona glomerulosa in all groups. These results clearly show that the outer fasciculata is the primary adrenal zone responsible for compensatory growth, responding to steroid-suppressible stress signals that alone are ineffective in increasing adrenal mass.

Adrenocortical zonation and ACTH

The clear morphological distinction between the cells of the different adrenocortical zones has attracted speculation and experiment to interpret their functions and the ways in which they are regulated. Considerable data have been produced in recent years that has benefited a fuller understanding of the processes of steroidogenesis and of cell proliferation at the molecular level. This now enables the reexamination of earlier concepts. It is evident that there is considerable species variation, and this article, dealing mainly with the rat, reaches conclusions that do not necessarily apply to other mammals. In the rat adrenal, however, the evidence suggests that the greatest differences between the functions of the zones are between the glomerulosa and the fasciculata. Here the sometimes all-or-nothing demarcation in their complement of components associated with steroidogenesis or with cell proliferation suggests a stark division of labor. In this model the fasciculata is the main engine of steroid hormone output and the glomerulosa is the site of cell proliferation, recruitment, and differentiation. Regulating these functions are angiotensin II and other paracrine components that modulate and maintain the glomerulosa, and ACTH, that maintains the fasciculata, and recruits new fasciculata cells by transformation of proliferating glomerulosa cells. Grafted onto this mostly vegetative function of the glomerulosa is CYP11B2, limited to just a fraction of the outer glomerulosa in rats on a normal laboratory diet and generating aldosterone (and 18-hydroxycorticosterone) from precursors whose origin is not, from the evidence summarized here, very clear, but may include the fasciculata, directly or indirectly. The biosynthesis of aldosterone in the rat certainly requires reinterpretation.

Adrenal growth is controlled by expression of specific pro-opiomelanocortin serine protease in the outer adrenal cortex

As previous work had shown that extreme N-terminal fragments of the ACTH precursor pro-opiomelanocortin (POMC) not containing gamma-melanotropin (gamma-MSH) were active adrenal mitogens but an antiserum raised against gamma-MSH paradoxically also inhibited adrenal growth we proposed that the adrenal mitogen is processed from pro-gamma-MSH by a neurally controlled protease at the growing adrenal. To this end we have characterised a novel serine protease (named adrenal secretory protease (AsP) as Psort predicted a leader motif) which is expressed at the glomerulosa/fasciculata boundary where mitosis takes place. The expression of AsP was also found to be essential for mitosis of the adrenal cortical tumor Y1 cell-line in POMC containing media and 3D homology modeling revealed the presence of a catalytic pocket flanked by the classical His/Asp/Ser motifs. An usual feature of the model was a cluster of arginine residues on the underside of the protease suggesting that this basically charged face would tend to retain it on the cell surface on secretion-immunocytochemistry using an antiserum raised against a synthetic peptide spanning residues 1-25 of AsP showed that this was the case for Y1 cells. Specificity of AsP (affinity purified from Y1 media) was demonstrated by its inability to cleave model substrates for either trypsin or pro-hormone converting enzymes but was able to cleave an internally quenched POMC (44-55) model peptide. Interestingly mass spectral analysis of products of the latter predicts that the protease cleaves between the bond between Val52 and Met53 suggesting the natural adrenal mitogen is POMC (1-52).

Identification of a receptor for N-POMC peptides

The adrenal cortex is a dynamic organ in which the cells of the outer cortex continually divide. It is well known that this cellular proliferation is dependent on constant stimulation from peptides derived from the ACTH precursor proopiomelanocortin (POMC) since disruption of pituitary corticotroph function results in rapid atrophy of the gland. Although ACTH has often been assumed to be the adrenal mitogen, results from our laboratory suggest that the true mitogen is a fragment derived from the N-terminal of POMC that does not contain the gamma-MSH sequence. Since these peptides are not generated during the processing of POMC in the pituitary it has been proposed that the mitogen is generated from circulating pro-gamma-MSH by an adrenal protease. We have recently substantiated this hypothesis by characterizing a serine protease expressed by the adrenal necessary for growth and lead us to propose that N-POMC (1-52) is the adrenal mitogen. Using N-POMC (1-28) linked to a solid support we have extended these studies in an attempt to identify the receptor through which this peptide elicits its actions. Using this approach we have isolated a 80 KDa candidate protein from membranes prepared from the adrenal cortical Y1 cell line.

