scholarly journals Inhibition of IMCD 11 beta-hydroxysteroid dehydrogenase type 2 by low pH and acute acid loading.

1997 ◽  
Vol 8 (4) ◽  
pp. 530-534
Author(s):  
P J Nolan ◽  
M A Knepper ◽  
R K Packer
Keyword(s):  
Conversion Rate ◽  
Intact Cell ◽  
Collecting Duct ◽  
Hydroxysteroid Dehydrogenase ◽  
Cell Suspensions ◽  
Mineralocorticoid Receptors ◽  
Medullary Collecting Duct ◽  
Acute Metabolic Acidosis ◽  
Acid Loading

Mineralocorticoid receptors in the inner medullary collecting duct (IMCD) are protected from glucocorticoid binding by an enzyme, 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD2). To study the role of 11 beta-HSD2 in acid-base homeostasis, 11 beta-HSD2 activity was measured in rat IMCD-enriched cell suspensions. Homogenates of cell suspensions were incubated in buffers ranging in pH from 6.00 to 8.15 in the presence of 1 microCi of 3H-corticosterone (CS) and 400 microM NAD+. Enzyme activity was expressed as the amount of 3H-CS converted to 3H-11-dehydrocorticosterone (DHCS). IMCD 11 beta-HSD2 activity at pH 6.5 was 49% of activity at pH 7.5; 22.5 versus 11.0 fmol/microgram of protein per h. Experiments also were performed on intact cell suspensions at pH 7.5 and 6.5. There was a 42% inhibition in the IMCD cell suspension conversion rate of 3H-CS to 3H-11-DHCS at pH 6.5; 13.1 versus 7.6 fmol/microgram per h (P < 0.005). In cell suspensions at pH 7.5, 1-day acid loading caused a 26% inhibition in conversion rate, 13.2 versus 9.9 fmol/microgram per h (P < 0.05), when compared with controls. These results suggest that during acute metabolic acidosis, IMCD 11 beta-HSD2 is inhibited and may allow access to the mineralocorticoid receptors by glucocorticoids.

Increased collecting duct urea transporter expression in Dahl salt-sensitive rats

2003 ◽  
Vol 285 (1) ◽  
pp. F143-F151 ◽  
Author(s):  
Robert A. Fenton ◽  
Chung-Lin Chou ◽  
Shana Ageloff ◽  
William Brandt ◽  
John B. Stokes ◽  
...  
Keyword(s):  
Collecting Duct ◽  
Hydroxysteroid Dehydrogenase ◽  
Plasma Corticosterone ◽  
Urea Transporter ◽  
Rt Pcr ◽  
Collecting Ducts ◽  
Medullary Collecting Duct ◽  
Transporter Expression ◽  
Solute Transporter

Because abnormalities of inner medullary function have been proposed in Dahl salt-sensitive (DS) rats vs. salt-resistant (DR) rats, we performed transporter profiling by semiquantitative immunoblotting to determine whether specific solute transporter abundances are altered in inner medullas of DS rats vs. DR rats. Although none of the expressed Na transporters were upregulated in the inner medullas of DS rats compared with DR rats, there were marked increases in the protein abundances of the collecting duct urea transporters UT-A1 (to 212% of DR) and UT-A3 (to 223% of DR). These differences were confirmed by immunocytochemistry. Quantitative real-time RT-PCR showed higher mRNA abundance in DS rats for both UT-A1 (to 256% of DR) and UT-A3 (to 210% of DR). In isolated, perfused inner medullary collecting ducts, urea permeability was significantly greater in DS rats. Because both UT-A1 and UT-A3 are transcriptionally regulated by glucocorticoids, we measured both plasma corticosterone levels and inner medullary 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) abundances. Although the plasma corticosterone concentrations were not different between DS and DR rats, immunoblotting and immunocytochemistry revealed a marked elevation of 11β-HSD2 abundance in DS rats. Consistent with the view that an elevated 11β-HSD2 level is responsible for increased urea transporter expression in the inner medullary collecting duct, administration of the 11β-HSD2 inhibitor carbenoxolone to DS rats decreased the abundances of UT-A1 and UT-A3 to levels similar to those seen in DR rats.

scholarly journals 11Beta-hydroxysteroid dehydrogenase, mineralocorticoid receptor, and thiazide-sensitive Na-Cl cotransporter expression by distal tubules.

