Immunohistochemical localization of endothelin-1 in non-neoplastic and neoplastic adrenal gland tissue

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Production and secretion of two vasoactive peptides, adrenomedullin and endothelin-1, by cultured human adrenocortical carcinoma cells

The production and secretion of peptides by adrenocortical tumors have not been well studied. We therefore studied the production and secretion of two vasoactive peptides, adrenomedullin and endothelin-1 in SW-13 human adrenocortical carcinoma cells by radioimmunoassay and Northern blot analysis. Both immunoreactive-adrenomedullin and immunoreactive-endothelin were detected in the culture medium of SW-13 cells (27.7 +/- 1.6 fmol/10 (5) cells/24 h and 11.0 +/- 0.8 fmol/10 (5) cells/24 h, respectively, mean +/- SEM, n = 6). Northern blot analysis showed the expression of adrenomedullin mRNA and endothelin-1 mRNA in SW-13 cells. On the other hand, no significant amount of calcitonin gene-related peptide, corticotropin-releasing hormone, neuropeptide Y, or urocortin was secreted by SW-13 cells. Treatment with ACTH (10(-9)-10(-7) mol/l), angiotensin II (10(-9)-10(-7) mol/l), or dexamethasone (10(-8)-10(-6) mol/l) for 24 h had no significant effects on immunoreactive-adrenomedullin levels and immunoreactive-endothelin levels in the culture medium of SW-13. Treatment with tumor necrosis factor (TNF)-alpha (20 ng/ml) increased significantly both immunoreactive-adrenomedullin levels and immunoreactive-endothelin levels in the culture medium. Interferon-gamma (100 U/ml) increased the immunoreactive-endothelin levels, but not immunoreactive-adrenomedullin levels, whereas interleukin-1 (IL-1)beta (10 ng/ml) increased immunoreactive-adrenomedullin levels, but not immunoreactive-endothelin levels. These findings indicate that SW-13 human adrenocortical carcinoma cells produce and secrete two vasoactive peptides, adrenomedullin, and endothelin-1 and that the secretion of these two peptides is modulated differently by cytokines.

Endothelin-secreting tumors and the idea of the pseudoectopic hormone secretion in tumors

Ectopic hormone secretion in tumor cells is here described as an amplification of hormone production already present in normal, nonendocrine tumor-originated tissue. This idea is tested on the available data regarding endothelin-1 (ET-1) secreting tumors. The endothelins are ubiquitous regulatory peptides produced by various tissues. The precursor cells of many tumor types secrete endothelins. ET-1 protein expression was detected in situ in all tested prostate cancers as well as in normal prostate tissue. The majority of hepatocellular carcinomas produce ET-1, while ET-1 is secreted by the normal hepatic stellate cells. Human breast cancer cells produce immunoreactive ET-1. Similar data exist for pancreatic tissue, the thyroid and large bowel. We can conclude that tumor cells might sustain endothelin secretions already present in the normal tumor-originated tissue. The model that is presented of the pseudoectopic hormone secretion consists of relations between a few parameters. The proportion of hormone-secreting tumors (Th) among all tumors (T) of that organ depends on the amount of the hormone-secreting cells (Ch) among all cells (C) susceptible to malignant transformation. The corrective factor (k) was introduced in the expression Th/T=Ch/C*k, to represent specific conditions altering the malignant transformation probability for a certain normal hormone-secreting cell. In prostate, breast and colon, the kvalue is predicted to be approximately 1, suggesting that ET-1-secreting normal cells are not more prone to the malignant transformation than their neighbours. In liver and pancreas, the incidence of ET-1-secreting tumors outnumbers the proportions of normal ET-1-secreting cells (k values >1). In these organs, normal ET-1-secreting cells seem more likely to turn malignant in comparison to their neighbours, perhaps due to their function, position and exposition to oncogenic factors, or even due to their ET-1 secretion. There are similar data for thyroid and adrenal glands. No ET-1 secretion was reported in kidney neoplasms. Normal renal ET-1 secreting cells might be less prone to turn malignant than other renal cells. Unlse the normal lung tissue, small cell lung cancers often secrete adrenocorticotrophic hormone (ACTH). The pancreatic islet cells do not secrete gastrin, but their tumors often do. Constant k would exceed 1 in both cases. We speculate that these tumors might originate from a small subset of cells with the described feature. Tumor cells sometimes lack features of the normal tissue, as in the cases of the steroid receptor-negative breast cancer. These tumors might originate from the hypothetical subset of receptor-free breast cells. Benign breast epithelial cells lacking oestrogen receptors have been described in cases of megalomastia. These cells might be constituents of normal breasts or, perhaps, present only in cases of increased breast cancer risk.

