Previously, we have shown in porcine inner medullary collecting duct (IMCD) cells that endothelin (ET), probably in an autocrine fashion, suppresses arginine vasopressin (AVP)-induced synthesis of cAMP and thereby, may modify the action of AVP on IMCD fluid transport. In the present study we investigated the effects of various stimuli including extracellular tonicity on ET synthesis in porcine IMCD cells in culture. IMCD cells produced ET in a saturationlike time-dependent manner over a period of 24 h. Neither AVP (10(-7) mol/L), bradykinin (10(-7) mol/L), nor atrial natriuretic peptide (10(-7) mol/L) affected basal ET synthesis of IMCD cells at extracellular isotonicity (323 mOsm/kg H2O). The calcium ionophore A23187 (10(-7) mol/L) increased ET production by 38% within 2 h (P < .05). Preincubation for 48 h with increased osmolality in the incubation media from 323 to 600 mOsm/kg H2O by raising the concentrations of 1) NaCl (n = 6), 2) urea (n = 6), or 3) NaCl+urea (n = 6) increased ET synthesis from a control value of 225 +/- 25 pg/mg cell protein/2 h in isotonic medium to 1) 555 +/- 13 pg/mg cell protein/2 h (P < .01), 2) 354 +/- 18 pg/mg cell protein/2 h (P < .05), and 3) 448 +/- 22 pg/mg cell protein/2 h (P < .05), respectively, in hypertonic media. These data suggest that increases in papillary osmolality are associated with enhanced ET synthesis possibly involving a calcium-dependent process and attenuating AVP-dependent fluid absorption in a short-loop feedback fashion.
Abstract-We have recently found in male homozygous hypertensive Ren-2 transgenic rats (TGRs) fed a high-salt diet that early onset selective endothelin (ET) A (ET A ) or nonselective ET A /ET B (ET B ) receptor blockade improved survival rate and reduced proteinuria, glomerulosclerosis, and cardiac hypertrophy, whereas selective ET A receptor blockade also significantly attenuated the rise in blood pressure. Because antihypertensive therapy in general is known to be more efficient when started at early age, our study was performed to determine whether onset of ET receptor blockade at a later age in animals with established hypertension will have similar protective effects as does early-onset therapy. Endothelin (ET)-1 is known to be one of the most powerful vasoconstrictors 5,6 and also a mitogen in vivo and in vitro. 7 The beneficial effects of ET receptor blockers in modulating target organ damage are attributed to their antiproliferative actions. 8 Numerous studies have shown that the ET system plays an important role in the pathogenesis of high blood pressure (BP) in salt-sensitive models of hypertension and in associated end-organ damage. 9 For the detrimental effects of ET-1 in the development of hypertension, activation of ETA (ET A ) receptors may be responsible, whereas the role of ET B (ET B ) receptors may be the mediation of peripheral vasorelaxation and the renal tubular natriuresis. Nonselective blockade, therefore, inhibits not only the deleterious effects of ET-1 mediated by ET A receptors but also concomitantly blocks its antihypertensive effects mediated by ET B receptors. However, because at present only conflicting data regarding selective ET A and nonselective ET A/B receptor blockade are available, the relative beneficial effects of selective versus nonselective ET receptor blockade remain to be elucidated.Several lines of evidence indicate that Ang II stimulates the release of ET-1, and it is known that the ET system plays an important role in the pathogenesis of hypertension and accompanying end-organ damage in salt-dependent and in Ang IIdependent models of hypertension induced by exogenous administration of Ang II. 10 Dietary sodium plays an important role in the pathogenesis of hypertension not only in humans 11 but also in salt-sensitive
A rise in blood pressure is the main side effect of erythropoietin (EPO) treatment in patients with renal anemia. The mechanisms, however, by which EPO may cause hypertension are still unclear. We therefore investigated the effects of EPO on endothelin (ET) synthesis and cytosolic free calcium concentration ([Ca2+]i) in vascular endothelial cells. Porcine endothelial cells were isolated from thoracic aorta, pulmonary artery, and vena cava. Studies were performed with cells of the first subculture. ET concentrations were measured radioimmunologically. Changes in [Ca2+]i were determined with the fluorescent probe fura-2. Cytotoxicity was assessed by sodium 3'-[1-(phenyl-amino-carbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)ben zene sulfonic acid hydrate (XTT) assay. ET synthesis was similar in cells of different vascular origins and was time-dependent, reaching approximately 2 pmol ET/mg protein within 12 h of incubation. EPO (12 to 200 U/mL) stimulated ET release time- and dose-dependently by up to 83.2% (P < .01) within 12 h in the absence of fetal calf serum and heparin. EPO induced an immediate significant rise in [Ca2+]i from 58 +/- 12 nmol/L to 495 +/- 85 nmol/L (P < .01) with a subsequent slow return to 257 +/- 3 nmol/L. During 2 h of incubation, the Ca-ionophore A 23187 (10(-8) mol/L) moderately but significantly stimulated endothelial ET synthesis. However, the Ca-channel blocker verapamil, the intracellular Ca-release blocker TMB-8, and nickel, an unspecific calcium channel blocker, had no consistent effects on [Ca2+]i or ET synthesis. The protein kinase C inhibitor H-7 stimulated basal [Ca2+]i and cellular ET synthesis. The tyrosine kinase inhibitor genistein suppressed the EPO-induced rise in [Ca2+]i and cellular ET synthesis. From these data we conclude that EPO may stimulate ET synthesis in vascular endothelial cells by activation of an EPO-receptor and via intracellular signalling mechanisms that comprise tyrosine kinase activation and a rise in [Ca2+]i. Therefore, the systemic hypertensive effects of EPO may be due at least in part to local stimulation of vascular endothelial ET synthesis via calcium mobilization.
The enhanced responses of RPF and sodium excretion to AT1 receptor blockade in TGR suggest that renal hemodynamics and sodium excretion in TGR are under strong ANG II influence. The compromised ability of the kidney to respond to BP elevations by appropriate increases in sodium excretion may contribute to the maintenance of high BP in TGR. Thus, the present findings provide new insights into the pathophysiology of hypertension in this model.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.