Cellular and molecular abnormalities of a macronodular adrenal hyperplasia causing beta-blocker-sensitive Cushing's syndrome

Cushing's syndrome due to ACTH-independent macronodular adrenal hyperplasia (AIMAH) can be associated with abnormal responses of aberrantly expressed adrenocortical receptors. This study aimed to characterize in vitro the pathophysiology of hypercortisolism in a beta-blocker-sensitive Cushing's syndrome due to AIMAH. Cortisol secretion profile under aberrant receptors stimulation revealed hyperresponsiveness to salbutamol (beta2-adrenoceptor agonist), cisapride (5-HT4 receptor agonist), and vasopressin in AIMAH cultured cells, but not in normal adrenocortical cells. By RT-PCR, AIMAH tissues revealed beta2-adrenoceptor overexpression rather than ectopical expression. MC2R expression was similar in both AIMAH and normal adrenocortical tissues. Curiously, cortisol levels of AIMAH cells under basal condition were 15-fold higher than those of control cells and were not responsive to ACTH. Analysis of culture medium from AIMAH cells could detect the presence of ACTH, which was immunohistochemically confirmed. Finally, the present study of AIMAH cells has identified: a) cortisol hyperresponsiveness to catecholamines, 5-HT4 and vasopressin in vitro, in agreement with clinical screening tests; b) abnormal expression of beta2-adrenoceptors in some areas of the hyperplastic adrenal tissue; c) autocrine loop of ACTH production. Altogether, the demonstration of aberrant responses to hormonal receptors and autocrine hormone production in the same tissue supports the assumption of multiple molecular alterations in adrenal macronodular hyperplasia.     

Expression of vasopressin receptors in ACTH-independent macronodular bilateral adrenal hyperplasia causing Cushing's syndrome: molecular, immunohistochemical and pharmacological correlates

Cortisol secretion in ACTH-independent macronodular adrenal hyperplasia (AIMAH) causing Cushing's syndrome can be controlled by illegitimate receptors. The aim of the present study was to characterize the molecular, immunohistochemical, and pharmacological profiles of vasopressin receptors in cells derived from three patients with AIMAH (H1-H3), in order to evaluate the role of ectopic vasopressin receptors in the physiopathology of hypercortisolism. Expression of mRNAs encoding the vasopressin receptor types (V(1a), V(1b), and V(2)) were analyzed by RT-PCR in adrenal tissues. The presence of V(1a) and V(2) receptors was studied by immunohistochemistry on adrenal sections. The pharmacological profiles of vasopressin receptors involved in the control of cortisol secretion were investigated using the V(1a) receptor antagonist SR49059 and the V(2) receptor agonist [deamino-Cys(1), Val(4), D-Arg(8)]-vasopressin on cultured cells. The V(1a) receptor protein was present and functional in H1 and H3 tissues, whereas the V(1b) receptor was not expressed in any of the tissues. RT-PCR experiments revealed that V(2) receptor mRNAs were detected in the three tissues. In contrast, immunohistochemical and cell incubation studies showed that the V(2) receptor was involved in the stimulatory effect of AVP on cortisol secretion in H1 and H2, but not in H3 cells. Taken together, these data show that expression of functional ectopic V(2) receptors and repression of eutopic V(1a) receptor can coexist in some hyperplastic corticosteroidogenic tissues. They also reveal that immunohistochemical and incubation studies are essential for the characterization of ectopic receptors actually involved in the control of cortisol secretion by AIMAHs.     

Eutopic overexpression of vasopressin v1a receptor in adrenocorticotropin-independent macronodular adrenal hyperplasia

