ACTH receptor mRNA in human adrenocortical tumors: overexpression in aldosteronomas

Renal Hypokalemia: An Endocrine Perspective

The majority of disorders that cause renal potassium wasting present with abnormalities in adrenal hormone secretion. While these findings frequently lead patients to seek endocrine evaluation, clinicians often struggle to accurately diagnose these conditions, delaying treatment and adversely impacting patient care. At the same time, growing insight into the genetic and molecular basis of these disorders continues to improve their diagnosis and management. In this review, we outline a practical integrated approach to the evaluation of renal hypokalemia syndromes that are seen in endocrine practice while highlighting recent advances in understanding of the genetics and pathophysiology behind them.

[Comparison of Different Doses of ACTH Used in ACTH Stimulation Test to Determine the Subtypes of Primary Aldosteronism]

Objective

To compare the diagnostic value of adrenocorticotropic hormone (ACTH) stimulation test (AST) with different doses of ACTH combined with midnight administration of 1 mg dexamethasone for the determination of the subtypes of primary hyperaldosteronism (PA).

Methods

This is a prospective observational study. Patients diagnosed with PA in the Department of Endocrinology, the First Medical Center of of Chinese PLA General Hospital from January 1, 2020 to September 30, 2022 underwent AST with different doses of ACTH. All patients received 1 mg dexamethasone at midnight for inhibition. Then, the patients were randomly assigned to 25-unit and 50-unit ACTH treatment groups by a ratio of 1:2. Subtype classification and diagnosis of aldosterone-producing adenoma (APA) and idiopathic hyperaldosteronism (IHA) was made on the basis of adrenal venous blood samples and/or postoperative pathology and clinical follow-up findings. Receiver operating characteristics (ROC) curves were plotted to examine the diagnostic efficacy and the difference of AST by varying doses of ACTH in distinguishing APA and IHA.

Results

A total of 82 patients, including 49 patients with APA (59.8%) and 33 patients with IHA (40.2%), were enrolled. There were 29 patients in the 25-unit ACTH group (35.4%) and 53 patients in the 50-unit ACTH group (64.6%). There were no significant differences in age, sex, blood pressure, minimum serum potassium, and biochemical parameters between the 25-unit and 50-unit groups. After ACTH stimulation, plasma aldosterone concentration (PAC), cortisol (F), and PAC/F at different points of time showed no statistical difference between the two groups (P>0.05). The area under the curve (AUC) of PAC in the 25-unit group was higher than that of PAC/F. The AUC of PAC reached the maximum at 90 minutes (0.948, 95% confidence interval [CI]: 0870-1.000) and the optimal cutoff was 38.0 ng/dL, which had a sensitivity of 92.9% and a specificity of 86.7% for differentiating APA and IHA. Similar to the 25-unit group, the maximum AUC of PAC in the 50-unit group was greater than that of PAC/F. The AUC of PAC reached the maximum 90 minutes (0.930, 95% CI: 0.840-0.994) and the optimal cutoff was 39.6 ng/dL, which had a sensitivity of 91.2% and a specificity of 83.3%. The AUC of PAC at different points of time in the 25-unit ACTH group (0.862-0.948) was greater than that of 50-unit ACTH group (0.823-0.930), but the difference was not statistical significance.

Conclusion

AST with 25-unit or 50-unit ACTH combined with small-dose dexamethasone can be used in PA subtype determination, ie, differentiation between APA and IHA. The optimal PAC cut-off values for 25-unit or 50-unit ACTH are similar, being 38.0 ng/dL and 39.6 ng/dL, respectively, and both cutoff values show higher sensitivity and specificity at 90 min. The AST with 25-unit ACTH has the smaller dose and the better safety. Therefore, it is recommended for the diagnosis of PA subtypes.

