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Biomedical subjects

G K van der Hem

Publications and source records attributed to G K van der Hem.

At least 19 recordsLinked to original sources
PubMed1994

Renal tubular sensitivity to atrial natriuretic factor in essential hypertension.

OBJECTIVE: To study the tubular site or sites of the natriuretic action of atrial natriuretic factor and the possible differences between healthy subjects and patients with essential hypertension. DESIGN: Nine healthy volunteers and six patients with essential hypertension were studied on four test days under standard conditions, water loading and hydropenia with mannitol or saline loading. On each test day baseline, atrial natriuretic factor infusion (1 microgram/min) and recovery measurements were performed after equilibrium had been reached. The measurements included the atrial natriuretic factor (ANF) plasma levels, blood pressure, glomerular filtration rate (GFR), effective renal plasma flow, urinary osmolality and the (fractional) excretions of (free) water, sodium and potassium. METHODS: Fractional free-water excretion and free-water reabsorption (as a function of osmolar clearance) were calculated during water loading and hydropenia with mannitol or saline loading, respectively, using standard formulae. [125I]-iothalamate and [131I]-hippuran were infused continuously for the measurement of GFR and effective renal plasma flow, respectively. RESULTS: The plasma ANF concentration rose five- to eightfold during the infusion of ANF, which induced an increase in urinary sodium excretion, a small increase in GFR and a decrease in the effective renal plasma flow. Moreover, ANF induced an increase in fractional free-water excretion and a decrease in fractional free-water reabsorption. These changes did not correlate with changes in GFR. The blood pressure and potassium excretion were not affected. The effects of ANF on the plasma ANF levels, natriuresis and renal haemodynamics did not differ between the normotensive and the essential hypertensives. However, the increase in fractional free-water excretion was significantly greater in the patients with essential hypertension and correlated significantly with blood pressure (r = 0.56, P < 0.05). CONCLUSIONS: These results indicate that the infusion of ANF at a low dose induces a similar natriuretic response in normotensive subjects and in patients with essential hypertension. This natriuresis is probably the result of both a glomerular and a tubular effect of ANF. Proximal as well as distal tubular sites seem to be involved. In essential hypertension an enhanced proximal as well as an impaired distal tubular action of ANF can be hypothesized.

Absorption↗
PubMed1992

Differences in erythrocyte sodium transport between human plasma and artificial medium: the role and character of sodium efflux and influx stimulating plasma factors.

The main objective of this study was to further characterize the plasma factor(s) which stimulate sodium efflux from erythrocytes, which we reported previously. Dialysis of plasma against an artificial medium using membranes with varying molecular mass cut-off points revealed relative molecular mass(es) of the factor(s) of 100-1000 Da. The factor(s) could be absorbed on Dowex at pH 1.5 and Amberlite at pH 11.0, indicating 'Zwitterionic' character. They are hydrophilic and resistant to acid hydrolysis. These characteristics and direct measurements of contents made amino acids likely candidates for the efflux stimulating properties of the factor(s). Indeed, plasma amino acids added to artificial medium could abolish the sodium efflux difference between plasma and the artificial medium. The efflux stimulating effect of amino acids appeared not to be the result of sodium influx stimulation. A coincident finding was that plasma also contains dialyzable sodium influx stimulating factor(s) which are not amino acids.

Adult↗
PubMed1992

Changes in renal function induced by ACE-inhibition in the conscious two-kidney, one-clip Goldblatt hypertensive dog.

In order to study why the diagnostic sensitivity of 123I-hippurate renography for a renal artery stenosis is improved by angiotensin converting enzyme (ACE-) inhibition we used the model of the conscious chronically instrumented two-kidney, one-clip Goldblatt hypertensive dog. Urine flow (UV), renal blood flow (RBF), glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured (with constant infusion of 125I-iothalamate and 131I-hippurate, respectively) for both kidneys separately before and after a bolus injection of a mild unilateral renal artery stenosis (approximately 30% reduction of RBF). During ACE-inhibition, there were remarkable falls in poststenotic GFR (from 37 +/- 5 to 4 +/- 2 ml/min, p less than 0.05), ERPF (from 111 +/- 13 to 21 +/- 10 ml/min, p less than 0.05) and UV (from 0.86 +/- 0.15 to 0.075 +/- 0.045 ml/min, p less than 0.05), whereas RBF of the poststenotic kidney slightly increased (from 193 +/- 18 to 237 +/- 27 ml/min, p less than 0.05). The concentration of hippurate and thalamate in the blood remained remarkably constant while the excretion of the tracers by the poststenotic kidney diminished and renal retention of 123I-hippurate was seen on the renogram. In 2 dogs, the experiments were repeated during mannitol infusion. In that situation, there was a much smaller decrease of poststenotic UV and GFR whereas ERPF even showed a small increase comparable to the RBF changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Atrial natriuretic factor influences renal diurnal rhythm in essential hypertension.