Arginine vasopressin (AVP) stimulates cortisol secretion through its vascular type V(1a) receptor in the adrenal glands, in addition to stimulating ACTH secretion through pituitary V(3) receptor. Because hyper-response of plasma cortisol to vasopressin is documented in some patients with Cushing's syndrome due to adrenal adenoma (CS) or ACTH-independent macronodular adrenocortical hyperplasia (AIMAH), we analyzed the expression of V(1a), V(2), V(3) receptor and AVP mRNA in human adrenal tissues by quantitative competitive RT-PCR or real-time PCRs. V(1a) receptor mRNA levels (ratio against glyceraldehyde 3-phosphate dehydrogenase) were 0.378 +/- 0.143 (mean +/- SE) in preclinical CS (n = 5) and 0.630 +/- 0.072 in AIMAH (n = 4), which were significantly higher than those (0.046 +/- 0.012; n = 9) in control adrenals, whereas those in overt CS (0.143 +/- 0.048; n = 10) or aldosterone-producing adenomas (0.069 +/- 0.018; n = 12) were similar to control adrenals. Although ectopic expression of V(2) or V(3) receptor was detected in half of AIMAH cases, the absolute levels were low. Furthermore, V(1a) receptor mRNA levels in the adjacent adrenal glands (0.190 +/- 0.039, n = 9) of aldosterone-producing adenomas were higher than those in control adrenals and in the corresponding tumor portions (0.079 +/- 0.024). In contrast, there were no significant differences in AVP mRNA levels among these groups. These results suggest that eutopic V(1a) receptor overexpression is involved in the etiology of AIMAH and a subset of adrenal adenomas causing overt or preclinical Cushing's syndrome. Our results imply a possible association of V(1a) receptor expression with adrenal hyperplasia.     

Vasopressin responsiveness of subclinical Cushing's syndrome due to ACTH-independent macronodular adrenocortical hyperplasia

OBJECTIVE: Vasopressin (AVP) is reported to be an important factor for regulating cortisol secretion in patients with Cushing's syndrome due to ACTH-independent macronodular adrenocortical hyperplasia (AIMAH). Recently, there have been several case reports of subclinical Cushing's syndrome due to AIMAH, in which the pathophysiological role of AVP has been unknown. The aim was to conduct an extensive investigation of AVP in the autonomous secretion of cortisol in subclinical Cushing's syndrome due to AIMAH. PATIENTS AND MEASUREMENTS: Five cases of AIMAH with subclinical Cushing's syndrome underwent prospective study including physical examination, imaging (MRI, CT and 131I-adosterol scintigraphy) and endocrinological evaluation that comprised basal plasma cortisol levels and urinary excretions of steroid metabolites, a dexamethasone suppression test and an AVP stimulation test. In case 1, left adrenalectomy was performed and the pathological diagnosis of AIMAH was established. An in vitro experiment using the cultured AIMAH adrenal cells was conducted to investigate cortisol secretion and expression of the V1-AVP receptor, mRNA by RT-PCR. RESULTS: All five cases were discovered incidentally to have bilateral adrenal nodules. Imaging by MRI and CT revealed large multinodular lesions in both adrenal glands, which showed positive uptake on 131I-adosterol scintigraphy. Although the basal values of plasma cortisol and urinary excretions of steroid metabolites were within normal limits, autonomous secretion of cortisol was assumed to occur because of lack of suppression during dexamethasone suppression. The five patients had no overt signs of Cushing's syndrome, and they were therefore diagnosed with subclinical Cushing's syndrome due to AIMAH. In all five patients, AVP stimulated cortisol secretion in vivo, whereas desmopressin acetate failed to affect cortisol secretion. In case 1, AVP stimulated cortisol secretion from cultured AIMAH adrenal cells, but this secretion had no relationship with cAMP production. In addition, over-expression of V1-AVP receptor mRNA in AIMAH tissue was determined by RT-PCR. CONCLUSION: Patients with subclinical Cushing's syndrome due to AIMAH commonly exhibit cortisol responsiveness to AVP, and this is probably mediated through activation of overexpressed V1-AVP receptors.     

Illicit hormone receptors in adrenal Cushing's syndrome

Recent studies from several groups have indicated that abnormal or ectopic expression and function of adrenal receptors for various hormones may regulate cortisol production in ACTH-independent hypercortisolism. GIP-dependent Cushing's syndrome has been described in patients with either unilateral adenomas or bilateral macronodular adrenal hyperplasia; this syndrome results from the adrenal overexpression of the GIP receptor, which was found to be without an activating mutation. An increased stimulation of cortisol secretion following administration of vasopressin was also reported by several investigators in patients with adrenal Cushing's syndrome; this was linked to an increased expression or abnormal response of the V1-vasopressin receptor. We have conducted a prospective in vivo evaluation of 20 patients with adrenal Cushing's syndrome in order to identify the presence of abnormal hormone receptors. In 6 cases of macronodular adrenal hyperplasia, we have identified, in addition to 2 cases of GIP-dependent Cushing's syndrome, 4 other patients in whom cortisol production was regulated abnormally either by vasopressin, B-adrenergic receptor agonists, hCG/LH, or serotonin 5-HT-4 receptor agonists. In 13 patients with unilateral adrenal adenoma, an abnormal response to a mixed meal or to vasopressin was found in 3 cases, suggesting that the presence of ectopic or abnormal hormone receptors is less prevalent than in macronodular adrenal hyperplasia. The identification of the presence of an abnormal adrenal receptor offers the possibility of a new pharmacological approach to control hypercortisolism by suppressing the endogenous ligands or by using specific antagonists of the abnormal receptors.     