Primary aldosteronism: molecular medicine meets public health

Primary aldosteronism is the most common single cause of hypertension and is potentially curable when only one adrenal gland is the culprit. The importance of primary aldosteronism to public health derives from its high prevalence but huge under-diagnosis (estimated to be <1% of all affected individuals), despite the consequences of poor blood pressure control by conventional therapy and enhanced cardiovascular risk. This state of affairs is attributable to the fact that the tools used for diagnosis or treatment are still those that originated in the 1970-1990s. Conversely, molecular discoveries have transformed our understanding of adrenal physiology and pathology. Many molecules and processes associated with constant adrenocortical renewal and interzonal metamorphosis also feature in aldosterone-producing adenomas and aldosterone-producing micronodules. The adrenal gland has one of the most significant rates of non-silent somatic mutations, with frequent selection of those driving autonomous aldosterone production, and distinct clinical presentations and outcomes for most genotypes. The disappearance of aldosterone synthesis and cells from most of the adult human zona glomerulosa is the likely driver of the mutational success that causes aldosterone-producing adenomas, but insights into the pathways that lead to constitutive aldosterone production and cell survival may open up opportunities for novel therapies.

Aldosterone is Aberrantly Regulated by Various Stimuli in a High Proportion of Patients with Primary Aldosteronism

CONTEXT

In primary aldosteronism (PA), aldosterone secretion is relatively independent of the renin-angiotensin system, but can be regulated by several other stimuli.

OBJECTIVE

To evaluate aldosterone response to several stimuli in a series of patients with PA secondary either to bilateral adrenal hyperplasia (BAH) or unilateral aldosterone-producing adenoma (APA).

DESIGN AND SETTING

Prospective cohort study conducted in a university teaching hospital research center.

PATIENTS

Forty-three patients with confirmed PA and subtyped by adrenal vein sampling (n = 39) were studied, including 11 with BAH, 28 with APA, and 4 with undefined etiology. We also studied 4 other patients with aldosterone and cortisol cosecretion.

INTERVENTIONS

We systematically explored aberrant regulation of aldosterone using an in vivo protocol that included the following stimulation tests performed over 3 days under dexamethasone suppression: upright posture, mixed meal, adrenocorticotropin (ACTH) 1-24, gonadotropin-releasing hormone (GnRH), vasopressin, and serotonin R4 agonist.

MAIN OUTCOME MEASURES

Positive response was defined as >50% renin or ACTH-independent increase in plasma aldosterone/cortisol concentration following the various stimulation tests.

RESULTS

Renin-independent aldosterone secretion increased in response to several aberrant stimuli (upright posture, GnRH) in up to 83% of patients with APA or BAH in whom ACTH 1-24 and HT4R agonists also produced aldosterone oversecretion in all patients. The mean significant aberrant responses per patient was similar in BAH (4.6) and in APA (4.0).

CONCLUSIONS

Aldosterone secretion in PA is relatively autonomous from the renin-angiotensin system, but is highly regulated by several other stimuli, which contributes to the large variability of aldosterone levels in PA patients.

Aldosterone-Regulating Receptors and Aldosterone-Driver Somatic Mutations

BACKGROUND

Somatic gene mutations that facilitate inappropriate intracellular calcium entrance have been identified in most aldosterone-producing adenomas (APAs). Studies suggest that angiotensin II and adrenocorticotropic hormone (ACTH) augment aldosterone production from APAs. Little is known, however, regarding possible variations in response to hormonal stimuli between APAs with different aldosterone-driver mutations.

OBJECTIVE

To analyze the transcript expression of type 1 angiotensin II receptors (AGTR1), ACTH receptors (MC2R), and melanocortin 2 receptor accessory protein (MRAP) in APAs with known aldosterone-driver somatic mutations.

METHODS

RNA was isolated from APAs with mutations in: KCNJ5 (n = 14), ATP1A1 (n = 14), CACNA1D (n = 14), and ATP2B3 (n = 5), and from normal adjacent adrenal tissue (n = 45). Transcript expression of MC2R, MRAP, AGTR1, aldosterone synthase (CYP11B2), 17α-hydroxylase/17,20-lyase (CYP17A1), and 11β-hydroxylase (CYP11B1) were quantified using quantitative RT-PCR and normalized to β-actin.