We investigated in six patients with essential hypertension the effect of a low dose atrial natriuretic factor infusion for 5 days on the diurnal rhythm of renal electrolyte excretion. Atrial natriuretic factor infusion increased the net excretion of sodium and caused a delay in its time of maximal diurnal urinary excretion. Similarly, atrial natriuretic factor caused an increase in the net excretion of chloride, calcium, and magnesium and also changed the diurnal rhythms of these electrolytes. In contrast, atrial natriuretic factor did not change the net excretion of potassium, phosphate, and uric acid, nor did atrial natriuretic factor change the diurnal rhythms of these solutes. During baseline, the time points of maximal urinary excretion of sodium and potassium overlapped, whereas atrial natriuretic factor infusion caused sodium excretion to peak 2.2 +/- 0.3 hours (p less than 0.02) after the potassium excretion peak. During baseline, the time of maximal urinary excretion of sodium did not correlate with the time of highest blood pressure, whereas it correlated negatively with mean plasma aldosterone concentration. In contrast, during atrial natriuretic factor infusion the time of maximal urinary excretion of sodium correlated positively with the time of highest blood pressure, whereas it did not correlate with mean plasma aldosterone concentration. These data suggest that atrial natriuretic factor is involved with the diurnal rhythm of the urinary excretion of sodium and that atrial natriuretic factor-induced natriuresis is mediated in part by blood pressure and plasma aldosterone.

Atrial Natriuretic Factor↗
PubMed1992

Explantation of mesangial cell 'hillocks': a method for obtaining human mesangial cells in culture.

A simple method is presented for selective cell culture of human mesangial cells using explantation of mesangial cell hillocks. Glomeruli which had been incubated with collagenase were explanted on plastic tissue culture flasks. Three to 6 weeks after explantation, a rapidly growing multilayer of elongated mesangial cells was observed to grow over the previously established monolayer of glomerular epithelial cells, ultimately forming multiple nodular foci of mesangial cells or 'mesangial cell hillocks'. By explanting mesangial cell hillocks selectively, pure mesangial cell cultures were easily obtained. When compared with mesangial cells grown in mixed cultures from glomerular explants, the hillock-derived cells were identical in morphology, growth characteristics, cell markers and synthesis of extracellular matrix. This system provides a simple method for the isolation of human mesangial cells in culture.

Adolescent↗
PubMed1991

Angiotensin II does not acutely reverse the reduction of proteinuria by long-term ACE inhibition.

Angiotensin converting enzyme (ACE) inhibitors are known to lower urinary protein excretion in human renal disease. This proteinuria lowering effect of ACE inhibition has been hypothesized to be a result of renal hemodynamic changes due to the inhibition of angiotensin II (Ang II) production. To test this hypothesis we studied the short-term effects of different doses of exogenous Ang II (5%, 10% and 20% of the pressor dose) on renal hemodynamics and urinary protein excretion in comparison with placebo infusion in six non-diabetic normotensive proteinuric patients, both before and after three months treatment with the ACE inhibitor, lisinopril. Lisinopril lowered proteinuria from 7.5 +/- 1.9 to 2.7 +/- 0.6 g/24 hr and induced a fall in blood pressure, renal vascular resistance and filtration fraction, whereas plasma Ang II levels were similar to the pre-treatment values. Ang II infusion induced typical effects which appeared to be similar before and during lisinopril treatment: a dose-related fall in renal plasma flow and rise in systemic blood pressure, renal vascular resistance and filtration fraction, while the glomerular filtration rate remained relatively stable. However, neither before nor during lisinopril therapy did any changes in urinary protein loss occur during the infusions of Ang II, despite the fact that Ang II reversed the long-term systemic and renal hemodynamic changes induced by the ACE inhibitor. We conclude that the long-term antiproteinuric effect of the ACE inhibitor, lisinopril, is neither mediated through changes in circulatory Ang II levels nor influenced by acute changes in systemic and renal hemodynamics, suggesting a non-hemodynamic mechanism of action.

