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Biomedical subjects

H Knauf

Publications and source records attributed to H Knauf.

At least 55 records · Page 3Linked to original sources
PubMed1987

Dissociation of the natriuretic and antikaliuretic properties of triamterene derivatives by dose-response experiments.

Several derivatives of triamterene were synthesized with the aim of obtaining physicochemical properties superior to those of triamterene. Their effects on electrolyte excretion were tested with dose-response curves in rats: a dissociation of ED50 values of Na+ excretion from those of K+ retention was found; while the ED50 values of natriuresis were structure independent, the ED50 values for potassium retention depended highly on the charge of the side chain of triamterene derivatives. Acidic compounds displayed low and amines high K+-retaining potencies. Hence we postulate that there are at least two sites of action of the tested compounds in the kidney. (i) The first is the Na+ difference; this is the main driving force for K+ secretion. The affinity to the Na+ conductance is not correlated with the basic/acidic properties of the compounds. (ii) The second site is the finite K+ conductance of the luminal membrane of the distal tubule. The affinity of the drugs to this K+ conductance depends strongly on the charge of the molecule. Only pteridine derivatives with a basic side chain, i.e., with a high pKa value, block the membrane K+ conductance and are therefore potent potassium-retaining drugs.

Animals↗
PubMed1987

Altered kinetics of etozolin and its active metabolite ozolinone in hepatitis and hepatic cirrhosis with ascites.

The single dose kinetics of (Z)-(3-methyl-4-oxo-5-piperidino-thiazolidin-2-ylidene)acetate (etozolin) and its active metabolite ozolinone were determined in 6 healthy volunteers, in 12 patients with acute hepatitis and in 15 patients with hepatic cirrhosis with ascites. In hepatitis, the elimination half-life of etozolin was 4 times longer resulting in a 2 fold rise in the AUC. At the same time, plasma levels of ozolinone were lower and consequently the AUC of his metabolite was reduced. In cirrhosis, the plasma level time curves of etozolin and ozolinone differed significantly from the controls and also from those of the patients with acute hepatitis. For etozolin Cmax was reduced to about 1/2, the elimination half-life being increased by a factor of 5. This resulted in a 3 fold higher AUC. As for ozolinone the reduction of plasma levels was more pronounced--Cmax fell to 1/6 of the control value--so that in spite of a longer elimination half-life, the AUC fell to 1/2. Ascites concentrations of etozolin and ozolinone were almost identical to the plasma concentration. The results suggest that acute hepatitis and hepatic cirrhosis lead to a reduced formation of ozolinone. As a result, etozolin accumulates and plasma levels of oxolinone drop. Moreover, both substances enter the ascites to a significant degree. It is concluded that these changes in the kinetics of this lipophilic diuretic do not allow a reliable dosage regimen in patients with hepatic cirrhosis and ascites.

Acute Disease↗
PubMed1987

Determination of verapamil and norverapamil in human biological material. Investigation of plasma concentrations after oral administration of two different verapamil formulations.

A method for the simultaneous determination of the cardiovascular agent verapamil and its major metabolite norverapamil in human plasma is described. Analysis is performed after alkaline extraction with n-heptane by subsequent ion-paired high performance liquid chromatographic (HPLC) separation, and direct fluorimetric measurement of both compounds (lambda maxex. = 278 nm, lambda maxem. = 320 nm). The sensitivity of the procedure (detection limit less than 1 ng/ml) is suitable for pharmacokinetic studies after therapeutic doses. The applicability of the method was tested by performing a clinical study. Plasma concentrations of two verapamil formulations for oral administration were examined. The active metabolite norverapamil was included in the investigation.

Administration, Oral↗
PubMed1986

Modelling of colonic Cl- and K+ transport under resting and secreting conditions.