RESULTS

Compared to adjacent normal adrenal tissue, APAs had higher transcript levels of CYP11B2 (2,216.4 [1,112.0, 2,813.5]-fold, p < 0.001), MC2R (2.88 [2.00, 4.52]-fold, p < 0.001), and AGTR1 (1.80 [1.02, 2.80]-fold, p < 0.001]), and lower transcript levels of MRAP, CYP17A1, and CYP11B1 (0.28-0.36, p < 0.001 for all). MC2R and CYP11B2 transcripts were lower in APAs with KCNJ5 vs. other mutations (p < 0.01 for both). MC2R expression correlated positively with that of AGTR1 in APAs harboring KCNJ5 and CACNA1D mutations, and with MRAP expression in APAs harboring ATPase mutations.

CONCLUSIONS

While MC2R and AGTR1 are expressed in all APAs, differences were observed based on the underlying aldosterone-driver somatic mutations. In tandem, our findings suggest that APAs with ATPase-mutations are more responsive to ACTH than KCNJ5-mutated APAs.

Aldosterone Suppression by Dexamethasone in Patients With KCNJ5-Mutated Aldosterone-Producing Adenoma

CONTEXT

Aldosterone biosynthesis is regulated principally by ACTH and gene mutations as well as by angiotensin II and serum potassium. In addition, previous studies have reported the potential effects of KCNJ5 mutations in aldosterone-producing adenoma (APA) on cardiovascular diseases. However, responsiveness to ACTH in APAs according to potassium inwardly rectifying channel, subfamily J, member 5 (KCNJ5) mutations remains unknown.

OBJECTIVE

To investigate KCNJ5 genotype-specific differences in aldosterone biosynthesis in response to ACTH stimulation.

DESIGN AND SETTING

A cross-sectional study through retrieval of clinical records.

PARTICIPANTS

One hundred forty-one patients aged ≥20 years with APA were examined.

MAIN OUTCOME MEASURES

Associations between KCNJ5 mutations and clinical parameters reflecting the renin-angiotensin system [saline infusion test (SIT)] and ACTH pathways [dexamethasone suppression test (DST)].

RESULTS

KCNJ5 mutations were detected in 107 cases. In the crude comparison, patients with mutations in KCNJ5 had higher plasma aldosterone concentrations (PACs) both at baseline and after the SIT. PAC after the DST showed a significant inverse association with KCNJ5 genotypes after controlling for age, sex, tumor size, and PAC after the SIT. Immunohistochemical analysis of 101 cases revealed more abundant immunoreactivity of CYP11B1 and CYP17 in the KCNJ5-mutated group than in the KCNJ5 wild-type group.

CONCLUSION

This report of marked suppression of PAC by dexamethasone in patients with KCNJ5-mutated APAs indicates that such APAs respond to endogenous ACTH more readily than APAs in nonmutated cases. Further molecular and epidemiologic studies are required to validate our results and clarify the clinical effectiveness of the DST for predicting KCNJ5 mutations before adrenalectomy.

Primary Aldosteronism: Changing Definitions and New Concepts of Physiology and Pathophysiology Both Inside and Outside the Kidney

In the 60 years that have passed since the discovery of the mineralocorticoid hormone aldosterone, much has been learned about its synthesis (both adrenal and extra-adrenal), regulation (by renin-angiotensin II, potassium, adrenocorticotrophin, and other factors), and effects (on both epithelial and nonepithelial tissues). Once thought to be rare, primary aldosteronism (PA, in which aldosterone secretion by the adrenal is excessive and autonomous of its principal regulator, angiotensin II) is now known to be the most common specifically treatable and potentially curable form of hypertension, with most patients lacking the clinical feature of hypokalemia, the presence of which was previously considered to be necessary to warrant further efforts towards confirming a diagnosis of PA. This, and the appreciation that aldosterone excess leads to adverse cardiovascular, renal, central nervous, and psychological effects, that are at least partly independent of its effects on blood pressure, have had a profound influence on raising clinical and research interest in PA. Such research on patients with PA has, in turn, furthered knowledge regarding aldosterone synthesis, regulation, and effects. This review summarizes current progress in our understanding of the physiology of aldosterone, and towards defining the causes (including genetic bases), epidemiology, outcomes, and clinical approaches to diagnostic workup (including screening, diagnostic confirmation, and subtype differentiation) and treatment of PA.

