Aberrant adrenal sensitivity to vasopressin in adrenal tumours associated with subclinical or overt autonomous hypercortisolism: is this explained by an overexpression of vasopressin receptors?

OBJECTIVE: Abnormal responsiveness to arginine vasopressin (AVP) was previously observed in cortisol-producing adrenocortical tumours but the mechanism remains unclear. The aim of this study was to characterize the effect of AVP on cortisol secretion from adrenocortical tumours compared to normal human adrenal gland. DESIGN: A multicentre study based on pharmacological, molecular and immunohistochemical experiments performed in adenomatous and normal adrenal tissues. PATIENTS: Twenty patients with adrenocortical adenomas and subclinical Cushing's syndrome (SCCS) or Cushing's syndrome (CS) were compared to six control normal subjects. MEASUREMENTS: In vivo and in vitro cortisol response to vasopressin, vasopressin receptor subtype mRNA measurement by real-time polymerase chain reaction (RT-PCR), immunohistochemical localization of AVP and its V1a receptor in tumour and normal adrenal tissues. RESULTS: Terlipressin in vivo enhanced cortisol plasma levels in 17/20 SCCS and 3/6 CS but in none of the control subjects. In vitro cortisol response to AVP was observed in nine tumours studied, with enhanced efficacy and/or potency of AVP in three SCCS tumours compared to normal tissues. AVP receptor subtype mRNA levels were similar in SCCS, CS cells and normal adrenal cells. Some SCCS tumour steroidogenic cells showed AVP and V1a receptor immunoreactivity. CONCLUSIONS: SCCS and CS adrenocortical tumours often exhibit in vivo and in vitro hyper-responsiveness to AVP, which is not related to vasopressin receptor overexpression, but may be explained by more efficient coupling pathways or by the indirect action of AVP through an autocrine/paracrine mechanism.

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.

The N-terminal neurotensin fragment, NT1-11, inhibits cortisol secretion by human adrenocortical cells.

CONTEXT: Neurotensin (NT) modulates corticosteroid secretion from the mammalian adrenal gland. OBJECTIVE: The objective of this study was to investigate the possible involvement of NT in the control of cortisol secretion in the human adrenal gland. DESIGN: In vitro studies were conducted on cultured human adrenocortical cells. SETTING: This study was conducted in a university research laboratory. PATIENTS: Adrenal explants from patients undergoing expanded nephrectomy for kidney cancer were studied. MAIN OUTCOME MEASURE: Cortisol secretion from cultured adrenocortical cells was measured. RESULTS: NT1-11, the N-terminal fragment of NT, dose-dependently inhibited basal and ACTH-stimulated cortisol production by human adrenocortical cells in primary culture. In contrast, NT had no influence on cortisol output at concentrations up to 10(-6) m. HPLC and RT-PCR analyses failed to detect any significant amounts of NT and NT mRNA, respectively, in adrenal extracts. Molecular and pharmacological studies were performed to determine the type of NT receptor involved in the corticostatic effect of NT1-11. RT-PCR analysis revealed the expression of NT receptor type (NTR) 3 mRNA but not NTR1 and NTR2 mRNAs in the human adrenal tissue. However, the pharmacological profile of the adrenal NT1-11 receptor was different from that of NTR3, indicating that this receptor type is not involved in the action of NT1-11 on corticosteroidogenesis. CONCLUSION: Our results indicate that NT1-11 may act as an endocrine factor to inhibit cortisol secretion through activation of a receptor distinct from the classical NTR1, NTR2, and NTR3.

Abnormal sensitivity of cortisol-producing adrenocortical adenomas to serotonin: in vivo and in vitro studies.