1998 ◽  
Vol 9 (8) ◽  
pp. 1347-1358
Author(s):  
M Bostanjoglo ◽  
W B Reeves ◽  
R F Reilly ◽  
H Velázquez ◽  
N Robertson ◽  
...  
Keyword(s):  
Mineralocorticoid Receptor ◽  
Collecting Duct ◽  
Hydroxysteroid Dehydrogenase ◽  
Receptor Expression ◽  
Salt Transport ◽  
Metabolic Enzyme ◽  
Thick Ascending Limb ◽  
Mineralocorticoid Receptors ◽  
Connecting Tubule

Mineralocorticoid hormones regulate salt transport along the distal nephron by binding to intracellular receptors and activating gene transcription. Previous experiments showed that systemic aldosterone infusions stimulate thiazide-sensitive Na and Cl transport by distal convoluted tubule (DCT) cells; this effect could have been direct or secondary to systemic hormonal effects. Aldosterone target tissues express both mineralocorticoid receptors and the metabolic enzyme 11beta-hydroxysteroid dehydrogenase type 2. Mineralocorticoid receptors have been localized to the DCT in some experiments, but not in others. Expression of 11beta-hydroxysteroid dehydrogenase type 2 by DCT cells has not been investigated. The present experiments were designed to test the hypothesis that rat DCT cells are targets of aldosterone action. Patterns of mineralocorticoid receptor, 11beta-hydroxysteroid dehydrogenase, thiazide-sensitive Na-Cl cotransporter, and Na/Ca exchanger expression along the distal tubule were examined. A polyclonal antibody was generated to localize the thiazide-sensitive Na-Cl cotransporter. Thiazide-sensitive Na-Cl cotransporter and 11beta-hydroxysteroid dehydrogenase expression were examined using both in situ hybridization and immunocytochemistry; Na/Ca exchanger and mineralocorticoid receptor expression were examined by immunocytochemistry. The results indicate that 11beta-hydroxysteroid dehydrogenase is expressed by DCT cells, as well as connecting tubule cells and principal cells of the collecting duct; expression levels are low near the junction with the thick ascending limb and rise near the transition to the connecting tubule. Mineralocorticoid receptors are expressed by DCT cells, as well as along the thick ascending limb, connecting tubule, and collecting duct. The results indicate that components of the mineralocorticoid receptor system are expressed by DCT cells, suggesting that these cells are targets of aldosterone action.

Importance of medullary events in ammonium excretion: studies in acute respiratory and acute metabolic acidosis

1983 ◽  
Vol 61 (1) ◽  
pp. 35-42 ◽  
Author(s):  
Andre Gougoux ◽  
Patrick Vinay ◽  
Guy Lemieux ◽  
Marc Goldstein ◽  
Bobby Stinebaugh ◽  
...  
Keyword(s):  
Metabolic Acidosis ◽  
Collecting Duct ◽  
Respiratory Acidosis ◽  
Renal Medulla ◽  
Hydrogen Ion ◽  
Ammonium Excretion ◽  
Urine Ph ◽  
Ion Secretion ◽  
Medullary Collecting Duct ◽  
Acute Metabolic Acidosis

The renal medulla can play an important role in acid excretion by modulating both hydrogen ion secretion in the medullary collecting duct and the medullary [Formula: see text]. The purpose of these experiments was to characterize the intrarenal events associated with ammonium excretion in acute acidosis. Cortical events were monitored in two ways: first, the rates of glutamine extraction and ammoniagenesis were assessed by measuring arteriovenous differences and the rate of renal blood flow; second, the biochemical response of the ammoniagenesis pathway was examined by measuring glutamate and 2-oxoglutarate, key renal cortical metabolites in this pathway. There were no significant differences noted in any of these cortical parameters between acute respiratory and metabolic acidosis. Despite a comparable twofold rise in ammonium excretion in both cases, the urine pH, [Formula: see text], and the urine minus blood [Formula: see text] difference (U-B [Formula: see text]) were lower during acute hypercapnia. In these experiments, the urine [Formula: see text] was 34 mmHg (1 mmHg = 133.322 Pa) lower than that of the blood during acute respiratory acidosis while the U-B [Formula: see text] was 5 ± 3 mmHg in acute metabolic acidosis. Thus there were significant differences in medullary events during these two conditions. Although the urine pH is critical in determining ammonium excretion in certain circumstances, these results suggest that regional variations in the medullary [Formula: see text] can modify this relationship.

