Low doses of endothelin-1 inhibit atrial natriuretic peptide secretion

C-type natriuretic peptide (CNP)/guanylate cyclase B (GC-B) system and endothelin-1(ET-1)/ET receptor A and B system in human vasculature

To assess the physiological and clinical implications of the C-type natriuretic peptide (CNP)/guanylyl cyclase B (GC-B) system in the human vasculature, we have examined gene expressions of CNP and its receptor, GC-B, in human vascular endothelial cells (ECs) and smooth muscle cells (SMCs) and have also compared the endothelin-1(ET-1)/endothelin receptor-A (ETR-A) and endothelin receptor-B (ETR-B) system in human aortic ECs (HAECs) and vascular SMCs (HSMCs) in vitro. We also examined these gene expressions in human embryonic stem (ES)/induced pluripotent stem cell (iPS)-derived ECs and mural cells (MCs). A little but significant amount of mRNA encoding CNP was detected in both human ES-derived ECs and HAECs. A substantial amount of GC-B was expressed in both ECs (iPS-derived ECs and HAECs) and SMCs (iPS-derived MCs and HSMCs). ET-1 was expressed solely in ECs. ETR-A was expressed in SMCs, while ETR-B was expressed in ECs. These results indicate the existence of a vascular CNP/GC-B system in the human vascular wall, indicating the evidence for clinical implication of the CNP/GC-B system in concert with the ET-1/ETR-A and ETR-B system in the human vasculature.

The heme oxygenase system suppresses perirenal visceral adiposity, abates renal inflammation and ameliorates diabetic nephropathy in Zucker diabetic fatty rats

The growing incidence of chronic kidney disease remains a global health problem. Obesity is a major risk factor for type-2 diabetes and renal impairment. Perirenal adiposity, by virtue of its anatomical proximity to the kidneys may cause kidney disease through paracrine mechanisms that include increased production of inflammatory cytokines. Although heme-oxygenase (HO) is cytoprotective, its effects on perirenal adiposity and diabetic nephropathy in Zucker-diabetic fatty rats (ZDFs) remains largely unclear. Upregulating the HO-system with hemin normalised glycemia, reduced perirenal adiposity and suppressed several pro-inflammatory/oxidative mediators in perirenal fat including macrophage-inflammatory-protein-1α (MIP-1α), endothelin (ET-1), 8-isoprostane, TNF-α, IL-6 and IL-1β. Furthermore, hemin reduced ED1, a marker of pro-inflammatory macrophage-M1-phenotype, but interestingly, enhanced markers associated with anti-inflammatory M2-phenotype such as ED2, CD206 and IL-10, suggesting that hemin selectively modulates macrophage polarization towards the anti-inflammatory M2-phenotype. These effects were accompanied by increased adiponectin, HO-1, HO-activity, atrial-natriuretic peptide (ANP), and its surrogate marker, urinary-cGMP. Furthermore, hemin reduced renal histological lesions and abated pro-fibrotic/extracellular-matrix proteins like collagen and fibronectin that deplete nephrin, an important transmembrane protein which forms the scaffolding of the podocyte slit-diaphragm allowing ions to filter but not massive excretion of proteins, hence proteinuria. Correspondingly, hemin increased nephrin expression in ZDFs, reduced markers of renal damage including, albuminuria/proteinuria, but increased creatinine-clearance, suggesting improved renal function. Conversely, the HO-blocker, stannous-mesoporphyrin nullified the hemin effects, aggravating glucose metabolism, and exacerbating renal injury and function. The hemin effects were less-pronounced in Zucker-lean controls with healthy status, suggesting greater selectivity of HO in ZDFs with disease. We conclude that the concomitant reduction of pro-inflammatory/oxidative mediators, macrophage infiltration and profibrotic/extracellular-matrix proteins, coupled to increased nephrin, adiponectin, ANP, cGMP and creatinine clearance may account for improved renal function in hemin-treated ZDFs. These findings suggest that HO-inducers like hemin may be explored against the co-morbidity of perirenal adiposity and diabetic nephropathy.

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.

Effects of cardiotrophin-1 on hemodynamics and endocrine function of the heart

Cardiotrophin-1 (CT-1), a member of the interleukin-6 superfamily of cytokines, possesses hypertrophic actions and atrial natriuretic peptide (ANP)-producing activity in vitro. The goal of our study is to elucidate whether CT-1 affects the cardiovascular system in vivo. Intravenous injection of CT-1 (4-100 microg/kg) in conscious rats evoked significant declines in blood pressure and reflex increases in heart rate (HR) in a dose-dependent manner. CT-1 induced no significant change in cardiac output (from 260.7 +/- 11.0 to 264.7 +/- 26.6 ml. min(-1). kg(-1), P = not significant), which was compatible with the results from isolated perfused rat hearts; HR, change in pressure over time, left ventricular developed pressure, and perfusion pressure were unaffected. Northern blot and RT-PCR analyses revealed that CT-1 increased expression of inducible nitric oxide synthase (iNOS) in lung and aorta but not in heart or liver. Pretreatment with aminoguanidine, a specific iNOS inhibitor, inhibited both iNOS mRNA production and the depressor effect of CT-1. Interestingly, CT-1 increased ventricular expression of ANP and brain natriuretic peptide (BNP). The data demonstrate that CT-1 elicits its hypotensive effect via a nitric oxide-dependent mechanism and that CT-1 induces ANP and BNP mRNA expression in vivo.