Adult↗
PubMed1990

Prevention of relapses in Wegener's granulomatosis by treatment based on antineutrophil cytoplasmic antibody titre.

58 patients with biopsy-proven Wegener's granulomatosis (WG) were prospectively screened for clinical evidence of the disease 3-monthly, with antineutrophil cytoplasmic antibody (ANCA) measurements every month. Over 24 months, ANCA rose in 20 patients, 9 of whom were randomly assigned to receive combined 9 and 3 month courses of cyclophosphamide and prednisolone, respectively, at the time of ANCA rise; and 11 patients who were untreated except if there was a clinical relapse. 6 of 11 untreated patients relapsed within 3 months of ANCA rise. 3 of the remaining 5 patients relapsed after 3 months. There were no early or late relapses in patients randomised to treatment. Patients receiving no treatment at the time of ANCA rise took more cyclophosphamide and prednisolone than patients who were treated. Side-effects did not significantly differ between the two groups.

Adult↗
PubMed1990

Association of autoantibodies to myeloperoxidase with different forms of vasculitis.

Antineutrophil cytoplasmic autoantibodies with specificity for myeloperoxidase (MPO) were found in 53 patient sera that were routinely submitted for antineutrophil cytoplasmic antibody determination. Based on clinical and histologic criteria, 15 of these 53 patients were classified as having systemic necrotizing vasculitis of the polyarteritis group, 11 patients were classified as having Wegener's granulomatosis (WG), and 14 were classified as having idiopathic crescentic glomerulonephritis. The remaining 13 patients did not fulfill the diagnostic criteria for these disorders, although most of these patients had clinical symptoms compatible with these disorders. While all patients with WG had renal involvement, only 4 of the 15 patients with systemic necrotizing vasculitis of the polyarteritis group had glomerulonephritis. The sensitivity of autoantibodies to MPO for either systemic necrotizing vasculitis of the polyarteritis group, WG, or idiopathic crescentic glomerulonephritis was further tested in all our patients with these disorders (n = 104). Twenty-seven of 104 patients had autoantibodies to MPO. Furthermore, 69 of the remaining 77 patients had autoantibodies specific for the 29-kd serine protease, which has been reported to be specifically associated with WG. Sera from 8 patients were negative for either of these antibodies (92% sensitivity of autoantibodies to MPO and/or the 29-kd serine protease). The specificity of autoantibodies to MPO for either systemic necrotizing vasculitis of the polyarteritis group, WG, or idiopathic crescentic glomerulonephritis was also tested in selected groups of patients who had closely related diseases. Two of 144 patients had autoantibodies to MPO (specificity 99%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Autoantibodies against myeloid lysosomal enzymes in crescentic glomerulonephritis.

To investigate the possible association of crescentic glomerulonephritis (CGN) with autoantibodies to myeloid lysosomal enzymes, we tested sera from 35 consecutive patients with CGN without diagnostic immunohistological findings in their renal biopsy for the presence of antineutrophil cytoplasmic antibodies directed against a 29 kD antigen from azurophilic granules (29 kD-ANCA), against myeloperoxidase (MPO-ANCA) and against elastase (elastase-ANCA), using antigen-catching ELISAs with well-defined monoclonal antibodies. 29 kD-ANCA were present in the sera of all nine patients with CGN as part of biopsy-proven Wegner's granulomatosis (WG), of ten patients with CGN and clinically suspected WG, and of two patients with idiopathic CGN. Sera from the remaining patients with clinically suspected WG (N = 5) or idiopathic CGN (N = 6) were negative for 29 kD-ANCA, but invariably positive for MPO-ANCA. Neither of these antibodies could be detected in sera from patients with CGN of infectious origin (N = 3), different forms of CGN (N = 7), other renal lesions (N = 34), or normal controls (N = 52). None of the sera tested were positive for elastase-ANCA. Our results indicate that both vasculitis-associated CGN and idiopathic CGN are associated with autoantibodies against myeloid lysosomal enzymes. This finding places these disorders within one spectrum of diseases.

Autoantibodies↗
PubMed1989

Human plasma contains low molecular weight factors which stimulate active sodium transport in erythrocytes.

