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Biomedical subjects

G Schubert

Publications and source records attributed to G Schubert.

At least 91 records · Page 5Linked to original sources
PubMed1984

Inactivation of atrial natriuretic substance by kallikrein.

To further characterize the properties of the potent natriuretic and diuretic substance that can be extracted from atrial tissue, we investigated its susceptibility to inactivation by kallikrein and other proteolytic enzymes. Extracts of rat atrial tissue (tissue wet wt 100 mg/ml) were incubated with enzymes under standard conditions and tested by injection into nondiuretic anesthetized rats. One hour of incubation at 37 degrees C with pure porcine pancreatic kallikrein at concentrations of 250 micrograms/ml or greater significantly reduced the activity of atrial natriuretic substance. The reduction in activity was dependent on both enzyme concentration and time of incubation. The kallikrein-catalyzed degradation was completely blocked by aprotinin but was only partially retarded by soybean trypsin inhibitor. Trypsin reduced natriuretic and diuretic activity of extracts at concentrations of 400 micrograms/ml or greater, with nearly complete inactivation at a concentration of 1,000 micrograms/ml. Carboxypeptidase B also caused a concentration-dependent inactivation of the natriuretic material. Last, alpha-chymotrypsin (1,000 micrograms/ml) and elastase (1,000 micrograms/ml) were found to destroy the natriuretic activity. In a separate set of experiments natriuretic activity was observed to be retained by a 1,000 mol wt cutoff membrane. Inactivation of the natriuretic peptide by renal kallikrein is a possible mechanism for in vivo regulation of natriuretic activity.

Animals↗
PubMed1984

Quantitative characterization of the tubuloglomerular feedback response: effect of growth.

Studies were performed to characterize quantitatively the effect of changing loop of Henle flow rate on single nephron glomerular filtration rate (SNGFR) in male Sprague-Dawley rats of varying body weight. Rats weighing 100, 220, and 350 g were studied using standard renal micropuncture techniques. The relationship between loop of Henle flow rate (VLP) and SNGFR was characterized for individual nephrons by multiple determinations of SNGFR during loop perfusion. An inverse sigmoidal relationship was observed that could be described as delta SNGFR = a/(1 + ek(b-VLP], where delta SNGFR is the change in SNGFR from the value measured at zero loop flow, a is delta SNGFRmax, the maximum change, b is V1/2, the flow rate at which the response is half maximum, and k is [4f' (V1/2)]/a with f' (V1/2) the slope at V1/2. delta SNGFRmax increased with increasing body size (7.9 +/- 1.16, 18.9 +/- 0.90, and 25.2 +/- 2.73 nl/min, respectively, in the three groups), and the curve shifted to the right (V1/2 = 10.3 +/- 0.8, 15.4 +/- 0.83, and 22.3 +/- 1.22 nl/min). The maximum slope increased (f' (V1/2) = 0.9 +/- 0.19, 1.7 +/- 0.16, and 3.2 +/- 0.70), but the exponential constant k was uninfluenced by growth. Independent of rat size, a 10% increase in loop flow at the midpoint produced at 5-10% decrease in SNGFR. Free-flow values of SNGFR and VLP were found to lie in the most sensitive range of the feedback curve.

Animals↗
PubMed1984

Opposing effects of captopril and aprotinin on tubuloglomerular feedback responses.

We investigated the effect of two protease inhibitors, captopril and aprotinin, on tubuloglomerular feedback. In anesthetized rats, 15 or 25 mg/kg captopril significantly reduced the change of early proximal flow rate achieved by raising loop of Henle perfusion rate from 0 to 40 nl/min. Consistent with this reduction of maximum responses, there was a rise of single nephron glomerular filtration rate from 30.7 +/- 1.15 to 35.0 +/- 0.93 nl/min (P less than 0.01) following 25 mg/kg captopril. Infusion of aprotinin at 40,000 KIU/h produced an increase in maximum feedback responses from 38.2 +/- 1.66 to 56.8 +/- 2.35% (P less than 0.05). Infusion of aprotinin in two different doses (20,000 or 40,000 KIU/h) diminished or prevented the effect of 25 mg/kg captopril on maximum feedback responses. Since the main action of aprotinin is believed to be kallikrein inhibition, our data suggest that the magnitude of feedback responses may be affected by the kallikrein-kinin system and that the action of captopril may be in part mediated by its interference with kinin metabolism.