Recent insights into organogenesis of the adrenal cortex

The primary endocrine organs responsible for steroid hormone biosynthesis--the adrenal cortex and gonads--are derived from the urogenital ridge. Several recent discoveries in human and mouse genetics have begun to unravel the complex genetic cascade that dictates adrenocortical cell lineage, proliferation and differentiation. The factors that regulate adrenocortical organogenesis and the maintenance of growth promote or block a cascade of transcription factors that differentially coordinate the proliferation and differentiation of the gland. Here, we outline the developmental milestones of the adrenal cortex with recent contributions to the field, focusing on factors that have been shown to play a role in vivo in humans and mice.

Characterization of a serine protease that cleaves pro-gamma-melanotropin at the adrenal to stimulate growth

The adrenal gland requires stimuli from peptides derived from the ACTH precursor, pro-opiomelanocortin (POMC), to maintain its tonic state. Studies have proposed that a specific postsecretional cleavage of the nonmitogenic N-terminal 16 kDa fragment, also known as pro-gamma-melanotropin (pro-gamma-MSH), is required, releasing shorter fragments that promote adrenal growth. Here, we provide evidence for this hypothesis by the cloning and characterization of a serine protease that is upregulated during growth of the adrenal cortex. It is expressed exclusively in the outer adrenal cortex, the site of cell proliferation, and in the Y1 adrenal cell line. We also show that it is required for growth of Y1 cells, remains bound to the cell surface, and cleaves its substrate, pro-gamma-MSH, at a specific bond.

Agouti related protein in the rat adrenal cortex: implications for novel autocrine mechanisms modulating the actions of pro-opiomelanocortin peptides

Agouti related protein (AgRP) is a recently discovered melanocortin receptors (MCR) antagonist implicated in the control of feeding behaviour. Expression of AgRP has been shown to be localized by in situ hybridization to the arcuate nucleus and median eminence of the brain, where it acts as an antagonist to the MC3 and MC4 receptors, while in the periphery the only significant expression was located in the adrenal medulla. As AgRP is only a weak antagonist of the MC2 and MC5 receptors, which are expressed principally by adipocytes and in the adrenal cortex, the question arizes as to the function of peripheral AgRP. In this study, we investigated the expression of AgRP in the rat adrenal and suggest that it is expressed in the adrenal cortex and not as previously described in the medulla. We also show that AgRP mRNA expression is upregulated in the adrenal during fasting and in the contralateral gland following unilateral adrenalectomy but not during chronic stress. These results indicate an as yet undefined role for AgRP in the periphery and are supportive of the suggestion that a further melanocortin receptor exists.

Bilateral adrenal enucleation-induced changes in adenohypophyseal pro-opiomelanocortin (POMC)-related peptides synthesis and secretion: a comparative study with adrenalectomized rats