Case of adrenocorticotropic hormone-independent macronodular adrenal hyperplasia with possible adrenal hypersensitivity to angiotensin II

With increasing case reports, it has been indicated that some cases with adrenocorticotropic hormone (ACTH)-independent macronodular adrenal hyperplasia (AIMAH) show abnormal responses in cortisol to various stimulation tests. Here we report a case of AIMAH that showed an aberrant response to angiotensin II via AT1 receptor in cortisol hypersecretion. A 53-yr-old man was admitted to our division seeking further examinations for the possible diagnosis of Cushing's syndrome. He had hypertension, diabetes mellitus, and physical stigmata, such as moon face and central obesity. His plasma ACTH level was undetectable, and plasma cortisol level was high. Plasma cortisol showed no normal diurnal rhythm and was not suppressed after the administration of 8 mg of dexamethasone. Abdominal computed tomography demonstrated nodular enlargement of bilateral adrenal glands. He was diagnosed with Cushing's syndrome owing to AIMAH. An injection of arginine vasopressin (AVP) increased plasma cortisol and aldosterone levels, whereas ACTH remained undetectable. After 4 h in an upright position, plasma cortisol and aldosterone levels were increased. Pretreatment with candesartan, angiotensin II receptor AT1 antagonist, blocked the increase in plasma cortisol level. These results suggested a possibility of adrenal hypersensitivity to angiotensin II and AVP in cortisol secretion. Bilateral laparoscopic adrenalectomy was performed. The histological findings of the specimen were compatible with AIMAH. In summary, we have made the first report on a case of AIMAH with possible hypersensitivity to angiotensin II.     

In vivo and in vitro screening for illegitimate receptors in adrenocorticotropin-independent macronodular adrenal hyperplasia causing Cushing's syndrome: identification of two cases of gonadotropin/gastric inhibitory polypeptide-dependent hypercortisolism

In ACTH-independent macronodular adrenal hyperplasia (AIMAH) causing Cushing's syndrome, cortisol production can be controlled by illegitimate membrane receptors. The aim of the present study was to evaluate in vivo and in vitro the sensitivity of AIMAH to various regulatory factors to detect the expression of illegitimate receptors by the tissues. Four consecutive patients with AIMAH and hypercortisolism (H1-H4) preoperatively underwent a series of pharmacological and/or physiological tests. After adrenalectomy, in vitro studies were conducted to investigate the cortisol responses of cultured cells, derived from hyperplastic tissues, to various membrane receptor ligands. The adrenal tissues of the two patients who responded in vivo to food intake (H2 and H4) were stimulated in vitro by gastric inhibitory polypeptide. GnRH and human chorionic gonadotropin, but not FSH, stimulated cortisol secretion in patients H2 and H4. In these two cases, human chorionic gonadotropin but not GnRH stimulated cortisol production from cultured adrenocortical cells. Cisapride induced a significant increase in cortisol levels in patient H1. In addition, serotonin (5-HT) was more efficient to stimulate cortisol production in H1 cells than in normal adrenocortical cells. Upright stimulation test provoked an increase in cortisol levels in patients H1, H2, and H3. H1 and H2 cells were more sensitive to the stimulatory action of angiotensin II than normal cells. Similarly, arginine vasopressin (AVP) more efficiently activated steroidogenesis in H1 cells than in normal cells. In H1 tissue, immunohistochemical studies revealed the presence of 5-HT- and AVP-like immunoreactivities within clusters of steroidogenic cells, suggesting that these two factors acted through an autocrine/paracrine mechanism to stimulate cortisol secretion. The present study provides the first demonstration of primary adrenal Cushing's syndrome dependent on both gonadotropin and gastric inhibitory polypeptide. Our data also show a hyperresponsiveness of hyperplastic adrenal tissues to 5-HT, angiotensin II, and AVP. Finally, they reveal for the first time the presence of paracrine regulatory signals in adrenal hyperplasia tissues.     

