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Biomedical subjects

S K Mujais

Publications and source records attributed to S K Mujais.

At least 19 recordsLinked to original sources
PubMed1999

Erythropoietin is produced by tubular cells of the rat kidney.

The cellular site of erythropoietin (epo) production within the mammalian kidney is still not completely understood. In the present study, we examined the expression of epo mRNA in microdissected rat nephron segments by RT-PCR after induction of epo expression with cobalt chloride. Erythropoietin mRNA was not detected in nephron segments from saline injected rats. In cobalt chloride injected animals, epo mRNA was found in the majority of samples from the cortical region of the nephron, PCT, and CAL. Medullary tubule preparations (MCT and MAL) were mostly negative for epo mRNA, and glomeruli were uniformly negative. The induction of epo transcripts in tubular cells by cobalt chloride was paralleled by stimulation of the major transport enzyme in the kidney, namely, Na-K ATPase in a tubular profile similar to that of induction of epo transcripts. These results support some earlier findings that epo gene expression in response to cobalt salt stimulation of rat kidney occurs in transporting tubular epithelial cells.

Adenosine Triphosphatases↗
PubMed1999

Platelet-leukocyte aggregates during hemodialysis: effect of membrane type.

Hemodialysis is associated with the formation of platelet-leukocyte aggregates. Whether this phenomenon is hemodialysis (HD) membrane dependent is unclear. To evaluate this process, we examined respectively platelet activation (anti-CD41, anti-CD62, and antifibrinogen monoclonal antibodies [MoAb] binding), leukocyte activation (CD11b expression), and the appearance of platelet specific antigens on leukocytes as an index of platelet-leukocyte aggregation during HD using 3 different membrane materials, Cuprophan, Hemophan, and polysulfone. Flow cytometric techniques and specific MoAb were used. All parameters were assayed 5 min after initiation of HD to avoid the confounding variable of leukopenia and resultant cell subpopulation analysis. Platelet activation (anti-CD62 and antifibrinogen binding) occurred only with Cuprophan. All 3 membranes induced equivalent increases in CD11b expression on neutrophils and similarly increased the binding of anti-CD41 to neutrophils, reflecting an increment in the formation of platelet neutrophil aggregates. However, only Cuprophan induced an increase in anti-CD62 binding to neutrophils, suggesting that the aggregated platelets linked to neutrophils were activated. Increased anti-CD41 binding by monocytes was similarly observed with all 3 membranes. However, only polysulfone induced an increase in CD11b expression and fibrinogen binding to monocytes. We conclude that while the formation of platelet leukocyte aggregates appears to be a universal phenomenon in HD occurring with a variety of membrane types, subtypes of this phenomenon consisting of activated platelets and fibrinogen binding may be membrane dependent. This phenomenon may serve as a new biocompatibility parameter and may shed light on some of the biologic consequences of hemodialysis.

Antibodies, Monoclonal↗
PubMed1999

Evaluation of urea kinetics utilizing stable isotope urea and pharmacokinetic modeling.

The determination of urea kinetics plays a central role in clinical dialysis prescription. There persist, however, significant limitations to current approaches, particularly as they pertain to rigorous explorations of urea metabolism, distribution, and removal. This report describes methodologies designed to address these limitations by coupling a stable nitrogen isotope method with strict compartmental pharmacokinetic modeling. The findings of the present study can be summarized as follows. First, the use of stable isotope labeled exogenous urea is a reliable clinically applicable method for determination of urea kinetics. Second, this method offers significant advantages in that it allows for an accurate measurement of urea distribution space, endogenous urea production, and non-renal clearance of urea. Third, this method is significantly more rigorous than urea kinetic models that utilize only endogenous urea and do not carefully fit data points. Finally, pharmacokinetic modeling suggests that a two-compartment model satisfies all aspects of urea distribution and removal, but these compartments should not be equated with specific physiologic spaces. The combination of stable isotope urea compartmental modeling is a rigorous methodology for the assessment and validation of urea kinetics.

Adult↗
PubMed1998

Transport enzymes and renal tubular acidosis.

By analogy to the findings with other transport disorders such as Bartter's or Liddle's syndrome, it might be expected that the various forms of renal tubular acidosis (RTA) could result from defects in H-ATPase or H-K-ATPase. However, the available data do not yet support such a simple explanation. With regard to distal RTA, inhibition of H-K-ATPase with inhibitors such as vanadate blocks the increase in enzyme activity observed with potassium depletion, but does not produce distal RTA. H-K-ATPase does not increase with metabolic acidosis, and inhibition of its activity does not decrease ammonium or total acid excretion unless K depletion is also present. Maleic acid administration produces proximal RTA along with other proximal tubular dysfunction in experimental animals. However, it acts by reducing Na,K-ATPase activity rather than by affecting specific H+ ion transporters. This is pertinent to the findings that Na,K-ATPase activity is reduced in obstructive uropathy. Although the acidification defect in this disorder has been ascribed to a defect in H-ATPase, Na-K-ATPase function is also impaired. Thus, the role of isolated defects in H+ transporters in the development of clinical acidification disorders remains to be elucidated.

