CREB transcription factor modulates Bcl2 transcription in response to C5a in HL-60-derived neutrophils

BACKGROUND

Complement fragment C5a and neutrophils have been implicated in the pathogenesis of renal disease and C5a has also been shown to delay apoptosis of human neutrophils via a transcription-independent pathway. However, transcription-dependent pathways have not been well described. The present study examined whether activation of HL-60-derived neutrophils by C5a modulates the transcription of two members of the Bcl2 family, Bax (pro-apoptotic) and Bcl2 (anti-apoptotic) molecules, and whether the cAMP-response element-binding protein (CREB) transcription factor mediates these effects through the phosphatidylinositol 3-kinase (PI3K)/Akt and extra-cellular signal-regulated kinase (ERK) signalling pathways.

MATERIALS AND METHODS

The human promyelocytic leukaemia HL-60 cell line was differentiated into neutrophils using 1.25% DMSO. Differentiated cells were incubated with recombinant human C5a for 30-120 min with, or without, pretreatment with wortmannin or PD98059. The cells were lysed and quantified for gene-specific Bax and Bcl2 mRNA. In separate experiments, cells were incubated with C5a for 5-30 min with, or without, pretreatment with wortmannin, PD98059, or alkaline phosphatase. Cells were then lysed and immunoblotted using antihuman phospho-CREB (Ser133) antibody. Apoptosis was assessed by measuring active caspase-3 in differentiated HL-60 cells.

RESULTS

C5a inhibited caspase-3 activation in HL-60-derived neutrophils (P=0.003). C5a significantly increased the expression of Bcl2 mRNA (P=0.028), which was time-dependent, peaking at 30 min, and was abrogated in the presence of either wortmannin or PD98059 (both P=0.028). The C5a had no impact on Bax mRNA expression. The Bax : Bcl2 mRNA ratio markedly decreased at 30 min (P=0.028). Time-dependent effect of C5a on CREB phosphorylation was demonstrable and rapid, peaking at 5 min, and was abrogated by either wortmannin or PD98059 (both P=0.028). Phosphorylation of CREB, but not of Akt and ERK, was inhibited by alkaline phosphatase (P=0.028). The effect of C5a on Bcl2 mRNA expression was abrogated by alkaline phosphatase (P=0.028). The Bax : Bcl2 mRNA ratio markedly increased in the presence of alkaline phosphatase (P=0.046).

CONCLUSIONS

This study demonstrates that C5a induces Bcl2 mRNA transcription in HL-60-derived neutrophils, which is mediated in part by CREB through the convergence of the PI3K/Akt and ERK-signalling pathways.

3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors upregulate inducible NO synthase expression and activity in vascular smooth muscle cells

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase ameliorate atherosclerosis by both cholesterol-dependent and cholesterol-independent mechanisms. We examined whether HMG-CoA reductase inhibitors affect the expression and activity of inducible NO synthase (iNOS) in cultured rat aortic vascular smooth muscle (VSM) cells. Atorvastatin (34 to 68 micromol/L) markedly increased nitrite production, an increase that was essentially abrogated by the NO synthase inhibitor N(G)-monomethyl-L-arginine (500 micromol/L). Activity of iNOS, determined by the conversion of L-arginine to L-citrulline, increased 9-fold after atorvastatin treatment. Western blot and semiquantitative reverse transcriptase-polymerase chain reaction revealed that atorvastatin (34 to 68 micromol/L) strongly upregulated iNOS protein and mRNA levels, respectively. These concentrations of atorvastatin did not cause cytotoxicity, as judged by the cell survival rate. Similarly, simvastatin and lovastatin (34 micromol/L) caused robust upregulation of the iNOS protein level. Transfection experiments demonstrated that the -1034- to 88-bp human iNOS promoter was strongly induced by atorvastatin (34 micromol/L). Electromobility and supershift assays using a nuclear factor-kappaB (NF-kappaB) consensus oligonucleotide and nuclear extracts from VSM cells as well as transfection studies using an NF-kappaB reporter plasmid suggested that the transcriptional activation of the iNOS gene by atorvastatin is not mediated via the NF-kappaB pathway. We conclude that HMG-CoA reductase inhibitors potently upregulate iNOS expression and activity in VSM cells, at least in part, by transcriptional mechanisms that do not depend on transcription factor NF-kappaB. These effects might have important implications for the impact of HMG-CoA reductase inhibitors on atherosclerosis.

Transcriptional regulation of the human iNOS gene by IL-1beta in endothelial cells

BACKGROUND

Vascular endothelium participates in the control of vascular tone and function via the release of nitric oxide (NO) by the endothelial-type NO synthase (eNOS). Inducible NO synthase (iNOS) expression in endothelial cells occurs in many clinical conditions following induction by lipopolysaccharide or cytokines and generates large quantities of NO that result in endothelial cell activation and dysfunction. No information exists on the transcriptional regulation of the human iNOS gene (or that of other species) in endothelial cells.

MATERIALS AND METHODS

We examined the transcriptional regulation of the human iNOS gene by interleukin-1beta (IL-1beta) in rat pulmonary microvascular endothelial cells (PVEC) by transient cotransfections of different iNOS-promoter constructs and cDNA of different transcription factors and regulatory proteins.

RESULTS

The -1034/+88 bp iNOS promoter was strongly induced by IL-1beta, the regulatory elements for such induction being localized downstream of -205 bp. Cotransfection experiments with NF-kappaB isoforms, IkappaB isoforms, and IKK mutants suggested that the NF-kappaB site at -115/-106 bp is important, but not sufficient, for induction of iNOS promoter and that the role of NF-kappaB is partially independent of its binding site. C/EBP sites within the -205/+88 bp region were shown to be responsible, along with NF-kappaB site, for induction of iNOS promoter by IL-1beta. Overexpression of C/EBPalpha, C/EBPdelta, and liver-enriched activator protein (LAP) activated the promoter, whereas overexpression of liver-enriched inhibitory protein (LIP) strongly suppressed it. C/EBPbeta (LAP and LIP isoforms) was constitutively present in PVEC and was induced (approximately 2-fold) by IL-1beta, whereas C/EBPdelta was not constitutively expressed but was strongly induced by IL-1beta. Both C/EBPbeta and C/EBPdelta participated in DNA-protein complex formation.

CONCLUSION

Both NF-kappaB and C/EBP pathways are important for the transcriptional regulation of the human iNOS gene by IL-1beta in PVEC.

Approach to patients with acid-base disorders

Disorders of acid-base balance are commonly encountered in clinical practice and can have a substantial impact on the prognosis of the patient. Moreover, identification of a particular acid-base disturbance can provide a clue to an underlying disorder. Proper evaluation and treatment of acid-base disorders requires a systematic and analytic approach including: (1) assess the accuracy of the acid-base values using the Henderson equation or Henderson-Hasselbalch equation, (2) obtain a complete history and physical examination, (3) calculate the serum anion gap, (4) identify the primary acid-base disturbance and determine whether a simple or mixed disturbance is present, (5) examine serum electrolytes and additional laboratory data, and (6) measure urine pH and urine electrolytes and calculate the urine anion and osmolal gaps. Strict adherence to these principles will enable the clinician to diagnose the acid-base disturbance in the majority of cases. To illustrate these principles, 5 cases of patients with acid-base disturbances are analyzed.