Transport of electrolytes, particularly of Cl- and K+, by the rat proximal colon was studied in vivo under conditions of high and low K+ diet and in the presence of transport inhibitors and secretagogues. The electrical parameters, PD, Isc, Rm, were monitored by direct clamping and via cable analysis. The present work reinforces own earlier work and that of others that - under control conditions - absorption of Na+ and Cl- is mainly electrically neutral. Low K+ diet reduced absorption of Na+ and Cl-, as well as secretion of K+, and increased HCO3- absorption. High K+ predominantly increased K+ secretion and reduced HCO3- absorption, these diet-induced changes being electrically neutral. Secretagogues such as PGE1 and theophylline reduced net absorption of Na+ and Cl-, increased the Isc and lowered the Rm. These effects could be reversed by the antidiarrheal drugs, loperamide and somatostatin, except the increase of K+ secretion, and reversed HCO3- transport absorption to secretion. A model consisting of absorptive columnar cells and secreting crypt cells is presented which encompasses the known and supposed aspects of colonic ion transport.

Alprostadil↗
PubMed1986

Ion transport in rat proximal colon in vivo.

Active Na+ absorption by the rat proximal colon in vivo is for the most part electrically silent. The rheogenic Na+ flux makes up only 8%. To elucidate the underlying transport pathways, the following experimental approaches were used: ion substitution experiments such as choline for Na+, cyclamate for Cl-, variation of luminal pH; administration of known inhibitors; and determination of changes in luminal CO2 tension and pH. The transcolonic ion fluxes as well as the electrical parameters potential difference, specific electrical resistance, and short-circuit current were monitored. Na+ transport was drastically reduced in the absence of luminal Cl-, and vice versa Cl- absorption was blocked at zero Na+. NaCl absorption was blocked by amiloride (10(-3) M) and 4-acetamido-4'-isothiocyanostilbene-2, 2'-disulfonic acid and was lowered by acetazolamide. Colonic NaCl absorption was not influenced by luminal furosemide. Na+ absorption increased with alkalinization of the luminal fluid. Tris instead of HCO-3 buffer at constant pH favored Cl- uptake. The results may easily be explained by the operation of a Na+-H+ antiport functionally coupled to a Cl(-)-HCO-3 antiport. These transport processes are supposed to be present in the columnar cells of the colonic epithelium. There is good evidence for the association of K+ secretion with rheogenic Cl- secretion by the crypt cells.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1986

[Effect of the angiotensin II analog saralasin before donor nephrectomy on primary transplant function].

Cadaver kidney donors were treated with Angiotensin II-Analogon-Saralasin before nephrectomy in order to reduce the rate of acute renal failure. Eighteen (64.3%) of the recipients of the 30 donor kidneys pretreated with Saralasin were primarily free from dialysis. Six recipients showed acute renal failure. Two donor kidneys never resumed their function and no reports could be obtained on two organs. In the control-group with no pre-treatment, acute renal failure appeared significantly more often (67.3%). Thus only 32.7% of the recipients needed no further dialysis. This difference is statistically significant.

Acute Kidney Injury↗
PubMed1985

Determination of rheogenic ion transport in rat proximal colon in vivo.

A direct clamping technique is demonstrated, which allows monitoring of rapid changes of the short-circuit current (Isc) and the specific transepithelial resistance (Rm) as well as measurement of ion fluxes under short-circuit conditions in vivo. Due to the cylindrical symmetry of the colon the intraluminal electrode was devised as a centrally fixed silver rod, by which radial current injection was achieved. The geometrical arrangement of the electrodes guaranteed zero potential difference (PD) along the whole axis of the colon segment. The Isc was determined to 3.3 +/- 0.7 mueq h-1 cm-2 and Rm equal to 121 +/- 5 omega cm2. These data obtained by direct short-circuiting agree well with our earlier Rm and Isc data based on cable analysis, where the Isc was calculated from the open-circuit PD and Rm. This is considered as evidence for the reliability of the two independent in vivo techniques. Their validity was confirmed by the expected effects of drugs acting on rheogenic ion transport. Both the indirect (via Rm) as well as the direct Isc determination may be used alternatively as required; one may serve to match the other. For larger tubular structures like the rat colon the direct clamping should be preferred as the standard procedure for the Isc determination in vivo.

Alprostadil↗
PubMed1985

Pharmacokinetics of carteolol in relation to renal function.