Subtype prediction in primary aldosteronism: measurement of circadian variation of adrenocortical hormones and 24-h urinary aldosterone

OBJECTIVE

Currently, adrenal venous sampling (AVS) is the only reliable method to distinguish unilateral from bilateral hyperaldosteronism in primary aldosteronism (PA). However, AVS is costly and time-consuming compared with simple blood tests. In this study, we conducted a retrospective study to determine whether circadian variation in plasma adrenocortical hormone levels (i.e. aldosterone, cortisol and ACTH) and a 24-h urinary aldosterone could contribute to the clinical differentiation between unilateral hyperaldosteronism (UHA) and bilateral hyperaldosteronism (BHA).

DESIGN

In 64 patients who were diagnosed with PA and underwent AVS, 32 and 22 patients were diagnosed with UHA and BHA, respectively. Plasma adrenocortical hormone levels at 0:00, 6:00, 12:00 and 18:00 and 24-h urinary aldosterone under a condition of 6 g daily dietary sodium chloride intake were measured.

RESULTS

Baseline plasma aldosterone concentration (PAC) and 24-h urinary aldosterone level in patients with UHA were significantly higher than in patients with BHA, particularly at 6:00. The area under the ROC curve for PAC at 0:00, 6:00, 12:00 and 18:00 and 24-h urinary aldosterone to discriminate UHA and BHA was 0·839 [95% confidence interval (CI); 0·73-0·95], 0·922 (95% CI; 0·85-1·00), 0·875 (95% CI; 0·78-0·97), 0·811 (95% CI; 0·69-0·93), 0·898 (95% CI; 0·81-0·99), respectively.

CONCLUSIONS

PAC at different blood sampling times and 24-h urinary aldosterone level may be diagnostically helpful in discriminating between UHA and BHA. We believe that these tests could reduce the number of unnecessary AVS procedures.

Role of ACTH and Other Hormones in the Regulation of Aldosterone Production in Primary Aldosteronism

The major physiological regulators of aldosterone production from the adrenal zona glomerulosa are potassium and angiotensin II; other acute regulators include adrenocorticotropic hormone (ACTH) and serotonin. Their interactions with G-protein coupled hormone receptors activate cAMP/PKA pathway thereby regulating intracellular calcium flux and CYP11B2 transcription, which is the specific steroidogenic enzyme of aldosterone synthesis. In primary aldosteronism (PA), the increased production of aldosterone and resultant relative hypervolemia inhibits the renin and angiotensin system; aldosterone secretion is mostly independent from the suppressed renin-angiotensin system, but is not autonomous, as it is regulated by a diversity of other ligands of various eutopic or ectopic receptors, in addition to activation of calcium flux resulting from mutations of various ion channels. Among the abnormalities in various hormone receptors, an overexpression of the melanocortin type 2 receptor (MC2R) could be responsible for aldosterone hypersecretion in aldosteronomas. An exaggerated increase in plasma aldosterone concentration (PAC) is found in patients with PA secondary either to unilateral aldosteronomas or bilateral adrenal hyperplasia (BAH) following acute ACTH administration compared to normal individuals. A diurnal increase in PAC in early morning and its suppression by dexamethasone confirms the increased role of endogenous ACTH as an important aldosterone secretagogue in PA. Screening using a combination of dexamethasone and fludrocortisone test reveals a higher prevalence of PA in hypertensive populations compared to the aldosterone to renin ratio. The variable level of MC2R overexpression in each aldosteronomas or in the adjacent zona glomerulosa hyperplasia may explain the inconsistent results of adrenal vein sampling between basal levels and post ACTH administration in the determination of source of aldosterone excess. In the rare cases of glucocorticoid remediable aldosteronism, a chimeric CYP11B2 becomes regulated by ACTH activating its chimeric CYP11B1 promoter of aldosterone synthase in bilateral adrenal fasciculate-like hyperplasia. This review will focus on the role of ACTH on excess aldosterone secretion in PA with particular focus on the aberrant expression of MC2R in comparison with other aberrant ligands and their GPCRs in this frequent pathology.