Admission serum potassium in patients with acute myocardial infarction: its correlates and value as a determinant of in-hospital outcome

STUDY OBJECTIVES

Although controversial, hypokalemia (LK) in patients with acute myocardial infarction (MI) is thought to predict increased in-hospital morbidity, particularly cardiac arrhythmias, and mortality. Also, the mechanism of low serum potassium in the setting of MI has not been delineated. We evaluated the frequency, attributes, and outcome, and speculated on the mechanism of LK in patients with MI.

DESIGN

This was a prospective cross-sectional study of 517 consecutive patients with MI admitted to the coronary care unit (CCU). Serum potassium was measured in the emergency department and repeatedly thereafter throughout hospitalization, and was used in the analysis, along with a large array of clinical and laboratory variables.

RESULTS

The patients were allocated to a LK and a normokalemic (NK) cohort, based on the emergency department serum potassium measurement. The 41 patients with LK (3.16+/-0.24 mEq/L; 7.9% of total) were comparable on admission in their baseline assessment to the 476 patients with normal serum potassium (4.28+/-0.56 mEq/L), except for lower emergency department magnesium (1.48+/-0.15 mg/dL vs. 1.96+/-0.26 mg/dL; p = 0.0005) and earlier presentation after onset of symptoms (3.0+/-4.1 h vs. 4.4+/- 6.2 h; p = 0.05). There was a poor correlation between serum potassium and magnesium on admission (r = 0.14). Peak creatine kinase (CK) and myocardial isomer of CK were higher in the LK patients (3,870+/-3, 840 IU/L vs. 2,359+/-2,653 IU/L [p = 0.018] and 358+/-312 IU/L vs. 228 +/- 258 IU/L [p = 0.013], respectively). Management of the two cohorts was the same, except for a higher rate of use of magnesium (14.6% vs. 4.6%; p = 0.007), serum potassium supplements (90.2% vs 43. 1%; p = 0.000005), and antiarrhythmic drugs (78.0% vs 50.4%; p = 0. 0007) in the LK patients. No difference was detected between the LK and NK patients in total mortality (24.4% vs. 18.3%; p = 0.34), cardiac mortality (17.1% vs. 15.3%; p = 0.52), atrial fibrillation (14.6% vs 13.9%; p = 0.89), and ventricular tachycardia (22.0% vs. 16.0%; p = 0.32), but ventricular fibrillation (VF) occurred more often (24.4% vs 13.0%; p = 0.04) in the LK patients. However, proportions of VF occurring in the emergency department, CCU, or wards in the two cohorts were not different, but they were higher during the time interval prior to emergency department admission in LK patients (17.1% vs 2.1%; p = 0.00001).

CONCLUSIONS

LK is seen in approximately 8% of patients with MI in the emergency department; LK is associated with low emergency department magnesium, and low serum potassium levels in the CCU and throughout hospitalization. LK has no relationship to preadmission use of diuretics, it is associated with early presentation to the emergency department, and it is not a predictor of increased morbidity or mortality.

Marked dilutional acidosis complicating management of right ventricular myocardial infarction

Dilutional acidosis is a poorly recognized cause of metabolic acidosis. Indeed, the prevailing view has been that even massive expansion of the extracellular fluid volume with non-bicarbonate-containing solutions would not lead to clinically significant hypobicarbonatemia. We describe the development of marked dilutional acidosis as a complication of management of right ventricular myocardial infarction. The pathogenesis, clinical significance, prevention, and treatment of the entity are discussed.

Aiding fluid prescription for the dysnatremias

OBJECTIVE

The goal of the present study was to develop a novel approach that facilitates the prescription of fluid therapy in patients with abnormal serum sodium concentration.

METHODOLOGY AND RESULTS

The novel approach is based on a simple equation, derived from established principles on the distribution of sodium in body fluids, that estimates the impact of a unit dose, i.e., 1 l of any infusate on the patient's serum sodium concentration. In accordance with the equation, the expected change in the patient's serum sodium concentration in response to 1 l of any infusate (delta[Na+]s) is obtained by subtracting the sodium concentration of the patient's serum from the sodium concentration of the infusate, each expressed in mEq/l, and dividing the result by the patient's estimated total body water expressed in liters (adding 1 l to account for the volume of the infusate). The amount of the particular infusate to be administered over the course of any given time period can be easily computed by dividing the desired delta[Na+]s at the end of the period by the calculated delta[Na+]s effected by 1 l of the infusate. The utility and limitations of the proposed approach are presented.

CONCLUSIONS

The novel equation is not a means for formulating therapy. Rather, it provides, simply and expeditiously, quantitative projections that can assist the physician in implementing the selected treatment plan for patients with dysnatremias.

Admission serum magnesium level does not predict the hospital outcome of patients with acute myocardial infarction

OBJECTIVE

To establish whether hypomagnesemia at admission predicts excessive morbidity, particularly cardiac arrhythmias, and mortality in patients with acute myocardial infarction.

METHODS

We compared hypomagnesemic and normomagnesemic patients with acute myocardial infarction in 517 patients admitted to the coronary care unit. The serum magnesium concentration, along with a large array of other parameters, was measured on admission to the emergency department. Other baseline attributes and variables related to the patients' hospital course were used to compare the 2 groups.

RESULTS

The 132 patients (25.9%) with low serum magnesium concentrations at admission (mean +/- SD, 0.61 +/- 0.06 mmol/L [1.48 +/- 0.15 mg/dL]) were comparable to the patients with normal serum magnesium concentrations (0.81 +/- 0.11 mmol/L [1.96 +/- 0.26 mg/dL]) except for a higher rate of prehospital use of diuretic agents (32.6% vs 22.5%, P = .02) and earlier presentation after onset of symptoms (mean +/- SD, 3.2 +/- 4.1 vs 4.8 +/- 6.6 hours, P = .003). There was no correlation between serum magnesium and potassium concentrations in the emergency department (r = 0.14). No difference was detected between the hypomagnesemic and normomagnesemic cohorts in rates of total mortality (18.9% vs 18.5%, P = .91), cardiac mortality (15.2% vs 15.3%, P = .99), atrial fibrillation (13.6% vs 13.8%, P = .97), ventricular tachycardia (18.2% vs 15.3%, P = .44), or ventricular fibrillation (15.2% vs 13.5%, P = .63). Management of the 2 cohorts was not different, except for higher rates of use of magnesium (17.4% vs 1.3%, P < .001) and potassium (59.8% vs 42.1%, P < .001) supplements and antiarrhythmic drugs (62.9% vs 48.7%, P = .005) in the hypomagnesemic patients. An endogenous rise in serum magnesium level was documented in a subgroup of 161 patients who had a repeated measurement (0.74 +/- 0.12 mmol/L [1.79 +/- 0.29 mg/dL] in the emergency department vs 0.77 +/- 0.09 mmol/L [1.88 +/- 0.23 mg/dL] in the coronary care unit, P < .001).

CONCLUSIONS

We conclude that hypomagnesemia is seen in approximately one fourth of patients with myocardial infarction, is not linked to hypokalemia, has some relationship to preadmission use of diuretic agents, is associated with early presentation to the hospital, and is not a predictor of increased morbidity or mortality.

