Nephrotoxic effects of aminoglycoside treatment on renal protein reabsorption and accumulation

To quantify the effects of gentamicin, kanamycin and netilmicin on renal protein reabsorption and accumulation, these drugs were administered to rats intraperitoneally (30 mg/kg/day) for 7, 14 or 21 days. Scanning electron microscopy of the glomerular endothelia, urinary measurements of sodium, potassium, endogenous lysozyme, N-acetyl-beta-D-glucosaminidase (NAG) as well as clearance and accumulation experiments after i.v. administration of egg-white lysozyme and measurements of inulin clearance (GFR) were done in each treatment group. Gentamicin administration decreased diameter, density and shape of endothelial fenestrae. Kanamycin and netilmicin appeared to have no effect at the dose used. All three aminoglycosides decreased GFR and increased urinary excretion of sodium and potassium. While gentamicin and kanamycin decreased the percentage reabsorption and accumulation of lysozyme after i.v. administration of egg-white lysozyme netilmicin had no effect. Daily excretion of total protein, endogenous lysozyme and NAG increased only after treatment with kanamycin and gentamicin. Thus, aminoglycosides may act as nephrotoxicants at glomerular and/or tubular level inducing impairment of renal reabsorption and accumulation of proteins.

Selective determination of the activities of neutral and acid alpha-glucosidase using discontinuous assays

Most biological fluids contain both neutral and acid alpha-glucosidase. Optimal conditions were therefore developed for the selective determination of the activity of neutral and acid alpha-glucosidase, using 2-step, discontinuous assays. In the first step of the assay of neutral alpha-glucosidase, glucose was liberated from maltose (citrate-phosphate buffer, pH 6.8, 20 mmol/l maltose, 25 mmol/l turanose). Under these incubation conditions, turanose inhibited the residual activity of acid alpha-glucosidase almost completely without influencing the activity of neutral alpha-glucosidase. In the first step of the acid alpha-glucosidase assay, glucose was liberated from maltose (citrate-phosphate buffer, pH 3.8, 50 mmol/l maltose, 2 mol/l potassium chloride). Under these incubation conditions, potassium ions stimulate the activity of acid alpha-glucosidase and simultaneously inhibit almost completely the residual activity of neutral alpha-glucosidase. In the second step of the assay of neutral and acid alpha-glucosidase, the liberated glucose was measured by hexokinase/glucose-6-phosphate dehydrogenase. The effect of turanose and potassium ions on neutral and acid alpha-glucosidase from human urine was characterized.

Excretion of neutral alpha-glucosidase, determined with a continuous assay, and of acid alpha-glucosidase in the urine of human reference subjects

The catalytic activities of neutral and acid alpha-glucosidase were selectively determined in human urine. Urinary excretion of neutral and acid alpha-glucosidase in reference subjects was found to be in the range 1.61 to 20.36 microkat/mol creatinine and 7.47 to 33.60 microkat/mol creatinine, respectively. Urinary excretion of both enzymes was not related to sex, age or diuresis. A continuous assay was introduced to improve the determination of neutral alpha-glucosidase.

Binding of lysozyme to brush border membranes of rat kidney

The binding of 125I-labelled egg-white lysozyme to isolated brush border membranes of rat kidney cortex was investigated. The lysozyme binding was reversible and saturable. The Scatchard plot revealed a one-component binding type with a dissociation constant of 7.8 microM and 15.6 nmol/mg membrane protein for the number of binding sites. The binding of the basic lysozyme could be reduced by basic amino acids such as L-lysine, L-ornithine or L-arginine, while neutral amino acids such as L-citrulline or L-alanine had no effect. The inhibitory effect of lysine was competitive.