The aim of the present study was to elucidate the modulatory effect of transient changes in endogenous glucocorticoids, occurring after bilateral adrenal enucleation (ENUC), on anterior pituitary (AP) proopiomelanocortin (POMC)-derived peptides synthesis and output in rats. For this purpose, adult female rats were either bilaterally ENUC, adrenalectomized (ADX), or sham-operated (SHAM) and killed by decapitation 2, 7, 14, and 21 days after surgery. Trunk blood was collected for measurements of ACTH, beta-endorphin (beta-END) and corticosterone (B) concentrations; APs were quickly dissected for the determination of ACTH, beta-endorphin (beta-END)-like (beta-END-LI) and gamma 3-MSH contents and adrenal glands were removed and submitted to histological study. The results indicate that ENUC and ADX increased AP POMC-related peptides synthesis and release in association with changes in the AP processing of peptides belonging to the N-terminal (gamma 3-MSH), mid (ACTH) and C-terminal (beta-LPH/ENDs) portions of POMC. While ADX abolished plasma B levels, ENUC induced a transient (day 2) decrease in plasma B concentrations which returned to SHAM levels at 7 days after surgery. These data tallied with the histological observations carried out, indicating a time-dependent regenerative process of the adrenal which was completed by three weeks after ENUC. There was a different pattern in plasma ACTH and beta-END levels between ENUC and ADX; maximal plasma peptide levels were found 7-14 days after ENUC, then falling down to SHAM values at 21 days post ENUC. Conversely, there was a constant increment in plasma peptide levels up to 21 days after ADX. At 2 days after both ENUC and ADX all peptides measured in the AP were lower than SHAM values, thus reflecting a rapid corticotrope secretion. Thereafter, 7 or more days after surgery, AP peptide content in ADX rats increased, in a time-related fashion, up to 21 days after surgery. Only beta-END-LI showed a similar AP content to that of the SHAM group, thereafter indicating a preferential cleavage of POMC to beta-END long after ADX (21 days). ENUC rats showed increased AP POMC peptides content throughout the whole time, and it was significantly different from SHAM and ADX values 14 days post-surgery. Interestingly, we found an increment in AP gamma 3-MSH, a peptide which is preferentially synthesized in the intermediate lobe of the rat pituitary, in both ENUC and ADX situations. Our results further indicate that: 1) glucocorticoids, from regenerating adrenal origin, induce a fast negative feedback mechanism on AP secretion, and 2) there might be a delayed inhibitory action of newly synthesized corticosteroids on higher levels of the central nervous system. The lack of glucocorticoids (ADX) clearly corroborates a persistent enhancement of AP POMC-related peptides synthesis and secretion. The differences in AP processing of POMC between ENUC and ADX might be due to qualitative/quantitative changes in hypothalamic ACTH secretagogues output.

IGF1 and 2 in two models of adrenal growth

Insulin-like growth factors (IGFs) 1 and 2 were measured in the adrenal glands of rats undergoing either compensatory growth following left unilateral adrenalectomy or adrenal regeneration following bilateral adrenal enucleation. In normal rat adrenal gland, the tissue concentration of IGF2 (7.45 +/- 0.99 pg/micrograms protein) wa higher than IGF1 (1.26 +/- 0.23 pg/micrograms protein), both peptides being more abundant in the inner zones of the adrenal gland compared to the capsule-glomerulosa. During compensatory growth of the right adrenal gland, IGF1 and 2 increased significantly compared with control right adrenal glands at 24 h following left unilateral adrenalectomy (P less than 0.001). At 68 h, the increase remained significant for IGF1 (P = 0.012). The two peptides were measured in the regenerating adrenal gland at 7, 14 and 21 days following bilateral enucleation. Whilst there was a trend towards an increase in the IGF1 and 2 content of regenerating adrenal glands, the increase was significant only for IGF2 in the left adrenal gland at 21 days following enucleation. Plasma IGF1 and 2 did not increase compared to controls during the experiments (110.97 +/- 1.95 and 46.33 ng/ml, respectively), suggesting that the changes in tissue IGF reflect increased local production during rapid growth of the adrenal gland.

Growth factor regulation of adrenal cortex growth and function

The control of adrenal cortex growth in vivo during development or under certain stress conditions is still very poorly understood at the molecular level. Some information can be collected however from in vitro experiments. Acidic and basic FGF appear to be the most potent mitogens, so far, for primary cultures of adult adrenocortical cells, whereas EGF can also stimulate growth of fetal cells. Several growth factors have emerged in the recent years as multifunctional molecules that play important regulatory functions on adrenocortical steroidogenesis. These include EGF, IL-1, insulin, IGF-1 and TGF beta. In certain cases (e.g. IGF-1, TGF beta), these factors participate in autocrine loops of regulation. The differential expression, release and activation of these factors might locally regulate the steroidogenic action of the hormonal signals delivered through the hypothalamo-pituitary-adrenal axis.

