Antibiotic availability for outpatient treatment of acute peritonitis in chronic peritoneal dialysis patients: A case series

BACKGROUND

Peritoneal dialysis (PD) is a commonly used form of renal replacement therapy for patients that have reached end-stage renal disease. Acute bacterial peritonitis (ABP) in chronic PD patients results in pain, increased costs, injury to the peritoneal membrane, and PD modality failure. Optimal antibiotic treatment of acute bacterial peritonitis (ABP) in chronic PD patients should be intraperitoneal, outpatient-based, appropriate, prompt, and uninterrupted. We investigated the frequency of and predisposition to suboptimal antibiotic courses for ABP in our chronic PD patients.

METHODS

Twenty-four charts of patients with ABP were reviewed, to test the null hypothesis that all ABP patients received antibiotics optimally.

RESULTS

After 12 patient exclusions (hospitalization), 9 suboptimal antibiotic events were detected in 6 of the remaining 12 patients, disproving the null hypothesis (p < 0.02). Most suboptimal antibiotics courses (7 of 9) resulted from delays and/or gaps in therapy or antibiotics prescribed outside of community standard. Suboptimal antibiotic events occurred on nights and weekends rather than during the workweek (p < 0.02) and in the emergency room rather than the PD clinic (p < 0.02).

CONCLUSIONS

Suboptimal ABP antibiotic therapy occurs commonly and is influenced by time and location of presentation and lack of knowledge by patients and physicians. Prevention of suboptimal antibiotic courses in the treatment of ABP in chronic PD patients includes education of patients and providers and allowing emergency rooms and PD clinics to dispense antibiotics for home use.

Hyperkalemia in chronic peritoneal dialysis patients

Background. Chronic peritoneal dialysis (PD) patients often develop hypokalemia but less commonly hyperkalemia.

Methods. We explored incidence and mechanisms of hyperkalemia in 779 serum samples from 33 patients on PD for 1 − 59 months. Normal serum potassium concentration was defined as 3.5 − 5.1 meq/l.

Results. Mean monthly serum potassium concentrations were normal (except for 1 month), but we observed hypokalemia (<3.5 meq/l) in 5% and hyperkalemia (>5.1 meq/l) in 14% of 779 serum samples. Incidence of hyperkalemia did not change over time on PD: Year 1 (15%), Year 2 (11%), Year 3 (19%), Years 4–5 (22%). Hyperkalemia was mostly modest but occasionally extreme [5.2–5.4 meq/l (55%), 5.5–5.7 meq/l (21%), 5.8–6.0 meq/l (10%), >6.0 meq/l (14%)]. Of 31 patients (2 excluded due to brief PD time), 39% displayed hyperkalemia only, 23% displayed hypokalemia only, and the remainder (38%) displayed both or neither. Comparing hypokalemia-only with hyperkalemia-only patients, we found no difference in potassium chloride therapy, medications interrupting the renin-angiotensin system, small-molecule transport status, and renal urea clearance. We compared biochemical parameters from the hypokalemic and hyperkalemic serum samples and observed lower bicarbonate concentrations, higher creatinine concentrations, and higher urea nitrogen concentrations in the hyperkalemic samples (p < 0.001 for each), without difference in glucose concentrations.

Conclusion. We observed hyperkalemia 3 times as frequently as hypokalemia in our PD population. High-potassium diet, PD noncompliance, increased muscle mass, potassium shifts, and/or the daytime period without PD might contribute to hyperkalemia.

Length of Interdialytic Intervals Affects Morbidity and Mortality in Chronic Haemodialysis Patients

Background

Chronic in-center hemodialysis (HD) patients may experience more morbidity and mortality after the weekend. Since our Veterans Administration Hospital HD unit is closed on the weekend, non-traditional HD schedules were created. Some schedules contained a 4-day weekend compared to the usual 3-day weekend. We hypothesized that there are more frequent cardiovascular events (CVEs) and higher mortality after longer interdialytic intervals.

Methods

Patients (n=85) were placed on HD schedules as they became available. The usual interdialytic interval group consisted of patients dialyzing on Mon-Wed-Fri or Mon-Tue-Fri (longest interdialytic gap 3 days, n=29), and the long interdialytic interval group consisted of patients dialyzing on Mon-Wed-Thu, Mon-Tue-Thu, Tue-Wed-Fri, or Tue-Thu-Fri (longest interdialytic gap 4 days, n=56).

Results

All-cause mortality was not different between groups, and CVEs occurred more frequently in the usual interdialytic interval group (maybe due to higher mean potassium and phosphorus concentrations). However, within each group, a similar pattern of CVE occurrence as a function of time after dialysis was observed. Compared to CVEs occurring during the 2 days after HD (the lowest frequency), CVEs occurred 2–3 times more frequently during and immediately after HD and 5–7 times more frequently during the third and fourth days after HD. The greatest risk of CVE occurred during the fourth day after HD, which exists only in the long interdialytic interval group.

Conclusion

In chronic HD patients, CVEs are most likely to occur after the longest interdialytic intervals.

Clathrin-dependent internalization of the angiotensin II AT₁A receptor links receptor internalization to COX-2 protein expression in rat aortic vascular smooth muscle cells

The major effects of Angiotensin II (AngII) in vascular tissue are mediated by AngII AT1A receptor activation. Certain effects initiated by AT1A receptor activation require receptor internalization. In rat aortic vascular smooth muscle cells (RASMC), AngII stimulates cyclooxygenase 2 protein expression. We have previously shown this is mediated by β-arrestin-dependent receptor internalization and NF-κB activation. In this study, a specific inhibitor of clathrin-mediated endocytosis (CME), pitstop-2, was used to test the hypothesis that clathrin-dependent internalization of activated AT1A receptor mediates NF-κB activation and subsequent cyclooxygenase 2 expression. Radioligand binding assays, real time qt-PCR and immunoblotting were used to document the effects of pitstop-2 on AngII binding and signaling in RASMC. Laser scanning confocal microscopy (LSCM) was used to image pitstop-2׳s effects on AT1 receptor/GFP internalization in HEK-293 cells and p65 NF-κB nuclear localization in RASMC. Pitstop-2 significantly inhibited internalization of AT1A receptor (44.7% ± 3.1% Control vs. 13.2% ± 8.3% Pitstop-2; n=3) as determined by radioligand binding studies in RASMC. Studies utilizing AT1A receptor/GFP expressed in HEK 293 cells and LSCM confirmed these findings. Pitstop-2 significantly inhibited AngII-induced p65 NF-κB phosphorylation and nuclear localization, COX-2 message and protein expression in RASMC without altering activation of p42/44 ERK or TNFα signaling. Pitstop-2, a specific inhibitor of clathrin-mediated endocytosis, confirms that internalization of activated AT1A receptor mediates AngII activation of cyclooxygenase 2 expression in RASMC. These data provide support for additional intracellular signaling pathways activated through β-arrestin mediated internalization of G protein-coupled receptors, such as AT1A receptors.