Acidosis, Renal Tubular↗
PubMed1996

Dialysis in rats with acute renal failure: evaluation of three different dialyzer membranes.

Exposure to complement-activating cellulosic dialysis membranes has been claimed to adversely affect the course of acute renal failure (ARF). To test this hypothesis, male Sprague-Dawley rats were allocated to 2 groups: in Group 1, ARF was induced by bilateral renal artery clamping whereas in Group 2, animals underwent a sham procedure. In each group, rats were further allocated to undergo hemodialysis with either a Cuprophan, a Hemophan, or a polyacrylonitrile minidialyzer on Days 4 and 8 after surgery, or no dialysis. Renal function was measured by inulin clearance on the days after dialysis. Additionally, total complement activity (CH50) was estimated on Days 1, 2, 4, and 8, and complement factor C3 was detected immunohistochemically. The degree of renal failure and the rate of recovery of renal function were similar in all the ARF groups irrespective of whether they had undergone dialysis or not, or of the type of the dialysis membrane. Furthermore, there were no significant differences in the course of CH50 or in the amount and distribution of complement factor C3 in the kidney tissue between the rats of Groups 1 and 2. Our findings refute the hypothesis that in ischemic ARF exposure to complement-activating cellulosic dialysis membranes impairs the recovery of renal function in rats.

Acrylic Resins↗
PubMed1996

Recovery from ischemic acute renal failure: independence from dialysis membrane type.

Exposure to complement-activating cellulosic dialysis membranes has been claimed to adversely affect the course of acute renal failure. To test this hypothesis, male Sprague-Dawley rats were allocated to two groups: in group I, acute renal failure was induced by bilateral renal artery clamping, while group II animals underwent a sham procedure. In each group, the rats were further allocated to undergo hemodialysis with either a Cuprophan, a Hemophan, or a PAN miniDialyzer membrane 3 and 7 days after surgery or no dialysis. The renal function was measured by inulin clearance on the days following dialysis. Temporary occlusion of the renal arteries led to a rapid increase in serum urea and creatinine levels that peaked between 24 and 48 h after surgery and declined slowly thereafter. Peak urea values were similar in the acute renal failure groups. The hemodialysis sessions were well tolerated. Degree and rate of recovery were similar in all acute renal failure groups irrespective of whether they underwent dialysis or not or the type of the dialysis membrane. Complete recovery was observed in all the acute renal failure groups by the end of the observation period. Our findings refute the hypothesis that in ischemic acute renal failure exposure to complement-activating cellulosic dialysis membranes impairs the recovery of renal function.

Acute Kidney Injury↗
PubMed1996

Inconsequence of membrane choice in acute renal failure?

The choice of hemodialysis membrane in acute renal failure has caused a heated debate, principally because of the dogmatism with which the results of preliminary clinical studies have been translated into prescription dictum. The issue, however, is not merely the limitations of these two studies, but rather the shift in emphasis they may have engendered in the approach to dialytic therapy in acute renal failure. Dogmatism based on limited or flawed data does not serve the interests of our patients, and the issue of hemodialysis in acute renal failure is far more complex than the exaggerated importance of membrane choice.

Acute Kidney Injury↗
PubMed1995

Synthetic modification of PAN membrane: biocompatibility and functional characterization.

A disturbing interaction of PAN membranes and the bradykinin generation system particularly in the presence of angiotensin converting enzyme inhibitors has been described. A modified new membrane, SPAN (special PAN), was produced by varying the polymer components in type and composition, in particular by a reduction in Na-Methallylsulfonate. Although the SPAN membrane successfully averted the bradykinin generating ability of PAN, it was important to determine whether such a modification did not lead to a loss of the satisfactory biocompatibility profile characteristic of the parent membrane. For this purpose, we conducted the present clinical study in nine patients comparing 3 membranes; (i) a polysulphone membrane (F60S); (ii) PAN; and (iii) SPAN, to examine the clinical biocompatibility profile and performance of the new membrane. A small increase in C5a with F60S and SPAN was found which is in the range expected for highly biocompatible synthetic membranes. The three dialysers had a similar inert profile for terminal complement complex arterial values, and had similar venous values. A minimal nonsignificant decline in white cell count was observed at 15 min for all dialysers, but otherwise WBC counts were unchanged. Platelet counts were unchanged throughout treatment for the three dialysers. Arterial and venous thrombin-anti-thrombin complex values were similar for all three dialysers. F60S and SPAN dialysers had similar urea clearances.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Platelet-leukocyte aggregation during hemodialysis.