The plasma levels and urinary excretion of carteolol and its main metabolites 8-hydroxycarteolol and carteolol glucuronide were investigated in 6 healthy subjects and 9 patients with varying degrees of renal impairment following a single oral dose of 30 mg carteolol hydrochloride. In healthy subjects the half-life of carteolol was 7.1 h. 63% of the administered dose was recovered unchanged in urine, and in all 84% was excreted by the kidneys. The renal clearance of carteolol was 255 ml/min. In chronic renal failure (CRF) the terminal half-life was increased to a maximum of 41 h. Both the elimination rate constant and renal clearance were closely related to the creatinine clearance. In CRF the recovery of carteolol and its metabolites from urine was considerably reduced, suggesting that another pathway of drug elimination becomes relevant in renal disease. To avoid an increase in side-effects due to drug accumulation, the dosage of carteolol should be adjusted in relation to the reduction in creatinine clearance. The maintenance dose should be reduced to a half in patients with a creatinine clearance below 40 ml/min and above 10 ml/min. In those with a creatinine clearance of 10 ml/min or less, the dose should be reduced to 1/4.

Adult↗
PubMed1985

Limitation on the use of amiloride in early renal failure.

The effect of a single oral dose of 10 mg amiloride was studied on urinary excretion of Na+, K+, Ca++ and Mg++ in healthy subjects and in patients with varying degrees of renal impairment. Amiloride produced a moderate diuresis and sodium excretion, and a slight calciuresis. Urinary excretion of potassium was significantly reduced as compared to the controls. Despite its diuretic and natriuretic effects, amiloride did not change the excretion of Mg++ as compared to the pretreatment period. When the creatinine clearance was below 50 ml/min, the net excretion of Na+ and Ca++ was drastically reduced. However, K+ retention and neutrality of Mg++ excretion were maintained down to end-stage renal disease. In the healthy volunteers the mean elimination half-life of amiloride was 20 h, and it rose to about 100 h in end-stage renal disease. This was because about 3/4 of native amiloride was eliminated through the kidney. Nonrenal elimination of amiloride was calculated to amount to only 1/4 of the total elimination. Therefore, the anticaliuretic amiloride is a valuable comedication in subjects with normal kidney function to prevent K+ and Mg++ loss. However, its use is hazardous if plasma creatinine is raised.

Adult↗
PubMed1985

Evidence for mitochondrial origin of the HCO3(-)-ATPase in brush border membranes of rat proximal tubules.

High HCO3(-)-ATPase activity is known to exist in mitochondria of renal tubular cells. In brush border membrane (BBM) preparations of proximal tubules such an anion-stimulated enzyme was also found. However, these preparations always contained mitochondrial markers. The putative localization and the role of this ATPase in BBM is still controversial. Some authors consider the HCO3(-)-ATPase in the BBM to be a mitochondrial contamination; others attribute to this ATPase a key role in H+ transport in the proximal tubule. To reinvestigate this problem, BBMs from rat kidney cortex were isolated by a simple, rapid (1.5-h) Ca2+-precipitation method, yielding a BBM fraction enriched 12.4-fold with respect to the marker enzyme leucine aminopeptidase (LAP). There was no basolateral Na+-K+-ATPase and no mitochondrial succinate dehydrogenase detectable. Cytochrome c oxidase was drastically reduced to 7 +/- 1% of that observed in the homogenate (TH). The activity of HCO3(-)-ATPase in the BBM fraction was 19 +/- 4 IU/g protein, i.e., 27% that of the homogenate. As sonication of the TH exclusively increases the activity of HCO3(-)-ATPase, its relative activity was 7.5% and thus equal to that of the mitochondrial marker. In many BBM preparations no HCO3(-)-ATPase was detectable. In those BBM preparations in which traces of HCO3(-)-ATPase were found, this activity coincided with that of cytochrome c oxidase in the respective preparation. There was a constant activity ratio of cytochrome c oxidase/HCO3(-)-ATPase in the TH, BBM, and pellet 1. The activity of HCO3(-)-ATPase in BBM did not depend on the activity of LAP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1984

Pharmacodynamics and kinetics of etozolin/ozolinone in hypertensive patients with normal and impaired kidney function.