Phosphate-dependent glutaminase activity in rat renal cortical and medullary tubule segments

1990 ◽  
Vol 259 (6) ◽  
pp. F961-F970 ◽  
Author(s):  
P. A. Wright ◽  
M. A. Knepper
Keyword(s):  
Collecting Duct ◽  
Proximal Tubules ◽  
Thick Ascending Limb ◽  
Loop Of Henle ◽  
Ammonium Accumulation ◽  
Ammonium Production ◽  
Medullary Collecting Duct ◽  
Acid Loading ◽  
Glutaminase Activity ◽  
Convoluted Tubules

To determine whether local production of ammonium by medullary renal tubule segments may contribute to medullary ammonium accumulation, we measured activities of phosphate-dependent glutaminase (PDG) in microdissected tubule segments from rat medulla and cortex. PDG activities were very low in medullary loop of Henle segments but surprisingly high in inner medullary collecting duct (IMCD). In cortex, PDG levels were highest in distal convoluted tubule and cortical thick ascending limb, but substantial levels were also found in proximal segments, as reported previously. To determine effects of acid loading and alkali loading on PDG activity, 0.28 M NH4Cl (acid) or 0.28 M NaHCO3 (alkali) was added to rats' drinking water for 7 days. PDG activities in medullary segments were not affected by acid or alkali intake. Acid intake by rats increased PDG activity in S1 and S2 proximal convoluted tubules severalfold but did not affect the other cortical segments. We conclude that medullary loop of Henle segments probably contribute relatively little to medullary ammonium accumulation because of their low activities. The high PDG activity in IMCD suggests that ammonium could be produced and secreted by this segment. However, because total tubule length of IMCD is very low compared with proximal tubules, it appears unlikely that IMCD contributes substantially to overall renal ammonium production. PDG activity is regulated only in S1 and S2 proximal tubules, consistent with the view that the proximal tubule is the major site of regulation of renal ammonium production.

scholarly journals Antifibrotic Effect of a Novel Selective 11β-HSD2 Inhibitor (WZ51) in a rat Model of Myocardial Fibrosis

2021 ◽  
Vol 12 ◽  
Author(s):  
Fei Zhuang ◽  
Qin Ge ◽  
Jiangchang Qian ◽  
Zhe Wang ◽  
Yaoyao Dong ◽  
...  
Keyword(s):  
Creatine Kinase ◽  
Myocardial Fibrosis ◽  
Myocardial Injury ◽  
Therapeutic Agent ◽  
Enzyme Inhibitor ◽  
Hydroxysteroid Dehydrogenase ◽  
Underlying Mechanism ◽  
Mineralocorticoid Receptors ◽  
End Stage

Myocardial fibrosis (MF) is one of the leading causes of end-stage heart disease. Many studies have confirmed that inflammation caused by aldosterone may play an important role in the process of MF. A selective 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) enzyme inhibitor can reduce the inactivation of cortisol, allowing cortisol to compete for mineralocorticoid receptors. This study investigated the protective effect of a novel selective 11βHSD2 inhibitor (WZ51) on MF and described its underlying mechanism. The administration of WZ51 in rats with MF significantly alleviated myocardial injury, accompanied by a decrease in lactate dehydrogenase and the creatine kinase myocardial band. Furthermore, WZ51 significantly inhibited the development of MF and increased the protein level of 11β-HSD2. The results of this study demonstrate that 11β-HSD2 plays an important pathological role in MF. Thus, WZ51 may be a potential therapeutic agent for the treatment of this condition.