Hemodialysis is associated with simultaneous changes in leukocytes and platelets, but it is unclear whether these alterations affect the interactions between these cell types. To evaluate this process, we examined the appearance of platelet specific antigens (CD41) on leukocytes as an index of platelet-leukocyte aggregation during hemodialysis using three different synthetic membranes. Patients with end-stage renal disease (ESRD) on long-term hemodialysis treatment were enrolled. Flow cytometric techniques and platelet specific monoclonal antibodies (MoAb) that recognize the glycoprotein complex on resting and activated platelets (anti-CD41), the activated GPIIb-IIIa complex receptor (anti-LIBS1), and the p selectin GMP140, that is exposed on platelet plasma membrane after activation and platelet degranulation (anti-CD62), were used. Subjects with ESRD had a lower predialysis platelet surface expression of CD41 and LIBS1 compared to normal controls, but unchanged CD62 expression. In parallel, patients with ESRD manifested a uniformly reduced platelet-leukocyte microaggregates predialysis compared to normal controls. When examined across the dialyzer, however, an increase in platelet-neutrophil and platelet-monocyte microaggregates was observed with all three synthetic membranes at both 15 and 30 minutes after initiation of dialysis. This phenomenon could be duplicated in vitro by physiologic concentrations of the platelet specific agonist ADP, but not by the complement factors C3a or C5a. We conclude that platelet-leukocyte aggregates occur during dialysis likely related to a primary platelet activation mechanism. This phenomenon may serve as a new biocompatibility parameter and may shed light on some of the biologic consequences of hemodialysis.

Adolescent↗
PubMed1994

Collecting duct changes in potassium depletion: effects of ACE inhibition.

Potassium depletion is associated with a hyperreninemia that may be responsible for some of the renal hemodynamic and functional changes observed in K-deficient states. The present study was designed to evaluate whether interruption of the renin-angiotensin system with enalapril alters the collecting duct changes observed in K depletion. Adrenalectomized male Sprague-Dawley rats were allocated to either a normal (NK) or low-K diet (LK), and they either received enalapril or vehicle for 3 wk. Na:K pump activity (pmol.mm-1.h-1) in microdissected cortical collecting (CCT) and medullary collecting tubules (MCT) was determined at 21 days after group allocations. K depletion had a minimal effect on CCT outer diameter. In contrast, a marked hypertrophy was observed in the MCT diameter (91% increase, P < 0.001) that was significantly attenuated by enalapril treatment (56% increase, P < 0.001 vs. LK). An increase in Na:K pump activity was observed with LK, in the CCT from 497 +/- 47 to 1,089 +/- 83 (P < 0.001) and in the MCT from 489 +/- 36 to 1,396 +/- 45 pmol.mm-1.h-1 (P < 0.01). In K-replete rats, enalapril had no effect on Na:K pump activity in either CCT or MCT. Enalapril administration during LK had no effect on the increase in Na:K pump activity in the CCT (1,023 +/- 75 pmol.mm-1.h-1, P < 0.001), not different from LK alone. In the MCT, however, enalapril reduced the increment in Na:K pump activity induced by LK (1,116 +/- 39 pmol.mm-1.h-1, less than the change with LK alone).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1994

Impaired function of platelet membrane glycoprotein IIb-IIIa in end-stage renal disease.

Impaired platelet function and a bleeding tendency are well-recognized complications of chronic renal failure. Because the fibrinogen receptor GPIIb-IIIa plays a central role in platelet aggregation and adhesion to the subendothelium, it was reasoned that a defect in this receptor may underlie the impaired platelet function in uremia. To test this hypothesis, the function of this receptor in the platelets of 11 uremic patients was studied. Aggregation studies were performed with flow cytometric techniques with anti-GPIIb-IIIa conformation-specific monoclonal antibodies (mAb) (anti-LIBS1 and anti-PMI-1). Antifibrinogen and antithrombospondin mAb were used to characterize fibrinogen binding to GPIIb-IIIa and the release of alpha-granules, respectively. Platelets from patients with chronic renal failure showed significantly decreased binding of conformation-dependent anti-LIBS1 mAb after ADP, phorbol myristate acetate, or RGD-peptide stimulation compared with normal controls, suggesting a defect related to the ability of the fibrinogen receptor to undergo a conformational change. Moreover, antifibrinogen and antithrombospondin binding to activated platelets were reduced in uremic patients, implying impairment of both ligand-binding and alpha-granule release. Hemodialysis partially restored GPIIb-IIIa function, which may account for the observed effects of this therapy in restoring platelet aggregation. These findings indicate that platelets of patients with chronic renal failure reveal an aggregation defect at least partially due to an intrinsic GPIIb-IIIa dysfunction and the presence of a putative uremic toxin that inhibits fibrinogen binding to GPIIb-IIIa.

Adenosine Diphosphate↗