Multiple aberrant hormone receptors in Cushing's syndrome

The mechanisms regulating cortisol production when ACTH of pituitary origin is suppressed in primary adrenal causes of Cushing's syndrome (CS) include diverse genetic and molecular mechanisms. These can lead either to constitutive activation of the cAMP system and steroidogenesis or to its regulation exerted by the aberrant adrenal expression of several hormone receptors, particularly G-protein coupled hormone receptors (GPCR) and their ligands. Screening for aberrant expression of GPCR in bilateral macronodular adrenal hyperplasia (BMAH) and unilateral adrenal tumors of patients with overt or subclinical CS demonstrates the frequent co-expression of several receptors. Aberrant hormone receptors can also exert their activity by regulating the paracrine secretion of ACTH or other ligands for those receptors in BMAH or unilateral tumors. The aberrant expression of hormone receptors is not limited to adrenal CS but can be implicated in other endocrine tumors including primary aldosteronism and Cushing's disease. Targeted therapies to block the aberrant receptors or their ligands could become useful in the future.

Integration of transcriptome and methylome analysis of aldosterone-producing adenomas

OBJECTIVE

The pathophysiology of aldosterone-producing adenomas (APA) has been investigated intensively through genetic and genomic approaches. However, the role of epigenetics in APA is not fully understood. In the present study, we explored the relationship between gene expression and DNA methylation status in APA.

METHODS

We conducted an integrated analysis of transcriptome and methylome data of paired APA-adjacent adrenal gland (AAG) samples from the same patient. The adrenal specimens were obtained from seven Japanese patients with APA who underwent adrenalectomy. Gene expression and genome-wide CpG methylation profiles were obtained from RNA and DNA samples that were extracted from those seven paired tissues.

RESULTS

Methylome analysis showed global CpG hypomethylation in APA relative to AAG. The integration of gene expression and methylation status showed that 34 genes were up-regulated with CpG hypomethylation in APA. Of these, three genes (CYP11B2, MC2R, and HPX) may be related to aldosterone production, and five genes (PRRX1, RAB38, FAP, GCNT2, and ASB4) are potentially involved in tumorigenesis.

CONCLUSION

The present study is the first methylome analysis to compare APA with AAG in the same patients. Our integrated analysis of transcriptome and methylome revealed DNA hypomethylation in APA and identified several up-regulated genes with DNA hypomethylation that may be involved in aldosterone production and tumorigenesis.

Melanocortin receptor accessory proteins in adrenal gland physiology and beyond

The melanocortin receptor (MCR) family consists of five G-protein-coupled receptors (MC1R-MC5R) with diverse physiological roles. MC1R controls pigmentation, MC2R is a critical component of the hypothalamic-pituitary-adrenal axis, MC3R and MC4R have a vital role in energy homeostasis and MC5R is involved in exocrine function. The melanocortin receptor accessory protein (MRAP) and its paralogue MRAP2 are small single-pass transmembrane proteins that have been shown to regulate MCR expression and function. In the adrenal gland, MRAP is an essential accessory factor for the functional expression of the MC2R/ACTH receptor. The importance of MRAP in adrenal gland physiology is demonstrated by the clinical condition familial glucocorticoid deficiency, where inactivating MRAP mutations account for ∼20% of cases. MRAP is highly expressed in both the zona fasciculata and the undifferentiated zone. Expression in the undifferentiated zone suggests that MRAP could also be important in adrenal cell differentiation and/or maintenance. In contrast, the role of adrenal MRAP2, which is highly expressed in the foetal gland, is unclear. The expression of MRAPs outside the adrenal gland is suggestive of a wider physiological purpose, beyond MC2R-mediated adrenal steroidogenesis. In vitro, MRAPs have been shown to reduce surface expression and signalling of all the other MCRs (MC1,3,4,5R). MRAP2 is predominantly expressed in the hypothalamus, a site that also expresses a high level of MC3R and MC4R. This raises the intriguing possibility of a CNS role for the MRAPs.