Renal handling of endogenous lysozyme in the rat

Quantitative studies of endogenous lysozyme (low molecular weight protein) were performed in rats. Urine and plasma concentrations of lysozyme and inulin were measured spectrophotometrically. An improved lysozyme assay (standard curve established by using egg white-lysozyme) enabled us to determine the mean plasma concentration of endogenous lysozyme (4.4 micrograms X ml-1) and the urinary concentrations of endogenous lysozyme (between 0.1 and 3.8 micrograms X ml-1. The urinary concentrations of endogenous lysozyme were found to be dependent on urinary flow rate. High urinary concentrations (ULy) were found at low urinary flow rates (V). The excreted amount of endogenous lysozyme (ULy X V) was independent of urinary flow rate and yielded a constant value of 0.02 micrograms X min-1. Mean glomerular filtration rate (GFR) was 1.2 ml X min-1 while clearance of endogenous lysozyme averaged 0.0039 ml X min-1. Inhibition of endogenous lysozyme reabsorption by cytochrome c was used to estimate the glomerular sieving coefficient of endogenous lysozyme in clearance experiments. CLy/GFR increased from a mean value of 0.0053 in control rats to 0.8 at maximal inhibition of tubular reabsorption of endogenous lysozyme by cytochrome c. Knowing the glomerular sieving coefficient, GFR and the lysozyme concentrations in plasma and urine samples, the filtered, excreted and reabsorbed lysozyme amounts could be calculated: 0.5% excreted and 99.5% reabsorbed. Reabsorbed endogenous lysozyme is stored in the kidney in high amounts (1,983 micrograms X g-1 kidney).

Early nephrotoxicity at high plasma concentrations of lysozyme in the rat

In clearance experiments, egg white lysozyme was intravenously infused into male Wistar and Wistar/Furth rats over different periods of time to achieve plasma concentrations of lysozyme in the range of 30 to 8000 micrograms per ml. The glomerular filtration rate and the appearance of glomerular and tubular epithelia were comparable to those of control rats below 3000 micrograms per ml. of plasma concentration of lysozyme and up to 60 minutes' infusion time when investigated by scanning electron microscopy. A 50 per cent drop in blood pressure occurred at a plasma lysozyme concentration of 3000 micrograms per ml., which could be prevented by the intravenous injection of an antihistamine or by using Wistar/Furth rats; however, the decrease of the glomerular filtration rate and of the fractional lysozyme reabsorption as well as the increase in sodium and potassium excretion could not be avoided. After 30 minutes of lysozyme infusion, the epithelial foot processes exhibited slight regional effacement, and in more than 50 per cent of the tubules protein cast formation was noted. Occurrence of foot process effacement and tubular casts increased with further increase of plasma lysozyme concentration and lysozyme infusion time. These morphologic changes were common for Wistar rats, antihistamine-pretreated Wistar rats, Wistar/Furth rats, and in situ-perfused rat kidneys. These results indicate that the cationic low molecular weight protein lysozyme induced functional and structural alterations that were correlated with plasma lysozyme concentration and lysozyme infusion time and caused acute renal failure.

Occupational exposure to hexachlorocyclohexane. IV. Sex hormone alterations in HCH-exposed workers

In a lindane (gamma-hexachlorocyclohexane)-producing factory 54 male workers (mean age 40 years, mean duration of exposure 8 years) were studied with regard to their blood levels of testosterone, LH, and FSH. Twenty clerks of nearly the same age were examined for control purposes in the same way. Serum-LH concentrations of the exposed workers were significantly higher than in controls. Geometric mean values were 8.8 mIU/ml and 5.7 mIU/ml respectively. On the other hand, FSH levels were insignificantly higher. Concerning testosterone concentrations in serum, these were found to be slightly lower in the group of workers than in control persons but this difference could not be proved to be statistically significant. These results indicate certain perturbations in sex hormone regulation probably as a consequence of HCH-exposure. To judge the pathological significance of these alterations further investigation will be necessary.