A case of ACTH-independent bilateral macronodular adrenal hyperplasia and severe congestive heart failure

Cortisol secretion in ACTH independent bilateral macronodular adrenal hyperplasia (AIMAH) can be regulated by aberrant adrenal receptors. We describe a patient with Cushing's syndrome (CS) due to AIMAH and concomitant Class IV congestive heart failure (CHF). Clinical testing for the presence of aberrant receptors revealed a pronounced serum cortisol (257%) and aldosterone response (212%) to the administration of ACTH and a partial serum cortisol (35%) and aldosterone (106%) response to upright posture. This suggested the possible presence of aberrant hormone receptors for ACTH [melanocortin 2 receptor (MC2-R)], vasopressin, catecholamines or angiotensin II (AT-II) on the patient's adrenal glands. Adrenal tissue from the patient demonstrated an eight-fold increased expression of MC2-R compared to normal adrenal tissue. This increased expression was consistent with the increase in cortisol and aldosterone seen in response to exogenous ACTH. We propose that the severe CHF resulted in activation of the renin-angiotensin system, with an increased production of AT-II. The elevated circulating levels of AT-II may have led to increased expression of MC2-R on the patient's adrenal glands and increased responsiveness to ACTH. This unusual case of CS may elucidate a heretofore unknown mechanism for the development of AIMAH.     

Expression of serotonin7 receptor and coupling of ectopic receptors to protein kinase A and ionic currents in adrenocorticotropin-independent macronodular adrenal hyperplasia causing Cushing's syndrome

CONTEXT: In ACTH-independent macronodular adrenal hyperplasia (AIMAH) causing Cushing's syndrome, cortisol secretion is controlled by illegitimate membrane receptors. OBJECTIVE: The aim of the present study was to characterize the pharmacological properties and the transduction mechanisms of illegitimate receptors, i.e. receptors for serotonin (5-HT), gastric inhibitory polypeptide (GIP), and LH/human chorionic gonadotropin (hCG), expressed by AIMAH tissues to evaluate the role of ectopic receptors in the physiopathology of Cushing's syndrome. DESIGN: We used in vitro studies on cultured adrenal hyperplasia cells. SETTING: The setting was a university research laboratory. PATIENTS: AIMAH tissues (H1-H3) were removed from three patients previously screened for illegitimate receptors. MAIN OUTCOME MEASURE(S): The main outcome measures were steroidogenic and electrical activities of cultured adrenal hyperplasia cells. RESULTS: In vitro studies showed that the corticotropic effect of 5-HT was mediated by ectopic 5-HT7 receptors in H1 and H2. GIP and hCG stimulated cortisol production via activation of cAMP-dependent protein kinase A in H2. On the contrary, the protein kinase A inhibitor H-89 did not affect hCG-induced cortisol production in H3. Activation of 5-HT7 or GIP receptors enhanced T-type calcium current in H1 or H2 and H3, respectively. In addition, GIP reduced the amplitude of transient and sustained potassium currents in H2. Conversely, hCG did not modify T-type calcium current in H3. CONCLUSIONS: These data show that, besides their coupling to the cAMP pathway, illegitimate adrenal receptors can activate additional transduction mechanisms, including modulation of membrane channels.     

Aberrant Expression of Hormone Receptors in Adrenal Cushing's Syndrome

In recent years, a novel understanding of the pathophysiology of adrenal Cushing's syndrome has emerged. The ectopic or aberrant expression of G-protein-coupled hormone receptors in the adrenal cortex was found to play a central role in the regulation of cortisol secretion in ACTH-independent macronodular adrenal hyperplasia (AIMAH) and in some unilateral adrenal adenomas. Various aberrant receptors, functionally coupled to steroidogenesis, have been reported: GIP, vasopressin, β-adrenergic, LH/hCG, and serotonin receptors have been best characterized, but angiotensin, leptin, glucagon, IL-1 and TSH receptors have also been described. The molecular mechanisms responsible for the aberrant expression of these receptors are currently unknown. One or many of these aberrant receptors are present in most cases of AIMAH and in some cases of adrenal adenomas with overt or sub-clinical secretion of cortisol. Clinical protocols to screen for such aberrant receptors have been developed and should be performed in all patients with AIMAH. The identification of such aberrant regulation of steroidogenesis in AIMAH provides the novel opportunity to treat some of these patients with pharmacological agents that either suppress the endogenous ligand or block the aberrant receptor, thus avoiding bilateral adrenalectomy. This work was supported by a grant from the Canadian Institutes of Health Research (MA-10339).     