Stimulation of Cyclooxygenase 2 Expression in Rat Peritoneal Mesothelial Cells

Objective: Since peritoneal dialysis causes peritoneal fibrosis, we examined how glucose (osmotic factor), mannitol (osmotic control), and angiotensin II (AngII) regulate proinflammatory cyclooxygenase 2 (COX-2) in primary rat peritoneal mesothelial cells. Materials and Methods: For this study, we used the following material (n = 4-8 cell lines): cells, passages 1-2; 125I-AngII receptor surface binding (AT1R antagonist losartan, AT2R antagonist PD123319; both 10 µM); intracellular calcium probe calcium-5; COX-2 immunoblotting (β-actin normalized); real-time PCR of COX-2 gene PTGS2, and NF-κB inhibitor Ro-1069920 (5 µM). Results: AngII surface receptors were predominantly AT1R (minimally AT2R). AngII and glucose increased COX-2 protein expression concentration dependently; mannitol also increased COX-2 expression. Maximal COX-2 protein expression was observed after 6 h (AngII) and 24 h (glucose, mannitol). The time course of increases in PTGS2 mRNA levels reflected that of COX-2 protein expression. At optimal exposure conditions (time/concentration), glucose was 5-fold more efficacious in stimulating COX-2 protein expression than AngII or mannitol. Losartan fully inhibited COX-2 protein responses to AngII and mannitol, but minimally inhibited responses to glucose. Ro-1069920 fully inhibited COX-2 protein responses to each effector. Conclusion: AngII, glucose, and osmotic stress (mannitol) activate COX-2; NF-κB may be an ideal site for COX-2 blockade, and COX-2 activation by osmotic stress requires AT1R, but activation by glucose is more robust and mechanistically complex. © 2014 S. Karger AG, Basel.

Angiotensin II activates NF-κB through AT1A receptor recruitment of β-arrestin in cultured rat vascular smooth muscle cells

Activation of the angiotensin type 1A receptor (AT1AR) in rat aorta vascular smooth muscle cells (RASMC) results in increased synthesis of the proinflammatory enzyme cyclooxygenase-2 (COX-2). We previously showed that nuclear localization of internalized AT1AR results in activation of transcription of the gene for COX-2, i.e., prostaglandin-endoperoxide synthase-2. Others have suggested that ANG II stimulation of COX-2 protein synthesis is mediated by NF-κB. The purpose of the present study was to examine the interrelationship between AT1AR activation, β-arrestin recruitment, and NF-κB activation in the ability of ANG II to increase COX-2 protein synthesis in RASMC. In the present study we utilized RASMC, inhibitors of the NF-κB pathway, β-arrestin knockdown, radioligand binding, immunoblotting, and immunofluorescence to characterize the roles of AT1AR internalization, NF-κB activation, and β-arrestin in ANG II-induced COX-2 synthesis. Ro-106-9920 or parthenolide, agents that inhibit the initial steps of NF-κB activation, blocked ANG II-induced p65 NF-κB nuclear localization, COX-2 protein expression, β-arrestin recruitment, and AT1AR internalization without inhibiting ANG II-induced p42/44 ERK activation. Curcumin, an inhibitor of NF-κB-induced transcription, blocked ANG II-induced COX-2 protein expression without altering AT1AR internalization, ANG II-induced p65 NF-κB nuclear localization, or p42/44 ERK activation. Small interfering RNA-induced knockdown of β-arrestin-1 and -2 inhibited ANG II-induced p65 NF-κB nuclear localization. In vascular smooth muscle cells, internalization of the activated AT1AR mediated by β-arrestins activates the NF-κB pathway, producing nuclear localization of the transcription factor and initiation of COX-2 protein synthesis, thereby linking internalization of the receptor with the NF-κB pathway.

Peritonitis from Mycobacterium wolinskyi in a chronic peritoneal dialysis patient

We report the case of acute peritonitis caused by a rapidly growing mycobacterium in a chronic peritoneal dialysis patient, whose renal failure had been caused by diabetic glomerulosclerosis. The organism cultured from the peritoneal dialysis fluid was Mycobacterium wolinskyi. Peritonitis caused by M. wolinskyi in a chronic peritoneal dialysis patient has never been reported before.

Prerenal azotemia from excessive sweating in an adult with a cystic fibrosis gene mutation

We present the case of a 58-year-old male with chronic kidney disease who was admitted to the hospital multiple times with extracellular fluid volume depletion and prerenal azotemia. Some episodes were associated with gastrointestinal fluid losses and others with profuse diaphoresis in the absence of gastrointestinal fluid losses. At the age of 57 years, a common cystic fibrosis transmembrane conductance regulator protein mutation and a family history of cystic fibrosis were documented. We hypothesize that the abnormal cystic fibrosis transmembrane conductance regulator resulted in repeated bouts of excessive sweating, extracellular fluid volume depletion, and acute renal failure. This case is unique because of the prolonged period of time over which multiple documented episodes of prerenal acute renal failure occurred and because of the onset of the episodes in adulthood.

Angiotensin II-induced cyclooxygenase 2 expression in rat aorta vascular smooth muscle cells does not require heterotrimeric G protein activation

Angiotensin II (AngII) initiates cellular effects via its G protein-coupled angiotensin 1 (AT(1)) receptor (AT(1)R). Previously, we showed that AngII-induced expression of the prostanoid-producing enzyme cyclooxygenase 2 (COX-2) was dependent upon nuclear trafficking of activated AT(1)R. In the present study, mastoparan (an activator of G proteins), suramin (an inhibitor of G proteins), 1-[6-[[17beta-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122; a specific inhibitor of phospholipase C), and sarcosine(1)-Ile(4)-Ile(8)-AngII (SII-AngII; a G protein-independent AT(1)R agonist) were used to determine the involvement of G proteins and AT(1A)R trafficking in AngII-stimulated COX-2 protein expression in human embryonic kidney-293 cells stably expressing AT(1A)/green fluorescent protein receptors and cultured vascular smooth muscle cells, respectively. Mastoparan alone stimulated release of intracellular calcium and increased COX-2 expression. Preincubation with mastoparan inhibited AngII-induced calcium signaling without altering AngII-induced AT(1A)R trafficking, p42/44 extracellular signal-regulated kinase (ERK) activation, or COX-2 expression. Suramin or U73122 had no significant effect on their own; they did not inhibit AngII-induced AT(1A)R trafficking, p42/44 ERK activation, or COX-2 expression; but they did inhibit AngII-induced calcium responses. SII-AngII stimulated AT(1A)R trafficking and increased COX-2 protein expression without activating intracellular calcium release. These data suggest that G protein activation results in increased COX-2 protein expression, but AngII-induced COX-2 expression seems to occur independently of G protein activation.

Identification of a putative nuclear localization sequence within ANG II AT(1A) receptor associated with nuclear activation

Angiotensin II (ANG II) type 1 (AT(1)) receptors, similar to other G protein-coupled receptors, undergo desensitization and internalization, and potentially nuclear localization, subsequent to agonist interaction. Evidence suggests that the carboxy-terminal tail may be involved in receptor nuclear localization. In the present study, we examined the carboxy-terminal tail of the receptor for specific regions responsible for the nuclear translocation phenomenon and resultant nuclear activation. Human embryonic kidney cells stably expressing either a wild-type AT(1A) receptor-green fluorescent protein (AT(1A)R/GFP) construct or a site-directed mutation of a putative nuclear localization sequence (NLS) [K307Q]AT(1A)R/GFP (KQ/AT(1A)R/GFP), were examined for differences in receptor nuclear trafficking and nuclear activation. Receptor expression, intracellular signaling, and ANG II-induced internalization of the wild-type/GFP construct and of the KQ/AT(1A)R/GFP mutant was similar. Laser scanning confocal microscopy showed that in cells expressing the AT(1A)R/GFP, trafficking of the receptor to the nuclear area and colocalization with lamin B occurred within 30 min of ANG II (100 nM) stimulation, whereas the KQ/AT(1A)R/GFP mutant failed to demonstrate nuclear localization. Immunoblotting of nuclear lysates with an anti-GFP antibody confirmed these observations. Nuclear localization of the wild-type receptor correlated with increase transcription for both EGR-1 and PTGS-2 genes while the nuclear-deficient KQ/AT(1A)R/GFP mutant demonstrated increases for only the EGR-1 gene. These results suggest that a NLS (KKFKKY; aa307-312) is located within the cytoplasmic tail of the AT(1A) receptor and that nuclear localization of the receptor corresponds with specific activation of transcription for the COX-2 gene PTGS-2.