Expression of mRNAs for different types of IP3 receptors in rat kidneys

1995 ◽  
Vol 268 (6) ◽  
pp. F1046-F1052 ◽  
Author(s):  
T. Yang ◽  
Y. Terada ◽  
H. Nonoguchi ◽  
K. Tomita ◽  
F. Marumo
Keyword(s):  
Collecting Duct ◽  
Rat Kidney ◽  
Ip3 Receptors ◽  
Ip3 Receptor ◽  
Receptor Mrna ◽  
Collecting Ducts ◽  
Different Types ◽  
Medullary Collecting Duct

Cloning studies have extensively characterized two types of inositol 1,4,5-trisphosphate (IP3) receptors from the rat. An IP3 receptor from the cerebellum is referred to as type 1, and a second, recently described, receptor is referred to as the type 2 IP3 receptor. The significance of different types of IP3 receptors, especially in vivo in the kidney, is not fully understood. We investigated the localization of mRNAs encoding these two types of IP3 receptors in microdissected nephron segments of rats using reverse transcription and polymerase chain reaction (RT-PCR) followed by Southern blot analysis. Type 1 IP3 receptor mRNA displayed a widespread, although not uniform, distribution along the nephron. In contrast, type 2 IP3 receptor mRNA was confined almost exclusively to collecting ducts, suggesting specific expression of type 2 IP3 receptor in collecting ducts. We then detected mRNAs for the two types of IP3 receptors in collecting ducts in dehydrated rats. Dehydration downregulated type 2 IP3 receptor mRNA in cortical collecting duct, outer medullary collecting duct, and the initial part of inner medullary collecting duct (IMCD), but not in the terminal part of IMCD. It had no effect on type 1 IP3 receptor mRNA expression in collecting ducts. We propose that different types of IP3 receptors may have different functions in the rat kidney. the initial part of inner medullary collecting duct (IMCD), but not in the terminal part of IMCD. It had no effect on type 1 IP3 receptor mRNA expression in collecting ducts. We propose that different types of IP3 receptors may have different functions in the rat kidney.

Endothelin-1 stimulates NO production and inhibits cAMP accumulation in rat inner medullary collecting duct through independent pathways

2006 ◽  
Vol 290 (6) ◽  
pp. F1315-F1319 ◽  
Author(s):  
Peter K. Stricklett ◽  
Alisa K. Hughes ◽  
Donald E. Kohan
Keyword(s):  
Collecting Duct ◽  
Cell Suspensions ◽  
No Production ◽  
Camp Accumulation ◽  
No Donors ◽  
Endothelin 1 ◽  
Inner Medullary Collecting Duct ◽  
Nos Inhibitors ◽  
Medullary Collecting Duct ◽  
Spermine Nonoate

Endothelin-1 (ET-1) inhibition of vasopressin (AVP)-stimulated cAMP accumulation in the collecting duct has been hypothesized to be mediated, at least in part, by nitric oxide (NO). To examine this, the effect of ET-1 on NO production by acutely isolated rat inner medullary collecting duct (IMCD) cell suspensions and the role of NO in mediating ET-1 effects on AVP-stimulated cAMP accumulation were studied. ET-1 dose dependently (first evident at 100 pM ET-1) increased IMCD NO production as determined by DAF-FM fluorescence. ETB receptor (BQ-788), but not ETA receptor (BQ-123), antagonism blocked this effect. Nonspecific NO synthase (NOS) inhibitors [ NG-nitro-l-arginine methyl ester (l-NAME) or NG-monomethyl-l-arginine] or NOS-1 inhibitors (SMTC or VNIO) inhibited the ET-1 response, whereas NOS-2 or NOS-3 inhibitors (l-NAA or 1400W) were ineffective. ET-1 also increased cGMP accumulation. ET-1 caused a 35% reduction in AVP-stimulated cAMP levels; however, this response was not affected by l-NAME or SMTC. The addition of l-arginine, NADPH, tetrahydrobiopterin, or tempol (to reduce superoxide-dependent conversion of NO to peroxynitrate) did not affect the response. NO donors (SNAP or spermine NONOate), at concentrations that stimulated DAF-FM fluorescence and increased cGMP levels, did not alter AVP-stimulated cAMP accumulation in the IMCD cell suspensions. In conclusion, ET-1 stimulates IMCD NO production through activation of the ETB receptor and NOS-1. However, neither ET-1-mediated NO production nor NO donors inhibit AVP-stimulated cAMP accumulation, indicating that NO does not mediate ET-1 inhibition of cAMP production by the IMCD.

scholarly journals Decreased 11β-Hydroxysteroid Dehydrogenase Type 2 Expression in the Kidney May Contribute to Nicotine/Smoking-Induced Blood Pressure Elevation in Mice

