endothelin-1 and Acidosis

Metabolic acidosis affects about 15% of patients with chronic kidney disease. As kidney function declines, the kidneys progressively fail to eliminate acid, primarily reflected by a decrease in ammonium and titratable acid excretion. Several studies have shown that the net acid load remains unchanged in patients with reduced kidney function; the ensuing acid accumulation can precede overt metabolic acidosis, and thus, indicators of urinary acid or potential base excretion, such as ammonium and citrate, may serve as early signals of impending metabolic acidosis. Acid retention, with or without overt metabolic acidosis, initiates compensatory responses that can promote tubulointerstitial fibrosis via intrarenal complement activation and upregulation of endothelin-1, angiotensin II, and aldosterone pathways. The net effect is a cycle between acid accumulation and kidney injury. Results from small- to medium-sized interventional trials suggest that interrupting this cycle through base administration can prevent further kidney injury. While these findings inform current clinical practice guidelines, large-scale clinical trials are still necessary to prove that base therapy can limit chronic kidney disease progression or associated adverse events.

Topics: Acidosis; Aldosterone; Ammonium Compounds; Angiotensin II; Citrates; Endothelin-1; Humans; Kidney; Renal Insufficiency, Chronic

The seriousness of scorpion envenomation results essentially from left cardiac function with pulmonary oedema and/or a state of shock. Adrenergic myocarditis, toxic myocarditis and myocardial ischemia are the 3 mechanisms that explain the cardiac dysfunction. Myocardial ischemia is not only due to the release of catecolamines but also the effect of the cytokines and/or neuropeptide Y on the coronary vessels. The cardiac damage can be due or enhanced by the depressive effect of the cytokines on the myocardial cells. The frequently observed hyperglycaemia only enhances the state of the already damaged myocardium.

Topics: Acidosis; Animals; beta-Thromboglobulin; Blood Platelets; Catecholamines; Cytokines; Endothelin-1; Humans; Hyperglycemia; Myocardial Ischemia; Myocarditis; Myocardium; Neuropeptide Y; Pulmonary Edema; Scorpion Stings; Scorpion Venoms; Scorpions; Shock, Cardiogenic; Stress, Physiological

Metabolic acidosis often accompanies low glomerular filtration rate and induces secretion of endothelin, which in turn might mediate kidney injury. Here we tested whether treatment of metabolic acidosis in patients with low glomerular filtration rate reduced the progression of kidney disease. Fifty-nine patients with hypertensive nephropathy and metabolic acidosis had their blood pressure reduced with regimens that included angiotensin-converting enzyme inhibition. Thirty patients were then prescribed sodium citrate, and the remaining 29, unable or unwilling to take sodium citrate, served as controls. All were followed for 24 months with maintenance of their blood pressure reduction. Urine endothelin-1 excretion, a surrogate of kidney endothelin production, and N-acetyl-beta-D-glucosaminidase, a marker of kidney tubulointerstitial injury, were each significantly lower, while the rate of estimated glomerular filtration rate decline was significantly slower. The estimated glomerular filtration rate was statistically higher after 24 months of sodium citrate treatment compared to the control group. Hence it appears that sodium citrate is an effective kidney-protective adjunct to blood pressure reduction and angiotensin-converting enzyme inhibition.

Topics: Acetylglucosaminidase; Acidosis; Biomarkers; Buffers; Citrates; Endothelin-1; Female; Glomerular Filtration Rate; Humans; Hypertension; Kidney; Male; Middle Aged; Prospective Studies; Renal Insufficiency, Chronic; Sodium Citrate

Retrospective analyses and single-center prospective studies identify chronic metabolic acidosis as an independent and modifiable risk factor for progression of CKD. In patients with CKD, untreated chronic metabolic acidosis often leads to an accelerated reduction in GFR. Mechanisms responsible for this reduction include adaptive responses that increase acid excretion but lead to a decline in kidney function. Metabolic acidosis in CKD stimulates production of intrakidney paracrine hormones including angiotensin II, aldosterone, and endothelin-1 (ET-1) that mediate the immediate benefit of increased kidney acid excretion, but their chronic upregulation promotes inflammation and fibrosis. Chronic metabolic acidosis also stimulates ammoniagenesis that increases acid excretion but also leads to ammonia-induced complement activation and deposition of C3 and C5b-9 that can cause tubule-interstitial damage, further worsening disease progression. These effects, along with acid accumulation in kidney tissue, combine to accelerate progression of kidney disease. Treatment of chronic metabolic acidosis attenuates these adaptive responses; reduces levels of angiotensin II, aldosterone, and ET-1; reduces ammoniagenesis; and diminishes inflammation and fibrosis that may lead to slowing of CKD progression.