Effects of melanocortins on adrenal gland physiology

The melanocortin-2-receptor (MC(2) receptor), also known as the ACTH receptor, is a critical component of the hypothalamic-pituitary-adrenal axis. The importance of MC(2) receptor in adrenal physiology is exemplified by the condition familial glucocorticoid deficiency, a potentially fatal disease characterised by isolated cortisol deficiency. MC(2)receptor mutations cause ~25% of cases. The discovery of a MC(2) receptor accessory protein MRAP, mutations of which account for ~15%-20% of familial glucocorticoid deficiency, has provided insight into MC(2) receptor trafficking and signalling. MRAP is essential for the functional expression of MC(2) receptor. MRAP2, a novel homolog of MRAP, can also facilitate MC(2) receptor cell surface expression and function. Like MRAP, MRAP2 is a small transmembrane domain glycoprotein capable of homodimerising. In addition, MRAP/MRAP2 can heterodimerise. The presence of MRAP2 adrenal expression suggests a possible role for MRAP2 in adrenal physiology, which has yet to be elucidated. Importantly, new data shows that the MRAPs can interact with all the other melanocortin receptors (MC(1,3,4,5) receptor). In contrast to MC(2) receptor, this interaction results in reduced melanocortin receptor surface expression and signalling. MRAP2 is predominantly expressed in brain. Hypothalamic expression has been demonstrated for both MRAP and MRAP2. The ability of MRAPs to modulate different members of the melanocortin receptor family in a bidirectional manner is intriguing. Furthermore, central nervous system expression of MRAPs points to a role beyond MC(2) receptor mediated adrenal steroidogenesis.

Functional consequence of a novel Y129C mutation in a patient with two contradictory melanocortin-2-receptor mutations

CONTEXT

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disease, characterised by isolated glucocorticoid deficiency in the absence of mineralocorticoid deficiency. Inactivating mutations in the ACTH receptor (melanocortin-2-receptor, MC2R) are well described and account for approximately 25% of cases. By contrast, activating MC2R mutations are extremely rare.

PATIENT

We report a child of Saudi Arabian origin who was diagnosed with FGD following hypoglycaemic episodes that resulted in spastic quadriplegia.

METHODS AND RESULTS

MC2R gene analysis revealed an unusual combination of two homozygous missense mutations, consisting of the novel mutation Y129C and the previously described F278C activating mutation. Parents were heterozygous at both of these sites. In vitro analysis of the Y129C mutation using a fluorescent cell surface assay showed that this mutant was unable to reach the cell surface in CHO cells stably transfected with MC2R accessory protein (MRAP), despite the demonstration of an interaction with MRAP by co-immunoprecipitation. The double mutant Y129C-F278C also failed to traffic to the cell surface.

CONCLUSION

The tyrosine residue at position 129 in the second intracellular loop is critical in MC2R folding and/or trafficking to the cell surface. Furthermore, the absence of cell surface expression of MC2R would account for the lack of activation of the receptor due to the F278C mutation located at the C-terminal tail. We provide a novel molecular explanation for a child with two opposing mutations causing severe FGD.

Regulation of aldosterone secretion by several aberrant receptors including for glucose-dependent insulinotropic peptide in a patient with an aldosteronoma

CONTEXT

Primary adrenal Cushing's syndrome can result from the aberrant adrenal expression of several hormone receptors; this mechanism has not been explored in detail in aldosterone-producing tumors.

OBJECTIVE

The objective of the study was to evaluate a 56-yr-old male patient with an aldosteronoma for the regulation of aldosterone secretion by aberrant hormone receptors.

RESULTS

Renin-independent stimulation of aldosterone secretion was observed in vivo after a mixed meal, oral glucose, or administration of glucose-dependent insulinotropic peptide (GIP), vasopressin, and tegaserod. The mixed meal-mediated stimulation of aldosterone was not present in five other cases of aldosteronoma. A smaller response of aldosterone after GIP infusion was observed in a normal subject. Aldosterone secretion was stimulated by GIP in primary cultures of this patient's aldosteronoma. Increased expression of GIP receptor was found in this aldosteronoma by real-time RT-PCR and immunohistochemistry. The GIP receptor protein was also found at lower levels in zona glomerulosa cells of the normal adjacent adrenal gland. Increased expression of serotonin 4 and ACTH receptors was also present in this aldosteronoma.

CONCLUSIONS

This case report provides new evidence of the implication of aberrant hormone receptors in the regulation of this aldosteronoma and suggests that further detailed studies of the role of aberrant hormone receptors in this frequent pathology should be undertaken.