The ectopic expression of the gastric inhibitory polypeptide receptor is frequent in adrenocorticotropin-independent bilateral macronodular adrenal hyperplasia, but rare in unilateral tumors

Control of cortisol secretion by the abnormal expression of the gastric inhibitory polypeptide receptor (GIP-R) have been observed in some rare cases of ACTH-independent, food-dependent Cushing's syndrome (FD-ACS) due to adrenal adenoma (AA) or bilateral macronodular hyperplasia (AIMAH). This study was performed to determine the prevalence of GIP-R ectopic expression in ACS and its correlation with fasting cortisol levels. GIP-R expression was studied by RT-PCR in 30 unilateral adrenal tumors [16 AA and 14 adrenocortical cancer (AC)] and 8 AIMAH tissues. Fasting and postprandial cortisol levels were assayed, respectively, at 0800 and 1200 h in AA, AC, and AIMAH, and 1 h after a morning standard meal in 6 AIMAH patients. Similar expression of 2 GIP-R isoforms was observed in 1 of 16 AA, 0 of 14 AC, and 4 of 8 AIMAH as well as in the 4 insulinomas used as positive controls. In vitro study of the GIP-R-expressing AA showed stimulation of cortisol secretion and cAMP production by GIP. The fasting 0800-h plasma cortisol level was above 276 nmol/liter in all patients except 1 AA case and 1 AIMAH case, both of whom expressed GIP-R. In the 3 additional AIMAH cases that expressed the GIP-R, fasting plasma cortisol levels were above 276 nmol/liter. This study demonstrates that ectopic expression of GIP-R is rare in AA and is usually associated with the low fasting plasma cortisol levels that characterize FD-ACS. In contrast, GIP-R expression is frequent in AIMAH and might not always be associated with a low fasting plasma cortisol level. This suggests that maintenance of hypercortisolemia in GIP-R- expressing AIMAH does not always depend solely on GIP-R, and that simultaneous abnormal expression of other membrane receptors might be present. The expression of GIP-R could not be observed during malignant transformation of the adrenal cortex. This study highlighted the major role of cAMP alterations secondary to GIP-R ectopic expression in the pathophysiology of AIMAH and in some rare cases of well differentiated benign adrenocortical tumors.     

Aberrant membrane hormone receptors in incidentally discovered bilateral macronodular adrenal hyperplasia with subclinical Cushing's syndrome.

Cortisol secretion in adrenal Cushing's syndrome can be regulated by the aberrant adrenal expression of receptors for gastric inhibitory polypeptide, vasopressin, catecholamines, LH/human CG (LH/hCG), or serotonin. Four patients with incidentally discovered bilateral macronodular adrenal hyperplasia without clinical Cushing's syndrome were evaluated for the possible presence of aberrant adrenocortical hormone receptors. Urinary free cortisol levels were within normal limits, but plasma cortisol levels were slightly elevated at nighttime and suppressed incompletely after dexamethasone administration. Plasma ACTH was partially suppressed basally but increased after administration of ovine CRH. A 51-yr-old woman had ACTH-independent increases of plasma cortisol after 10 IU AVP im (292%), 100 microg GnRH iv (184%), or 10 mg cisapride orally (310%); cortisol also increased after administration of NaCl (3%), hCG, human LH, and metoclopramide. In a 61-yr-old man, cortisol was increased by AVP (349%), GnRH (155%), hCG (252%), and metoclopramide (191%). Another 53-yr-old male increased plasma cortisol after AVP (171%) and cisapride (142%). Cortisol secretion was also stimulated by vasopressin in a 54-yr-old female. This study demonstrates that subclinical secretion of cortisol can be regulated via the aberrant function of at least V1-vasopressin, LH/hCG, or 5-HT4 receptors in incidentally identified bilateral macronodular adrenal hyperplasia.     

