Digitalislike immunoreactive substances and extracellular fluid volume status in chronic hemodialysis patients

Endogenous cardiotonic steroids in kidney failure: a review and an hypothesis

In response to progressive nephron loss, volume and humoral signals in the circulation have increasing relevance. These signals, including plasma sodium, angiotensin II, and those related to volume status, activate a slow neuromodulatory pathway within the central nervous system (CNS). The slow CNS pathway includes specific receptors for angiotensin II, mineralocorticoids, and endogenous ouabain (EO). Stimulation of the pathway leads to elevated sympathetic nervous system activity (SNA) and increased circulating EO. The sustained elevation of circulating EO (or ouabain) stimulates central and peripheral mechanisms that amplify the impact of SNA on vascular tone. These include changes in synaptic plasticity in the brain and sympathetic ganglia that increase preganglionic tone and amplify ganglionic transmission, amplification of the impact of SNA on arterial tone in the vascular wall, and the reprogramming of calcium signaling proteins in arterial myocytes. These increase SNA, raise basal and evoked arterial tone, and elevate blood pressure (BP). In the setting of CKD, we suggest that sustained activation/elevation of the slow CNS pathway, plasma EO, and the cardiotonic steroid marinobufagenin, comprises a feed-forward system that raises BP and accelerates kidney and cardiac damage. Block of the slow CNS pathway and/or circulating EO and marinobufagenin may reduce BP and slow the progression to ESRD.

The kidney and hypertension: causes and treatment

Chronic kidney disease is both a cause and a consequence of hypertension. Extracellular volume expansion is an important, if not the most important, contributing factor to hypertension seen in chronic kidney disease. Beyond volume expansion, chronic kidney disease-related hypertension is without truly defining characteristics. Consequently, the sequencing of antihypertensive medications for the patient with chronic kidney disease and hypertension becomes arbitrary. Prescription practice in such patients should be mindful of the need for multiple drug classes with at least one of them being a diuretic. Blood pressure goals in the patient with chronic kidney disease and hypertension are set at lower levels than those for patients with essential hypertension alone. It remains to be determined to what level blood pressure should be lowered in the patient with chronic kidney disease, however.

Pathologic Basis and Treatment Considerations in Chronic Kidney Disease-Related Hypertension

Chronic kidney disease (CKD) is both a cause and an effect of hypertension and is multifactorial in its origin. Beyond volume expansion, CKD-related hypertension is without defining characteristics of any consistency. Consequently, the order in which antihypertensive medications are given to the CKD patient with hypertension is arbitrary, although prescription practice is for the most part mindful of the need for multiple drug classes with at least one of them being a diuretic. It is not without reason that blood pressure goals in the hypertensive CKD patient are set at lower levels than those for patients with essential hypertension, but it remains to be determined how much the blood pressure should be decreased in the CKD patient.

Digoxin-like immunoreactive substance in renal transplant patients

Digoxin-like immunoreactive substance (DLIS) has been detected in several patient populations that were not receiving digoxin, including those patients with end-stage renal disease. The structure and physiologic significance of this compound are unknown, and the fate of DLIS after renal transplantation has not been studied. The authors prospectively evaluated 163 patients (not receiving digoxin) before and after transplantation for the presence of DLIS. Three different assays were used: radioimmunoassay (RIA), affinity mediated immunoassay (ACA), and fluorescence polarization immunoassay (TDX I). Depending on the assay method used, 11% (RIA), 6% (ACA), and 9% (TDX) of patients had detectable DLIS pretransplant. Using all 3 assays, a total of 34 patients (21%) were found to have DLIS. The mean serum digoxin concentration was 0.41 +/- 0.13 ng/mL (range: 0.2-1.2 ng/mL) and DLIS was detectable by greater than 1 assay method in seven patients. DLIS persisted longer in patients who had delayed allograft function (13.7 +/- 7 days) than in those who did not (3 +/- 1.9 days), P less than .05. In summary, detection of DLIS in renal transplant recipients appears to be an infrequent occurrence when using a single digoxin assay method. When detected, the concentration of DLIS is often below the usual therapeutic range for digoxin and disappears once allograft function is established. The authors conclude that the presence of DLIS is unlikely to be clinically significant in the renal transplant population.

Dialyzability and binding of digoxin-like immunoreactive factors (DLIF) with serum macromolecules in uremic patients on hemodialysis

Digoxin-Like Immunoreactive Factors (DLIF) which cross-react with antidigoxin antibodies are present in elevated concentrations in patients on hemodialysis, uremia, hypertensives, liver failure, pre-eclampsia and premature birth. DLIF may have a potential role as a natriuretic hormone with a speculated low molecular weight (less than 1000). We studied the dialyzability and bindings of DLIF with serum components in hemodialysis patients. We analyzed DLIF concentrations in sera and protein free ultrafiltrates of 31 patients and 22 normal volunteers using a fluorescence polarization assay for digoxin. The DLIF concentrations were expressed as nmol/L Digoxin Equivalent. The gel filtration analysis was done using three different Bio-Gel columns with molecular weight cut-offs of 10,000, 20,000 and 40,000. Molecules with lower molecular weight than cut-off were absorbed in the column. Only 3 out of 22 normal volunteers (13.6%) showed measurable DLIF. However 23 out of 31 patients (74.2%) showed measurable DLIF. The concentrations of DLIF were significantly higher in patients with renal failure on hemodialysis (P less than 0.05) by both chi-squared and Fisher's exact test. We observed no statistically significant difference in the concentrations of DLIF in pre and post-dialysis sera, indicating that DLIF were not filtered during hemodialysis. We observed no DLIF activity in the protein free ultrafiltrates of any DLIF positive sera (patients and normal volunteers), indicating that unlike digoxin (where we observed 70-80% of total digoxin concentrations in ultrafiltrates), DLIF were strongly bound to serum components. With Bio-Gel filtration experiments (five different serum pools), we recovered all DLIF activities in the fraction equivalent to the void volume of the column with Bio-Gel P6 and P10 columns, indicating that DLIF were almost completely bound to serum components with molecular weight greater than 20,000. On the other hand, we recovered no DLIF activities in the void volume when the same serum pools were passed through the Bio-Gel P30 column, indicating that DLIF were strongly bound to serum macromolecules with molecular weight less than 40,000. In sharp contrast, when serum containing digoxin was subjected to the same series of experiments, we recovered only 20-30% of digoxin concentrations in void volume with all three columns as expected since digoxin is only 25% bound to albumin (MW 67,000).

Correlation of blood pressure in end-stage renal disease with platelet cytosolic free-calcium concentration

The fluorescent probe Quin-2 showed the cytosolic free-calcium concentration in platelets to be elevated in 12 hypertensive hemodialysis patients, who were compared with 12 normotensive hemodialysis patients. There was a close correlation between the free-calcium level of platelets and mean arterial pressure (r = 0.88). Short-term antihypertensive treatment resulted in a reduction of free-calcium concentration and a concomitant fall in blood pressure. These results suggest an integrative contributory role for calcium in the pathophysiology of hypertension accompanying end-stage renal disease.