Primary hyperaldosteronism is associated with derangement in the regulation of the hypothalamus-pituitary-adrenal axis in humans

Hippocampal mineralocorticoid receptors (MR) play a major role in the control of hypothalamus- pituitary-adrenal (HPA) axis. The functional profile of HPA axis and the impact of MR blockade under chronic exposure to mineralocorticoid excess are unknown. To clarify this issue, ACT H, cortisol, and aldosterone secretions were studied in 6 patients with primary hyperaldosteronism (HA) and 8 controls (NS) during placebo, placebo+human CR H (hCR H) (2 microg/kg iv bolus at 22:00 h), potassium canrenoate (CAN, 200 mg iv bolus at 20:00 h followed by 200 mg infused over 4 h) or CAN+hCR H. During placebo, both aldosterone and ACT H levels were higher (p<0.01) in HA than in NS, while cortisol levels were not significantly different. Both HA and NS showed significant ACT H and cortisol responses to hCR H (p<0.004), although the hormonal responses in HA were higher (p<0.02) than in NS. CAN infusion did not modify aldosterone levels in both HA and NS. Under CAN infusion, ACT H showed progressive rise in NS (p<0.05) but not in HA, while cortisol levels showed a significant (p<0.05) but less marked and delayed increase in HA compared to NS. CAN enhanced hCRH-induced ACTH and cortisol responses in NS (p<0.05), but not in HA. In conclusion, in humans primary hyperaldosteronism is associated with deranged function of the HPA axis. In fact, hyperaldosteronemic patients show basal and hCR H-stimulated HPA hyperactivity that is, at least partially, refractory to further stimulation by mineralocorticoid blockade with canrenoate. Whether this hormonal alteration can influence the clinical feature of hypertensive patients with primary hyperaldosteronism needs to be clarified.

Dynamic testing with high-dose adrenocorticotrophic hormone does not improve lateralization of aldosterone oversecretion in primary aldosteronism patients

OBJECTIVE

Diagnosing aldosterone-producing adenoma (APA) involves a demonstration of the lateralization of aldosterone oversecretion because adrenal incidentalomas are common in hypertensive individuals and many small-sized APA escape identification with available imaging techniques. However, because of the pulsatile pattern of aldosterone secretion this can be a difficult undertaking. Stimulation of aldosterone secretion before adrenal vein sampling (AVS) can overcome this difficulty, but anecdotal data exist. We, therefore, prospectively investigated the usefulness of AVS with dynamic testing in primary aldosteronism (PA) patients.

METHODS

We enrolled 24 consecutive consenting patients with a biochemical diagnosis of PA from a tertiary referral centre to measure the effects of adrenocorticotrophic hormone (ACTH) on selectivity, the lateralization of aldosterone secretion to the APA side, and adverse effects. After correcting the hypokalemia we performed bilateral AVS. After 3 h supine resting, blood was simultaneously obtained from both sides. A high-dose ACTH (250 mug intravenous) bolus was then administered and AVS was repeated after 30 min.

RESULTS

AVS was bilaterally selective in 88% of patients; no adverse effects occurred. Of the 21 patients with bilaterally selective AVS, three had idiopathic hyperaldosteronism and 18 an APA that was surgically removed in 12 with an ensuing fall in blood pressure at follow-up. After ACTH patients showed a significant increase (P = 0.007) of aldosterone from contralateral adrenal vein blood, but not from the APA gland. Therefore, lateralization of aldosterone secretion on the APA side did not improve.

CONCLUSION

AVS is safe and accurate for identifying APA. However, at a statistical power of 99%, these results do not support the usefulness of high-dose ACTH testing to improve the diagnostic accuracy of AVS.