Topics: Acid-Base Equilibrium; Acidosis; Adaptation, Physiological; Aldosterone; Angiotensin II; Biomarkers; Disease Progression; Endothelin-1; Female; Follow-Up Studies; Glomerular Filtration Rate; Humans; Kidney Failure, Chronic; Male; Prospective Studies; Renal Insufficiency, Chronic; Retrospective Studies; Risk Assessment; Severity of Illness Index; Time Factors; Treatment Outcome

Endothelin-1 inhibits collecting duct sodium reabsorption and stimulates proximal and distal tubule acidification in experimental animals both directly and indirectly via increased mineralocorticoid activity. Diet-induced acid loads have been shown to increase renal endothelin-1 activity, and it is hypothesized that increased dietary acid-induced endothelin-1 activity may be a causative progression factor in human renal insufficiency and that this might be reversed by provision of dietary alkali. We sought to clarify, in normal human volunteers, the role of endothelin-1 in renal acidification and to determine whether the effect is dependent on dietary sodium chloride. Acid-base equilibrium was studied in seven normal human volunteers with experimentally induced metabolic acidosis [NH(4)Cl 2.1 mmol·kg body weight (BW)(-1)·day(-1)] with and without inhibition of endogenous endothelin-1 activity by the endothelin A/B-receptor antagonist bosentan (125 BID p.o./day) both during dietary NaCl restriction (20 mmol/day) and NaCl repletion (2 mmol NaCl·kg BW(-1)·day(-1)). During NaCl restriction, but not in the NaCl replete state, bosentan significantly increased renal net acid excretion in association with stimulation of ammoniagenesis resulting in a significantly increased plasma bicarbonate concentration (19.0 ± 0.8 to 20.1 ± 0.9 mmol/l) despite a decrease in mineralocorticoid activity and an increase in endogenous acid production. In pre-existing human metabolic acidosis, endothelin-1 activity worsens acidosis by decreasing the set-point for renal regulation of plasma bicarbonate concentration, but only when dietary NaCl provision is restricted.

Topics: Acid-Base Equilibrium; Acidosis; Adult; Bosentan; Diet; Endothelin Receptor Antagonists; Endothelin-1; Homeostasis; Humans; Kidney; Male; Sodium Chloride, Dietary; Sulfonamides

Metabolic acidosis often complicates chronic kidney disease (CKD) and adversely affects bone, nutrition, and metabolism. Phisitkul et al. demonstrate that sodium citrate may ameliorate kidney injury in CKD patients not on dialysis. Further, they provide evidence in humans that treatment lowers urinary endothelin levels, and hence increased endothelin may be part of the mechanism whereby acidosis hastens CKD progression.

Topics: Acidosis; Buffers; Citrates; Endothelin-1; Humans; Renal Insufficiency, Chronic; Sodium Citrate

Metabolically generated acid is the major physiological stimulus for increasing proximal tubule citrate reabsorption, which leads to a decrease in citrate excretion. The activity of the Na-citrate cotransporter, NaDC-1, is increased in vivo by acid ingestion and in vitro by an acidic pH medium. In opossum kidney cells the acid stimulatory effect and the ability of endothelin-1 (ET-1) to stimulate NaDC-1 activity are both blocked by the endothelin B (ET(B)) receptor antagonist, BQ788. Acid feeding had no effect on brush border membrane NaDC-1 activity in mice in which ET(B) receptor expression was knocked out, whereas a stimulatory effect was found in wild-type mice. Using ET(A)/ET(B) chimeric and ET(B) C-terminal tail truncated constructs, ET-1 stimulation of NaDC-1 required a receptor C-terminal tail from either ET(A) or ET(B). The ET-1 effect was greatest when either the ET(B) transmembrane domain and C-terminal tail were present or the ET(B) C-terminal tail was linked to the ET(A) transmembrane domain. This effect was smaller when the ET(B) transmembrane domain was linked to the ET(A) C-terminal tail. Thus, the acid-activated pathway mediating stimulation of NaDC-1 activity requires a functional ET(B) receptor in vivo and in vitro, as does acid stimulation of NHE3 activity. Since increased NaDC-1 and NHE3 activities constitute part of the proximal tubule adaptation to an acid load, these studies indicate that there are similarities in the signaling pathway mediating these responses.