Inhibition of renal accumulation of lysozyme (basic low molecular weight protein) by basic proteins and other basic substances

Together the two rat kidneys accumulated a total of 31.7 +/- 1.6% of the intravenously injected amount of 7 nmoles egg-white-lysozyme (measured as iodine 125 lysozyme) within 10 min. The low molecular weight protein lysozyme and other basic substances were injected simultaneously in order to evaluate whether these basic substances can inhibit the renal lysozyme accumulation. The inhibitory effect of various basic compounds was dose-dependent with a maximal reduction of lysozyme accumulation to 11.7 +/- 0.08%. The basic substances could be divided into three groups depending upon the micromolar amount injected at which a 50% inhibition was achieved (0.3-1.2 micromoles: cytochrome C, ribonuclease; 10.9 micromoles; spermine; 501-688 micromoles: L-arginine, L-lysine). The neutral myoglobin had no effect on renal lysozyme accumulation. The inhibitory potency appeared to increase with increasing molecular weight and pI value of the substance tested. Microperfusion experiments of proximal convoluted tubules of rat kidney revealed that luminal reabsorption of the basic lysozyme can be inhibited by the basic protein cytochrome C in a dose-dependent fashion. In these experiments the perfusion solution contained 57 micromol .l-1 lysozyme, an intratubular lysozyme concentration at which the tubular lysozyme reabsorption was found to be about 80% saturated. A 50% inhibition of the tubular endocytic lysozyme reabsorption was achieved a cytochrome C concentration of 102 micromol.l-1.

Occupational exposure to hexachlorocyclohexane. II. Health conditions of chronically exposed workers

Sixty male workers in a lindane (gamma-hexachlorocyclohexane)-producing factory were examined with regard to health in comparison with an external control group of 20 clerks. Case history, physical examination, neurologic status, and ECG revealed no significant differences between groups. However, the following significant differences in clinical-chemical blood tests were ascertained: higher polymorphonuclear leukocyte count, lower lymphocyte count, higher reticulocyte count, lower prothrombin (Quick's) test, and lower blood concentrations of creatinine and uric acid. No significant differences were observed in total red and white blood cell as well as platelet counts, hemoglobin content, the other counts of differential blood picture, gamma-GT, GOT, GPT, LDH, cholinesterase, triglycerides, cholesterol, and urea. In spite of a pronounced exposure to the alpha-, beta-, and gamma-isomers of hexachlorocyclohexane, no signs of severe impairment of health were observed; only small deviations in some laboratory tests were found having no pathologic significance. However, biological monitoring and health supervision of HCH-exposed workers should be carried out.

Occupational exposure to hexachlorocyclohexane. I. Body burden of HCH-isomers

In a lindane (gamma-hexachlorocyclohexane = gamma-benzenehexachloride)-producing factor 57 workers were studied with regard to their blood levels of the three hexachlorocyclohexane isomers: alpha-, beta-, and gamma-HCH. The TLV-TWA (MAK value 1979) for gamma-HCH of 0.5 mg/m3 was not exceeded at any of the workplaces where HCH is synthesized and purified to lindane. Additionally, in some of the workers samples of s.c. adipose tissue were taken for determination of HCH-isomer content. An external group of 20 clerks was examined in the same way for control purposes. In contrast to the control persons, none of whom had HCH-concentrations in serum above the respective detection limits, the values determined in serum of the exposed workers were in the following ranges: alpha-HCH: 10-273 microgram/1, beta-HCH: 17-760 microgram/l, and gamma-HCH: 5-188 microgram/1. Of special interest is the observation of a significant increase of beta-HCH-concentration in serum with the time of employment in lindane production, indicating a pronounced accumulation of this substance in the human organism. Concentrations of this isomer in s.c. adipose tissues were about 300-fold higher than in serum. A significant correlation between both parameters could be established. The results of this study show that adherence to the TLV-TWA of gamma-HCH is not sufficient for control of HCH-exposure. Furthermore, biological monitoring of exposed workers is necessary taking into account the three more important isomers alpha-, beta-, and gamma-HCH.

[Hormone-producing thyroid carcinoma with hyperthyroidism. Analysis of 6 cases and review of the literature]

Report on 6 female patients with follicular thyroid carcinoma producing hyperthyroidism. Two of them had large metastases with hormone production, while 4 mimicked an autonomously functioning thyroid adenoma. Hormone synthesis was investigated in the tumor tissue of one patient and was found to be similar to that of normal thyroid tissue.