Functional and nonfunctional adrenocortical tumors demonstrate a high responsiveness to low-dose adrenocorticotropin

Aldosterone-producing adenomas (APAs) demonstrate exquisite sensitivity to endogenous ACTH. We previously showed an ACTH receptor overexpression in APAs compared with the other adrenal tumors. To evaluate the meaning of such findings, we investigated the response of aldosterone, cortisol, and 17OH progesterone (17OHP) to 1 microg ACTH in 42 patients with adrenocortical tumors (23 NHAs, 9 APAs, and 10 CPAs) and 10 normal subjects (C). All 52 subjects were responsive to ACTH, and hormone peak levels were reached at 30 min. The aldosterone peak level was significantly higher in APAs [mean +/- SEM: 84.3 +/- 13.1 ng/dl (2335.1 +/- 362.9 pmol/liter)] than in other tumors and control (C). Cortisol peak levels was higher in CPAs [37.1 +/- 3.9 microg/dl (1023.9 +/- 107.6 nmol/liter)] than in NHAs (P < 0.01), in C (P < 0.01) and in APAs (P = n.s.). 17OHP peak levels were significantly higher in patients with adrenocortical tumors toward C. In summary: 1) low-dose ACTH induces an important stimulation in all tumors, suggesting preservation of high responsiveness to ACTH; 2) this is especially true for aldosterone in APA and could be of primary importance when performing diagnostic tests for hyperaldosteronism; and 3) 17OHP-hyperresponsiveness to low-dose ACTH is the most common alteration both in functional and nonfunctional tumors.

Variable expression of the transcription factors cAMP response element-binding protein and inducible cAMP early repressor in the normal adrenal cortex and in adrenocortical adenomas and carcinomas

The molecular mechanisms leading to adrenocortical tumorigenesis have been only partially elucidated so far. Because the pituitary hormone ACTH, via activation of the cAMP pathway, regulates both cell proliferation/differentiation and steroid synthesis in the adrenal cortex, in this study we focused on the cAMP-dependent transcription factors cAMP responsive element modulator (CREM) and cAMP responsive element binding protein (CREB). We studied CREM and CREB expression by RT-PCR in human normal adrenal cortex (n = 3), adrenocortical adenomas (n = 8), and carcinomas (n = 8). We found transcripts corresponding to the isoforms alpha, beta, gamma, and tau2 of the CREM gene in all of the normal adrenal tissues, in the adenomas, and in seven of eight carcinomas. On the other hand, mRNA for the inducible cAMP early repressor isoforms, which derive from an internal promoter of CREM gene, was detected in the normal adrenal and in seven of eight adenomas, but in only three of eight carcinomas. Similarly, CREB transcripts were readily detectable in all normal adrenals and adenomas, whereas they were not found in four of eight adrenal carcinomas. To further characterize the carcinomas, telomerase activity and the expression of the ACTH receptor gene were determined. Telomerase activity in the carcinomas resulted in levels significantly higher than in the adenomas, whereas the levels of ACTH receptor mRNA were lower in the carcinomas. No correlation was found in the carcinomas between the levels of the ACTH receptor transcript and the loss of expression of CREB/inducible cAMP early repressor, suggesting that this alteration is not secondary to an upstream disregulation at the receptor level. In conclusion, our results suggest that an alteration in cAMP signaling may be associated with malignancies of the adrenal cortex.

Ectopic and abnormal hormone receptors in adrenal Cushing's syndrome

The mechanism by which cortisol is produced in adrenal Cushing's syndrome, when ACTH is suppressed, was previously unknown and was referred to as being "autonomous." More recently, several investigators have shown that some cortisol and other steroid-producing adrenal tumors or hyperplasias are under the control of ectopic (or aberrant, illicit, inappropriate) membrane hormone receptors. These include ectopic receptors for gastric inhibitory polypeptide (GIP), beta-adrenergic agonists, or LH/hCG; a similar outcome can result from altered activity of eutopic receptors, such as those for vasopressin (V1-AVPR), serotonin (5-HT4), or possibly leptin. The presence of aberrant receptors places adrenal cells under stimulation by a trophic factor not negatively regulated by glucocorticoids, leading to increased steroidogenesis and possibly to the proliferative phenotype. The molecular mechanisms responsible for the abnormal expression and function of membrane hormone receptors are still largely unknown. Identification of the presence of these illicit receptors can eventually lead to new pharmacological therapies as alternatives to adrenalectomy, now demonstrated by the long-term control of ectopic P-AR- and LH/hCGR-dependent Cushing's syndrome by propanolol and leuprolide acetate. Further studies will potentially identify a larger diversity of hormone receptors capable of coupling to G proteins, adenylyl cyclase, and steroidogenesis in functional adrenal tumors and probably in other endocrine and nonendocrine tumors.