Evidence for a local endothelin-angiotensin-atrial natriuretic peptide systemin bovine mature follicles in vitro: effects on steroid hormones and prostaglandin secretion

Recent evidence suggests the presence of a functional endothelin-angiotensin-atrial natriuretic peptide system at the ovarian level. This study aimed to investigate 1) the local interrelationships among angiotensin II (Ang II), endothelin-1 (ET-1), and atrial natriuretic peptide (ANP); 2) the possible effect of each vasoactive peptide on the secretion of steroid hormones and prostaglandins (PGs) in isolated bovine mature follicles; and 3) the expression of mRNAs for Ang II, ET-1, and ANP receptors in the theca layer of follicles at different developmental stages. Each preovulatory follicle obtained before the LH surge (based on the concentrations of steroids and PGs) received implants of 4 capillary dialysis membranes into the theca layer. The follicles were then incubated in organ culture chambers and perfused with Ringer's solution for 12 h. Stimulation by infusion of the different substances into the microdialysis system was carried out between 4 and 8 h. The infusion of ET-1 (10(-7) M) stimulated the release of ANP and estradiol but inhibited the release of androstenedione and progesterone. The infusion of ANP (10(-7) M) stimulated the release of Ang II, progesterone, and androstenedione. Moreover, the infusion of Ang II (10(-5) M) inhibited the release of ANP but stimulated the release of ET-1, progesterone, and estradiol. All three peptides examined increased PGE(2) and PGF(2) release. In the reverse transcription-polymerase chain reaction analysis, expression of the mRNAs for ET type A and type B, and Ang II type 1 receptors did not change with the follicular size and the intrafollicular estradiol concentrations. Expression of the mRNA for the Ang II type 2 receptor dropped in follicles when the estradiol concentration ranged from 20 to 180 ng/ml and increased again when the estradiol concentration was > 180 ng/ml. The levels of expression of ANP type C receptor mRNA were slightly greater in follicles with estradiol concentrations > 20 ng/ml than in follicles with estradiol concentrations < 20 ng/ml. These results demonstrate a complex interaction among Ang II, ET-1, and ANP that may contribute to increasing the follicular production of PGs and modulate steroidogenesis in the bovine mature follicle, thus providing evidence for a local functional endothelin-angiotensin-ANP system.

Combined inhibition of endothelin and angiotensin II receptors blocks volume load-induced cardiac hormone release

Volume expansion has been shown to increase plasma atrial natriuretic peptide (ANP) levels, but the precise role of paracrine and autocrine factors in stretch-induced cardiac hormone release is not clear. In the present study, we report the effects of endothelin (ET) and angiotensin receptor (AT receptor) antagonists on baseline and atrial stretch-induced immunoreactive ANP (IR-ANP) and immunoreactive N-terminal ANP (IR-NT-ANP) release in vivo by using BQ-123 (ETA receptor antagonist), bosentan (ETA and ETB receptor antagonist), and losartan (AT1 receptor antagonist). Intravenous administration of BQ-123 had no significant effect on baseline hemodynamics in conscious rats, whereas bosentan (10 mg/kg) and losartan (10 mg/kg) decreased slightly (4 to 7 mm Hg, P < .05 to .001) the mean arterial pressure. Both the ETA receptor antagonist BQ-123 and ETA/ETB receptor antagonist bosentan decreased plasma ANP and NT-ANP responses to volume load (P < .05 to .001), whereas the AT1 receptor antagonist losartan had no significant effect on this response. The relative increase in plasma IR-ANP corresponding to a 3 mm Hg increase in right atrial pressure was 2.7-fold in the vehicle-treated group. BQ-123 (0.3 and 1.0 mg/kg) decreased this response 2.5- and 2.1-fold (P < .05); bosentan (3 and 10 mg/kg), 1.7-fold (P < .001) and 1.9-fold (P < .05); and bosentan (10 mg/kg)+losartan (10 mg/kg), 1.6-fold (P < .001). The responses in plasma IR-NT-ANP decreased simultaneously. These results indicate that combined inhibition of ETA/B and AT1 receptors almost completely blocks ANP response to acute volume load. Therefore, our study shows that endogenous paracrine and/or autocrine factors liberated in response to atrial wall stretch rather than myocyte stretch itself are responsible for the activation of ANP peptide secretion in response to acute volume load. Our results also show that ETA receptors are more important in the regulation of mechanical stretch-induced changes in cardiac hormone secretion than AT1 receptors.

Effects of anesthesia and surgery on plasma endothelin levels

To investigate the clinical significance of endothelin (ET), a potent and long-acting vasoconstrictor peptide in anesthesia and surgery, we measured plasma ET-like immunoreactivity (ET-LI) levels by using radioimmunoassay in patients undergoing various kinds of surgery under general anesthesia. No significant changes in plasma ET-LI levels were observed in patients undergoing relatively minor surgery under general anesthesia with nitrous oxide and halothane (n = 6), enflurane (n = 6), or isoflurane (n = 5). Although plasma ET-LI levels after surgery in patients undergoing total knee replacement (12.4 +/- 0.9 [mean +/- SEM] pg/mL, n = 7), hysterectomy (11.4 +/- 0.6 pg/mL, n = 8) or cholecystectomy (14.8 +/- 1.2 pg/mL, n = 9) were no different from those before surgery, plasma ET-LI levels after surgery in patients undergoing gastrectomy (20.4 +/- 1.9 pg/mL, n = 15), esophagectomy (24.7 +/- 2.5 pg/mL, n = 12), hepatectomy (27.5 +/- 3.4 pg/mL, n = 12), or heart surgery (43.1 +/- 4.1 pg/mL, n = 18) were higher than those before surgery (P < 0.05). Changes in plasma ET-LI levels during surgery had positive correlations with the duration of the operation (n = 100, r = 0.51, P < 0.01) and intraoperative blood loss (n = 100, r = 0.30, P < 0.01). In patients undergoing subtotal esophagectomy, the plasma ET-LI level did not increase during the initial 2 h, but increased gradually during surgery, reached a peak within a few hours after surgery, and declined slowly thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)