The aim of this study was to establish whether differences in sodium efflux rate constants (ke) in human erythrocytes occur when artificial media are compared with plasma. Using a 22Na tracer method, a mean total ke of 0.49 +/- 0.10 h-1 and significantly (p less than 0.05) lower ke values in Hanks' solution (0.43 +/- 0.08 h-1) and Basic Salt Solution (0.37 +/- 0.07 h-1) were observed. Exhaustive dialysis of plasma against Hanks' solution over a membrane with relative molecular mass cut-off of 1000 Da resulted in a decrease of the plasma total ke value to that measured in Hanks' solution. After equilibrium dialysis of plasma against Hanks' solution a decrease of total ke was found in plasma and an increase of the ke in Hanks' solution was measured. The data suggest the presence of an excess of dialyzable, active sodium transport stimulating plasma factor(s) with relative molecular mass below 1000 Da.

Adult↗
PubMed1989

Association between active Wegener's granulomatosis and anticytoplasmic antibodies.

Autoantibodies reacting with the cytoplasm of granulocytes and monocytes (anticytoplasmic antibodies [ACPAs]) were found in 42 of 45 patients with active Wegener's granulomatosis (WG) (sensitivity, 93%). Specificity was tested in selected groups of patients with closely related diseases. Of 58 patients without a diagnosis of WG, 2 had ACPAs (specificity, 97%). The significance of ACPA titration for assessing or predicting disease activity was evaluated in a 16-month prospective study of 35 patients with WG. Seventeen relapses were observed and all were preceded by a significant rise of the ACPA titer. Anticytoplasmic antibodies are a specific and sensitive marker for active WG; a rising titer is a sensitive marker for the development of a relapse.

Adult↗
PubMed1989

Complement activation during an active cytomegalovirus infection after renal transplantation: due to circulating immune complexes or alternative pathway activation?

In 32 patients with a renal allograft, serial determinations after transplantation were made of C3d, the stable conversion product of the complement factor C3, as well as serial measurements of the anaphylatoxin C3a des arg. Furthermore, serial determinations were made on the presence of circulating immune complexes using three different assays (C1q binding assay, polyethylene glycol precipitation test, and indirect granulocyte phagocytosis test). Twenty patients were studied during an active cytomegalovirus (CMV) infection, and 12 patients were studied during allograft rejection or during stable phase after renal transplantation. In 12 patients with a CMV infection serial measurements were made of AP50 (alternative pathway of complement). During an active CMV infection elevated C3d as well as elevated C3a des arg levels were found and not in the control group (P less than 0.01). In 8 out of the 12 patients tested, with CMV infection, a decreased hemolytic activity of the alternative pathway (AP50) was found, together with the elevated levels of C3d and C3a des arg. Serum C4 levels were normal or high during CMV infection. Furthermore, circulating immune complexes were found to be positive in 15 out of the 20 patients with a CMV infection (both primary and secondary infections), and in 2 out of 12 patients of the control group. The complement activation found in the CMV group was not related to the presence of circulating immune complex-like material, since complement activation was present in advance of the appearance of the immune complexes, suggesting that complement activation was not due to classical pathway activation by those complexes. We conclude that our data are consistent with complement activation and the formation of biologically active peptides like C3a des arg in patients with an active CMV infection. The decreased hemolytic activity of the alternative pathway (AP50) together with the normal or high C4 levels suggest involvement of the alternative pathway, although further studies of the alternative pathway of C are warranted to confirm this hypothesis.

Adolescent↗
PubMed1989

Efficacy and variability of the antiproteinuric effect of ACE inhibition by lisinopril.

We studied the efficacy of the ACE inhibitor lisinopril in treating overt proteinuria in comparison with the NSAID indomethacin, and evaluated some of the conditions that could influence this antiproteinuric effect. In 12 patients with a proteinuria varying from 3.2 to 10.5 g/24 hr, a diastolic BP ranging from 64 to 105 mm Hg, and a GFR varying from 34 to 127 ml/min, the effect of different lisinopril doses and of changing dietary sodium intake was evaluated. Proteinuria fell by 27 +/- 20% from 6.1 +/- 2.1 to 4.5 +/- 1.9 g/24 hr on a low dose (median 5 mg/day) lisinopril and by 50 +/- 17% to 3.1 +/- 1.4 g/24 hr on a higher dose (median 10 mg/day), irrespective of initial proteinuria, BP, or GFR. This antiproteinuric effect was abolished by increasing salt intake from 50 to 200 mmol/day, and was recovered again by re-instituting the sodium restricted diet. The antiproteinuric effect of 10 mg/day lisinopril was comparable to the reduction in proteinuria (by 57 +/- 21% to 2.8 +/- 2.0 g/24 hr) on 150 mg/day indomethacin, while adverse effects were less and renal hemodynamic effects were more favorable during lisinopril. In some patients it took several weeks before the effect of the ACE inhibitor on proteinuria was stabilized. Thus, the antiproteinuric effect of the ACE inhibitor lisinopril appears to be dose and time related, and is strongly dependent on dietary sodium restriction, whereas it does not depend on initial proteinuria, BP, or GFR. The effect is comparable to that of indomethacin, while adverse effects are less.

