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J Stepanek

Publications and source records attributed to J Stepanek.

At least 19 recordsLinked to original sources
PubMed1989

A new proposal for the mechanism of cyclosporine A nephrotoxicity. Inhibition of renal microsomal protein chain elongation following in vivo cyclosporine A.

In this paper, we report experiments examining the effect of cyclosporine A on "run-off" translation in microsomes isolated from tissues of Sprague-Dawley rats. In microsomes isolated from rat brain, kidney and thymus, cyclosporine A added in vitro in concentrations of up to 100 micrograms/ml did not reduce [3H]L-leucine incorporation relative to controls. A small dose-dependent reduction in [3H]leucine incorporation was observed in microsomes isolated from rat liver when cyclosporine A was added in high concentrations (5 and 6% at 25 and 100 micrograms/ml). However, when cyclosporine A was injected at 50 mg/kg/day for 10 days, [3H]L-leucine incorporation was inhibited 99.9% in microsomes isolated from kidney. The oral administration of cyclosporine A at 50 mg/kg/day for 6-10 days produced a 75% inhibition of incorporation by isolated renal microsomes. These changes were observed in the absence of measurable reductions in "run-off" transcription measured as [3H]UTP incorporation by renal nuclei exposed to cyclosporine A in concentrations of up to 100 micrograms/ml in vitro or isolated from animals given oral cyclosporine A at 50 mg/kg/day for 6 days. Cross-over experiments were performed using microsomes and microsomal supernatant fractions (cell saps) from tissues of animals treated with cyclosporine A and control vehicle. Renal cell sap from cyclosporine A treated animals inhibited [3H]L-leucine incorporation by microsomes isolated from the kidneys or other tissues of animals treated with control vehicle. These experiments demonstrated that a translation inhibitor was present in the cell sap of cyclosporine A treated animals which could directly block translation elongation in microsomes from control animals. When renal cell sap from both control and cyclosporine A treated animals was added to control microsomes, inhibition was still prominent, suggesting the presence of an inhibitor rather than the absence of an elongation factor. Oral administration of cyclosporine A at 50 mg/kg/day for 6 days depressed renal microsomal [3H]L-leucine incorporation equally in male and female rats to 25% of control. The dose-response relationship for microsomal protein synthesis inhibition after 6 days of oral cyclosporine A administration was: 5 mg/kg, 73.7% of control; 10 mg/kg, 64.1% of control; 25 mg/kg, 54.9% of control and 50 mg/kg, 24.1% of control. Renal microsomal protein synthesis following oral cyclosporine A at 50 mg/kg/day was reduced to 54% of control by day 2 and was maximally inhibited at 25-30% of control by day 4.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Effect of calcium channel antagonists on calcium uptake and release by isolated rat cardiac mitochondria.

The effects of calcium channel antagonists on Ca2+ uptake and Na+-induced Ca2+ release were studied in isolated rat cardiac mitochondria. Diltiazem, nitrendipine and nimodipine were more effective inhibitors of Na+-induced Ca2+ release (IC50 = 19-100 microM) than of Ca2+ uptake (IC50 = 0.2-1 mM). Nitrendipine and nimodipine had virtually identical IC50 values for inhibiting Ca2+ uptake, but nitrendipine was 3-4 times more potent than nimodipine at inhibiting Na+-induced Ca2+ release. If these calcium channel antagonists achieve intracellular concentrations in the range of 10(-5)-10(-4) M, our results suggest that calcium channel antagonists would preferentially inhibit mitochondrial calcium release more than mitochondrial calcium uptake.

Animals↗
PubMed1987

Studies on the mechanism of glucocorticoid hormone induced alterations in rat thymic transcription--II. Partial purification and characterization of RNA polymerases II from hydrocortisone and control vehicle treated animals.

In experiments designed to study the mechanism of glucocorticoid hormone induced reductions in rat thymic transcription, adrenalectomized rats were injected with hydrocortisone (50 mg/kg) or control vehicle 12 h prior to sacrifice. Thymic nuclei were used to prepare soluble nuclear extracts containing RNA polymerase II. Nuclear extract RNA polymerases II were then partially purified (600-fold) on DEAE-Sephadex columns and characterized. The responses of partially purified thymic RNA polymerases II from rats treated in vivo with hydrocortisone or vehicle were similar to: pH, temperature, ionic strength, trypsin proteolysis, and inhibition by alpha-amanitin; however, RNA polymerase II from hydrocortisone treated animals was consistently reduced in activity compared to control RNA polymerase II. Determination of the apparent specific activities of peak RNA polymerase II fractions from DEAE-Sephadex columns suggested that the specific activity of RNA polymerase II from hydrocortisone treated animals was reduced compared to RNA polymerase II activity from control animals. The fact that both nuclear extract and partially purified RNA polymerases II from hydrocortisone treated rats were reduced in activity when assayed in reconstituted transcriptive systems suggests a denatured, defective or modified RNA polymerase II molecule acting as a transcription inhibitor. Thermally denatured nucleoplasmic RNA polymerase II fractions were shown to interfere with transcription by native nucleoplasmic RNA polymerase II in vitro, but did not appear to inhibit transcription to he degree observed in vitro following in vivo hydrocortisone administration.