Effects of intravenously administered iron on systemic blood pressure in hemodialysis patients

BACKGROUND/AIMS

Although maintenance of iron stores by intravenous iron infusion has become increasingly common in chronic hemodialysis patients, the effects of intravenous iron on blood pressure are not clear.

METHODS

In 52 mostly African-American patients in an urban setting, we reviewed blood pressure data over the course of hemodialysis on days that intravenous iron was administered and on control days.

RESULTS

The drop in blood pressure from the beginning to the end of hemodialysis was more pronounced when iron was not administered (9.9 +/- 1.2 mm Hg) compared to when iron was administered (4.1 +/- 1.7 mm Hg; p < 0.01). In a subset of chronic hemodialysis patients, blood pressure was actually higher at the end of hemodialysis compared to at the onset (9.6% of control hemodialysis sessions and 32.7% of sessions in which iron was administered; p < 0.01). The incidence of intra-dialytic hypotension and related symptoms was similar on iron and non-iron days.

CONCLUSION

Intravenous iron therapy, well entrenched in clinical practice for the treatment of the anemia of end-stage renal disease, may reduce the incidence and magnitude of post-dialytic hypotension.

Peritonitis With Multiple Rare Environmental Bacteria in a Patient Receiving Long-Term Peritoneal Dialysis

We describe a patient receiving long-term peritoneal dialysis who experienced 2 episodes of peritonitis in successive months caused by unusual bacteria of environmental origin: Agrobacterium radiobacter, Pseudomonas oryzihabitans, and Corynebacterium aquaticum. A radiobacter and P oryzihabitans occurred simultaneously in the first episode of peritonitis, and C aquaticum, in the second episode. The patient's vocation necessitated exposure to moist soiled conditions. Both episodes responded promptly to antibiotics commonly used to treat peritonitis. Although these organisms rarely lead to loss of life and commonly are considered to be contaminants, they can cause symptomatic peritonitis and peritoneal dialysis catheter loss. A review of previous case reports is included.

The missense mutation in Abcg5 gene in spontaneously hypertensive rats (SHR) segregates with phytosterolemia but not hypertension

BACKGROUND

Sitosterolemia is a recessively inherited disorder in humans that is associated with premature atherosclerotic disease. Mutations in ABCG5 or ABCG8, comprising the sitosterolemia locus, STSL, are now known to cause this disease. Three in-bred strains of rats, WKY, SHR and SHRSP, are known to be sitosterolemic, hypertensive and they carry a missense 'mutation' in a conserved residue of Abcg5, Gly583Cys. Since these rat strains are also know to carry mutations at other genetic loci and the extent of phytosterolemia is only moderate, it is important to verify that the mutations in Abcg5 are causative for phytosterolemia and whether they contribute to hypertension.

METHODS

To investigate whether the missense change in Abcg5 is responsible for the sitosterolemia we performed a segregation analysis in 103 F2 rats from a SHR x SD cross. Additionally, we measured tail-cuff blood pressure and measured intestinal lipid transport to identify possible mechanisms whereby this mutation causes sitosterolemia.

RESULTS

Segregation analysis showed that the inheritance of the Gly583Cys mutation Abcg5 segregated with elevated plant sterols and this pattern was recessive, proving that this genetic change is responsible for the sitosterolemia in these rat strains. Tail-cuff monitoring of blood pressure in conscious animals showed no significant differences between wild-type, heterozygous and homozygous mutant F2 rats, suggesting that this alteration may not be a significant determinant of hypertension in these rats on a chow diet.

CONCLUSION

This study shows that the previously identified Gly583Cys change in Abcg5 in three hypertension-susceptible rats is responsible for the sitosterolemia, but may not be a major determinant of blood pressure in these rats.

N-Acetylcysteine Decreases Angiotensin II Receptor Binding in Vascular Smooth Muscle Cells

Antioxidants seem to inhibit angiotensin II (Ang II) actions by consuming stimulated reactive oxygen species. An alternative hypothesis was investigated: Antioxidants that are also strong reducers of disulfide bonds inhibit the binding of Ang II to its surface receptors with consequent attenuation of signal transduction and cell action. Incubation of cultured vascular smooth muscle cells, which possess Ang II type 1a receptors, with the reducing agent n-acetylcysteine (NAC) for 1 h at 37 degrees C resulted in decreased Ang II radioligand binding in a concentration-dependent pattern. NAC removal restored Ang II binding within 30 min. Incubation with n-acetylserine, a nonreducing analogue of NAC, did not lower Ang II binding, and oxidized NAC was less effective than reduced NAC in lowering Ang II binding. NAC did not decrease Ang II type 1a receptor protein content. Other antioxidants regulated Ang II receptors differently: alpha-Lipoic acid lowered Ang II binding after 24 h, and vitamin E did not lower Ang II binding at all. NAC inhibited Ang II binding in cell membranes at 21 or 37 but not 4 degrees C. Dihydrolipoic acid (the reduced form of alpha-lipoic acid), which contains free sulfhydryl groups as NAC does, decreased Ang II receptor binding in cell membranes, whereas alpha-lipoic acid, which does not contain free sulfhydryl groups, did not. Ang II-stimulated inositol phosphate formation was decreased by preincubation with NAC (1 h) or alpha-lipoic acid (24 h) but not vitamin E. In conclusion, certain antioxidants that are reducing agents lower Ang II receptor binding, and Ang II-stimulated signal transduction is decreased in proportion to decreased receptor binding.

Mechanisms of vascular angiotensin II surface receptor regulation by epidermal growth factor

We investigated mechanisms by which epidermal growth factor (EGF) reduces angiotensin II (AngII) surface receptor density and stimulated actions in vascular smooth muscle cells (VSMC). EGF downregulated specific AngII radioligand binding in intact cultured rat aortic smooth muscle cells but not in cell membranes and also inhibited AngII-stimulated contractions of aortic segments. Inhibitors of cAMP-dependent kinases, PI-3 kinase, MAP kinase, cyclooxygenase, and calmodulin did not prevent EGF-mediated downregulation of AngII receptor binding, whereas the EGF receptor kinase inhibitor AG1478 did. Total cell AngII AT1a receptor protein content of EGF-treated and untreated cells, measured by immunoblotting, did not differ. Actinomycin D or cytochalasin D, which interacts with the cytoskeleton, but not the protein synthesis inhibitor cycloheximide, prevented EGF from downregulating AngII receptor binding. Consistently, EGF inhibited AngII-stimulated formation of inositol phosphates in the presence of cycloheximide but not in the presence of actinomycin D or cytochalasin D. In conclusion, EGF needs an intact signal transduction pathway to downregulate AngII surface receptor binding, possibly by altering cellular location of the receptors.