The stimulatory effect of endothelin-1 on frog adrenocortical cells is mediated through both the phospholipase C and the adenylyl cyclase transduction pathways

We have previously shown that endothelin-1 (ET-1) stimulates corticosterone and aldosterone secretion by the frog adrenal gland through activation of ET(A) receptors. In the present study, we have investigated the transduction pathways involved in the corticotropic action of ET-1. Exposure of frog adrenal explants to ET-1 provoked a time- and dose-dependent increase in inositol phosphate production and a parallel decrease in membrane polyphosphoinositide content. Incubation of adrenal explants with ET-1 also induced a dose-related increase of cAMP formation. The selective ET(A) receptor antagonist BQ-485 totally abolished the stimulatory effects of ET-1 on both inositol phosphate and cAMP production. In contrast, the selective ET(B) receptor agonist IRL 1620 did not significantly modify polyphosphoinositide hydrolysis or cAMP formation. Administration of the phospholipase C inhibitor U-73122 or the protein kinase A inhibitor H-89 to perifused frog adrenal slices significantly reduced the stimulatory effect of ET-1 on corticosterone and aldosterone secretion. Concomitant administration of the two inhibitors almost completely suppressed the corticotropic effect of ET-1. Taken together, these data indicate that, in the frog adrenal gland, the stimulatory effect of ET-1 on corticosteroid secretion is mediated through activation of both the phospholipase C and the adenylyl cyclase transduction pathways.

Endothelin-1 stimulates steroid secretion of human adrenocortical cells ex vivo via both ETA and ETB receptor subtypes

The role played by endothelins (ETs) and their receptor subtypes (ETA and ETB) in the regulation of steroid hormone secretion in human adrenal gland remains unclear. Therefore, we investigated the gene expression of ET-1 and its receptors in highly pure preparations of human adrenocortical cells and the effect of ET-1 on their secretory activity. Reverse transcription-PCR with primers specific for prepro-ET-1, ET-converting enzyme-1, ETA, and ETB complementary DNAs demonstrated the expression of all of these genes in human adrenocortical cells. ET-1 increased the secretion of aldosterone and cortisol by enhancing both earlier and late steps of their synthesis. The secretory response to ET-1 was partially (60%) inhibited by BQ-123 and BQ-788, which are selective antagonists of the ETA and ETB receptors, respectively. When added together, the two antagonists suppressed the secretagogue effect of ET-1. Collectively, these findings suggest that ET-1, acting via both ETA and ETB receptors, may exert an autocrine/paracrine regulation of the function of the human adrenal cortex.

The role of endothelins in the paracrine control of the secretion and growth of the adrenal cortex

Endothelins (ETs) are a family of vasoactive peptides (ET-1, ET-2, and ET-3) mainly secreted by vascular endothelium and widely distributed in the various body systems, where they play major autocrine/paracrine regulatory functions, acting via two subtypes of receptors (ETA and ETB): Adrenal cortex synthesizes and releases ETS and expresses both ETA and ETB. Zona glomerulosa possesses both ETA and ETB, whereas zona fasciculata/reticularis is almost exclusively provided with ETB. ETS exert a strong mineralocorticoid and a less intense glucocorticoid secretagogue action, mainly via ETB receptors. ETS also appear to enhance the growth and steroidogenic capacity of zona glomerulosa and to stimulate its proliferative activity. This trophic action of ETS is likely to be mediated mainly by ETA receptors. The intraadrenal release of ETS undergoes a multiple regulation, with the rise in blood flow rate and the local release of nitric oxide being the main stimulatory factors. Data are also available that indicate that ETS may also have a role in the pathophysiology of primary aldosteronism caused by adrenal adenomas and carcinomas.