Amanitins↗
PubMed1979

[Pathogenesis of acute hypercapnic hyperammoniaemia (author's transl)].

Alterations in the ammonia concentration in arterial blood due to drug-induced portal vasoconstriction (oxprenolol 1 mg/kg) or vasodilatation (phentolamine 0.5 mg/kg) were studied in anaesthetized and artificially respirated mongrel dogs during normal air ventilation, during hypercapnia induced by ventilation with an appropriate gas mixture, and during episodes. The NH3 values in arterial-blood plasma were in the region of 41 microgram/100 ml and those in portal-blood plasma 3--4 times higher. The induction of progressive levels of hypercapnia opened the portal-to-systemic venous shunt, producing an increase in arterial NH3 and, to a lesser extent, NH3 in the CSF. The portal vasoconstriction caused by oxprenolol 1 mg/kg i.v. resulted in the functional elimination of the shunt during normoxia or hypercapnia, leading to a decrease in the NH3 concentration in the arteral blood and hence also in the CSF. The vasodilating effect of phentolamine 0.5 mg/kg i.v., on the other hand, caused a transient, stastically significant increase in arterial NH3 during normoxia; during hypercapnia the NH3 values did not differ from the controls.

Ammonia↗
PubMed1978

[Broncholytic therapy--beta 2 stimulation and vagolysis from an animal experimental viewpoint].

Continuous recordings of heart rate, respiration rate, minute volume and bronchial resistance were made over a period of altogether 3 h in spontaneously breathing dogs anesthetized with chloralose. At hourly intervals, before and 1 and 2 h after the administration of bronchodilators, bronchial spasm was induced by inhalation of an acetylcholine solution. Terbutaline, a beta-stimulant, was administered by inhalation in doses of 0.5, 0.16 and 0.05 mg/kg. For comparison, an atropine derivative, ipratrapium bromide, was given in doses of 0.04 and 0.01 mg/kg. Controls received normal saline. Terbutaline caused an increase in heart rate, respiration rate and minute volume. Acetylcholine-induced bronchial spasm was inhibited to the extent of 10-70% for 2 h after the administration of terbutaline. The acetylcholine antagonist ipratropium bromide caused only transient changes in heart rate, respiration rate and minute volume. Acetylcholine-induced bronchial spasm was inhibited by 95% and 80% for 2 h after doses of 0.04 and 0.01 mg/kg respectively. Terbutaline had a slight stimulant effect; ipratropium bromide displayed no stimulant activity.

Acetylcholine↗
PubMed1978

[Experimental hyperammoniemia].

The effect of chloralose anesthesia and of hypoxia or hypercapnia of altogether 40 minutes' duration on the concentrations of ammonia in the arterial blood was investigated in mongrel dogs. The NH3 values increased marginally as a result of chloralose anesthesia and only slightly as a result of severe (Pao2=32 mm Hg), acute hypoxia. Hypercapnia (Paco2=75 or 111 mm Hg) induced with a mixture of gases was accompanied by an increase of commensurate degree in the blood ammonia levels which was presumably attributable to an augmented protal-to-systemic shunt circulation.

Ammonia↗
PubMed1978

Haemodynamic effects of the beta-receptor blocking agents metoprolol and propranolol in the anesthetized dog.

The haemodynamic effects produced by intravenous infusions of the beta-blocking agents metoprolol and propranolol in doses of 0.3 and 1 mg/kg/10 min were compared in anaesthetized dogs. When administered in a dose of 0.3 mg/kg/10 min, metoprolol caused a longer-lasting increase in pulmonary-arterial pressure and total pulmonary resistance, a greater increase in pulmonary capillary pressure and a more marked decrease in O2 partial pressure in the arterial blood than propranolol. These differences are probably due to differences in the pharmacokinetics of the two drugs. The effects of the two beta-blockers in a dose of 1 mg/kg/10 min were similar. At neither of the dose-levels tested were the changes induced by the compounds in the various parameters studied clearly dose-related.