Topics: Acidosis; Animals; Biological Transport; Cell Line; Dicarboxylic Acid Transporters; Disease Models, Animal; Endothelin B Receptor Antagonists; Endothelin-1; Hydrogen-Ion Concentration; Kidney; Mice; Mice, Knockout; Microvilli; Oligopeptides; Opossums; Organic Anion Transporters, Sodium-Dependent; Piperidines; Protein Structure, Tertiary; Receptor, Endothelin A; Receptor, Endothelin B; Recombinant Fusion Proteins; Signal Transduction; Symporters; Time Factors; Transfection

Rats with 5/6 nephrectomy have metabolic acidosis with a progressive decline in the glomerular filtration rate (GFR) ameliorated by endothelin and aldosterone antagonists and by dietary alkali. Interestingly, rats with 2/3 nephrectomy have no metabolic acidosis yet have a progressive GFR decline induced by acid retention and ameliorated by dietary alkali. Because patients without metabolic acidosis but with a moderately reduced GFR have a progressive GFR decline, ameliorated by oral sodium bicarbonate, we used rats with 2/3 nephrectomy to model these patients. Kidney acid content, endothelin-1, and aldosterone (measured by microdialysis) were higher in the rats with 2/3 nephrectomy than those with a sham operation despite no differences in plasma acid-base parameters. The GFR of the former but not the latter was lower at 25 than at 1 week after nephrectomy. Endothelin and aldosterone antagonism improved the preservation of GFR; however, this remained lower at week 24 than at week 1. By contrast, the GFR at weeks 24 and 1 was not different if the rats were given dietary alkali to normalize the kidney acid content. Antagonist of endothelin and aldosterone yielded no added GFR benefit. Thus, our study shows that (1) the decline in GFR in 2/3 nephrectomy is mediated by acid retention-induced kidney endothelin and aldosterone production; (2) receptor antagonism and dietary alkali are not additive; and (3) dietary alkali better preserves GFR than both endothelin and aldosterone receptor antagonism.

Topics: Acid-Base Equilibrium; Acidosis; Administration, Oral; Aldosterone; Animals; Bicarbonates; Calcium Gluconate; Dietary Supplements; Disease Models, Animal; Endothelin A Receptor Antagonists; Endothelin-1; Eplerenone; Female; Glomerular Filtration Rate; Kidney; Male; Microdialysis; Mineralocorticoid Receptor Antagonists; Nephrectomy; Phenylpropionates; Pyrimidines; Rats; Rats, Wistar; Receptor, Endothelin A; Renal Insufficiency; Spironolactone; Time Factors

There is increasing evidence that alkali therapy can retard progression of chronic kidney disease (CKD). We summarize recent studies and discuss a mechanism whereby alkali therapy may neutralize acid production associated with typical Western diets, which generate acid. We emphasize the rationale for using alkali therapy early in the course of CKD, even in the absence of overt metabolic acidosis, and we urge the pharmaceutical industry to develop palatable alkali-containing solutions.

Topics: Acid-Base Equilibrium; Acidosis; Administration, Oral; Aldosterone; Animals; Bicarbonates; Chronic Disease; Dietary Supplements; Disease Progression; Endothelin-1; Glomerular Filtration Rate; Humans; Kidney; Kidney Diseases