Receptor autoradiographic localization of insulin-like growth factor-I (IGF-I) binding sites in human fetal and adult adrenal glands

We report here the first evidence of insulin-like growth factor-I (IGF-I) binding sites in human fetal and adult adrenal glands, obtained at autopsy. Sections of tissue were incubated with 0.1 nM [125I]IGF-I and analyzed using [3H]Ultrofilm autoradiography with image analysis coupled to computerized microdensitometry. Specific binding sites of [125I]IGF-I were found to be localized in the definitive zone, fetal zone, and fetal medulla of the fetal adrenal glands. In the adult adrenal glands, the entire cortex and medulla were specifically labeled with [125I]IGF-I. Specific binding obtained at a concentration of 0.1 nM [125I]IGF-I to areas in the fetal and adult human adrenal glands was competitively displaced by unlabeled IGF-I, with an IC50 value of 0.34-2.54 nM, and 0.38-0.73 nM, respectively, whereas insulin was much less potent in displacing the binding. Acquisition of this knowledge will aid in studies on cell growth and steroid-catecholamines biosynthesis of the human adrenal gland.

Compensatory adrenal growth in dexamethasone treated rats

The changes in right adrenal weight and adrenocortical mitotic activity have been quantified in the early (up to 72 h) stages following left adrenalectomy or sham adrenalectomy in adult male Sprague Dawley rats. These have been compared with the changes seen in rats pretreated for 14 days with a daily intraperitoneal injection of the synthetic glucocorticoid, dexamethasone (200 micrograms/kg) body weight. The results indicate a significant proliferative response in both groups of animals, although basal proliferative activity and the amplitude of the response was lower in the dexamethasone treated animals. In addition, they suggest two waves of mitotic activity at 24 and 72 h.

Effect of 3 day infusion of ACTH or CRF on the pituitary-adrenal axis

1. The effects of 72 h subcutaneous infusion of graded doses of rat CRF and ACTH(1-24) were studied in rats of initial weight 150-170 g. Rat CRF was infused at 30, 100 or 300 ng/h, and ACTH(1-24) at 125, 250 or 500 ng/h. 2. There was a progressive though modest increase in adrenal weight for all CRF doses, and an associated reduction of thymus weight. Circulating ir-ACTH, ir-beta-endorphin and corticosterone levels, and adrenal DNA content, were not increased after 3 days. Adrenal RNA and protein content were increased at the highest CRF dose used. 3. ACTH infusion caused a progressive increase in adrenal weight and thymic involution which was marked at the higher doses; circulating corticosterone levels were not significantly altered by the lowest dose but were significantly raised by the higher doses. As expected, plasma ir-beta-endorphin was suppressed to low levels with all doses. Adrenal DNA did not alter but there were progressive increases in adrenal protein and RNA. 4. There was a marked difference in gain between the two infusion regimens in terms of all parameters measured, suggesting that potent mechanisms exist to temper the pituitary-adrenal response to markedly different levels of peripheral CRF input. The damped effect of CRF infusion compared with that of ACTH may represent desensitization of CRF receptors at the pituitary; alternatively, it may reflect binding and substantial inactivation of CRF in peripheral blood.