Absorption↗
PubMed1984

[Technic of rectum anastomoses in rectum resection. A controlled study: instrumental suture versus hand suture].

Stapler and manual sutures in rectal end-to-end anastomoses were compared in a controlled trial. The following results were obtained: For the analysis the cases naturally separated into three groups, A (manual suture), B (planned stapler suture) and WD ("withdrawn" cases, from both groups, in which continence could be maintained only with a stapler suture). The distribution of the WD cases in dependence on localization and sex varied significantly from groups A and B, while A and B remained comparable, in spite of the WD cases. The analysis of the date showed no, or only slight, clinical differences. In a comparison of the two stapler groups B and WD, significantly more suture dehiscences, colocutaneous fistulae and post-operative disturbances in bladder function were found in group WD. As a general conclusion we can state that: In comparable anastomosis localizations it is possible to achieve almost the same clinical results with both suture techniques. With a circular stapler it is, however, technically possible to perform rectum resections in cases in which this was not previously possible, particularly in men with a narrow pelvis and a stale pelvic floor. To what extent this still is an advantage after the local recurrences are taken into consideration remains to be seen.

Clinical Trials as Topic↗
PubMed1983

Texture examinations on grain and thin section preparations of calcium oxalate calculi and their relations to pathogenetic parameters.

Texture examinations were made on 416 thin section and on 1,000 grain preparations of calcium oxalate calculi. The frequency of occurrence of four basic texture types in relation to pathological urine parameters, age and sex of the patients as well as types of stone removal are discussed. Percentage share of texture type I that correlates to hyperuricosuria shows a steady increase with increasing age. The proportions of types III and IV that are linked to hypercalciuria decrease with increasing age. The examinations show the feasibility of texture-type determinations within routine stone analysis and create the precondition for texture types to be included in metaphylaxis of calcium oxalate lithiasis.

Adult↗
PubMed1983

Separate examinations on core and shell of urinary calculi.

Separate core and shell examinations were made on 10,000 urinary stones using a combined crystal-optical X-ray diffractometric method of analysis. 29.5% of these concrements showed differences in qualitative phases between central and peripheral stone parts. All the more frequent stone components were found in core and shell to the same extent. Only weddellite and uric acid dihydrate show a clear preference of the shell. Our method of analysis showed cores to be mostly monomineralic and peripheral stone parts mostly bimineralic. Consequences of this topographic stone analysis for metaphylaxis of urolithiasis are pointed out.

Apatites↗
PubMed1983

[Scanning electron microscopy studies of the structure of calcium oxalate urinary calculi].

The examination of calcium oxalate calculi under a scanning electron microscope confirmed the 4 structural types distinguished under a polarising microscope using microsections. The fine structure of the radial-concentric-shelled structural type I is characterized as a dense pack of radially ordered prismatic bundles. In combination with energy-dispersive analysis the occurrence of the finely crystalline type II is confirmed. Energy-dispersive analysis shows an unexpected variety of element distribution in the microscopic range.

Calcium Oxalate↗
PubMed1982

Micropuncture studies of the renal effects of atrial natriuretic substance.

Micropuncture studies of the renal effects of atrial natriuretic substance. Injection of atrial extract produced by homogenization, boiling and centrifugation of atrial tissue from one heart caused a 10fold increase in urine flow rate and a 30-fold increase in Na excretion. Similarly prepared extracts of ventricle were without effect. To identify the site of action of atrial natriuretic substance, extract was infused intravenously at rates corresponding to 3 or 6 atria per hour. During infusion at a rate of 3 atria per hour mean urine flow increased from 9.5 +/- 2.8 to 17.2 +/- 1.2 microliter/min and Na excretion from 0.14 +/- 0.06 to 1.78 +/- 0.14 mumol/min. Glomerular filtration rate (GFR), single nephron filtration rate (SNGFR) and proximal and loop of Henle fluid absorption did not change significantly. During infusion of 6 atria per hour, paralleling a greater rise in urine flow rate (from 6.4 +/- 2.09 to 40.3 +/- 7.5 microliter/min) and in sodium excretion (from 0.18 +/- 0.0008 to 5.97 +/- 0.93 mumol/min), filtration rate, measured for either the single nephron or the whole kidney, rose. As a consequence of the rise in GFR, delivery of fluid and chloride into the distal tubule increased significantly. These data suggest that to a major extent the natriuresis is caused by transport inhibition along collecting tubules and collecting ducts. In addition, at high doses a rise in filtration rate contributes to the natriuretic effect of atrial extracts.