Dietary casein promotes a progressive decline in the glomerular filtration rate (GFR) of remnant kidneys associated with metabolic acidosis and an endothelin-mediated increase in renal acidification. We tested whether diets that affect the acid-base status contributes to the decline of GFR through endothelin receptors in rats with a remnant kidney. Rats on a casein diet had metabolic acidosis at baseline and developed a progressive decline in GFR after renal mass reduction. Dietary sodium bicarbonate but not sodium chloride ameliorated metabolic acidosis and prevented the decrease in GFR but only after the sodium bicarbonate-induced increase in blood pressure was treated. Dietary soy protein did not induce baseline metabolic acidosis and rats with remnant kidney on a soy diet had no decrease in their GFR. By contrast, rats with a remnant kidney on soy protein given dietary acid developed metabolic acidosis and a decreased GFR. This decline in GFR was prevented in either case by endothelin A but not endothelin A/B receptor antagonism. Our study suggests that the casein-induced decline in GFR of the remnant kidney is mediated by metabolic acidosis through endothelin A receptors.

Topics: Acidosis; Animals; Bicarbonates; Blood Pressure; Carbon Dioxide; Caseins; Dietary Proteins; Endothelin-1; Glomerular Filtration Rate; Male; Nephrectomy; Rats; Receptors, Endothelin; Sodium Chloride

Management of trauma victims with uncontrolled hemorrhage remains a major problem in combat casualty care at the far-forward battlefield setting. The neuroendocrine response to hemorrhage is to maintain perfusion to the heart and brain, often at the expense of other organ systems. Decreased organ perfusion after hemorrhagic shock is associated with metabolic acidosis, in which the up-regulated endothelin-1 plays an important role. We have recently shown that vascular responsiveness to adrenomedullin (AM), a newly discovered vasodilator peptide, is depressed after hemorrhage and resuscitation. Down-regulation of AM binding protein (AMBP-1) appears to be responsible for this hyporesponsiveness. We therefore hypothesized that administration of AM/AMBP-1 would prevent metabolic acidosis after uncontrolled hemorrhage via down-regulation of endothelin-1.. Prospective, controlled, and randomized animal study.. A research institute laboratory.. Male Sprague-Dawley rats (275-325 g).. A rat model of uncontrolled hemorrhage with an extremely low volume of fluid resuscitation was used to mimic the combat situation.. Both lumbar veins of male adult rats were isolated and severed at the junction to the vena cava. The abdomen was kept open but covered with a saline wet gauze for 45 mins and then closed in layers. The animals received 1 mL of normal saline (vehicle) with or without AM (12 microg/kg of body weight) and AMBP-1 (40 microg/kg of body weight) over 45 mins. Various variables were measured at 4 hrs after resuscitation. The bleed-out volumes in the vehicle group and the AM/ AMBP-1 treatment group were 6.78 +/- 0.19 and 6.81 +/- 0.25 mL/rat, respectively. The results indicate that AM/AMBP-1 administration prevented metabolic acidosis, mitigated organ injury, down-regulated preproendothelin-1 gene expression, and decreased plasma levels of endothelin-1 after hemorrhage.. AM/AMBP-1 may provide a novel approach for the treatment of uncontrolled hemorrhage. The beneficial effect of AM/AMBP-1 is associated with down-regulation of endothelin-1.

Topics: Acidosis; Adrenomedullin; Animals; Blood Volume; Cardiac Output; Complement Factor H; Down-Regulation; Endothelin-1; Gene Expression; Hematocrit; Male; Oxygen; Rats; Rats, Sprague-Dawley; Renal Circulation; Resuscitation; RNA, Messenger; Shock, Hemorrhagic; Vasodilator Agents