Transcriptional regulation of the human iNOS gene in vascular-smooth-muscle cells and macrophages: evidence for tissue specificity

We have cloned the 5' upstream -1034 to +88 fragment of the human inducible nitric oxide synthase (hiNOS) gene and demonstrate its competence to promote luciferase gene transcription in vascular-smooth-muscle (VSM) cells and macrophages. Sequential 5' end-deletions localized positive regulatory elements of hiNOS transcription in VSM A7r5 cells downstream of nucleotide -205 and demonstrated the functional importance of the resident NF-kappaB site (nucleotides -115 to -106). The hiNOS promoter/enhancer was induced strongly by LPS and IFN-gamma, and modestly by IL-1beta in RAW 264.7 cells, but not in VSM cells. Truncation of the NF-kappaB site markedly diminished, but did not eliminate, LPS-inducibility. Sodium salicylate and ibuprofen down-regulated the basal transcriptional activity of the hiNOS promoter/enhancer in VSM but not in RAW 264.7 cells. These results indicate that the transcriptional regulation of the hiNOS gene features considerable complexity and tissue specificity.

Predominant tubulointerstitial lupus nephritis

Predominant tubulointerstitial lupus nephritis is rare. Only eight cases have been described in the literature. We report the case of a 59-year-old man with systemic lupus erythematosus who presented with acute renal failure. On renal biopsy, he was found to have chronic tubulointerstitial nephritis with a mononuclear infiltrate. The immunofluorescence showed immune deposits in the tubular basement membranes, interstitium, and glomerular capsule. The glomeruli were minimally involved. He was initially treated with high-dose corticosteroids and supported with hemodialysis. Renal function improved and dialysis was discontinued after three treatments. The corticosteroid dosage was gradually tapered. Renal function after 72 months of follow-up has remained stable (serum creatinine, approximately 1.9 mg/dL) and except for one relapse, there has been no clinical or serologic evidence of lupus activity. Furthermore, 24-hour urinary protein excretion has remained within the normal range.

Role of C/EBP proteins in hepatic and vascular smooth muscle transcription of human NHE1 gene

We have recently shown that regulatory element D (nucleotides -239 to -215) of the 0.25-kb promoter of the human growth factor-activatable Na+/H+ exchanger (NHE1) is important for gene transcription in cells of hepatic origin (Hep G2) and vascular smooth muscle origin (VSM A7r5). This element contains a sequence (nucleotides -230 to -222) with complete homology to the C/EBP binding site. We now demonstrate that nucleotide substitution mutations disrupting this C/EBP site suppressed transcription in Hep G2 cells, VSM A7r5 cells, and Sprague-Dawley VSM cells in primary culture. These mutations abolished the binding of rat liver nuclear activities as well as transcription factors C/EBP alpha, C/EBP beta, and C/EBP delta expressed in COS-1 cell lysates to element D. Anti-C/EBP antibodies supershifted DNA-protein complexes formed between hepatic nuclear activities or C/EBP proteins expressed in COS-1 cell lysates and regulatory element D. Finally, cotransfection experiments of NHE1 0.25-kb promoter-chloramphenicol acetyltransferase (CAT) construct and C/EBP expression vectors showed that C/EBP alpha and C/EBP delta are transactivators of the NHE1 proximal promoter in Hep G2 and VSM A7r5 cells. These results indicate that members of the C/EBP family of transcription factors are involved in the regulation of hepatic and vascular smooth muscle transcription of the human NHE1 gene.

Effect of chronic respiratory acidosis on calcium metabolism in the rat

Chronic metabolic acidosis typically results in hypercalciuria and negative calcium balance. The impact of chronic respiratory acidosis on calcium metabolism has been less well studied. To address this issue, metabolic balance and static bone histomorphometric data were obtained during a 14-day exposure of rats to 10% CO2 (blood pH 7.33, PaCO2 83 mm Hg) and were compared with pair-fed controls. All rats were fed a 0.8% calcium diet. Urinary calcium excretion (mg/period, mean +/- SEM) was increased during both week 1 and week 2 (16 +/- 3 vs 9 +/- 1 and 16 +/- 2 vs 9 +/- 1, CO2 group vs controls, respectively [p < 0.05]). Net intestinal calcium absorption (intake minus fecal excretion) was increased throughout the period of hypercapnia (week 1, 213 +/- 19 mg vs 135 +/- 15 mg; week 2, 135 +/- 16 mg vs 43 +/- 14 mg; and cumulatively, 344 +/- 27 mg vs 178 +/- 20 mg, CO2 group vs controls [p < 0.01]). As a consequence of the marked increment in intestinal calcium absorption during hypercapnia, mean net calcium balance was more positive than that of controls throughout the study (week 1, 197 +/- 18 mg vs 126 +/- 15 mg; week 2, 120 +/- 15 mg vs 34 +/- 15 mg; and cumulatively, 317 +/- 25 mg vs 159 +/- 20 mg, CO2 group vs controls, respectively [p < 0.01]). There were no significant differences in calcium intake, plasma total calcium, immunoreactive parathyroid hormone, 25-hydroxyvitamin D, or creatinine clearance between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental renal failure in the rat modulates cardiac Na,K-ATPase alpha 2 mRNA but not protein

The decreased abundance and enzymatic activity of myocardial Na,K-ATPase have been recognized previously to occur in chronic uremia. However, the activity of the cardiac sodium pump as defined by the uptake of 86Rb is normal. The discrepancies between these findings may have resulted from the inability to distinguish between the different Na,K-ATPase isoforms now known to exist in cardiac muscle. To investigate this question, steady-state levels of Na,K-ATPase alpha and beta mRNA isoforms, alpha 1, alpha 2, and beta 1 protein, and specific high-affinity binding of [3H]ouabain were quantitated in cardiac muscle from uremic and pair-fed, sham-operated control rats. Steady-state levels of alpha 2 and beta 2 mRNA were significantly decreased (percentage of control levels: alpha 2, 48 +/- 10; beta 2, 74 +/- 9; N = 10; P < 0.025) in chronic renal failure without any change in alpha 1, alpha 3, or beta 1 expression. The number of high-affinity [3H]ouabain-binding sites and Na,K-ATPase alpha 1, alpha 2, and beta 1 subunits was not different from control. In acute renal failure, alpha 2 and beta 2 mRNA levels also were significantly decreased (percentage of control levels: alpha 2, 24 +/- 5; beta 2, 44 +/- 8; N = 6; P < 0.001), but there was no change in the level of alpha 3 or beta 1 mRNA, the number of high-affinity [3H]ouabain-binding sites, or the level of Na,K-ATPase alpha 2 and beta 1 subunits.(ABSTRACT TRUNCATED AT 250 WORDS)

Proximal regulatory elements and nuclear activities required for transcription of the human Na+/H+ exchanger (NHE-1) gene

We herein demonstrate competence of the 5' upstream region -1374 to +16 of the human growth factor-activatable Na+/H+ exchanger (NHE-1) gene to promote transcription of the chloramphenicol acetyltransferase gene in cells of hepatic origin (HepG2), vascular-smooth-muscle origin (VSM A7r5) and fibroblasts (3T3). We also describe the mapping of the regulatory elements required for such transcription. Sequential 5' end-deletions indicated that the 5' boundary of the positive regulatory elements of NHE-1 transcription is localized downstream of nucleotide -252 in both HepG2 and VSM A7r5 cells but downstream of nucleotide -654 in 3T3 cells. Footprinting analysis of the 0.25-kb promoter fragment using rat liver nuclear extracts identified 4 protected regions as follows: A, -31 to -9; B, -108 to -65; C, -124 to -111; and D, -239 to -215. Internal deletion and nucleotide substitutions within regulatory element D revealed its essential role for transcription of the human NHE-1 gene in HepG2 and VSM A7r5 cells. DNA binding and competition assays using rat liver nuclear extracts indicated that regulatory element D is recognized by 5 nuclear activities. Four of these activities (designated as NHE-1D1-4) are competed out completely by oligonucleotides containing the binding sites of transcription factors CREB, AP3, NFY, and other CCAAT box-binding proteins (C/EBP alpha or related proteins). This competition profile might be explained by the presence of homology between regulatory element D and the consensus sequence of C/EBP as well as the other competitor oligonucleotides. The actual relationship between these nuclear activities and the C/EBP family of proteins (or other transcription factors) remains to be determined.