Volume of brain ventricles in man determined by computer tomography

In order to measure the absolute ventricular volumes in ml we developed a method using the numerical prints of CT (EMI, CT 1000) on which--by comparing with corresponding Polaroid photos--the margin between brain tissue and ventricles was drawn. For further evaluation, a curve digitizer and a digital computer were used. In 51 patients without any abnormal findings in CT, we studied the volume of single ventricles. The mean value of the whole ventricular system was 30.9 +/- 5.7 ml. Reproducibility by this method is within a range of 5%.

Quantitative studies of protein uptake in microperfused renal proximal tubules

Proximal convoluted tubules were microperfused with an iodine 125 egg-white-lysozyme containing perfusion solution. The intraluminal lysozyme concentration decreased about 10% per mm tubular length over a wide range of intraluminal lysozyme concentrations tested indicating a constant fractional reabsorption over a wide concentration range. Lysozyme reabsorption at a high intraluminal lysozyme concentration of 10 mg/ml indicated that the tubular protein uptake by endocytosis is a saturable process. High intraluminal concentrations of basic amino acids inhibited the cellular uptake of lysozyme, while neutral amino acids had no effect.

The mechanism of action of harmaline on renal solute transport

The effect of the hallucinogenic drug harmaline was tested on rat kidney proximal tubular solute and water transport, using in vivo micropuncture and electrophysiological techniques as well as in vitro biochemical techniques. During peritubular application harmaline (5 mmol/l) was found to block net tubular volume absorption reversibly (by 85%) through inhibition of active Na+ transport and possibly active HCO-3 transport. The inhibition was accompanied by a rapid strong depolarization of the tubular cell membranes. As a biochemical equivalent harmaline inhibited the Na+-K+-ATPase and the Mg2+-ATPase of peritubular cell membrane fractions as well as the HCO-3-stimulated ATPase of a brush border membrane fraction with similar kinetics. By studying glucose tracer efflux and by measuring cell membrane potential and conductance changes in response to glucose perfusions, no evidence for a direct effect of harmaline on Na+-glucose (or amino acid) cotransport mechanisms in the brush border could be obtained. The data suggest that harmaline does not specifically compete with Na+ for transport sites. Neither are the cotransport systems in the brush border membrane specifically inhibited, nor could the inhibition of the Na+ pump in the peritubular cell membrane simply result from a competition between harmaline and Na+.

Effect of parathyroid hormone and cyclic adenosine 3',5'-monophosphate on isotonic fluid reabsorption: polarity of proximal tubular cells

Isotomic fluid reabsorption (JV) of rat renal proximal tubules was examined by the shrinking droplet method in combination with simulatneous perfusion of blood capillaries. Sensitivity of JV measurement was improved by using each punctured tubule for control measurements: 1) Parathyroid hormoen (PTH) on the contraluminal cell side reduced JV in a dose-response behavior. The maximal inhibition was achieved at a PTH concentration of 10(-5) M, the half maximal inhibition at a concentration of 3 X 10(-9) M. PTH on the luminal cell side had a small inhibitory effect. 2) Cyclic AMP inhibited JV preferentially when applied to the luminal cell side. On the luminal cell side, both cyclic AMP and dibutyryl cyclic AMP inhibited JV in a similar dose-dependent behavior. Concentrations of both nucleotides as low as 10(-10) M had a definite inhibitory effect. Tested at a high concentration, N6-butyryl cyclic AMP was almost as effective as cyclic AMP. Deoxy cyclic AMP, 5' AMP, cyclic guanosine monophosphate (cyclic GMP), dibutyryl cyclic GMP had no effect. ATP inhibited JV to a very small extent. 3) The reduction of JV after administration of PTH and dibutyryl cyclic AMP was not additive. The similar inhibitory effect of PTH at the contraluminal cell face and of cyclic AMP at the luminal cell face suggests the following sequence of events in the mediation of the action of PTH: 1) activation of adenylate cyclase by PTH in the contraluminal cell membrane, and 2) action of the generated cyclic AMP on the luminal cell membrane. The interaction of cyclic AMP and the luminal cell membrane is initiated at the luminal cell surface.