The role of adrenal nerves in the regulation of adrenocortical functions

There is now convincing evidence for the distribution of several nerve plexuses in the outer zone of the adrenal cortex. At the ultrastructural level, the close proximity of nerve boutons to cortical cells establishes the anatomical substrate for a direct neural effect on adrenal cortical cell functions. Of those neurotransmitters and neuropeptides identified to date, catecholamine, VIP, and NPY appear to be most prevalent. Importantly, the amounts of morphologically identifiable catecholamine, VIP and NPY are differentially sensitive to alteration of several physiological conditions. Furthermore, the VIP plexus appears to be intrinsic to the adrenal while the catecholamine and NPY nerve fibers enter the adrenal along blood vessels. Together, these results suggest that these multiple nerve plexuses might exert control on several adrenocortical cellular processes in addition to the regulation of adrenal blood flow. Compensatory adrenal growth, a rapid proliferative response to unilateral adrenalectomy, was previously shown to be neurally mediated. The role of the catecholamine innervation in the mediation of this process has now been demonstrated. The elimination of the sympathetic nervous system by neonatal sympathectomy inhibited the proliferative response as measured by DNA synthesis. In vivo administration of beta-adrenergic receptor blockers did not inhibit the compensatory growth response. Furthermore, the beta-adrenergic agonist isoproterenol, inhibited the rate of DNA synthesis both in vivo and in vitro. The direct action of the beta-adrenergic agonist on the adrenocortical cell DNA synthesis rate suggests that the catecholaminergic nerves tonically inhibit cell proliferation associated with compensatory growth and that the release from the beta-adrenergic inhibition is necessary for compensatory growth. Whether inhibition of the beta-adrenergic innervation is the trigger for compensatory growth or whether it is permissive to the action of a still unidentified mitogenic substance, is not yet known. The direct role of VIP and catecholamines in the regulation of steroidogenesis has been investigated in vitro using the perifused capsule-glomerulosa preparation which is representative of a normal outer zone of the adrenal and is the site of the neural plexuses and identified receptors. Both VIP and isoproterenol stimulate steroidogenesis and specifically cause a greater increase in secretion of aldosterone than corticosterone. Although the concentrations of VIP and isoproterenol required to stimulate steroidogenesis are greater than reported circulating levels, release from resident nerves could provide high local concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

The pharmacological mediation of epithelial cell proliferation

In the past, it has been necessary for pharmacological intervention of epithelial proliferation to mostly be limited to non-specifically arresting or killing actively proliferating cells. As our understanding of the mechanisms involved in mediating the processes of growth and differentiation increases, we can hope to see the development of a new pharmacology, in which proliferation of individual systems may be regulated in a less drastic manner.

Effects of mineralocorticoids and glucocorticoids on compensatory adrenal growth in rats

The rapid compensatory growth seen in the remaining adrenal gland of the rat after unilateral adrenalectomy appears to require a functioning neural arc between the adrenal glands and the hypothalamus, but the role of adrenal or pituitary hormones is unclear. We have examined the effect of several steroids on the compensatory adrenal growth (CAG). Female and male rats (average wt 140 g) were unilaterally adrenalectomized and treated with aldosterone (2.1 micrograms/day), corticosterone (B, 28 micrograms/day), dexamethasone (28 micrograms/day), 9 alpha-fluorocortisol (9 alpha FC, 28 micrograms/day), or deoxycorticosterone (DOC, 28 micrograms/day) by continuous infusion for 3 days and then killed. The growth in the remaining adrenal was compared both with sham-operated rats treated with steroid infusions and with noninfused controls. In rats of this size females have larger adrenals than males; untreated male rats have significantly heavier left than right adrenals. In male rats the extent of CAG after no treatment or treatment with aldosterone B, 9 alpha FC, or DOC depended on the size of the adrenal gland removed. In both male and female rats CAG was not significantly affected by aldosterone, in contrast with a recent report, nor by B, 9 alpha FC, or DOC; no significant CAG was seen after dexamethasone. Taken together, these results and previous reports suggest that neurally mediated activation of pituitary and/or local adrenal growth factors may be responsible for CAG.