Stimulation of basolateral Na(+)-HCO3- cotransporter by angiotensin II in rabbit renal cortex

Angiotensin (ANG) II is now recognized as a powerful direct controller of Na+ reabsorption in the proximal convoluted tubule, a property that predominantly reflects stimulation of the transepithelial NaHCO3 flux. Numerous studies have established that this effect of ANG II represents stimulation of the apical Na+/H+ exchanger, but a single microperfusion study has also suggested direct stimulation of the basolateral Na(+)-HCO3- cotransporter. We have carried out studies in basolateral membrane vesicles from rabbit renal cortex to examine directly whether ANG II exerts an independent effect on the Na(+)-HCO3- cotransporter. Preincubation of vesicles with ANG II (10(-11) to 10(-9) M) for 15 min enhanced the activity of the cotransporter, the greatest effect occurring at 10(-11) M (41 +/- 1.1%, P < 0.005). This stimulation reflected an increase in the maximal enzyme reaction velocity of the cotransporter but no change in the Michaelis constant for Na+. ANG II had no effect on Na(+)-dependent succinate transport. ANG I (10(-9) M) and ANG III (10(-10) M) also stimulated the Na(+)-HCO3- cotransporter, and captopril (10(-4) M) attenuated the ANG I stimulation by 68 +/- 3.5% (P < 0.01) but not that of ANG II and III. Saralasin (10(-11) to 10(-8) M) by itself behaved as an agonist, and its stimulation was additive to that by ANG II. The nonpeptide ANG II receptor antagonist, losartan potassium (10(-6) M), and the disulfide-reducing agent, dithiothreitol (10 mM), each by itself had no effect on the cotransporter but each markedly attenuated the ANG II effect (by 77 +/- 1.4%, P < 0.01 and 74 +/- 1.6%, P < 0.005, respectively) in accord with the view that the basolateral receptor belongs to subtype 1. These results identify physiological concentrations of ANG II as a potent, direct, and specific stimulator of the basolateral Na(+)-HCO3- cotransporter.

Serum creatinine as an index of renal function: new insights into old concepts

The serum creatinine concentration is widely interpreted as a measure of the glomerular filtration rate (GFR) and is used as an index of renal function in clinical practice. Glomerular filtration of creatinine, however, is only one of the variables that determines its concentration in serum. Alterations in renal handling and metabolism of creatinine and methodological interferences in its measurement may have a profound impact on the serum concentration of creatinine. We review the fundamental principles of physiology, metabolism, and analytical chemistry that are necessary to correctly interpret the serum creatinine concentration. These principles are then applied to important clinical circumstances, including aging, pregnancy, diabetes mellitus, drug administration, and acute and chronic renal failure. Despite numerous limitations, serum creatinine remains a useful clinical tool, but more accurate measures of renal function are frequently necessary.

Serum Creatinine as an Index of Renal Function: New Insights into Old Concepts

The serum creatinine concentration is widely interpreted as a measure of the glomerular filtration rate (GFR) and is used as an index of renal function in clinical practice. Glomerular filtration of creatinine, however, is only one of the variables that determines its concentration in serum. Alterations in renal handling and metabolism of creatinine and methodological interferences in its measurement may have a profound impact on the serum concentration of creatinine. We review the fundamental principles of physiology, metabolism, and analytical chemistry that are necessary to correctly interpret the serum creatinine concentration. These principles are then applied to important clinical circumstances, including aging, pregnancy, diabetes mellitus, drug administration, and acute and chronic renal failure. Despite numerous limitations, serum creatinine remains a useful clinical tool, but more accurate measures of renal function are frequently necessary.

Endothelin-1 stimulates the Na+/H+ and Na+/HCO3- transporters in rabbit renal cortex

Endothelin-1 (ET-1) is the most potent endogenous vasoconstrictor identified to date, raising the strong possibility of its involvement in the pathogenesis of systemic hypertension. Whether ET-1 exerts a direct stimulating effect on sodium reabsorption in the renal proximal convoluted tubule, the dominant locus of sodium reabsorption in the nephron, is currently unknown. Such an effect would suggest yet another mechanism by which ET-1 might mediate systemic hypertension. In studies on membrane vesicles prepared from rabbit renal cortex, we show that ET-1 (10(-8) to 10(-11) M) exerts dose-dependent stimulation of the apical Na+/H+ exchanger and the basolateral Na+/HCO3- cotransporter; preincubation of vesicles with 10(-10) M ET-1 for five minutes enhanced the activity of each transporter by approximately 25%. This stimulation reflected an increase in the Vmax of each transporter but no change in the Km for sodium. The stimulatory effect of ET-1 was blocked in the presence of an ET-1 antiserum. Moreover, the stimulation of the apical Na+/H+ exchanger and the basolateral Na+/HCO3- cotransporter by ET-1 displayed specificity as indicated by the lack of effects on the activities of the apical Na(+)-glucose transporter and the basolateral Na(+)-succinate transporter. The data implicate ET-1 as a novel, direct and specific modulator of sodium reabsorption in the proximal tubule. As such, ET-1 might be a direct determinant of extracellular fluid volume under normal and pathophysiologic circumstances, including hypertensive disorders.

A comparison of the safety of therapeutically equivalent doses of isradipine and diltiazem for treatment of essential hypertension

We compared the safety of a new dihydropyridine calcium entry blocker, isradipine, with an equipotent dose of diltiazem in 174 mild hypertensives (diastolic blood pressure [DBP] 95 to 105 mm Hg). After appropriate washout and placebo periods, patients were randomly assigned to receive either 1.25 mg isradipine twice daily (Group I) or 40 mg diltiazem thrice daily (Group D). If DBP remained above 90 mm Hg, doses were increased to a maximum of 5 mg isradipine twice daily or 120 mg diltiazem thrice daily. Active therapy was given for a total of 12 weeks. Only 18 patients (nine from each group) did not complete the protocol. The patients were well-matched at baseline with a mean BP of 149/100 mm Hg for those who were randomized to isradipine and completed the protocol and 153/99 mm Hg for the diltiazem group. The responses to each drug were excellent with 72% of the isradipine patients and 73% of the diltiazem group having DBP less than 90 mm Hg at the completion of the study. Of the 156 patients who completed the protocol, only 18 patients (ten in Group I and eight in Group D) failed to respond. Both drugs were well-tolerated. No adverse reactions were reported by 68 percent of the patients in Group I and 65% of those in Group D. The most common side effect was headache (9.0% in Group I and 7.8% in Group D) followed by fatigue (5.2% in Group I and 3.9% in Group D). Age and race did not predict response to either agent but men responded slightly better to diltiazem than women. We conclude that isradipine and diltiazem are equally well tolerated and can be used successfully as a monotherapy to treat hypertension in a wide variety of patients.