On the action of nifedipine under conditions of variable stimulation patterns and [Ca2+]0 in guinea-pig atrium

The effect of nifedipine is studied in perfused isolated guinea-pig left atrium at a temperature of 37 degrees C and a stimulation rate between 60 and 240/min. Rhythmical stimulation at 240/min was interrupted by interposed stimulus intervals (test intervals) in a range of 0.1-4 s. The pressure amplitudes developed during subsequent test contractions rise up to a maximum with increasing test intervals. This time course is described as restitution in contractile response. Results. Restitution is somewhat faster in earlier than in later stages of perfusion. A rise in [Ca2+]0 accelerates restitution without changing maximal pressure development. Lowering [Ca2+]0 depresses pressure amplitudes over the whole range of test intervals. Nifedipine slows down restitution but has (in concentrations up to 10(-6) M) no effect on the maximum achieved after long test intervals following stimulation at 240/min. The negative inotropic effect of nifedipine on rhythmical pressure development rises with increasing stimulation frequency in the range from 60-240/min. An elevation in [Ca2+]0 does not reestablish control pressure-frequency relationship. Conclusions. In respect to the restitution process and also to the pressure-frequency relationship the effect of nifedipine can neither be simulated by a reduction in [Ca2+]0 nor abolished by an elevation in [Ca2+]0.

Delay in diastolic restitution of full myocardial contractility in guinea pig atrium

In an isolated perfused left atrium of guinea pig, pressure amplitudes were recorded at 37 degrees C and a stimulation rate of 240/min with interposed variable resting pauses. After prolonged intervals the preparation develops maximum pressure, which does not depend on perfusion time or on any positive inotropic intervention. The latter is found to shorten the time needed for restitution of full contractility. Nifedipine (5 X 10(-7)M) exerts its negative inotropic effect mainly by a delay in restitution time; acetylcholine (2 X 10(-7)M), by a concomitant reduction of all pressure amplitudes over the whole range of stimulus intervals. The latter effect is similar to that of lowering [Ca2+]o.

[The effect of sudden changes in the stimulation rate of the heart on peak systolic pressure (author's transl)]

The changes in systolic pressure were studied in 48 patients during artificially (by electrical stimulation) induced sudden increases and consecutive decreases in heart rate. Various patterns could be separated respective to phase A (sudden switch from low (80-120 impulses/min) to higher heart rate (140-180 impulses/min)) and to phase B (sudden switch-back from high to lower (control) beating rate): AI) The systolic peak-pressure of the first contraction after the shortened stimulation interval is very low and often stays ineffective (below the aortic opening pressure). The second contraction develops already a higher pressure than the first one, during the consecutive beats the systolic pressure increases gradually until a new steady state is reached, which is usually lower than the systolic pressure during the foregoing lower beating rate. Sometimes however it can be equal or even higher. Accordingly after an elevation of heart rate arterial mean pressure can drop, stay constant or increase. AII) The systolic peak-pressure of the first contraction after the shortened stimulation interval stays relatively high and drops continuously with the succeeding contractions until a new steady state is reached according to the higher heart rate, it is however always lower than the one at a lower stimulation rate. Therefore arterial mean pressure is always decreased. AIII) Finally we observed changes in arterial systolic pressure in some patients that could not be grouped according to one or to the other pattern described above.- BI) The systolic peak of the first contraction after the switch-back from the high to the lower (control) rate is much higher than that of the last at the higher rate. The peak pressures of the consecutive contractions are then dropping continuously to the new steady-state, that can be higher, equal or lower than that at the higher stimulation rate. BII) ....