Mitogen-induced Rapid Phosphorylation of Serine 795 of the Retinoblastoma Gene Product in Vascular Smooth Muscle Cells Involves ERK Activation

We examined the relationship between mitogen-activated MEK (mitogen and extracellular signal-regulated protein kinase kinase) and phosphorylation of the gene product encoded by retinoblastoma (hereafter referred to as Rb) in vascular smooth muscle cells. Brief treatment of the cells with 100 nm angiotensin II or 1 microm serotonin resulted in serine phosphorylation of Rb that was equal in magnitude to that induced by treating cells for 20 h with 10% fetal bovine serum ( approximately 3 x basal). There was no detectable rapid phosphorylation of two close cousins of Rb, p107 and p130. Phosphorylation state-specific antisera demonstrated that the rapid phosphorylation occurred on Ser(795), but not on Ser(249), Thr(252), Thr(373), Ser(780), Ser(807), or Ser(811). Phosphorylation of Rb Ser(795) peaked at 10 min, lagging behind phosphorylation of MEK and ERK (extracellular signal-regulated protein kinase). Rb Ser(795) phosphorylation could be blocked by PD98059, a MEK inhibitor, and greatly attenuated by apigenin, an inhibitor of the Ras --> Raf --> MEK --> ERK pathway. The effect also appears to be mediated by CDK4. Immunoprecipitation/immunoblot studies revealed that serotonin and angiotensin II induced complex formation between CDK4, cyclin D1, and phosphorylated ERK. These studies show a rapid, novel, and selective phosphorylation of Rb Ser(795) by mitogens and demonstrate an unexpected rapid linkage between the actions of the Ras --> Raf --> MEK --> ERK pathway and the phosphorylation state of Rb.

ERK Is Regulated by Sodium-Proton Exchanger in Rat Aortic Vascular Smooth Muscle Cells

The purposes of this study were to test 1) the relationship between two widely studied mitogenic effector pathways, and 2) the hypothesis that sodium-proton exchanger type 1 (NHE-1) is a regulator of extracellular signal-regulated protein kinase (ERK) activation in rat aortic smooth muscle (RASM) cells. Angiotensin II (Ang II) and 5-hydroxytryptamine (5-HT) stimulated both ERK and NHE-1 activities, with activation of NHE-1 preceding that of ERK. The concentration-response curves for 5-HT and Ang II were superimposable for both processes. Inhibition of NHE-1 with pharmacological agents or by isotonic replacement of sodium in the perfusate with choline or tetramethylammonium greatly attenuated ERK activation by 5-HT or Ang II. Similar maneuvers significantly attenuated 5-HT- or Ang II-mediated activation of MEK and Ras but not transphosphorylation of the epidermal growth factor (EGF) receptor. EGF receptor blockade attenuated ERK activation, but not NHE-1 activation by 5-HT and Ang II, suggesting that the EGF receptor and NHE-1 work in parallel to stimulate ERK activity in RASM cells, converging distal to the EGF receptor but at or above the level of Ras in the Ras-MEK-ERK pathway. Receptor-independent activation of NHE-1 by acute acid loading of RASM cells resulted in the rapid phosphorylation of ERK, which could be blocked by pharmacological inhibitors of NHE-1 or by isotonic replacement of sodium, closely linking the proton transport function of NHE-1 to ERK activation. These studies identify NHE as a new regulator of ERK activity in RASM cells.

Hemodynamic effects of chronic hemodialysis therapy assessed by pulse waveform analysis

Cardiovascular responses to hemodialysis have been characterized by invasive monitoring techniques. These techniques are not feasible for evaluation of hemodynamic status during dialysis in the outpatient setting. In this study, we used pulse waveform analysis (PWA), a noninvasive tool designed for the ambulatory setting, to assess hemodynamic responses of dialysis treatments in 27 stable subjects with end-stage renal disease receiving chronic hemodialysis. In our population, systolic, diastolic, and pulse pressures were unaffected by dialysis despite the mean fluid removal of 3.0 +/- 0.2 kg. However, using PWA, we observed that stroke volume and cardiac output progressively declined by 17% to 19% (P <.001) with a concomitant increase in systemic vascular resistance by 22% from 1654 +/- 88 to 2020 +/- 121 dynes. sec. cm(-5) (P <.001). Also, we observed a significant reduction in small artery compliance from 4.7 +/- 0.5 to 3.3 +/- 0.4 mL. mm Hg(-1). 100 (P =.01), whereas large artery elasticity was unaffected. These findings suggest that changes in small artery vascular compliance contribute to the elevation in systemic vascular resistance during dialysis. This study confirms that hemodynamic adaptations to the dialysis procedure can be detected using PWA and are consistent with data obtained by invasive monitoring techniques. Furthermore, the observed reduction in vascular compliance in response to dialysis may contribute to the high cardiovascular risk in patients undergoing chronic hemodialysis therapy.

Mitogen-induced activation of Na+/H+ exchange in vascular smooth muscle cells involves janus kinase 2 and Ca2+/calmodulin

The sodium/proton exchanger type 1 (NHE-1) plays an important role in the proliferation of vascular smooth muscle cells (VSMC). We have examined the regulation of NHE-1 by two potent mitogens, serotonin (5-HT, 5-hydroxytryptamine) and angiotensin II (Ang II), in cultured VSMC derived from rat aorta. 5-HT and Ang II rapidly activated NHE-1 via their G protein-coupled receptors (5-HT(2A) and AT(1)) as assessed by proton microphysiometry of quiescent cells and by measurements of intracellular pH on a FLIPR (fluorometric imaging plate reader). Activation of NHE-1 was blocked by inhibitors of phospholipase C, CaM, and Jak2 but not by pertussis toxin or inhibitors of protein kinase C. Immunoprecipitation/immunoblot studies showed that 5-HT and Ang II induce phosphorylation of Jak2 and induce the formation of signal transduction complexes that included Jak2, CaM, and NHE-1. The cell-permeable Ca(2+) chelator BAPTA-AM blocked activation of Jak2, complex formation between Jak2 and CaM, and tyrosine phosphorylation of CaM, demonstrating that elevated intracellular Ca(2+) is essential for those events. Thus, mitogen-induced activation of NHE-1 in VSMC is dependent upon elevated intracellular Ca(2+) and is mediated by the Jak2-dependent tyrosine phosphorylation of CaM and subsequent increased binding of CaM to NHE-1, similar to the pathway previously described for the bradykinin B(2) receptor in inner medullary collecting duct cells of the kidney [Mukhin, Y. V., et al. (2001) J. Biol. Chem. 276, 17339-17346]. We propose that this pathway represents a fundamental mechanism for the rapid regulation of NHE-1 by G(q/11) protein-coupled receptors in multiple cell types.

Bradykinin B2 receptor activates extracellular signal-regulated protein kinase in mIMCD-3 cells via epidermal growth factor receptor transactivation

Bradykinin (BK) has been implicated in the regulation of renal function. Activation of extracellular signal-regulated protein kinase (ERK1/2) has been demonstrated in several models of toxic or proliferative renal injury. We studied activation of ERK1/2 by BK in a cell model of the most distal part of the nephron, inner medullary collecting duct (mIMCD-3) cells. Exposure of mIMCD-3 cells to BK (10(-10)-10(-5) M) resulted in a concentration-dependent increase in tyrosine phosphorylation of ERK1/2, with maximal effect at 10(-8) M BK. ERK1/2 activation by BK was observed as early as 1 min, peaked at 5 min, and was sustained at least for 1 h. The effect of BK was mediated by the B(2) receptor and was pertussis toxin-independent. Inhibition of phospholipase C, protein kinase C, or phosphatidylinositol 3-kinase did not alter ERK1/2 activation by BK. BK-induced ERK1/2 activation was Ca(2+)-calmodulin-independent but was sensitive to genistein, an inhibitor of tyrosine kinase(s). AG1478, a specific inhibitor of epidermal growth factor receptor (EGFR) kinase, completely blocked the effect of BK, suggesting an essential role of EGFR in ERK1/2 activation by BK. Immunoprecipitation/Western blot studies revealed that BK stimulated tyrosine phosphorylation of EGFR, its association with an adapter molecule Grb2, and complex formation between Grb2 and the adapter protein Shc. Activation studies of monomeric G protein Ras showed that BK-induced stimulation of Ras was dependent on EGFR tyrosine kinase activity. These studies demonstrate that BK stimulates Ras-dependent activation of ERK1/2 in mIMCD-3 cells via transactivation of EGFR through a novel mechanism.