Effect of sulfhydryl compounds on ATP-stimulated H+ transport and Cl- uptake in rabbit renal cortical endosomes

The vacuolar H+ ATPase is inhibited by N-ethylmaleimide (NEM), a sulfhydryl compound, suggesting the involvement of a sulfhydryl group in this transport process. We have examined the effects of several sulfhydryl-containing compounds on the vacuolar H+. ATPase of rabbit renal cortical endosomes. A number of such compounds were effective inhibitors of endosomal H+ transport at 10(-5)-10(-6) M, including NEM, mersalyl, aldrithiol, 5,5' dithiobis (2-nitrobenzoic acid), p-chloromercuribenzoic acid (PCMB) and p-chloromercuriphenyl sulfonic acid (PCMBS). NEM, mersalyl, aldrithiol and PCMBS had no effect on pH-gradient dissipation, whereas PCMB decreased the pH gradient faster than control. In the absence of ATP, PCMB (10(-4) M) stimulated endosomal 36Cl- uptake, particularly in the presence of an inside-alkaline pH gradient (pHin = 7.6/pHout = 5.5). This result was not an effect of PCMB on the Cl(-)-conductive pathway. The less permeable PCMBS did not stimulate 36Cl- uptake. The effects of PCMB were concentration dependent and were prevented by dithioerithritol. ATP-dependent 36Cl- uptake was decreased by addition of PCMB. Finally, PCMB had no effect on 45Ca2+ uptake. These results support the presence of two functionally important sulfhydryl groups in this endosomal preparation. One such group is involved with ATP-driven H+ transport and must be located on the cytoplasmic surface of the endosomal membrane. The second sulfhydryl group must reside on the internal surface of the endosomal membrane and relates to a PCMB-activated Cl-/OH- exchanger that is functional both in the presence and absence of ATP. This endosomal transporter is similar to the PCMB-activated Cl-/OH- exchanger recently described in rabbit renal brush-border membranes.

Rat kidney band 3 mRNA modulation in chronic respiratory acidosis

Recent evidence indicates the existence of a protein related to the erythroid chloride-bicarbonate exchanger (band 3 protein) in the basolateral aspect of type A intercalated cells of the distal nephron. To probe the possible participation of this transporter in the renal adaptation to chronic hypercapnia, we examined the steady-state abundance of band 3 mRNA in the kidney during respiratory acidosis of variable duration. Total RNA was isolated from renal cortex and medulla of rats maintained in a 10% CO2 atmosphere for 2 or 5 days and from contemporaneous controls. The RNA was analyzed by Northern blot assay using cDNA probes for band 3 and beta-actin genes. Using a 3' cDNA probe encoding the membrane-associated domain of band 3 protein that is involved in anion exchange, we found a two- to threefold increase in steady-state mRNA levels (whether or not correction for the beta-actin signals was applied) in renal cortex and medulla at 5 days of hypercapnia. Similar, but less definitive, increases were observed at the 2-day time point. Using a 5' cDNA probe encoding an erythroid-protein segment absent from the kidney band 3 major transcript, we detected meager hybridization in renal tissue and no measurable variation during hypercapnia. Use of splenic RNA as a positive control for the 5' probe disclosed marked reduction of band 3 mRNA levels in hypercapnia, indicating organ specificity of band 3 gene expression. We conclude that steady-state levels of kidney band 3 mRNA increase in chronic respiratory acidosis as a result of transcriptional or posttranscriptional regulatory mechanisms. This adaptation might be involved in the augmentation of renal acidification characteristic of chronic hypercapnia.

Effect of chronic respiratory acidosis on urinary calcium excretion in the dog

It is currently believed that the two chronic acidemic disorders exert disparate effects on urinary calcium excretion: chronic metabolic acidosis induces consistent hypercalciuria, but no appreciable change or even a decrease in calcium excretion is reported to attend chronic respiratory acidosis. Whereas the effect of metabolic acidosis is well documented, little work has been carried out in chronic hypercapnia. In fact, most of the studies on chronic respiratory acidosis were short in duration, had employed only mild hypercapnia, or had failed to control carefully the prevailing metabolic conditions. We have carried out balance observations in nine dogs exposed to a 10% CO2 atmosphere in an environmental chamber for a period of two weeks. Chronic respiratory acidosis led to a significant increase in urinary calcium excretion from a mean control value of 0.4 +/- 0.1 mmol/day to 0.6 +/- 0.1 mmol/day during both week 1 and 2 of hypercapnia (P less than 0.05). Hypercalciuria occurred even though filtered load of calcium fell. Mean fractional excretion of calcium increased significantly during each week of hypercapnia averaging 0.60 +/- 0.12% during control, 1.05 +/- 0.13% during week 1, and 1.26 +/- 0.17% during week 2 of hypercapnic exposure (P less than 0.05). There were no changes in plasma levels of immunoreactive parathyroid hormone or 1,25-dihydroxyvitamin D3. These findings suggest that chronic respiratory acidosis, just like chronic metabolic acidosis, augments urinary calcium excretion by a direct depressive effect on the tubular reabsorption of calcium.

Na(+)-H+ exchange, but not Na(+)-K(+)-ATPase, is present in endosome-enriched microsomes from rabbit renal cortex

Previous studies have demonstrated a Na(+)-dependent decrease in the ATP-generated acidification of endosomes and have attributed it to the presence of either a Na(+)-H+ exchanger or a Na(+)-K(+)-adenosinetriphosphatase (ATPase) in parallel with the vacuolar H(+)-ATPase. In the present study we have examined the possibility that both of these two Na+ transporters might be present in endosome-enriched microsomes isolated from rabbit renal cortex. After the establishment of a stable pH gradient by ATP in this preparation, addition of Na+ induced a decrease in the pH gradient. Expression of this effect of Na+ did not require the presence of ATP or K+. Choline and K+ had no effect on the ATP-dependent pH gradient, but addition of Li+ caused a small reduction in the pH gradient. Amiloride, ouabain, and vanadate had no effect on the Na(+)-induced dissipation of the ATP-driven pH gradient. In addition, a pH gradient-dependent 22Na+ uptake by the endosomal vesicles that was insensitive to amiloride, ouabain, or vanadate was demonstrated. These results provide evidence against the presence of a Na(+)-K(+)-ATPase in endosome-enriched microsomes from the renal cortex and support the existence of an amiloride-insensitive Na(+)-H+ exchanger in parallel with the vacuolar H(+)-ATPase. This endosomal Na(+)-H+ exchanger might have important implications for the regulation of vacuolar H(+)-ATPase activity as well as proximal tubule acidification.

Influence of acute and chronic respiratory alkalosis on preexisting chronic metabolic alkalosis

The severity of the alkalemia produced by a reduction in arterial carbon dioxide tension (PaCO2) in normal humans and animals is ameliorated by buffer and renal responses that diminish the levels of plasma bicarbonate concentration ([HCO3-]p). These adjustments have even greater potential importance in preventing extreme degrees of alkalemia when hypocapnia occurs in the presence of an initially elevated [HCO3-]p (mixed respiratory and metabolic alkalosis). The aim of the present study was to characterize the acute (approximately 3 h) and chronic (5 days) acid-base effects of respiratory alkalosis when superimposed on chronic metabolic alkalosis. Ten dogs were made alkalotic by the repeated administration of ethacrynic acid and the provision of a chloride-restricted diet. Hypocapnia (delta PaCO2 = 10 mmHg) was then superimposed by exposing the animals to 11% O2 in an environmental chamber. A large fall in [HCO3-]p occurred in the acute hypocapnic phase that was further augmented in the chronic phase; the corresponding delta [HCO3-]p/delta PaCO2 slopes were 0.43 and 0.71 meq.l-1.mmHg-1, respectively, values substantially larger than those previously reported for hypocapnia in normals as well as in animals with preexisting HCl acidosis. Hyperlactatemia was responsible, on average, for 43% of the decrement in [HCO3-]p during acute hypocapnia but for only 20% of the delta [HCO3-]p during the chronic phase of the study. The striking decrement in [HCO3-]p observed in response to the chronic reduction in PaCO2 was sufficient not only to prevent the development of extreme alkalemia but also to offset entirely the effect of hypocapnia on plasma [H+].