Renal phosphate transport: inhomogeneity of local proximal transport rates and sodium dependence

The standing droplet method has been used in combination with the peritibular perfusion of blood capillaries to determine the build up of transtubular concentration differences of phosphate (Piota) in the renal proximal convoluted tubule of parathyroidectomized rats. Electron probe analysis was used to estimate Piota. At zero time both the intraluminal and the contraluminal Piota concentration was 2 mM. The time dependent decrease of the intraluminal Piota concentration was approximately 4 times faster in the early than in the late proximal convoluted tubule. After 45 sec an intraluminal steady state concentration of 0.20 mM Piota was achieved in the early part. In the late part the intraluminal Piota concentration approached a steady statevalue of 0.54 mM at 123 sec. When sodium free solutions were used the intaluminal Piota concentration increased to 2.22 mM in the earlier and to 2.76 mM in the late part. The data indicate that in the proximal convoluted tubule 1. the rate of phosphate reabsorption is greater in the early part than in the later part, and 2. phospate reabsorption might occur as co-transport with Na+ ions.

Renal proximal tubular buffer-(glycodiazine) transport. Inhomogeneity of local transport rate, dependence on sodium, effect of inhibitors and chronic adaptation

Using the stop flow microperfusion technique with simultaneous capillary perfusion the secretory rate of H+ ions in the proximal tubule was evaluated by measuring the level flow reabsorption as well as the static head concentration difference of 3H labeled glycodiazine. At ambient glycodiazine concentration of 21 mmol/l the level flow reabsorption is in the same range as that of bicarbonate. In the early proximal loops the reabsorption is 20% greater than in the late proximal loops. The carbonic anhydrase inhibitors acetazolamide and 3,4-methylene-dioxyphenyl-sulfonamide (both 10(-4) M) as well as furosemide (10 (-3) M) inhibit the glycodiazine reabsorption 43%, 27% and 22% respectively. Thiocyanate (2-10(-2) M), however, exerted only an insignificant inhibition (12%). When Na+ in the ambient perfusion solutions was replaced by Li+ or choline+ the glycodiazine transport was strongly reduced. Ouabain (5-10(-2) M) inhibited too, but amiloride (10(-3) M) had no effect on glycodiazine transport. The glycodiazine transport was 28% reduced in metabolic alkalosis and to a smaller although significant extent (17%) in metabolic acidosis; it was unchanged in chronic hypercapnia. In chronic K+ depletion the glycodiazine reabsorption was accelerated by 12% only in the early proximal loops. Chronic parathyroidectomy as well as acute substitution with parathyroid hormone had no effect on the glycodiazine absorption. The main conclusions are: Proximal H+ transport proceeds with suitable buffers. Although independent of HCO3- and carbonic anhydrase, it could be partially inhibited by CA inhibitors. H+ transport is supposed to proceed as countertransport with Na+ ions. In chronic alkalosis the H+ transport is reduced.

[Stress sensitivity and adaptation]

On the basis of theoretical, clinical and experimental analyses the influence of different stress categories, especially of psycho-emotional and socio-emotional stress, upon cerebro-visceral regulation processes is investigated. Central-nervous information processing in various brain areas (neocortex, limbic system, hypothalamus, formatio reticularis mesencephali etc.) and learning processes are equally affected by stress factors as are haemodynamic and biochemical parameters. Changes of the carbohydrate and lipid metabolism, of plasma renin activity, catechol amine release and the counter-regulatory insulin enhancement are especially pronounced in "stress-sensitive risk persons", e.g. in the hypertensive as a maladaptive dysregulation-as opposed to the adaptive regulation capacity of healthy individuals. The investigated functional patterns of different systems of the organism allow the distinction of hyper- and hyporeactive forms of maladaptation. The pathogenetic efficiency of stress is determined not only by the quantity, quality, duration of exposure and basic processes of the central nervous system, but also by man's personality structure and his sensitivity to stress (genetic predisposition and/or acquired maladaptation). More insight into the neuro-biological processes underlying the motivational and psycho-emotional performance of the brain and its connection withe humoral-hormonal and cardiovascular systems is necessary to treat and to control cerebrovisceral dysregulations such as arterial essential hypertension. It will be a task of psychotherapy to help improve man's adaptive capacity and to desensibilize stress-sensitive risk persons.