Adult↗
PubMed1989

Atrial natriuretic peptide-induced decreases in renal blood flow in man: implications for the natriuretic mechanism.

1. We studied the effect of a low-dose infusion of atrial natriuretic peptide (ANP) on renal blood flow in healthy volunteers. We additionally investigated the effect of ANP on renal haemodynamic function and on urinary sodium excretion. 2. ANP induced a rise in packed cell volume and a slight increase (but no decrease) in the renal extraction of hippuran. These changes did not offset the observed fall in effective renal plasma flow. Renal blood flow thus truly decreased and renal vascular resistance increased. 3. ANP induced an increase in glomerular filtration rate and a decrease in urinary osmolality in the first hour of ANP infusion, whereas absolute and fractional sodium excretion increased significantly only in the second hour of ANP infusion. The decrease in urinary osmolality in the first hour of ANP infusion correlated with the induced natriuresis. The changes in urinary osmolality and sodium excretion both correlated with the changes in plasma ANP levels. 4. These data indicate that ANP may cause a decrease in renal blood flow and an increase of renal vascular resistance in man. Our results suggest a role for ANP-induced (intra)renal haemodynamic changes in ANP-induced natriuresis, possibly through an increase in the filtered load of sodium into a washed-out medullary interstitium.

Adult↗
PubMed1989

Antihypertensive effect of a 5-day infusion of atrial natriuretic factor in humans.

Atrial natriuretic factor was infused in a low dose (0.2 microgram/min) during 5 days in six patients with essential hypertension. Atrial natriuretic factor infusion caused plasma levels of atrial natriuretic factor to increase from 49 +/- 10 to 106 +/- 19 pg/ml. Within 4 hours after the start of the atrial natriuretic factor infusion, urinary sodium excretion increased in all subjects. Sodium balance was regained after 24 hours with a net loss of 72.3 +/- 14.6 mmol. However, systolic as well as diastolic blood pressure started to decrease gradually in all subjects only after 12 hours of atrial natriuretic factor infusion, reaching a stable level after 36 hours with a decrease of 11.5 +/- 1.5% and 10.3 +/- 0.8%, respectively. Heart rate increased in parallel by 12.6 +/- 3.1%. Hematocrit rose 7.1 +/- 2.3%. After cessation of atrial natriuretic factor infusion, plasma atrial natriuretic factor levels, sodium balance, and hematocrit returned to baseline within 24 hours, whereas blood pressure slowly returned toward baseline values over 3 days. These data show that chronic atrial natriuretic factor infusion in patients with essential hypertension causes a negative sodium balance and a rise in hematocrit, followed by a smooth decrease in blood pressure with a rise in heart rate until a new equilibrium is reached after approximately 2 days. Thus, atrial natriuretic factor in low doses appears intimately involved in the regulation of sodium balance and blood pressure in humans. Moreover, these data suggest that atrial natriuretic factor-like substances will eventually become useful antihypertensive drugs.

Antihypertensive Agents↗
PubMed1989

Diagnostic use of angiotensin converting enzyme inhibitors in radioisotope evaluation of unilateral renal artery stenosis.

Iodine-123 hippurate renography, [99mTc]diethylenetriaminepentaacetic acid (DTPA) renography, and [99mTc]dimercapto succinic acid (DMSA) renal scintigraphy were performed before and during angiotensin converting enzyme (ACE) inhibition in a group of 15 hypertensive patients with angiographically "significant" unilateral renal artery stenosis. Visual and quantitative evaluation of the three radioisotope methods before ACE inhibition already disclosed abnormalities suggestive of renal artery stenosis in a high percentage (87%, 60%, and 60%, respectively) in this group of patients, but ACE inhibition further improved the diagnostic yield in all three methods (93%, 86%, and 80%). Iodine-123 hippurate renography was at least as useful as [99mTc]DTPA renography in this respect, while [99mTc]DMSA scintigraphy can be used particularly in segmental stenosis. Despite a large drop in blood pressure after ACE inhibition little adverse reactions were seen and overall renal function was fairly well maintained, the exceptions noted in patients with initially a more impaired renal function.

Adolescent↗