Potential importance of glomerular citrate synthase activity in remnant nephropathy

BACKGROUND

Aldosterone fosters progressive renal injury, but the mechanism is unknown. Both Wistar-Furth rats, which are resistant to aldosterone actions, and adrenalectomized Sprague-Dawley rats, which lack aldosterone, are characterized by resistance to remnant nephropathy and by reduced whole kidney citrate synthase activity. Increase in citrate synthase activity is a well-characterized, specific renal response to aldosterone. Therefore, we performed experiments to test the hypothesis that enhanced citrate synthase activity contributes to remnant nephropathy.

METHODS

Rat models included Wistar (control for Wistar-Furth), Wistar-Furth (resistant to aldosterone), Sprague-Dawley (normal), adrenalectomy (lacking aldosterone), and 5/6 nephrectomy (renal injury). Glomeruli were obtained by differential sieving. Citrate synthase activity was determined spectrophotometrically. Binding characteristics of cytosolic mineralocorticoid receptors were determined by equilibrium competition binding between tritiated and unlabeled aldosterone. Gene sequencing was performed with reverse transcription-polymerase chain reaction (RT-PCR) and fluorescent dye terminators.

RESULTS

In glomeruli isolated from adrenalectomized Wistar rats with intact renal mass, aldosterone stimulated a threefold increase in citrate synthase activity; this stimulation was not observed in glomeruli from Wistar-Furth rats. Similarly, citrate synthase activity in glomeruli isolated from adrenally intact Sprague-Dawley rats was 65% greater than that from adrenalectomized Sprague-Dawley rats. Compared to sham surgery, subtotal nephrectomy resulted in 100% greater glomerular citrate synthase activity in Sprague-Dawley rats. In Wistar-Furth rats, mineralocorticoid receptor binding was not reduced, and mutations in the mineralocorticoid receptor DNA binding segment were not found.

CONCLUSION

Citrate synthase activity is elevated in remnant glomeruli, and experimental models characterized by reduced glomerular citrate synthase activity (Wistar-Furth rats, adrenalectomized Sprague-Dawley rats) are protected from remnant nephropathy.

L-carnitine administration reverses acute mental status changes in a chronic hemodialysis patient with hepatitis C infection

A chronic hemodialysis patient presented with elevated serum ammonia concentration (189 micromol/l) and acutely altered mental status. He had been adequately dialyzed over the prior months and had no evidence of liver dysfunction, despite serological evidence for hepatitis C virus infection. His mental status deteriorated to coma despite vitamin replenishment, intensive hemodialysis, lactulose treatment, and blood pressure control over a 3-day period. Blood free L-carnitine concentration was depressed, and total carnitine concentrations was normal. Three hours after a single 2 g dose of L-carnitine was administered intravenously, the mental status reverted to normal. Hyperammonemia resolved over a 5-week period. We suspect that subclinical liver dysfunction and dialysis status in tandem contributed to the carnitine deficiency, hyperammonemia, and confusion and that the L-carnitine administration reversed these biochemical and clinical abnormalities.

A functional angiotensin II receptor-GFP fusion protein: evidence for agonist-dependent nuclear translocation

We constructed an expression vector for a fusion protein [ANG II type 1a receptor-green fluorescent protein (AT(1a)R-GFP)] consisting of enhanced GFP attached to the COOH terminus of the rat AT(1a)R. Chinese hamster ovary (CHO) cells transfected with AT(1a)R-GFP demonstrated specific, high-affinity (125)I-labeled ANG II binding (IC(50) 21 nM). ANG II exposure stimulated sodium-proton exchange and cytoplasmic calcium release to a similar extent in cells transfected with AT(1a)R or AT(1a)R-GFP; these responses were desensitized by prior exposure to ANG II and were sensitive to the AT(1)R blocker losartan. ANG II-driven internalization of AT(1a)R-GFP in transfected CHO cells was demonstrated both by radioligand binding and by laser scanning confocal microscopy. Colocalization of GFP fluorescence with that of the nuclear stain TOTO-3 in confocal images was increased more than twofold after 1 h of ANG II exposure. We conclude that AT(1a)R-GFP exhibits similar pharmacological behavior to that of the native AT(1a)R. Our observations also support previous evidence for the presence of AT(1a)R in the nucleus and suggest that the density of AT(1a)R in the nucleus may be regulated by exposure to its ligand.

Role of citrate synthase in aldosterone-mediated sodium reabsorption

Aldosterone and other mineralocorticoids increase citrate synthase activity in the kidney and enhance renal sodium reabsorption, but it is unclear whether the increased citrate synthase activity is involved in renal sodium transport. We used the Wistar-Furth rat, an inbred strain found to be deficient in renal citrate synthase activity, as an experimental model to investigate this issue. We confirmed that renal citrate synthase activity from adrenalectomized Wistar-Furth rats was decreased compared with that from control Wistar rats (by 28%). Similarly, urinary citrate excretion was 23% lower in Wistar-Furth rats. Subnormal citrate formation in Wistar-Furth rats could not be accounted for by differences in systemic pH or circulating potassium levels. Because renal citrate synthase activity was reduced in Wistar-Furth rats, we hypothesized that renal sodium excretory responses to mineralocorticoids would be reduced as well. Four-hour sodium excretion after intraperitoneal injection of 5 microg of aldosterone was reduced by 56% in adrenalectomized Wistar rats and by 52% in adrenalectomized Wistar-Furth rats (both P<0.01 compared with vehicle injection). Similarly, the pattern of urinary sodium excretion in response to subcutaneous injections of deoxycorticosterone acetate over a 2-week period was similar in adrenalectomized Wistar and Wistar-Furth rats. In summary, acute and chronic antinatriuretic responses to mineralocorticoids are maintained in Wistar-Furth rats at the level of Wistar rats, despite the marked reduction in citrate synthase activity. These findings are not consistent with an important role for citrate synthase activity in mineralocorticoid-mediated renal sodium transport.

Mechanisms of MAPK activation by bradykinin in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation is a prominent feature of the atherosclerotic process occurring after endothelial injury. A vascular wall kallikrein-kinin system has been described. The contribution of this system to vascular disease is undefined. In the present study we characterized the signal transduction pathway leading to mitogen-activated protein kinase (MAPK) activation in response to bradykinin (BK) in VSMC. Addition of 10(-10)-10(-7) M BK to VSMC resulted in a rapid and concentration-dependent increase in tyrosine phosphorylation of several 144- to 40-kDa proteins. This effect of BK was abolished by the B(2)-kinin receptor antagonist HOE-140, but not by the B(1)-kinin receptor antagonist des-Arg(9)-Leu(8)-BK. Immunoprecipitation with anti-phosphotyrosine antibodies followed by immunoblot revealed that 10(-9) M BK induced tyrosine phosphorylation of focal adhesion kinase (p125(FAK)). BK (10(-8) M) promoted the association of p60(src) with the adapter protein growth factor receptor binding protein-2 and also induced a significant increase in MAPK activity. Pertussis and cholera toxins did not inhibit BK-induced MAPK tyrosine phosphorylation. Protein kinase C downregulation by phorbol 12-myristate 13-acetate and/or inhibitors to protein kinase C, p60(src) kinase, and MAPK kinase inhibited BK-induced MAPK tyrosine phosphorylation. These findings provide evidence that activation of the B(2)-kinin receptor in VSMC leads to generation of multiple second messengers that converge to activate MAPK. The activation of this crucial kinase by BK provides a strong rationale to investigate the mitogenic actions of BK on VSMC proliferation in disease states of vascular injury.