Hypertension ◽  
2021 ◽  
Author(s):  
Ying Wang ◽  
Jian Wang ◽  
Rong Yang ◽  
Piwen Wang ◽  
Rene Porche ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Collecting Duct ◽  
Systolic Arterial Pressure ◽  
Receptor Occupancy ◽  
Hydroxysteroid Dehydrogenase ◽  
Nicotine Exposure ◽  
Cortical Collecting Duct ◽  
Blood Pressure Elevation ◽  
Pressure Elevation

Chronic nicotine exposure significantly increases hypertensive risk in smokers, but the underlying mechanisms are poorly understood. In the kidneys, 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) catalyzes the conversion from active into inactive glucocorticoids and plays a pivotal role in the regulation of blood pressure. We hypothesized that nicotine-induced blood pressure elevation is in part mediated by change in renal 11β-HSD2 leading to higher MR (mineralocorticoid receptor) occupancy. Here, we show that nicotine exposure markedly decreased the expression and activity of renal 11β-HSD2 and increased the mean systolic arterial pressure in C57BL/6J mice. Reduction of renal 11β-HSD2 expression by nicotine was correlated with the suppression of C/EBPβ (CCAAT/enhancer-binding protein-β) and activation of Akt protein kinase phosphorylation (pThr 308 Akt/PKB) within the kidney. Conversely, nicotine-treated mice had elevated renal MR and epithelial sodium channel-α abundance. Treatment with the MR antagonist spironolactone significantly decreased the elevated mean systolic blood pressure and corrected ENaC along with inhibition of pThr 308 Akt/PKB within the kidney in nicotine-treated mice. Suppression of Akt/PKB activation by spironolactone was accompanied by upregulation of renal C/EBPβ and amelioration of nicotine-mediated reduction of 11β-HSD2. Addition of nicotine to mouse renal cortical collecting duct M1 cells downregulated 11β-HSD2 and stimulated MR expression, and these effects are likely mediated by activation of Akt coupled inhibition of C/EBPβ. These findings suggest that nicotine-mediated suppression of 11β-HSD2 in the kidney may contribute to the development of nicotine/smoking-induced hypertension through decreasing the intrarenal deactivation of glucocorticoids. Spironolactone may prove useful in protecting against the hypertensive risks of nicotine/smoking.

Acute metabolic acidosis augments collecting duct acidification rate in the rat

1981 ◽  
Vol 241 (6) ◽  
pp. F669-F676 ◽  
Author(s):  
M. L. Graber ◽  
H. H. Bengele ◽  
E. Mroz ◽  
C. Lechene ◽  
E. A. Alexander
Keyword(s):  
Metabolic Acidosis ◽  
Collecting Duct ◽  
Direct Evaluation ◽  
Acid Addition ◽  
Arterial Ph ◽  
Nephron Segment ◽  
Medullary Collecting Duct ◽  
Acute Metabolic Acidosis

It is generally assumed that at least part of distal acidification occurs along the collecting duct. Complete and direct evaluation of acidification along this nephron segment is unavailable, however. The purpose of these experiments was to quantify the net acidification rate along the inner medullary collecting duct (IMCD) and to measure the effect of acute HCl acidosis. In 13 control rats (arterial pH, 7.39 +/- 0.01; PCO2, 39 +/- 1 mmHg) and 11 HCl-infused rats (arterial pH 7.18 +/- 0.01; PCO2, 40 +/- 1 mmHg) we obtained four to eight IMCD samples by a modified microcatheterization technique that also permitted measurement of in situ and in vitro pH. Tubular fluid pH decreased along the IMCD in both groups and was more acidic by 0.2–0.4 pH units in the acid-infused rats. Bicarbonate reabsorption was noted in both groups as delivery along the IMCD decreased from 205 +/- 127 to 26 +/- 6 nmol/min in control rats and from 219 +/- 118 to 17 +/- 4 nmol/min in the acidotic group. Ammonia delivery to and addition along the IMCD was significantly greater in the acidotic rats--from 193 +/-- 59 to 462 +/- 53 nmol/min in control and from 887 +/- 126 to 1,396 +/- 90 nmol/min in acidotic rats. No significant change in total or titrated phosphate was seen. Net acid addition along the IMCD was over twice as great in acidotic rats, 450 vs. 970 nmol/min. Our results indicate that significant net acid addition occurs along the IMCD and that during acidosis this acidification rate increases.

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