12例ACTH非依赖性肾上腺皮质大结节样增生的诊治

目的 探讨ACTH非依赖性肾上腺皮质大结节样增生(AIMAH)的诊断与治疗.方法 回顾性分析12例AIMAH患者的临床表现、内分泌检查、影像与病理特点以及治疗和预后.男性5例,女性7例,平均年龄48岁(29～66岁).结果 7例有典型库欣综合征表现,5例则仅有高血压或高血糖等非特异性症状.内分泌检查显示皮质醇分泌失去昼夜节律,大、小剂量地塞米松抑制试验均不被抑制.CT或MRI示双肾上腺弥漫性增大伴多发结节.11例行手术治疗,其中双侧肾上腺切除3例;一侧肾上腺全切,对侧肾上腺次全切除1例;单侧肾上腺切除7例.病理诊断肾上腺结节样或腺瘤样增生.随访14～124个月,库欣综合征症状消失.双侧肾上腺切除者无Nelson综合征出现,单侧肾上腺切除者血尿皮质醇在正常范围,对侧肾上腺无明显增大.结论 AIMAH有独特的临床病理特点,单侧肾上腺切除是一种安全、有效的治疗选择.对症状不缓解或复发者可行双侧肾上腺切除或一侧肾上腺全切、对侧肾上腺次全切除.

Abstract：

Objective To explore the diagnosis and treatment of adrenocorticotropin-independent macronodular adrenal hyperplasia (AIMAH). Methods The clinical symptoms, endocrinological and radiological characteristics, treatment modalities, and postoperative clinical course of 12 AIMAH patients were retrospectively reviewed. There were 5 men and 7 women with an average age of 48 years old. Results All cases had some clinical features and biochemical evidence of Cushing's syndrome. The circadian rhythm of serum cortisol was abnormal. Low- and high-dose dexamethasone suppression tests failed to suppress cortisol secretion. CT or MRI scan showed bilateral enlargement of the adrenal glands with multiple macronodules. Bilateral adrenalectomy was performed in three patients and unilateral adrenalectomy combined with contralateral subtotal adrenalectomy was performed in one patient. Seven patients underwent unilateral adrenalectomy of the larger gland. The removed adrenal glands weighted within 8-96 g range and pathologic diagnoses were nodular or adenomatoid hyperplasia of adrenal cortex. The duration of postoperative follow-up was 14 to 124 months. Clinical symptoms of Cushing's syndrome disappeared after surgery in all cases and there was no Nelson's syndrome after bilateral adrenalectomy. Urinary free cortisol and serum cortisol were within normal ranges. No further enlargement of the contralateral gland has been noticed in patients who received unilateral adrenalectomy during the follow-up.Conclusions AIMAH had unique endocrinological and pathological features. Unilateral adrenalectomy appears to be an effective and safe alternative treatment for AIMAH. Bilateral adrenalectomy or unilateral adrenalectomy combined with contralateral subtotal adrenalectomy may be performed if the symptoms had not been improved or recurred after unilateral adrenalectomy.     

Overexpression of serotonin4 receptors in cisapride-responsive adrenocorticotropin-independent bilateral macronodular adrenal hyperplasia causing Cushing's syndrome

The serotonin4 (5-HT4) receptor agonists cisapride and/or metoclopramide have been shown to stimulate cortisol secretion in some patients with ACTH-independent bilateral macronodular adrenal hyperplasias (AIMAH) causing Cushing's syndrome. In the present study, we have investigated quantitatively and qualitatively the expression of the 5-HT4 receptor in both normal adrenal cortex and tissues removed from six patients (P1-P6) with cisapride-responsive AIMAH and Cushing's syndrome. Real-time quantitative PCR assay revealed that the 5-HT4 receptor was overexpressed in four of the six hyperplasias studied when compared with normal adrenal cortex. In these tissues, 5-HT4 receptor mRNA expression was 3 to 16 times higher than in normal glands, likely explaining the abnormal in vivo cortisol response to cisapride. Characterization of 5-HT4 receptor splice variants by RT-PCR in both hyperplastic and normal adrenals showed that the variants present in the two hyperplasias that did not overexpress the 5-HT4 receptor, i.e. P2 and P5, could also be detected in the normal adrenal tissue. In addition, sequencing of the full-length cDNAs encoding 5-HT4 receptors in hyperplasias P2 and P5 did not reveal any mutation. Taken together, our results show an overexpression of the 5-HT4 receptor in cisapride-responsive AIMAH. However, in two cases, the level of expression of the receptor in the hyperplastic adrenal cortex was similar to that of normal adrenal gland. The enhanced sensitivity of these two tissues to 5-HT4 receptor agonists was not due to ectopic expression of 5-HT4 receptor isoforms or to the occurrence of somatic gain-of-function mutation of the receptor.