A protocol-based treatment for intradialytic hypotension in hospitalized hemodialysis patients

Human serum albumin is used in hemodialysis (HD) units as treatment for hypotension despite its high cost and undetermined efficacy. During a 4-month period in 1995, albumin was used in 22% of 1,296 consecutive HD treatments in the HD unit or intensive care units (ICUs) at our tertiary-care hospital. We evaluated the safety and efficacy of a protocol designed to minimize albumin use for treating HD-associated hypotension (HDAH). The protocol consisted of the stepwise use of saline, mannitol, and albumin for the purpose of achieving physician-determined ultrafiltration goals. Patients were exempted from receiving the protocol for age younger than 18 years, freshly declotted angioaccess, or cardiovascular instability. The protocol was evaluated prospectively in 2,559 consecutive dialysis sessions (15% in ICUs) in 442 patients. Hypotension occurred during 608 sessions (24%), and attending nephrologists elected to initiate the protocol in 71% of these cases. Of the 433 instances in which the protocol was begun, reversal of hypotension was achieved without the need for albumin in 91% and with the addition of albumin in an additional 2%. Protocol treatment was not completed because of nursing error in 1% or clotting of filter or angioaccess in 4%. Use of the protocol failed to reverse hypotension in only 2% of the cases in which it was completed. Albumin was administered in only 6% of the 2,559 HD treatments. In summary, our protocol-based approach to HDAH was effective, easy for nurses to use, albumin sparing, and cost reducing.

Resistance to remnant nephropathy in the Wistar-Furth rat

The Wistar-Furth rat, an inbred strain resistant to actions of mineralocorticoids, was used to study the concept that mineralocorticoids contribute to progressive renal injury. It was postulated that if chronic nephropathy depends on aldosterone and if Wistar-Furth rats are resistant to aldosterone, remnant nephropathy would be attenuated in Wistar-Furth rats. Wistar-Furth rats and control Wistar rats were subjected to 5/6 nephrectomy or a sham procedure and then followed for 4 wk. Renal ablation resulted in hypertension at 4 wk in both strains (164+/-5 [Wistar-Furth] versus 184+/-7 [Wistar] mm Hg mean arterial pressure), with sham animals remaining normotensive (134+/-6 mm Hg). Renal damage in response to 5/6 nephrectomy was greatly decreased in Wistar-Furth rats compared with Wistar rats. Albuminuria was markedly less in Wistar-Furth rats (12.7+/-4.2 [Wistar-Furth] versus 97.4+/-22.6 [Wistar] mg/d per 100 g body wt, P<0.01). Glomerular damage, consisting of mesangial proliferation, mesangial lysis, and segmental necrosis, was observed in 42% of glomeruli from Wistar rats but in 0% of glomeruli from Wistar-Furth rats (P<0.01). To address the possibility that higher BP in partially nephrectomized Wistar rats mediated the greater renal damage, the study was repeated, with Wistar rats (not Wistar-Furth rats) being treated with a hydralazine-reserpine-hydrochlorothiazide regimen. Although this antihypertensive regimen equalized BP (conscious systolic) (144+/-8 mm Hg [Wistar] versus 157+/-7 mm Hg [Wistar-Furth] at 4 wk), albuminuria remained more than 10-fold greater in Wistar rats. In summary, renal damage upon 5/6 nephrectomy was markedly reduced in Wistar-Furth rats, a finding not attributable to reduced systemic BP. Since Wistar-Furth rats have been shown previously to be resistant to the actions of mineralocorticoids, the data from the present study support the hypothesis that aldosterone mediates, at least in part, the renal injury attendant to renal mass reduction.

Expression, characterization, and purification of C-terminally hexahistidine-tagged thromboxane A2 receptors

Thromboxane A2 (TxA2) receptors belong to the class of G-protein-coupled receptors. Knowledge of the relationship of structure to function for TxA2 receptors is limited because of their low levels of expression, lengthy purification procedures and poor recoveries. A C-terminal hexahistidine-tag (C-His) was ligated to the alpha-isoform of TxA2 receptors and expressed in COS-7 and Chinese hamster ovary cells. The C-His-TxA2 receptors bound the radioligands 125I-7-[(1R,2S,3S,5R)-6, 6-dimethyl-3-(4-benzenesulfonylamino)bicyclo[3.1. 1]hept-2-yl]-5(Z)-heptenoic acid, an antagonist, and 125I-[1S-1alpha, 2beta(5Z),3alpha(1E,3S*), 4alpha]-7-[3[(3-hydroxy-4-(4'-phenoxy)-1butenyl)-7-oxabicycl o-[2.2. 1]heptan-2-yl]-5-heptanoic acid, an agonist, with affinities not significantly different from those of the wild type (wt)-TxA2 receptors. LipofectAMINE transfection of the cDNAs resulted in high levels of expression (Bmax = 95 +/- 6 pmol/mg) of the C-His-TxA2 receptors. In competition binding studies the IC50 values of five different ligands were not significantly different between C-His-TxA2 and wt-TxA2 receptors. Agonist-induced stimulation of cAMP and total inositol phosphate formation were not significantly different between the two receptors. Purification on a Ni2+-NTA column resulted in a rapid (within 4 h) purification with a 36 +/- 2% recovery and a 30 +/- 6-fold purification (n = 5). The partially purified receptors were resolved on SDS-polyacrylamide gel electrophoresis, transferred to a nitrocellulose membrane, dissolved in acetone/trifluoroacetic acid/hexafluoroisopropanol/sinapinic acid, and successfully subjected to matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis. The results suggest that the combination of a high level of expression of C-His-TxA2 receptors and a rapid purification procedure followed by SDS- polyacrylamide gel electrophoresis may provide a useful approach for mass-spectrometry based structure-function and other studies of TxA2 receptors.

Regulation of vascular angiotensin II receptors by EGF

After vascular endothelial injury, angiotensin II (ANG II) plays a role in the resulting hypertrophic response, and expression of epidermal growth factor (EGF) is enhanced. Therefore, we tested the possibility that EGF regulates vascular ANG II action and receptor expression. Incubation of cultured aortic vascular smooth muscle cells (VSMC) with EGF (or basic fibroblast growth factor but not platelet-derived growth factor isoforms) resulted in concentration-dependent (1-50 ng/ml EGF), time-dependent (>8 h), and reversible decreases in ANG II surface receptor density. For example, a 50% reduction was observed after exposure to 50 ng/ml EGF for 24 h. Incubation of cultured VSMC with 50 ng/ml EGF for 24 h resulted in a 77% reduction in ANG II-stimulated inositol phosphate formation. EGF not only prevented but also reversed ANG II receptor upregulation by 100 nM corticosterone. The specific tyrosine kinase inhibitor tyrphostin A48 (50 microM) reduced EGF-stimulated thymidine incorporation and EGF-stimulated phosphorylation of mitogen-activated protein kinase but did not prevent EGF from reducing ANG II receptor density. Neither pertussis toxin (100 ng/ml) nor downregulation of protein kinase C by phorbol myristate acetate (100 nM for 24 h) prevented EGF from reducing ANG II receptor density. In summary, EGF is a potent negative regulator of vascular ANG II surface receptor density and ANG II action by mechanisms that do not appear to include tyrosine phorphorylation, pertussis toxin-sensitive G proteins, or phorbol ester-sensitive protein kinase C. The possibility that EGF shifts the cell culture phenotype to one that exhibits reduced surface ANG II density cannot be eliminated by the present studies.