Two patients with incidentally discovered adrenocortical adenomas underwent a series of pharmacological and physiological tests after pretreatment with dexamethasone. Illicit plasma cortisol responses to the serotonin (5-HT)4 receptor agonist cisapride were observed in the two patients. Significant increases in plasma cortisol levels were also noticed after glucagon and combined TRH/GnRH/GHRH stimulation tests in patient 1 and after administration of the lysine vasopressin precursor terlipressin in patient 2. After adrenalectomy, in vitro studies were conducted to investigate the cortisol responses of cultured tumor cells to serotonergic ligands and peptide hormones. In the two cases, 5-HT stimulated cortisol secretion from tumor cells with increased efficacy and/or potency to activate steroidogenesis by comparison with normal adrenocortical cells. The corticotropic effect of 5-HT was inhibited by the specific 5-HT4 receptor antagonist GR 113808 and more potently by methiothepin, a nonspecific serotonergic antagonist having no affinity for the 5-HT4 receptor. These results show that the hypersensitivity of the tumors to 5-HT was related to tissue expression of an ectopic serotonergic receptor in addition to the eutopic 5-HT4 receptor. In the two adenoma tissues, immunohistochemical studies revealed the presence of 5-HT-like immunoreactivity within clusters of steroidogenic cells, suggesting that 5-HT acted through an autocrine/paracrine mechanism to stimulate steroidogenesis. Glucagon and GnRH but not TRH, GHRH, and human chorionic gonadotropin stimulated cortisol secretion from tumor 1 cells. In conclusion, this study provides the first observation of adrenocortical cortisol-producing adenomas hypersensitive in vivo and in vitro to serotonergic agonists. Our results also show that cortisol-producing adenomas can express simultaneously several illegitimate receptors.

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.

Activation of 5-HT(7) receptor in rat glomerulosa cells is associated with an increase in adenylyl cyclase activity and calcium influx through T-type calcium channels.

Serotonin (5-HT) stimulates aldosterone secretion from the rat adrenal gland through 5-HT(7) receptors. The aim of the present study was to investigate the transduction mechanisms associated with activation of 5-HT(7) receptors in rat glomerulosa cells. The stimulatory effect of 5-HT on aldosterone secretion and cAMP formation was significantly reduced by the 5-HT(7) receptor antagonist LY 215840. Pretreatment of cells with the adenylyl cyclase inhibitor SQ 22536 or the PKA inhibitor H-89 markedly attenuated the effect of 5-HT on aldosterone secretion. Conversely, type 2 and 4 phosphodiesterase inhibitors potentiated the 5-HT-induced stimulation of aldosterone secretion. Administration of 5-HT in the vicinity of cultured glomerulosa cells induced a slowly developing and robust increase in cytosolic calcium concentration ([Ca(2+)](i)). The effect of 5-HT on [Ca(2+)](i) was suppressed by mibefradil, a T-type calcium channel blocker. Patch-clamp studies confirmed that 5-HT activated a T-type calcium current. Mibefradil also induced a dose-dependent inhibition of 5-HT-induced aldosterone secretion. The sequence of events associated with activation of 5-HT(7) receptors was investigated. The PKA inhibitor H-89 markedly attenuated both the [Ca(2+)](i) response and the activation of T-type calcium current induced by 5-HT. In contrast, reduction of the calcium concentration in the incubation medium did not affect 5-HT- induced cAMP formation. Preincubation of glomerulosa cells with cholera toxin abolished the stimulatory effect of 5-HT on aldosterone secretion, but pertussis toxin had no effect. Taken together, these data demonstrate that, in rat glomerulosa cells, activation of native 5-HT(7) receptors stimulates cAMP formation through a G(salpha) protein, which in turn provokes calcium influx through T-type calcium channels. Both the adenylyl cyclase/PKA pathway and the calcium influx are involved in 5-HT-induced aldosterone secretion.

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.

Identification of the secretogranin II-derived peptide EM66 in pheochromocytomas as a potential marker for discriminating benign versus malignant tumors.

EM66 is a novel secretogranin II-derived peptide present in chromaffin cells of the human adrenal gland. The aim of the present study was to investigate the possible occurrence of EM66 in benign and malignant pheochromocytomas. Immunohistochemical labeling using specific antibodies revealed intense staining in both benign and malignant tumors. Coincubation of pheochromocytoma slices with EM66 and tyrosine hydroxylase antibodies showed that the immunostaining was restricted to chromaffin cells. RIA experiments indicated that serial dilutions of extracts of benign and malignant tumors generated displacement curves that were parallel to those produced by recombinant EM66. RIA quantification revealed concentrations of EM66 immunoreactivity ranging from 3.2-210 ng/mg protein (median = 25.6 ng/mg protein) in benign pheochromocytomas, and from 2.9-6.3 ng/mg protein (median = 3.8 ng/mg protein) in malignant tumors. The EM66-like immunoreactivity contained in the pheochromocytoma extracts was characterized by HPLC analysis combined with RIA detection. All of the benign and malignant tumors examined exhibited a single immunoreactive peak coeluting with recombinant EM66. These data indicate that the secretogranin II-derived peptide EM66 is generated in human tumoral chromaffin tissue. The significant difference in EM66 concentrations observed between benign and malignant pheochromocytomas suggests that measurement of EM66 levels may help identifying patients with higher risk of progression of such tumors.