Stimulation of canine kidney BBMV ATPase activity by acidic pH in the presence of Zn2+: an ATPase activity distinct from transport ATPases and alkaline phosphatase that may be an ecto-ATPase

Renal brush border membrane vesicles (BBMV) of the dog possess at least two ATPase activities. In the present study, we have examined the effect of pH, ions, and inhibitors on the activity of ATPase in BBMV. Two different sets of conditions were identified that produced stimulation of ATPase activity. A unique stimulation of BBMV ATPase activity occurred at acidic pH in the presence of 1 mM ZnCl2. In the absence of Zn2+, a second ATPase activity was stimulated by alkaline pH values with peak stimulation occurring between pH 8.5 and 9.0. The results suggest that the alkaline pH-stimulated hydrolysis of ATP probably represents the activity of BBMV alkaline phosphatase. The unique acidic pH + Zn2(+)-stimulated ATPase activity must represent the activity of a second protein other than the alkaline phosphatase, since purified alkaline phosphatase did not show this activity. The biochemical identity and physiological function of this renal BBMV ATPase activity remain to be determined, but it may be an ecto-ATPase.

Arteriovenous acid-base disparity in circulatory failure: studies on mechanism

The normal relationship between arterial and venous acid-base composition is altered in hemodynamic compromise. Because the mechanism of this phenomenon remains conjectural, we have studied the acid-base profile and the end-tidal PCO2 of dogs with normal or depressed hemodynamic status in association with either normal ventilation or respiratory arrest. Reductions in cardiac output widened the arteriovenous difference in PCO2 and pH, largely due to arterial hypocapnia but also to venous hypercapnia, and decreased end-tidal PCO2. The arteriovenous gradients for PCO2 and pH of -5.1 +/- 0.4 mmHg and 0.02 +/- 0.01, respectively, during normal hemodynamics widened progressively with graded circulatory compromise reaching values of -30 +/- 5 mmHg for PCO2 (P less than 0.01) and 0.35 +/- 0.05 for pH (P less than 0.01) during cardiac arrest. Development of this disparity, however, required the presence of substantial pulmonary ventilation, since respiratory arrest obliterated the arteriovenous gradients. We propose that arterial hypocapnia, which occurs in association with reduced CO2 excretion, is secondary to an increased ventilation-to-perfusion ratio that reflects a disproportionate decrement in cardiac output. Venous hypercapnia, on the other hand, results from a greater than normal addition of CO2 per unit of blood traversing the capillaries of the hypoperfused peripheral tissues and a diminished CO2 excretion because of pulmonary hypoperfusion. Titration of bicarbonate stores by ongoing production of organic acids might also contribute to venous hypercapnia.

H+/Ca2+ exchange in rabbit renal cortical endosomes

We have examined the effect of second messengers on ATP-driven H+ transport in an H+ ATPase-bearing endosomal fraction isolated from rabbit renal cortex. cAMP (0.1 mM) had no effect on H+ transport. Acridine orange fluorescence in the presence of 0.5 mM Ca2+ (+1 mM EGTA) was 19 +/- 6% of control. Inhibition of ATP-driven H+ transport by Ca2+ was concentration dependent; 0.25 and 0.5 mM Ca2+ (+1 mM EGTA) inhibited acridine orange fluorescence by approximately 50 and approximately 80%, respectively. Ca2+ also produced a concentration-dependent increase in the rate of pH-gradient dissipation. Ca2+ did not affect ATP hydrolysis. ATP-dependent Br- uptake was virtually unchanged in the presence of 0.5 mM Ca2+ (+1 mM EGTA). These vesicles were also shown to transport Ca2+ in an ATP-dependent mode. Inositol 1,4,5-trisphosphate had no effect on ATP-dependent Ca2+ uptake. These results are consistent with the co-existence of an H+ ATPase and an H+/Ca2+ exchanger on these endosomes, the latter transport system using the H+ gradient to energize Ca2+ uptake. Attempts to demonstrate an H+/Ca2+ antiporter in the absence of ATP have been unsuccessful. Yet, when a pH gradient was established by preincubation with ATP and residual ATP was subsequently removed by hexokinase + glucose, stimulation of Ca2+ uptake could be demonstrated. A Ca2(+)-dependent increase in H+ permeability and an ATP-dependent Ca2+ uptake might have important implications for the regulation of vacuolar H+ ATPase activity as well as the homeostasis of cytosolic Ca2+ concentration.

Adaptation of rabbit renal cortical Na+-H+ exchange activity in chronic hypocapnia

We have examined the activity and kinetic characteristics of the Na+-H+ exchanger in renal cortical brush-border membrane vesicles (BBMV) prepared from rabbits adapted to chronic hypocapnia in order to address whether this transporter might contribute to the suppressed proximal bicarbonate reabsorption characteristic of this disorder. Chronic hypocapnia was induced by exposing animals to 9% O2 for a 5-day period. In comparison with paired, contemporaneous controls, an average delta PaCO2 of 13 mmHg and an average delta [HCO3-] of 7.3 meq/l were obtained. Chronic hypocapnia led to a significant suppression of the 22Na+ uptake by BBMV; at the 3-s mark, a 30% suppression was observed (chronic hypocapnia, 4.05 +/- 0.43 nmol/mg protein; control, 5.72 +/- 0.39 nmol/mg protein) (P less than 0.01). A significant decrease in the Vmax of the antiporter was noted (chronic hypocapnia, 622.7 +/- 86.8 nmol.mg protein-1.min-1; control 857.5 +/- 64.8 nmol.mg protein-1.min-1) (P less than 0.01), whereas the Km for sodium remained unaltered. The specificity of this adaptation was supported by showing that Na+-dependent uptake of D-[3H]glucose by BBMV was not significantly different between chronic hypocapnia and control. Chronic normocapnic hypoxemia left Na+-H+ exchange activity undisturbed. We conclude that the observed change in the BBMV Na+-H+ antiporter might be responsible, at least in part, for the suppressed renal bicarbonate reabsorption characteristic of chronic hypocapnia and that a consequence of the hypocapnic state itself mediates this adaptation.

Techniques for isolation of brush-border and basolateral membrane vesicles from dog kidney cortex

Two methods are reported for renal membrane preparation from the dog kidney cortex. One method is a simultaneous preparation of brush-border (BBMV) and basolateral (BLMV) membranes. Using readily available laboratory equipment, differential centrifugation produced a supernatant which was treated with Mg2+. The Mg2+ treatment produced a pellet (crude BLMV) which was added to Percoll and centrifuged to produce purified BLMV. The supernatant after Mg2+ treatment eventually yielded pure BBMV after additional Mg2+ precipitations. The second method used an acidic medium in conjunction with divalent-cation precipitation to prepare BBMV. Whichever method was used, BBMV and BLMV showed appropriate enzyme and transport activities.