To evaluate the role of intestinal endotoxemia in the genesis of hepatopulmonary syndrome.. A rat model of cirrhosis was prepared with the method of compound factors. At the end of the eighth week, rats with cirrhosis were treated with 300 microg LPS/100 g body weight, and 1 g/rat of glycine about four h prior to LPS. After three h of LPS treatment, blood and tissues were collected for various measurements. Kupffer cells were isolated from male Wistar rats and cultured, and divided into five groups. Supernatant was harvested at 3 h after treatment with LPS for measurement of tumor necrosis factor-alpha (TNF-alpha).. Our results showed that in rats with cirrhosis, slowed and deepened breath with occasional pause was. PaO2, PaCO2 and standard bicarbonate (SB) in arterial blood were decreased. Arterial O2 and actual bicarbonate (AB) were markedly decreased. There was a close correlation between decreased O2 and endotoxin. Metabolic acidosis accompanying respiratory alkalosis was the primary type of acid-base imbalance. The alveolar-arterial oxygen gradient was sharply widened. Massive accumulation of giant macrophages in the alveolar spaces and its wall and widened alveolar wall architecture were observed. The number of bacterial translocations in mesenteric lymph nodes increased. The ratio of TC99M-MAA brain-over-lung radioactivity rose. Endotoxin, and TNF-alpha, endothelin-1 (ET-1), nitric oxide (NO) in plasma and ET-1, carbon monoxide (CO) in lung homogenates increased. After administration of a given dosage of LPS in rats with cirrhosis, various pathological parameters worsened. Plasma level of endotoxin was related to TNF-alpha, ET-1, NO in plasma and ET-1, NO, CO in lung homogenates. TNF-alpha level was related to ET-1 and NO in plasma and lung homogenates and CO in lung homogenate as well. The level of TNF-alpha increased after infusion of LPS into culture supernatant of Kupffer cells in vitro. However, TNF-alpha significantly decreased after pretreatment with glycine, PD98059 and SB212850. Glycine could antagonize the effect of LPS in vivo and in vitro.. Intestinal endotoxemia accompanying by cirrhosis may be an important mechanism in the development of hepatopulmonary syndrome in rats. Overproduction of TNF-alpha due to endotoxin stimulation of Kupffer cells via mitogen-activated protein kinase (MAPK) signal transduction pathway may be a major mechanism mediating the pathologic alterations of hepatopulmonary syndrome.

Topics: Acid-Base Imbalance; Acidosis; Animals; Bacterial Translocation; Brain; Carbon Monoxide; Endothelin-1; Endotoxemia; Hepatopulmonary Syndrome; Kupffer Cells; Lipopolysaccharides; Liver Cirrhosis; Lung; Male; MAP Kinase Signaling System; Nitric Oxide; Rats; Rats, Wistar; Respiratory Mechanics; Sulfhydryl Compounds; Technetium Tc 99m Aggregated Albumin; Tumor Necrosis Factor-alpha

Chronic hypokalemia increases NHE3 activity in OKP cells. The aim of the present study was to determine whether an autocrine mechanism is involved in this activation.. After incubation of OKP cells in normal-K(+) and low-K(+) media for 24 h, the potassium concentration in the low-K(+) media was adjusted to a normal level. These conditioned media were then used as the normal-K(+) and low-K(+) supernatants. Other OKP cells were incubated in these normal-K(+) and low-K(+) supernatants and the mechanism of Na(+)/H(+) antiporter activation was examined.. The EIPA-resistant Na(+)/H(+) antiporter activity of OKP cells increased after 4 h incubation in the low-K(+) supernatant, and the amount of NHE3 protein increased at 24 h. Since both BQ788 and saralasin blocked this antiporter activation, the supernatant concentration of endothelin I (ET-I) and angiotensin II (Ang-II) were measured. The ET-I concentration was reduced, but the Ang-II concentration remained unchanged. There was a significant association between a reduction in the ET-I concentration and an increase in Na(+)/H(+) antiporter activity, but only when Ang-II was present in the supernatant.. An autocrine mechanism is involved in the activation of NHE3 in OKP cells. Both ET-I and Ang-II play a role in this activation.

Topics: Acidosis; Amiloride; Angiotensin II; Animals; Autocrine Communication; Benzoquinones; Cell Line; Culture Media, Conditioned; Dose-Response Relationship, Drug; Endothelin B Receptor Antagonists; Endothelin-1; Hydrogen-Ion Concentration; Kidney; Lactams, Macrocyclic; Oligopeptides; Opossums; Piperidines; Potassium; Protein-Tyrosine Kinases; Quinones; Receptor, Endothelin B; Rifabutin; Sodium-Hydrogen Exchanger 3; Sodium-Hydrogen Exchangers; Time Factors