Tyrosine phosphorylation of phosphatidylinositol 3-kinase and of the thromboxane A2 (TXA2) receptor by the TXA2 mimetic I-BOP in A7r5 cells

Thromboxane A2 (TXA2) interacts with its G-protein coupled receptor, the TP receptor, to produce contraction and proliferation of vascular smooth muscle cells. We have shown previously that proliferation of primary cultures of vascular smooth muscle cells initiated by [1S-(1alpha, 2beta(5Z), 3alpha(1E, 3R), 4alpha]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxab icyclo-[2.2.1]heptan-2yl]-5'-heptenoic acid (I-BOP), a stable TXA2 mimetic, is mediated by activation of mitogen-activated protein (MAP) kinase. In the present study, we examined further the intracellular mediators involved in TXA2 activation of vascular smooth muscle cells. Transient transfection of the cDNA for the TP receptor into A7r5 vascular smooth muscle cells resulted in expression of TP receptors with a receptor density, Bmax, of 0.7 +/- 0.2 pmol/mg protein and a receptor affinity, Kd, of 0.6 +/- 0.1 nM (N = 7). Mock transfected cells lacked significant receptor expression. In TP receptor transfected cells, I-BOP increased the activation of MAP kinase 2-fold, stimulated tyrosine phosphorylation of cellular proteins of relative molecular mass (Mr) of 140, 85, 60, 56, and 45 kDa, and increased the message for c-jun, a nuclear transcription factor involved in mitogenesis, 2.6-fold. Immunoblot analysis indicated that the 85-kDa protein represented phosphoinositide 3-kinase (PI3-K), while the 60 kDa protein was the TP receptor. The activity of PI3-K was increased 3.5-fold by the addition of I-BOP (0.1 microM). In summary, the present study demonstrated that stimulation of the TP receptor results in tyrosine phosphorylation of the receptor and of PI3-K.

Resistance to mineralocorticoids in Wistar-Furth rats

Wistar-Furth rats (WF) do not develop hypertension when treated with salt and mineralocorticoids and therefore may be useful for investigating the mechanisms of mineralocorticoid action and hypertension. In the present studies, we determined vascular and renal responses of WF to mineralocorticoids. Control Wistar rats (W) developed deoxycorticosterone acetate (DOCA)-NaCl and dexamethasone hypertension, whereas WF rats developed dexamethasone hypertension only. Aldosterone treatment of vascular smooth muscle cells cultured from WF resulted in 82% less upregulation of angiotensin II radioligand binding, 50% less induction of angiotensin II AT1a receptor mRNA, and 76% less potentiation of angiotensin II-stimulated inositol phosphates than did aldosterone treatment of cells from W. Similarly, DOCA-NaCl potentiated angiotensin II- and phenylephrine-stimulated contractions in aortic rings from W but not from WF. Although DOCA-NaCl treatment affected hypokalemia to an equal degree in WF and W, increases in renal citrate synthase activity (a specific renal mineralocorticoid response) were greater in W than in WF. WF manifest a partial defect in mineralocorticoid responsiveness in vascular smooth muscle and, possibly, in the kidney.

Potentiation of angiotensin II action by corticosteroids in vascular tissue

OBJECTIVES

Studies were performed to determine if corticosteroids act directly on the vasculature to potentiate the vasoconstrictor action of angiotensin II and to determine whether corticosteroids upregulate angiotensin II receptors by receptor redistribution or by synthesis of new receptors.

METHODS

Aortic rings from normal Sprague-Dawley rats were incubated ex vivo with corticosteroids in aerated Krebs-Henseleit buffer to avoid secondary systemic effects prior to stimulated contraction. In cultured vascular smooth muscle cells, these experimental techniques were used: colchicine (blocker of microtubule assembly), chloroquine (inhibitor of endosomal pH gradients), measuring surface-bound 125I-Ang II internalization rate, immunoblotting of angiotensin AT1 receptor protein, and incorporation of [35S]methionine into AT1 receptor protein.

RESULTS

Contractions to 100 nM angiotensin II in rings incubated with 1 microM aldosterone or dexamethasone for 10 min ex vivo were not different from contractions in control rings. However, angiotensin II-stimulated (but not KCl-stimulated) contractions were enhanced by almost 100% if ex vivo incubation with aldosterone (or corticosterone) lasted for 24 h. Endothelium-dependent relaxation was not significantly reduced by aldosterone pre-incubation. Incubation of cultured vascular smooth muscle cells with a number of corticosteroids for > 8 h resulted in concentration-dependent upregulation of angiotensin II receptor binding and was reversible upon removal of the corticosteroid. Aldosterone did not affect the rate of internalization of surface-bound angiotensin II. In addition, concomitant incubation of colchicine or chloroquine with aldosterone did not hamper angiotensin II receptor upregulation. Incubation of cells with various concentrations of aldosterone for 24 h resulted in concentration-dependent increases in total cell angiotensin II receptor protein content and increases in [35S]methionine incorporation into immunoprecipitated AT1 receptor protein.

CONCLUSIONS

At least a portion of the enhancement of angiotensin II action by corticosteroids is via direct interaction of corticosteroids with the vasculature. Corticosteroids appear to upregulate angiotensin II receptors by synthesis of new receptor protein rather than by alterations in receptor trafficking.

Carbenoxolone damages endothelium and enhances vasoconstrictor action in aortic rings

Carbenoxolone causes hypertension indirectly by inhibition of 11beta-hydroxysteroid dehydrogenase and consequent elevation of intracellular glucocorticoid levels and enhancement of vasoconstrictor action. We performed the present study to determine whether carbenoxolone also enhances vascular tone directly by mechanisms independent of glucocorticoids and other systemic influences. Exposure of rat aortic rings to 10 to 100 micromol/L carbenoxolone in aerated Krebs-Henseleit buffer for 24 hours resulted in concentration-dependent increases in angiotensin II (Ang II) (100 nmol/L)-stimulated contractions and significant shifting of the phenylephrine cumulative contraction curve to the left but not increases in KCI (120 mmol/L)-stimulated contractions. Maximal enhancement of Ang II contraction was 39 percent. In contrast, brief (15-minute) exposure to 100 micromol/L carbenoxolone did not alter Ang II contractions. Mechanical denudation of the endothelium obviated enhancement of Ang II contractions by carbenoxolone, suggesting interaction of carbenoxolone with the endothelium. Endothelium-dependent relaxation of precontracted rings to acetylcholine or ATP was reduced by more than 90 percent by 24-hour pretreatment with 100 micromol/L carbenoxolone but not with 100 micromol/L deoxycorticosterone acetate (a mineralocorticoid) or 100 mu mol/L glycyrrhizic acid (a natural 11beta-hydroxysteroid dehydrogenase inhibitor). Vascular smooth muscle relaxation with sodium nitroprusside was not inhibited by carbenoxolone. Incubation of cultured endothelial cells with 100 mu mol/L carbenoxolone for 24 hours did not inhibit nitric oxide synthase activity, as measured by conversion of [3H]L-arginine to [3H]L-citrulline. Electron micrography demonstrated that endothelial cell ultrastructure but not vascular smooth muscle cell ultrastructure was abnormal after incubation of rings for 24 hours with 100 micromol/L carbenoxolone. These studies suggest that carbenoxolone concentrations higher than 10 micromol/L enhance vasoconstrictor action via selective toxicity to the endothelium and elimination of endothelium-dependent relaxation.