Assessing acid-base status in circulatory failure. Differences between arterial and central venous blood

To assess arteriovenous differences in acid-base status, we measured the pH and partial pressure of carbon dioxide (PCO2) in blood drawn simultaneously from the arterial and central venous circulations in 26 patients with normal cardiac output, 36 patients with moderate and 5 patients with severe circulatory failure, and 38 patients with cardiac or cardiorespiratory arrest. The patients with normal cardiac output had the expected arteriovenous differences: venous pH was lower by 0.03 unit, and venous PCO2 was higher by 0.8 kPa (5.7 mm Hg). These differences widened only slightly in those with moderate cardiac failure. Additional simultaneous determinations in mixed venous blood from pulmonary arterial catheters were nearly identical to those in central venous blood. In the five hypotensive patients with severe circulatory failure there were substantial differences between the mean arterial and central venous pH (7.31 vs. 7.21) and PCO2 (5.8 vs. 9.0 kPa [44 vs. 68 mm Hg]). Large arteriovenous differences were present during cardiac arrest in patients whose ventilation was mechanically sustained, whether sodium bicarbonate had been administered (pH, 7.27 vs. 7.07; PCO2, 5.8 vs. 8.6 kPa [44 vs. 65 mm Hg]) or not (pH, 7.36 vs. 7.01; PCO2, 3.7 vs. 10.2 kPa [28 vs. 76 mm Hg]). By contrast, in patients with cardiorespiratory arrest, large arteriovenous differences were noted only when sodium bicarbonate had been given (pH, 7.24 vs. 7.01; PCO2, 9.5 vs. 16.9 kPa [71 vs. 127 mm Hg]). We conclude that both arterial and central venous blood samples are needed to assess acid-base status in patients with critical hemodynamic compromise. Although information about arterial blood gases is needed to assess pulmonary gas exchange, in the presence of severe hypoperfusion, the hypercapnia and acidemia at the level of the tissues are detected better in central venous blood.

Percutaneous transluminal renal angioplasty in management of atherosclerotic renovascular hypertension: results in 100 patients

The long-term effect of percutaneous transluminal renal angioplasty (PTRA) on blood pressure and renal function was assessed in 100 consecutive patients with atherosclerotic renovascular hypertension. Technical success rates (complete plus partial) of a first PTRA averaged 76.2%, 74.1%, and 67.7% for the unilateral (n = 42), bilateral (n = 27), and solitary (n = 31) groups, respectively. Of the technical successes, 59% (43/73) experienced sustained blood pressure benefit (mostly amelioration) during a mean follow-up period of 29 months. Rates of blood pressure benefit were similar in the three groups. Ostial lesions comprised the majority of blood pressure benefit failures. Repeat angioplasty in 14 patients resulted in a 71% technical success rate and a 50% blood pressure benefit rate during a mean follow-up period of 22 months. Long-term stability of mean serum creatinine level was observed after technically successful angioplasty in all three groups. Acute renal insufficiency, which was reversible in all but one patient, complicated 26% of the procedures. Mechanical complications occurred in 14% (20/145) of the arteries acted on; surgical intervention was required in five patients. The mortality rate was 2%. These results suggest that angioplasty is effective in both the long-term management of renovascular hypertension and the preservation of renal function in a large fraction of patients with atherosclerotic renovascular hypertension.

Hyperkalemia-like ECG changes simulating acute myocardial infarction in a patient with hypokalemia undergoing potassium replacement

A pseudo-infarctional ECG pattern, previously noted to occur rarely in association with hyperkalemia, was observed in a patient with severe hypokalemia in the course of K+ replacement but while she was still hypokalemic. It is inferred that this puzzling ECG feature reflected a reduction of intracellular/extracellular [K+] ratio in a patient with decreased intracellular K+ concentration undergoing rapid K+ repletion.

Cl(-)-dependent ATP-driven H+ transport in rabbit renal cortical endosomes

An endosomal fraction isolated from rabbit renal cortex by a novel, fast, and simple procedure was enriched in ATP-dependent H+ pumping that was oligomycin insensitive but was inhibited by dicyclohexylcarbodiimide (DCCD), N-ethylmaleimide (NEM), Zn2+, Hg2+, diethylstilbestrol, mersalyl, and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole. No substantial Na+-H+ exchange was detected. Electrogenicity of the pump was demonstrated using [14C]-SCN-. In addition, these membranes featured ATP-dependent Cl- flux. The ATP-driven H+ pumping had an absolute requirement for Cl-: an inside-negative membrane potential was not a substitute for Cl-. The protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone inhibited ATP-driven Cl- uptake but no inhibition was observed with nigericin. Finally, both ATP-driven H+ pumping and ATP-dependent Cl- flux were inhibited by Cl(-)-channel inhibitors. Part, or all, of the absolute dependence on Cl- may derive from a Cl- channel, the function of which is intimately related to H+ pumping by the ATPase. Flux through this Cl- channel may be regulated by one or more factors, including ATP, membrane potential, and pH.

The effect of potassium ion depletion on postinfarction canine cardiac arrhythmias

The effect of potassium ion (K+) depletion on postmyocardial infarction ventricular arrhythmias was investigated in 32 dogs: 12 control animals, 10 animals that ate a diet extremely low in K+ for 15 days, and 10 others that, in addition to dietary K+ deprivation, received 50 mg of hydrochlorothiazide four times. The experimental myocardial infarction was created by proximal left anterior descending coronary artery ligation. In a subgroup of 24 animals selected for relatively uniform size of myocardial infarction (14% to 22% of left ventricular mass), eight animals with mean cumulative K+ balance of -4.01 +/- 2.19 meq/kg developed spontaneous ventricular fibrillation within 4 to 17 min of coronary ligation, whereas 16 animals with a mean cumulative K+ balance of -0.11 +/- 1.82 meq/kg didn't. By univariate analysis cumulative K+ deficit (p = .001) and plasma K+ concentration (p = .039) correlated significantly with spontaneous ventricular fibrillation. Multivariate analysis of the entire population of 32 animals identified cumulative K+ deficit and size of myocardial infarction as the only independent predictors of ventricular fibrillation. Cumulative K+ deficit was also an independent predictor of ventricular fibrillation induced by programmed cardiac stimulation in the conscious state 1 day after myocardial infarction.

Serum creatinine and renal function

Serum creatinine is widely interpreted as a measure only of renal function; however, the serum level reflects not only renal excretion, but also the generation, intake, and metabolism of creatinine. In this review, we demonstrate that serum creatinine does not provide an adequate estimate of glomerular filtration rate (GFR), and contrary to recent teachings, that the slope of the reciprocal of serum creatinine vs time does not permit an accurate assessment of the rate of progression of renal disease. In clinical investigation, it is essential to utilize more accurate and sensitive measures of renal function to estimate GFR and progression. As effective treatments for progressive renal diseases are discovered, it will also be necessary to employ these measurements in clinical practice.

Severe lactic acidosis as a presenting feature of pheochromocytoma

High plasma concentrations of epinephrine and norepinephrine have the potential for generating substantial hyperlactatemia by virtue of their metabolic and vasoconstrictor effects; both these influences affect lactate metabolism in the direction of overproduction and underutilization. Nonetheless, lactic acidosis is not a recognized presenting feature of pheochromocytoma. In this report, we describe a patient with pheochromocytoma in whom the endogenous outpouring of epinephrine and norepinephrine resulted in severe lactic acidosis that featured prominently in the clinical presentation. Pheochromocytoma should be listed among the clinical entities associated with or predisposing to lactic acidosis.