Chronic metabolic acidosis leads to an increase in NHE3 activity that is mediated by endothelin-1 (ET-1) expression and activation of the proximal tubule endothelin B receptor. Chronic metabolic acidosis increases preproET-1 mRNA abundance in kidney cortex, but the cell responsible has not been identified.. PreproET-1 mRNA abundance was quantified by competitive reverse transcription-polymerase chain reaction (RT-PCR) on tissue harvested from control rats or rats in which chronic metabolic acidosis was induced by addition of NH(4)Cl to the drinking water.. Chronic metabolic acidosis leads to an increase in preproET-1 mRNA expression in kidney cortex, proximal tubules, and glomeruli. The increase in preproET-1 expression correlates with the decrease in blood [HCO3(-)]. ET-1 expression is also increased by acidosis in abdominal aorta, but not in cardiac muscle.. In the renal proximal tubule, chronic metabolic acidosis induces an increase in preproET-1 expression, providing a mechanism for autocrine regulation of proximal tubule NHE3 activity. This response is not unique to the proximal tubule cell, but is also not ubiquitous.

Topics: Acidosis; Animals; Aorta; Autocrine Communication; Chronic Disease; Endothelin-1; In Vitro Techniques; Kidney Cortex; Kidney Glomerulus; Kidney Tubules, Proximal; Male; Myocardium; Rats; Rats, Sprague-Dawley; RNA, Messenger; Sodium-Hydrogen Exchanger 3; Sodium-Hydrogen Exchangers

To determine whether plasma endothelin-1 (ET-1) relates to clinical manifestations of sepsis in the newborn, especially with systemic hypotension, acidosis, severe hypoxemia (which may represent pulmonary hypertension) and oliguria.. Prospective study of 35 consecutive newborns with clinical sepsis: 22 with hemoculture-positive (HC+) sepsis and 13 hemoculture-negative (HC-). Plasma ET-1 concentrations were measured within 2 days of the diagnosis of sepsis. SNAP-II severity score was performed at the time of highest clinical severity.. Newborns with HC+ sepsis had higher plasma ET-1 concentrations and SNAP-II scores (especially PO 2 /FiO 2 ratio) than HC- septic children. Plasma ET-1 concentrations increased linearly with each item of the SNAP-II score, but only reached significant differences in lowest mean blood pressure (P=0.030), lowest pH (P=0.048), multiple seizures (P=0.010) and lowest urine output (P=0.013). Leukocyte count, immature/total neutrophil ratio and C-reactive protein value were not different. Each item of the SNAP-II score was independently related only to ET-1 level. Oliguria, acidosis and systemic hypotension were more correlated (R 2 >0.5).. Plasma ET-1 levels in neonatal sepsis are related to the severity of clinical manifestations, especially oliguria, acidosis and systemic hypotension.

Topics: Acidosis; Candida; Endothelin-1; Female; Gram-Negative Bacteria; Gram-Positive Bacteria; Humans; Hypotension; Infant, Newborn; Infant, Newborn, Diseases; Intensive Care Units, Neonatal; Male; Oliguria; Predictive Value of Tests; Prospective Studies; Sepsis; Severity of Illness Index; Spain

Acid addition to the body activates a series of homeostatic responses, one example of which is activation of NHE3, the proximal tubule Na(+)/H(+) antiporter. Feeding acid to rats increases apical membrane NHE3 abundance. Similarly, addition of acid to the media of OKP cells, a proximal tubule cell line, leads to an increase in apical membrane NHE3 activity that is due to increased trafficking of NHE3 to the apical membrane, and increased NHE3 mRNA and protein expression. Endothelins also increase NHE3 activity by inducing trafficking of NHE3 to the apical membrane, an effect mediated by the ET(B), but not the ET(A) receptor. Receptor specificity resides in the C-terminal loop and the second intracellular loop of the ET(B) receptor. In addition, the ET(B) receptor is required for acid signaling. An acid-induced signaling cascade has been defined that includes Pyk2, c-Src, ERK, c-fos, c-jun, and endothelin expression.