Rusty peritoneal dialysis fluid after intravenous administration of iron dextran

Rusty-colored peritoneal dialysate fluid was observed after intravenous administration of iron dextran to a patient with peritonitis being treated with vancomycin and rifampicin. The discoloration gradually cleared over a 24-hour period. Analysis of the fluid demonstrated that the discoloration could not be explained by the presence of erythrocytes or free hemoglobin. Iron (52 micrograms/dL) was detected in the fluid and decreased to undetectable levels as the discoloration cleared. Addition of iron dextran to an unused bag of peritoneal dialysis fluid to achieve an iron concentration of 52 micrograms/dL resulted in no discoloration. Addition of rifampicin at a clinically relevant serum concentration (10 micrograms/dL) to a different unused bag caused a light orange discoloration. Addition of iron dextran and rifampicin simultaneously in the concentrations mentioned to an unused bag caused a rusty discoloration almost as dark as that observed in our patient. We postulate, therefore, that a combination of iron and rifampicin caused the marked discoloration of our patient's peritoneal effluent.

Oleic acid inhibits endothelial nitric oxide synthase by a protein kinase C-independent mechanism

Many obese hypertensive individuals have a cluster of cardiovascular risk factors. This cluster includes plasma nonesterified fatty acid concentrations and turnover rates that are higher and more resistant to suppression by insulin than in lean and obese normotensive individuals. The higher fatty acids may contribute to cardiovascular risk in these patients by inhibiting endothelial cell nitric oxide synthase activity. To test this hypothesis, we quantified the effects of oleic (18:1[cis]) and other 18-carbon fatty acids on nitric oxide synthase activity in cultured bovine pulmonary artery endothelial cells by measuring the conversion of [3H]L-arginine to [3H]L-citrulline. Oleic acid (from 10 to 100 mumol/L) caused a concentration-dependent decrease in nitric oxide synthase activity at baseline and during ATP and ionomycin (Ca2+ ionophore) stimulation. At 100 mumol/L, linoleic (18:2[cis]) and oleic acids caused similar reductions of nitric oxide synthase activity, whereas elaidic (18:1[trans]) and stearic (18:0) acids had no effect. Oleic acid also inhibited the endothelium-dependent vasodilator response to acetylcholine in rabbit femoral artery rings preconstricted with phenylephrine (P < .05) but had no effect on the response to nitroprusside. The pattern of 18-carbon fatty acid effects on nitric oxide synthase activity in endothelial cells is consistent with activation of protein kinase C. Although oleic acid increased protein kinase C activity in endothelial cells, neither depletion of protein kinase C by 24-hour pretreatment with phorbol 12-myristate 13-acetate nor its inhibition with staurosporine eliminated the inhibitory effect of oleic acid on nitric oxide synthase.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticosterone metabolism and effects on angiotensin II receptors in vascular smooth muscle

It has been postulated that mineralocorticoids can bind to corticosteroid receptors in the kidney, because glucocorticoids are metabolized to inactive compounds. The present study was performed to delineate glucocorticoid metabolism by rat vascular tissue and to determine the activity of these metabolites. Vascular segments converted 25% to 30% of corticosterone (compound B), the major glucocorticoid in the rat, to 11-dehydrocorticosterone (compound A) but not to aldosterone or 6 beta-hydroxycorticosterone. In cultured vascular smooth muscle cells, 10% of compound B was converted to compound A, whereas > 60% of compound A was converted to compound B. The 11 beta-hydroxysteroid dehydrogenase inhibitor carbenoxolone (1 mumol/L) completely blocked conversion in both directions. Whereas 6 beta-hydroxycorticosterone did not upregulate angiotensin II receptor binding (a marker for corticosteroid action in vascular smooth muscle), compound A caused concentration-dependent upregulation. Compound A was almost (75%) as effective and as potent as compound B in upregulating angiotensin II binding. Upregulation elicited by exposure to compound A persisted in the presence of 1 mumol/L carbenoxolone, which completely prevented the conversion of compound A to compound B. Compound A, even in the presence of carbenoxolone, effected other glucocorticoid actions by inhibiting cell growth and potentiating angiotensin II-stimulated inositol phosphate formation. In summary, compound B and compound A are interconverted in vascular tissue, and the latter displays significant glucocorticoid action. The concentration excess of compound B in the circulation and the activity of its metabolite compound A will make it difficult for mineralocorticoids to gain access to corticosteroid receptors in the vasculature.

Potentiation of angiotensin II-stimulated vascular contraction by lithium

Previous studies have suggested that lithium prolongs or enhances vascular contractions stimulated by alpha-adrenergic agents. The present study was performed to determine whether a similar phenomenon occurs with angiotensin II (ANG II)-stimulated contractions and whether this phenomenon results from interactions with the phosphoinositide signaling system. Contractions of rat aortic rings with 100 nM ANG II were 38% greater in the presence of 20 mM LiCl than in its absence (0.47 +/- 0.07 vs. 0.34 +/- 0.05 g tension/mg dry tissue wt, P < 0.01). The effects of lithium on inositol phosphate responses, diacylglycerol responses, and intracellular calcium concentration on single or repeated stimulations with ANG II were then examined in vascular smooth muscle cells cultured from rat aorta. Cells exposed twice to 100 nM ANG II contained 50% lower inositol trisphosphate levels (InsP3) and 10% lower diacylglycerol levels than cells exposed to ANG II only once. LiCl or lithium acetate abolished these desensitizations in a concentration-dependent manner. Similarly, InsP3 and diacylglycerol responses to a single exposure of ANG II were heightened by lithium (by 75 and 25%, respectively), and the duration of the responses was prolonged by lithium (5- and 2-fold, respectively). In contrast, ANG II-stimulated calcium transients were not enhanced or prolonged by lithium, nor was desensitization of ANG II-stimulated cytosolic calcium mobilization upon serial exposures abolished by lithium. When ring contraction studies were repeated in the presence of the protein kinase C inhibitor staurosporine (150 nM), lithium no longer potentiated ANG II contractions [0.38 +/- 0.03 (control) vs. 0.35 +/- 0.06 g tension/mg dry tissue wt (lithium)].(ABSTRACT TRUNCATED AT 250 WORDS)

Sex steroid regulation of thromboxane A2 receptors in cultured rat aortic smooth muscle cells

Thromboxane A2 (TXA2) has been implicated as an important mediator of cardiovascular diseases, and male rat aortas are reported to be more sensitive to it than female aortas. The effects of sex steroids to regulate the expression of TXA2 receptors in cultured male rat aortic smooth muscle cells (RASMC) were determined. TXA2 receptor density (Bmax) and affinity (Kd) were determined via radioligand binding studies with [125I]BOP, a TXA2 receptor agonist. Testosterone increased Bmax in a concentration-dependent manner without any significant change in Kd. Cycloheximide, actinomycin D, and the 5 alpha-reductase inhibitor L645,390 significantly (P < 0.01) blocked the effect of testosterone. Dihydrotestosterone, the active metabolite of testosterone, increased Bmax and was more potent than testosterone. To determine if there is a sex-related difference in response to testosterone, its effect in cultured female RASMC was assessed. Testosterone increased Bmax in female RASMC but the increase was significantly (P < 0.001) less than that seen in male RASMC. These results indicate that androgenic steroids regulate the expression of vascular TXA2 receptors.