Enalapril in the management of hypertension associated with renal artery stenosis

Enalapril maleate (MK-421) is a new non-sulfhydryl-containing converting-enzyme inhibitor that has been shown to be effective and well tolerated in patients with essential hypertension. Data on its effectiveness and safety in patients with renovascular hypertension are limited and have involved predominantly short-term observations. This is particularly true with respect to the long-term effects of enalapril on renal function. We report our experience using the combination of enalapril and hydrochlorothiazide (HCTZ) in a group of nine patients with moderate to severe hypertension associated with renal artery stenosis. The enalapril-HCTZ combination successfully controlled blood pressure in seven patients during a six-week period of study. Adverse effects were not noted, and detailed renal hemodynamic studies did not reveal any significant changes of renal plasma flow and glomerular filtration rate during this time interval. Five patients were continued on this regimen for a period of six to 18 months. In this group of patients, the regimen continued to be well tolerated and to provide excellent blood pressure control: glomerular filtration rate was maintained in two patients and variable grades of decrease were noted in three. The mechanism of this delayed renal dysfunction as well as its relationship to enalapril treatment remain unclear. The long-term impact of converting-enzyme inhibition on renal function requires further study.

Mineralocorticoid-stimulated renal acidification: the critical role of dietary sodium

Recent in vitro studies of isolated distal nephron segments have demonstrated that mineralocorticoid hormone stimulates H+ secretion by both Na+-dependent and Na+-independent mechanisms, and the Na+-independent acidification mechanism has a greater capacity. These in vitro data suggest that mineralocorticoid administration in vivo might increase renal acid excretion when an augmentation in distal Na+ reabsorption is precluded by rigid restriction of dietary Na+; under these circumstances, virtually all Na+ delivered to the distal nephron is reabsorbed in the basal state. In the present studies, prolonged (12 days) administration of DOC (15 mg/day) was undertaken in both Na+-fed and rigidly Na+-restricted dogs with chronic HCl acidosis. Na+-fed animals responded to DOC administration with a large increment in net acid excretion and complete correction of metabolic acidosis. Marked hypokalemia and significant kaliuresis also occurred. Na+-restricted dogs experienced no changes in renal acid excretion, systemic acid-base equilibrium, plasma [K+] or K+ balance. These results suggest that both renal H+ and K+ excretory responses to prolonged mineralocorticoid hormone administration in vivo are critically dependent on the availability for reabsorption of surplus Na+ within the distal nephron; this requirement is met when the diet, and hence the final urine, contains Na+ but cannot be satisfied when dietary Na+ is rigidly restricted.

Renal acidification during chronic hypercapnia in the conscious dog

Enhanced renal acidification during chronic hypercapnia (CH) results in transient augmentation in net acid excretion (NAE) (adaptation phase) and persistent acceleration in renal bicarbonate reclamation (adaptation and steady-state phases). The mechanisms responsible for the return of NAE to control values despite persistent acidemia during the steady state phase of CH remain undefined. In addition, it remains unsettled whether the enhancement of renal ammoniagenesis known to occur during the adaptation phase of CH persists during the steady-state phase. Furthermore it is uncertain if the alteration in whole-kidney acidification observed in CH originates from augmentation in the acidification of both proximal and distal nephronal segments. To shed further light on these issues, observations on the profile of the urine acid-base moieties during the adaptive and steady-state phases of CH were carried out in dogs chronically exposed to hypercapnia (10% FiCO2) in an environmental chamber (13 days). Additionally, collecting duct hydrogen ion secretion (CDH+S) was evaluated by employing the U-B PCO2 in alkaline urine in intact unanesthetized dogs with either CH (10% FiCO2) or eucapnia. The balance studies demonstrated that NAE increased in early hypercapnia (4.84 meq/kg body weight, control 3.27 meq/kg body weight, p less than 0.05) and returned to baseline thereafter; by contrast, urine NH+4 which was augmented during the adaptation phase (3.71 meq/kg body weight, control 1.97 meq/kg body weight, p less than 0.05) remained elevated throughout (3.25 meq/kg body weight).(ABSTRACT TRUNCATED AT 250 WORDS)

The renal response to chronic mineral acid feeding: a re-examination of the role of systemic pH

It has been widely held that systemic acidemia represents the proximate event signaling the kidney to elicit its acidification response to chronic metabolic acidosis. However, a previous study from this laboratory has cast serious doubt on the validity of this conventional viewpoint. When a large acid load (7 mEq/kg/day) was fed chronically to dogs as HCl, H2SO4 or HNO3, net acid excretion increased similarly in all three groups of animals despite wide variability in the prevailing systemic acid-base composition. Marked or moderate hypobicarbonatemia and acidemia were observed in the HCl- or H2SO4-fed animals respectively, but strikingly, plasma [HCO3-] and pH did not change significantly from the control in the HNO3-fed animals. That study concluded that the renal response to chronic mineral acid feeding appears to be triggered, not by acidemia, but by the interplay of sodium delivery to and sodium avidity of the distal nephron as modulated by the reabsorbability of the "acid" anion. We have re-examined the above provocative conclusion in the light of the observation that the only evidence for a dissociation of the renal response from systemic acidemia in that study was derived from preprandial (8:00 a.m.) blood samples obtained some 23 hr after the ingestion of the daily acid load (administered at 9:00 a.m.). We investigated the diurnal variation of plasma acid-base composition in two groups of dogs fed chronically a large acid load (7 mEq/kg/day) as either HCl or HNO3. Both groups exhibited significant diurnal oscillations of plasma acid-base composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug-induced hyperkalemia

After reviewing the available data on drug-induced hyperkalemia, we conclude that the situation has not improved since Lawson quantitatively documented the substantial risks of potassium chloride over a decade ago (90). As discussed, the risk of developing hyperkalemia in hospital remains at least at the range of 1 to 2% and can reach 10%, depending on the definition used (Table 2). Potassium chloride supplements and potassium-sparing diuretics remain the major culprits but they have been joined by a host of new actors, e.g., salt substitutes, beta-blockers, converting enzyme inhibitors, nonsteroidal antiinflammatory agents, and heparin, among others. Readily identifiable risk factors (other than drugs) for developing hyperkalemia are well-known but seem to be consistently ignored, even in teaching hospitals. The presence of diabetes mellitus, renal insufficiency, hypoaldosteronism, and age greater than 60 years results in a substantial increase in the risk of hyperkalemia from the use of any of the drugs we have reviewed. If prevention of hyperkalemia is the goal, as it should be, the current widespread and indiscriminate use of potassium supplements and potassium-sparing diuretics will need to end. We remain intrigued by Burchell's prescient pronouncement of over a decade ago that "more lives have been lost than saved by potassium therapy" (28).

Spurious assessment of acid-base status due to dilutional effect of heparin

A patient was encountered in whom clinically significant spurious hypocapnia and hypobicarbonatemia were diagnosed resulting from the dilutional effect of excessive amounts of sodium heparin solution in the blood sample. This report presents the relevant data in this patient, summarizes the effects of heparin on the determination of the acid-base status, and provides suggestions for avoiding this important pitfall in clinical practice.