Characterization of serotonin(4) receptors in adrenocortical aldosterone-producing adenomas: in vivo and in vitro studies.

We have previously shown that serotonin (5-HT) stimulates aldosterone secretion from the human adrenal gland through activation of 5-HT(4) receptors. The aim of the present study was to investigate in vivo and in vitro the presence of 5-HT(4) receptors in aldosterone-producing adenomas (aldosteronomas). Eight patients with aldosteronoma received a single oral dose of placebo or cisapride (10 mg). Cisapride administration significantly increased plasma aldosterone within 120 min without any significant change in renin, cortisol, or potassium levels. In two patients, a marked decrease in the plasma aldosterone response to cisapride was observed after surgical removal of the tumor. The effects of 5-HT and selective 5-HT(4) ligands on aldosterone production from aldosteronoma tissues were studied in vitro using a perifusion system technique. 5-HT and the 5-HT(4) receptor agonist cisapride (10(-7) M, 20 min) both stimulated aldosterone secretion from aldosteronoma slices. The 5-HT- and cisapride-evoked aldosterone responses were inhibited by concomitant administration of the specific 5-HT(4) receptor antagonist GR 113808 (10(-7) M, 150 min). PCR amplification revealed the expression of 5-HT(4) receptor mRNA in 13 of 14 aldosteronomas studied. Taken together, these data show that most aldosteronomas, like normal glomerulosa cells, express a functional 5-HT(4) receptor. Our results also suggest that 5-HT, which can be locally released by intratumoral mast cells, may play a role in the pathophysiology of these tumors.

QTL mapping for traits associated with stress neuroendocrine reactivity in rats.

In the present study we searched for quantitative trait loci (QTLs) that affect neuroendocrine stress responses in a 20-min restraint stress paradigm using Brown-Norway (BN) and Wistar-Kyoto-Hyperactive (WKHA) rats. These strains differed in their hypothalamic-pituitary-adrenal axis (plasma ACTH and corticosterone levels, thymus, and adrenal weights) and in their renin-angiotensin-aldosterone system reactivity (plasma renin activity, aldosterone concentration). We performed a whole-genome scan on a F2 progeny derived from a WKHA x BN intercross, which led to the identification of several QTLs linked to plasma renin activity (Sr6, Sr8, Sr11, and Sr12 on chromosomes RNO2, 3, 19, and 8, respectively), plasma aldosterone concentration (Sr7 and Sr9 on RNO2 and 5, respectively), and thymus weight (Sr10, Sr13, and Srl4 on RNO5, 10, and 16, respectively). The type 1b angiotensin II receptor gene (Agtrlb) maps within the confidence intervals of QTLs on RNO2 linked to plasma renin activity (Sr6, highly significant; LOD = 5.0) and to plasma aldosterone level (Sr7, suggestive; LOD = 2.0). In vitro studies of angiotensin II-induced release of aldosterone by adrenal glomerulosa cells revealed a lower receptor potency (log EC50 = -8.16 +/- 0.11 M) and efficiency (Emax = 453.3 +/- 25.9 pg/3 x 10(4) cells/24 h) in BN than in WKHA (log EC50 = -10.66 +/- 0.18 M; Emax = 573.1 +/- 15.3 pg/3 x 10(4) cells/24 h). Moreover, differences in Agtr1b mRNA abundance and sequence reinforce the putative role of the Agtr1b gene in the differential plasma renin stress reactivity between the two rat strains.

Molecular design based on 3D pharmacophores. Applications to 5-HT7 receptors.

A definition of a pharmacophore for the 5-HT7 antagonists was carried out by searching the common chemical features of selective antagonists from the literature. A molecular design is described by analyzing the differences between this new pharmacophore and three other 3D serotonin pharmacophores previously described. This comparison led to the synthesis of a new series of potent 5-HT7 antagonists.