Animals↗
PubMed1982

Further evidence for an inverse relationship between macula densa NaCl concentration and filtration rate.

It has been concluded that tubulo-glomerular feedback mechanism is triggered by changes in NaCl concentration ([NaCl]) at the macula densa. This conclusion is based on the demonstration that changes in filtration rate produced during retrograde perfusion of the loop of Henle depend upon the perfusate [NaCl]. Experiments were performed to evaluate whether the effect on glomerular function of orthograde perfusion of the loop of Henle is consistent with this conclusion. Early proximal flow rate (VEP), stop-flow pressure (PSF), early distal chloride concentration ([C]), and flow rate were measured during perfusion of the loop of Henle with mannitol solution (300 mosm kg-1), 30mM NaCl + mannitol (300 mosm kg-1), 140 mM Na isethionate and artificial tubular fluid. When distal flow exceeded 10 nl min-1, the magnitude of the glomerular response was predictable from the [Cl]. The linear regression line, delta VEP = -0.27 [Cl] + 4.3, did not differ from that obtained previously with the retrograde technique. Retrograde perfusion with 140 mM Na isethionate was without effect on VEP. We conclude that the effect on glomerular function of perfusion of the loop of Henle in either an orthograde or a retrograde direction with these solutions depends upon the chloride concentration at the macula densa.

Animals↗
PubMed1982

10,000 analyses of urinary calculi using X-ray diffraction and polarizing microscopy.

To make qualitative as well as semiquantitative analyses of 10,000 urinary calculi of large city population, a combined crystal-optical X-ray diffractometric method proved to be very useful. This combination goes to complement the advantages of polarization microscopy (with its minimal substance requirements, its proof limits of less than 1%, and its insight into stone texture) with those of X-ray diffraction (with its fast semiquantitative analysis and simple differentiation of all the stone components). About 30% of the calculi were found to have a monomineral composition. The most frequent types of calculi in our examination were: 33.2% whewellite/weddellite, 24.9% whewellite, 13.5% whewellite/weddellite/apatite, 7.0% struvite/apatite, and 3.9% uric acid/uric acid dihydrate.

Humans↗
PubMed1981

[Tumor register: information system for tumor centers (author's transl)].

The different activities in the scope of the tumor center already shows in the multiplicity of concepts for which incidence register, therapy register, clinical register or the supplies register are only a few examples. Such terms circumscribe a few interests from the therapeutic, epidemiologic or clinical and scientific aspects, which are projected on tumor centers as an expectation or a duty. From the compilation of these interests a bundle of unspecific aims results for which a classification according to various levels of information is suggested. Only cooperation of all levels makes possible a tumor register as an information system for medicine which supports the tasks of all those involved and makes the questions of the population more easily and more quickly answerable.

Cancer Care Facilities↗
PubMed1980

Urolithiasis after kidney transplantation--clinical and mineralogical aspects.

Urolithiasis is a rare complication following kidney transplantation. Experience with this complication in 6 of 426 transplantations performed from 1968 to 1979 is reviewed. The clinical symptoms are different from the disease in non-transplant patients. Three major predisposing causes for the development of calculi after kidney transplantation were found in our patients--urodynamic disorders following complications of the ureterovesical anastomosis, persistent bacteriuria and renal tubular acidosis and, less importantly, the presence of hypercalcemia and hypercalciuria as a result of secondary hyperparathyroidism. Crystal-optical and x-ray-diffraction studies contributed to the interpretation of the constituents and texture of the calculi and of the aetiological factors concerned.

Adolescent↗
PubMed1980

Mass spectrometry of ring D hydroxylated 3-methoxy-1,3,5(10)-estratrienes.

Mass spectra and fragmentation patterns of the epimeric 17-, 16-, 15- and 14-hydroxy derivatives of 3-methoxy-1,3,5(10)-estratriene are compared. The main fragmentation pathways are differently influenced, depending on the position of the hydroxy group. The different configuration of the hydroxy groups is reflected only in the spectra of the epimeric 15- and 14-hydroxy compounds. Possibilities of mass spectrometric differentiation between the hydroxy-estratrienes are discussed.

Chemical Phenomena↗