Compensatory adrenal cortical growth is inhibited by sympathectomy

After the surgical removal of one adrenal gland, the cortex of the remaining adrenal gland increases in size. This compensatory adrenal growth is characterized by increased weight and DNA content of the remaining adrenal 72 h after unilateral adrenalectomy. In these experiments, chemical sympathectomy prevented compensatory adrenal growth. In rats sympathectomized by neonatal injections of 6-hydroxydopamine or guanethidine and unilaterally adrenalectomized at 40 days of age, the compensatory increase in weight in the remaining gland was attenuated (relative to a vehicle-injected control group) and not accompanied by the usual increase in DNA content. Augmented RNA content was observed after unilateral adrenalectomy in sympathectomized as well as vehicle-injected animals; presumably this reflects increased steroidogenesis because, despite the loss of one adrenal, the rats maintained normal plasma corticosterone and aldosterone levels (relative to the sham-adrenalectomized group). The sympathectomy procedures themselves did not significantly alter adrenal weight, adrenal nucleic acid content, or plasma aldosterone relative to vehicle-injected control levels; however, plasma corticosterone levels were significantly reduced. We conclude that the sympathetic nervous system mediates the adrenal cortical cell proliferation that occurs after unilateral adrenalectomy.

Adrenal and urinary catecholamines during and after severe ethanol intoxication in rats: A profile of changes

Adrenal and urinary levels of adrenaline and noradrenaline were determined in rats subjected to severe ethanol intoxication for periods of up to 96 hours, in rats undergoing withdrawal and in a post-withdrawal period, and in controls. Adrenaline and noradrenaline content of adrenal glands fell markedly to less than eight and twenty percent, respectively, after four days of intoxication. Noradrenaline content, but not adrenaline content, had recovered after a subsequent four day period of recovery. The depletion in adrenal catecholamine levels was coincident with increases in urinary adrenaline and noradrenaline levels over the first 48 hours of intoxication. Urinary catecholamine levels remained higher than control values for the next 48 hours of intoxication. Adrenal glands were larger after 12 hours of intoxication, although there was no increase in dry weight. At later times adrenal enlargement was associated with increased dry weight and protein content. This increase in mass was found to be of cortical origin. These results demonstrate that severe ethanol intoxication promotes an intense stimulation of the rat adrenal gland with enhanced synthesis and release of catecholamines, and cortical hypertrophy.

Stimulation of adrenal DNA synthesis in cadmium-treated male rats

Cadmium chloride (CdCl2) at a dose of 1 mg/kg body wt was injected into male rats of the Wistar strain, weighing 250 g on the average, twice a day (12-hr intervals) for 7 consecutive days. DNA and RNA contents and [3H]-thymidine and [3H]-uridine incorporation into the acid-insoluble fraction significantly increased in the adrenals or rats treated with Cd for 2 and 7 consecutive days. Adrenal protein content and weight also significantly increased. These results indicate that continued treatment with Cd stimulates DNA and RNA synthesis in the adrenal cortex, which in turn results in the increase of the total protein contents of the adrenal gland and subsequently in the enlargement of the gland. Serum adrenocorticotrophin (ACTH) and insulin levels in Cd-treated rats were not higher than control levels, suggesting that the stimulation of DNA synthesis in the adrenals of Cd-treated rats is due to factor(s) other than serum ACTH and insulin. Treatment with Cd inhibited DNA synthesis in cultured adrenocortical cells at concentrations of 10(-4) to 10(-8) M, suggesting that Cd does not directly stimulate DNA synthesis in the adrenal gland in vivo. Although the adrenal gland became enlarged, the total adrenal corticosterone content decreased significantly. The decrease of total adrenal corticosterone content may be due to the fall in serum ACTH level of Cd-treated rats.

Pro-opiocortin: the multiple adrenal hormone precursor. Review

Corticotropin (ACTH) is biosynthesized in the human pituitary gland as a long polypeptide precursor (pro-opiocortin) of some 240 residues. When ACTH is secreted in response to stress, the peptides derived from the rest of this precursor, pro-gamma-melanotropin (gamma-MSH) and beta-lipotropin (beta-LPH), are also secreted (Fig. 1). This article will describe the search for a biological significance for this phenomenon.