Animals↗
PubMed1978

Bronchial spasmolytic action of terbutaline and fenoterol compared with that of ipratropium bromide in the anaesthetized dog.

Continuous recordings of heart rate, respiration rate, minute volume and bronchial resistance were made over a period of altogether three hours in spontaneously breathing dogs anaesthetized with chloralose. At hourly intervals, before and 1 and 2 hr after the administration of bronchodilators, bronchial spasm was induced by inhalation of an acetylcholine solution. Two beta2-stimulants, terbutaline and fenoterol, were administered by inhalation in doses of 0.5, 0.16 and 0.05 mg/kg and 0.1, 0.3 and 0.01 mg/kg respectively. For comparison, an atropine derivative, ipratropium bromide, was also given by the same route in doses of 0.04 and 0.01 mg/kg. Controls received normal saline. Terbutaline and fenoterol caused an increase in heart rate, respiration rate and minute volume. Acetylcholine-induced bronchial spasm was inhibited to the extent of 10--70% for 2 hr after the administration of terbutaline, and by 15--70% after fenoterol. The acetylcholine antagonist ipratropium bromide caused only transient changes in heart rate, respiration rate and minute volume. Acetylcholine-induced bronchial spasm was inhibited by 95% and 80% for 2 hr after doses of 0.04 and 0.01 mg/kg, respectively. Fenoterol had a slightly greater central stimulant effect than terbutaline; ipratropium bromide displayed no stimulant activity.

Acetylcholine↗
PubMed1977

[Metabolic effects of acute experimental hypoxia and hypercapnia].

Hypoxia and the hypercapnia were produced in anesthetized dogs by artificial respiration with appropriate gas mixtures, and a study was conducted of the effects of these conditions on various metabolic parameters, viz. catecholamines, renin activity, lactate, pyruvate, cortisol, non-esterified free fatty acids (FFA), and ammonia, in the plasma of the arterial blood. Hypercapnia caused a distinct increase in catecholamine concentrations, renin activity and ammonia, and a decrease in lactate and pyruvate; cortisol and FFA levels were only slightly altered. Hypoxia increased lactate, pyruvate and--though only to a slight extent--FFA, cortisol and NH3. The changes induced by hypercapnia were chiefly attributable to activation of the sympathico-adrenal system; those induced by hypoxia were not.

Ammonia↗
PubMed1977

[Experimentally induced alterations in wedge pressure and O2-partial pressure during acute hypoxia].

Suprarenal occlusion of the aorta by means of a balloon catheter results in an increase in wedge pressure, alterations in blood flow in the pulmonary circulation, and an increase in O2 partial pressure in the arterial blood. It is demonstrated that these changes take place after occlusion of the aorta during normoxia or hypoxia (Pao2:43 mmHg) in anaesthetized normotensive or spontaneously hypertensive mongrel dogs.

Acute Disease↗
PubMed1976

[Increasing the bronchial resistance by means of aortic occlusion in the dog].

In 11 spontaneously breathing, anesthetized dogs, suprarenal occlusion of the aorta was produced by means of a ballon-tipped catheter and maintained for 20 min. The obstruction led to an increase in O2 saturation in arterial blood (the rise in wedge pressure alters pulmonary perfusion), in aortic pressure and in bronchial resistance. Bronchial resistance could be partially diminished by inhalations of atropine or terbutalin.

Airway Resistance↗
PubMed1976

[Hemodynamic concomitant effects of experimentally increased pulmonary capillary pressure].

An acute suprarenal occlusion of the aorta was produced in anaesthetized dogs by means of a ballon-tipped catheter. The resultant increase in wedge-pressure led to changes in pulmonary perfusion and raised O2 partial pressure in the arterial blood. The additional, simultaneous occlusion of the left subclavian artery by means of a second balloon-tipped catheter aggravated the haemodynamic manifestations of the pressure-load on the heart; but did not cause a proportionate increase in wedge pressure and O2 partial pressure.

Animals↗
PubMed1975

[Proceedings: Experimentally induced effects on the plasma renin activity].

In dogs, plasma renin activity (PRA) was increased by anesthesia, by hypercapnia and by extreme hypoxia (paO2 47.6 mm Hg). Relatively moderate hypoxia (paO2 47.6 mm Hg) and artificial respiration had no appreciable influence on PRA. It appears that the sympathomimetic stimulus of CO2 has an important bearing on PRA.

Anesthesia↗