Topics: Acidosis; Acids; Animals; Diet; Endothelin-1; Endothelins; Hypokalemia; Kidney Tubules, Proximal; Mice; Mice, Inbred C57BL; Mice, Knockout; Models, Biological; Rats; Receptor, Endothelin A; Receptor, Endothelin B; RNA, Messenger; Sleep; Sodium-Hydrogen Exchanger 3; Sodium-Hydrogen Exchangers

Endothelin-1 (ET-1) and nitric oxide (NO) exert opposite effects in the cardiovascular system, and there is evidence that the NO counters the potential deleterious effects of ET-1. We investigated whether NO affects the increased mRNA expression of ET-1 and endothelin receptors induced by (i) 30 min of ischemia with or without 30 min reperfusion in myocytes from isolated rat hearts or (ii) ischemic conditions (acidosis or hypoxia) in cultured rat neonatal ventricular myocytes. Ischemia with or without reperfusion produced more than a twofold increase in mRNA expression of ET-1 as well as the ET(A) and ET(B) receptor (P < 0.05), although these effects were completely blocked by the NO donor 3-morpholinosydnonimine (SIN-1; 1 microM). To assess the possible factors regulating ET expression, myocytes were exposed to acidosis (pH 6.8-6.2) or to hypoxic conditions in an anaerobic chamber for 24 h in the presence or absence of SIN-1. At all acidic pHs, ET-1 and ET(A) receptor mRNA expression was significantly (P < 0.05) elevated approximately threefold, although the magnitude of elevation was independent of the degree of acidosis. These effects were completely prevented by SIN-1. ET(B) receptor expression was unaffected by acidosis. Hypoxia increased ET-1 as well as ET(A) and ET(B) receptor expression threefold (P < 0.05), although this was unaffected by SIN-1. Our results demonstrate that myocardial ischemia and reperfusion upregulate the ET system, which is inhibited by NO. Although increased expression of the ET system can be mimicked by both acidosis and hypoxia, only the effects of the former are NO sensitive. NO may serve an endogenous inhibitory factor which regulates the expression of the ET system under pathological conditions.

Topics: Acidosis; Animals; Animals, Newborn; Blotting, Southern; Cells, Cultured; Electrophoresis; Endothelin-1; Gene Expression; Male; Molsidomine; Mutation; Myocardial Reperfusion Injury; Myocytes, Cardiac; Nitric Oxide Donors; Polymerase Chain Reaction; Rats; Rats, Sprague-Dawley; RNA; Transcription, Genetic

Decreases in blood pH activate NHE3, the proximal tubular apical membrane Na/H antiporter. In cultured renal epithelial cells, activation of the endothelin-B (ET(B)) receptor increases NHE3 activity. To examine the role of the ET(B) receptor in the response to acidosis in vivo, the present studies examined ET(B) receptor-deficient mice, rescued from neonatal lethality by expression of a dopamine beta-hydroxylase promoter/ET(B) receptor transgene (Tg/Tg:ET(B)(-/-) mice). In proximal tubule suspensions from Tg/Tg:ET(B)(+/-) mice, 10(-8) M endothelin-1 (ET-1) increased NHE3 activity, but this treatment had no effect on tubules from Tg/Tg:ET(B)(-/-) mice. Acid ingestion for 7 days caused a greater decrease in blood HCO(3)(-) concentration in Tg/Tg:ET(B)(-/-) mice compared with Tg/Tg:ET(B)(+/+) and Tg/Tg:ET(B)(+/-) mice. Whereas acid ingestion increased apical membrane NHE3 by 42-46% in Tg/Tg:ET(B)(+/+) and Tg/Tg:ET(B)(+/-) mice, it had no effect on NHE3 in Tg/Tg:ET(B)(-/-) mice. In C57BL/6 mice, excess acid ingestion increased renal cortical preproET-1 mRNA expression 2.4-fold and decreased preproET-3 mRNA expression by 37%. On a control diet, Tg/Tg:ET(B)(-/-) mice had low rates of ammonium excretion, which could not be attributed to an inability to acidify the urine, as well as hypercitraturia, with increased titratable acid excretion. Acid ingestion increased ammonium excretion, citrate absorption, and titratable acid excretion to the same levels in Tg/Tg:ET(B)(-/-) and Tg/Tg:ET(B)(+/+) mice. In conclusion, metabolic acidosis increases ET-1 expression, which increases NHE3 activity via the ET(B) receptor.