Regulation of adrenocortical cell proliferation in culture

The regulation of the proliferation of adrenocortical cells in culture is reviewed. The hormones and growth factors affecting adrenocortical proliferation in culture and their physiological relevance are discussed. The following general conclusions are made: (i) ACTH is growth-stimulatory in vivo, but directly replication-inhibitory both in culture and in vivo, and is therefore an indirect mitogen. (ii) Insulin, IGFs, some pituitary and brain growth factors, and other unknown factors in serum, stimulate growth in culture, but their role in control of adrenocortical size in vivo is unknown. (iii) Pure, known pituitary hormones, other than ACTH, have no effect on adrenocortical proliferation in culture. (iv) Angiotensin is mitogenic in culture and perhaps also in vivo under some circumstances.

Control of adrenocortical growth in vivo

Adrenocortical growth is discussed with respect to its relation to body weight, elevated ACTH (provoked by sustained stress, adrenal enzyme deficiency, and adrenal enucleation), and unilateral adrenalectomy. It seems likely that these three conditions under which adrenal growth occurs are each controlled and mediated by different agents. Least is known about the growth of adrenals with the growth of the organism; however, because treatment with growth hormone is known to stimulate adrenal mitogenesis, and because adrenals grow in proportion to body growth by increasing cell number, it is proposed that this growth may be mediated by growth hormone (via somatomedin). ACTH causes primarily adrenocortical cellular hypertrophy which is subsequently followed by hyperplasia. It has been shown that the application of a sustained stressor, induction of adrenal enzyme deficiency and adrenal enucleation all result in persistent elevation in circulating ACTH levels and adrenal growth. It appears that the stimulus to ACTH secretion is a virtual or real decrease in corticosteroid feedback signal, and that ACTH secretion is regulated by corticosteroid levels. An additional humoral factor may be triggered by adrenal enucleation, and the possibility that a fragment of the N-terminal peptide of the ACTH precursor molecule plays this role is entertained. Finally, the evidence that the proliferative adrenal growth after unilateral adrenalectomy is mediated by afferent and crossed efferent neural pathways, and is regulated by aldosterone, pineal peptides and exposure to constant light is discussed.

Pro-gamma-melanocyte-stimulating hormone cleavage in adrenal gland undergoing compensatory growth

Regulation of the rapid compensatory growth seen in the remaining adrenal gland of rats following unilateral adrenalectomy is poorly understood. The role of adrenocorticotropic hormone (ACTH) is obscure as immunoneutralization of circulating ACTH does not affect the observed compensatory growth or hyperplasia. This finding, together with the fact that mechanical manipulation of one adrenal without extirpation is followed by growth only in the contralateral gland, has led to the concept of neural regulation of compensatory adrenal growth via a loop from one adrenal through the hypothalamus and back to the contralateral gland which is independent of ACTH secretion. We recently showed that peptides from the N terminal of ACTH precursor proopiocortin (POC), not containing the gamma-melanocyte-stimulating hormone (gamma-MSH) sequence, can stimulate adrenal mitogenesis and proposed that normal long-term adrenal growth and proliferation involves post-secretional proteolytic cleavage of pro-gamma-MSH [or N-POC(1-74)] to generate the mitogenic factor N-POC(1-48/49) and a C-terminal fragment N-POC(50-74), or rat gamma 3-MSH. We have now investigated this hypothesis further in rats by selectively quenching different regions of circulating POC peptides with specific antisera and observing the effect on the increases in weight, RNA and DNA normally seen in the remaining gland following unilateral adrenalectomy. Our results, reported here, suggest that neurally mediated proteolytic cleavage of the circulating inactive mitogenic precursor pro-gamma-MSH at the adrenal gland is the major mechanism of control of compensatory growth.