The effect on urinary electrolyte excretion, renin release and plasma norepinephrine of single oral doses of 400 mg etozolin (E) and of 40 mg furosemide (F) were studied in hypertensive patients with normal (n = 6) and impaired kidney function (n = 6). E caused a marked saluresis up to 24 hours, showing its long duration of action. F, however, displayed a brief, brisk peak diuresis, followed by a rebound from the 4th to the 24th hours. The brisk peak diuresis induced by F was associated with pronounced release of renin, almost twice that induced by E. In chronic renal failure the renin release in relation to the magnitude of the diuresis was increased, i.e. the sensitivity of these patients to changes in water homeostasis was increased. E and F stimulated the sympathetic system to roughly the same extent. Patients with essential hypertension had higher plasma levels of norepinephrine than hypertensive patients with chronic renal failure. In addition, hypertensive patients with normal renal function (n = 4) and varying degrees of renal impairment (n = 11) were also given 400 mg daily for 2 weeks. Effects on blood pressure and electrolyte homeostasis were monitored, as well as the plasma kinetics of metabolite I, ozolinone. At the end of the 2 week treatment E had significantly lowered systolic (-12 mm Hg) and diastolic (-9 mm Hg) blood pressure, and had produced a significant loss of body weight, without altering plasma electrolytes or blood chemistry. There was no accumulation of the effective metabolite ozolinone under conditions of severe impairment of kidney function.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Pharmacodynamics and pharmacokinetics of xipamide in patients with normal and impaired kidney function.

The effect of a single oral dose of 40 mg xipamide on urinary excretion of Na+, K+, Cl-, Ca2+ and Mg2+ in healthy subjects and in patients with varying degrees of renal impairment was compared with various conventional diuretics. Xipamide caused marked excretion of Na+ and Cl-, whereas the diuretic produced only moderate kaliuresis; urinary excretion of Ca2+ was increased in proportion to Na+, like the loop diuretics. Xipamide affected electrolyte excretion even in patients with a creatinine clearance below 30 ml/min, as do the loop diuretics, too. Therefore, the pharmacodynamic characteristics of xipamide are more like those of a loop diuretic than of a thiazide. Xipamide was good bioavailable, its t 1/2 beta was 7 h and urinary recovery of the undegraded drug was 40% of the given dose. In renal insufficiency, t 1/2 beta increased from 7 to only 9h, yielding a moderate increase in the AUC. Urinary recovery of the drug was reduced in proportion to the reduction in the creatinine clearance of the patient. Therefore, significant extrarenal elimination of the diuretic must be postulated, which suffices to prevent significant drug accumulation in renal failure.

Adult↗
PubMed1984

Pharmacokinetics of nadolol in healthy subjects.

In 7 healthy subjects (3 males and 4 females), the kinetics of nadolol was investigated after oral doses of 60 and 120 mg. The t 1/2 was 14.0 +/- 1.8 h. The peak plasma level was doubled on doubling the dose (from 69 +/- 15 to 132 +/- 27 ng/ml, respectively) and the urinary excretion (13.5%) rose similarly. The half-life of elimination was longer at night than in the day, probably because of the slower nocturnal flow of urine.

Adult↗
PubMed1984

Determination of short-circuit current in the in vivo perfused rat colon.

Current pulses (I) were injected into the lumen of proximal colonic segments in vivo, and the corresponding voltage deflections (delta PD) superimposed on the transcolonic PD were recorded. From the exponential decay of delta PD along the colon axis, the electrical length constant (lambda) was determined. Based on cable analysis the input resistance (= delta PD x = 0/I) and lambda made it possible to calculate the specific resistance (Rm) of the colonic epithelium as 128 +/- 16 omega X cm2. As Rm proved to be an ohmic resistor, the extrapolation from open-circuit PD (8-12 mV, lumen negative) to zero PD was feasible and made the calculation of short-circuit current (= PD/Rm) equal to 70 +/- 16 microA/cm2. In the presence of amiloride short-circuit current decreased to about 50%, whereas with theophylline it increased by about 30%. Substitution of luminal Na+ with choline or Cl- with cyclamate was associated with a marked increase of Rm. The rheogenic component of net Na+ transport was estimated to be only 8%. Electroneutral Na+ absorption functionally coupled with Cl- absorption displayed the characteristic feature of ion transport in the rat proximal colon.

Animals↗