Topics: Acidosis; Ammonia; Animals; Bicarbonates; Chronic Disease; Citric Acid; Culture Techniques; Endothelin-1; Endothelins; Kidney Tubules, Proximal; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Protein Precursors; Receptor, Endothelin B; Receptors, Endothelin; RNA, Messenger; Sodium; Sodium-Hydrogen Exchanger 3; Sodium-Hydrogen Exchangers

The renin angiotensin system is highly activated in shock states and has been suggested to be involved in the pathophysiology of the markedly deteriorated splanchnic circulation seen in septic shock. The purpose of the present study was to elucidate the capability of losartan, a nonpeptide angiotensin II type 1 (AT1) receptor antagonist, to attenuate splanchnic blood flow disturbances and counteract intestinal mucosal acidosis in endotoxin shock. A total of 20 pigs were anesthetized and catheterized. Central and regional hemodynamics were monitored. A tonometer in the ileum was used for measurement of mucosal pH. Onset of endotoxin challenge was followed by losartan administration (n = 10) 2 h later. Ten animals receiving endotoxin only served as controls. The experiments were terminated 5 h after onset of endotoxin challenge. Endotoxin infusion induced an hypodynamic shock with a reduction in cardiac index and systemic oxygen delivery. Losartan reduced both systemic vascular resistance and pulmonary capillary wedge pressure while stroke volume was improved. Pulmonary hypertension induced by endotoxin was significantly reduced by losartan without further changes in gas exchange. The profound reduction in gut oxygen delivery in response to endotoxin was counteracted by losartan administration. However, losartan failed to improve the markedly deteriorated intestinal mucosal pH and mucosal-arterial PCO2gap (i.e., difference in intestinal mucosal PCO2 and arterial PCO2). Also the mucosal-portal venous PCO2gap, used as a monitor of the mucosa in relation to the gut as a whole (including the spleen and pancreas), was greatly increased by endotoxemia but unaffected by losartan administration. In summary, although the angiotensin II type 1 receptor antagonist losartan improved gut oxygen delivery and reduced pulmonary hypertension during established endotoxin shock, it had no effect on intestinal mucosal acidosis. These findings suggest contribution of the angiotensin II type 1 receptor to perfusion disturbances, but not to deterioration of intestinal mucosal homeostasis seen during endotoxemia.

Topics: Acidosis; Angiotensin Receptor Antagonists; Animals; Antihypertensive Agents; Dose-Response Relationship, Drug; Endothelin-1; Endotoxins; Female; Hemodynamics; Hemoglobins; Intestinal Mucosa; Losartan; Lung; Male; Oxygen; Pulmonary Gas Exchange; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Renin; Shock, Septic; Splanchnic Circulation; Swine; Urination

Acidosis affects multiple steps in the excitation-contraction coupling pathway of myocardium, producing decreased calcium sensitivity of myofibrils and modification of the function of the sarcoplasmic reticulum. Our aim was to evaluate the effectiveness of three different classes of inotropic agents under acidotic conditions: 1) forskolin, an adenylate cyclase activator that enhances cellular cyclic AMP concentrations, 2) elevated extracellular Ca2+ and 3) endothelin-1, an activator of the inositol triphosphate, diacylglycerol pathway. Ferret papillary muscles were mounted in organ baths containing normal physiological solution (pH = 7.4). After baseline tension was measured, the muscles were bathed in an acidotic solution (pH = 6.98) that decreased tension to 40% of the control; subsequently, the muscles were washed with normal physiological solution until they returned to baseline. Each inotropic agent was added to the bathing solution in a concentration sufficient to increase tension by 40% above the baseline. Then the solution was made acidotic (pH = 6.98) in the continuous presence of that concentration of inotropic agent and the resultant steady-state developed tension measured. The increases in tension induced by each inotropic agent at normal pH were adjusted to be similar: in contrast, the response to each drug in acidosis was significantly different. Under acidotic conditions, endothelin-1 was the most effective inotropic agent in restoring the depressed developed tension. This was possibly due to enhancement of the myofilament sensitivity to Ca2+, which was more effective than increasing [Ca2+]i through elevating extracellular Ca2+ or the addition of forskolin which increased [Ca2+]i but desensitized the myofilaments to Ca2+.

Topics: Acidosis; Adenosine Monophosphate; Animals; Calcium; Colforsin; Electrophysiology; Endothelin-1; Ferrets; Hydrogen-Ion Concentration; In Vitro Techniques; Male; Myocardial Contraction; Papillary Muscles; Stimulation, Chemical