Showing papers in "Biomedica biochimica acta in 1989"

Strategies for calibrating a subcutaneous glucose sensor.

Abstract: The calibration of the glucose sensor is a critical issue for the subcutaneous implantation of such devices, since it allows from the sensor output the estimation of the prevailing subcutaneous glucose concentration. This study has compared estimations of subcutaneous glucose concentration in rats, calculated from the sensor's signal by using calibration parameters (sensitivity coefficient and background current) determined either under in vitro or in vivo conditions. The in vitro calibration was performed in phosphate buffer at 37 degrees C. The in vivo parameters were calculated by comparing changes in the sensor output current to concomitant changes in blood glucose concentration, induced by intravenous insulin injection and glucose infusion. The apparent subcutaneous glucose concentration, calculated with in vitro parameters, remained much lower than the concomitant blood glucose levels throughout the experiments. By contrast, when it was calculated with the calibration parameters determined in vivo, either in the hypoglycemia or hyperglycemia range, the apparent subcutaneous glucose concentration well reflected blood glucose levels with a five min time lag. We conclude that it is the two-point in vivo calibration procedure which allows the calculation of an apparent subcutaneous glucose concentration best reflecting blood glucose levels.

In situ calibration of implanted electrochemical glucose sensors.

Abstract: A feasible and reliable method of in situ checking and calibration of implanted glucose sensors is required to compensate for alterations in the overall sensitivity of the "sensor plus subcutaneous fluid glucose compartment" system. In a study on nondiabetic dogs, the linear regression analysis of paired plasma glucose/sensor current data is validated as a potential basis of recalibration of intracorporal glucose sensors. These sensors were amperometric glucose oxidase/hydrogen peroxide electrodes of which the in vitro response time to square alterations in the ambient glucose concentration T95 was less than 5 min. The method presented may be incorporated into the data handling system of portable glucose monitors or of miniaturized artificial beta-cells. For its performance, no steady state glycaemia but a minimum alteration in the intracorporal glucose concentration is needed. The latter can be provided both by tests or by fluctuations as they occur spontaneously during the course of the day.

Similar endothelium-independent arterial relaxation by carbon monoxide and nitric oxide.

Abstract: In organ bath and bioassay experiments the relaxing effect of carbon monoxide on femoral, carotid and coronary artery preparations of the dog was shown to be similar to those of endothelium-derived relaxing factor and nitric oxide.

Inhibition of expression of SV40 virus large T-antigen by antisense oligodeoxyribonucleotides.

Abstract: Expression of large T-antigen in COS cells can be inhibited by treatment of cell monolayers with oligodeoxyribonucleotides complementary to large T mRNA, which were covalently linked to poly-L-lysine Strongest inhibition was observed with conjugates of oligodeoxynucleotides that hybridize to the sequence immediately 3' to the cap structure of the mRNA Treatment of SV40 virus-infected CV-1 cells with the same conjugates reduces the virus-induced large T-antigen expression by more than 80%

Oxygen tension at the subcutaneous implantation site of glucose sensors.

Abstract: To elucidate potential influences of the average tissue pO2 on the function of implanted glucose sensors, non-miniaturized polarographic oxygen electrodes and glucose oxidase/H2O2 glucose electrodes were implanted in the subcutaneous tissue of spontaneously breathing normal and diabetic dogs. There was no appreciable run-in phenomenon of oxygen sensors but normally a pronounced initial decrease in current after implantation of glucose sensors. The subcutaneous pO2 amounted to an average of 7 kPa in air-breathing animals with no difference between normal and insulin-dependent diabetic dogs. It showed oscillations of approximately +/- 2 kPa but the mean was stable over the maximum duration of experiments of 16 h. Induced alterations of tissue pO2 between less than 2 and greater than 20 kPa (as verified by measurements of arterial pO2) were not followed by alterations in the current of nearby implanted glucose sensors. It is concluded that the frequently observed instabilities and losses in sensitivity of the system "implanted glucose sensor in situ + tissue glucose compartment" are not caused by alterations in tissue pO2.

Domperidone, an inhibitor of the D2-receptor, blocks a late phase of an electrically induced long-term potentiation in the CA1-region in rats.

Abstract: The influence of the D2-receptorblocker domperidone (DP) at a concentration of 1 microM was investigated on an electrically induced long-term potentiation (LTP) measured as the enhancement of the population spike (PS) amplitude in the hippocampal CA1. It could be shown that the drug does not influence the initiation but the maintenance of LTP. The results once again support the hypothesis that different phases of LTP exist which are realized by different cellular inputs.

The ratio of oxidized/reduced glutathione as an index of oxidative stress in various experimental models of shock syndrome.

Abstract: Red blood cells are well equipped to handle intracellular oxidative stress, their membranes are permeable to O2- and H2O2, and in this way they are important regulators of oxygen reactions occurring in their surroundings. The protective effect against reduced oxygen species - generated during the endothelial cell injury of various tissues - is attributed mainly to the glutathione metabolism of red blood cells. The blood concentration of reduced (GSH) and oxidized glutathione (GSSG) was determined by a sensitive method using glutathione reductase in experimental shock syndromes induced by paraquat toxicity, tourniquet ligature and endotoxin in rats, by bleeding and reperfusion in dogs and by transient ligature of thoracic aorta in newborn piglets. Under these conditions the concentration of GSSG was elevated and GSH was lowered, resulting in an increase in the redox ratio: [GSSG/(GSH + GSSG)] x 100 (GSSG/GSH); particularly during reperfusion. Determination of the GSSG/GSH seems to be a reliable index to assess the degree of oxidative stress "in vivo".

In vivo response of microfabricated glucose sensors to glycemia changes in normal rats.

Abstract: A planar glucose sensor based on an amperometric detection of H2O2 is presented. The transducer part which is a planar three-electrode cell consisting of two Pt-electrodes and one Ag/AgCl-thin film electrode is realized using microelectronic technology. The overall dimensions are 0.8 mm x 3 mm x 0.38 mm and the working electrode area is 0.1 mm2. GOD is immobilized using glutaraldehyde as a cross-linking agent and bovine serum albumin as a carrier protein. The resulting membrane has a typical thickness of 25 microns. Also, an outer polyurethane membrane is dip-coated all around the tip of the electrode. The influence of pO2 on the sensor response as well as the sensor temperature coefficient, sensitivity and linear range have been investigated. The sensor has been tested in vivo in a subcutaneous tissue of anaesthetised rats. During experiments, blood sampling allows to measure changes in venous plasma glucose using a Beckman analyzer. The sensor response following hyperglycaemic clamps as well as intravenous glucose loads is discussed.

Prevention of cardiac arrhythmias by adaptation to hypoxia: regulatory mechanisms and cardiotropic effect.

Abstract: Adaptation to intermittent hypoxia had a pronounced antiarrhythmic effect in acute myocardial ischemia in conscious animals This effect was less pronounced in anesthesia and was absent in isolated heart In reperfusion, the prophylactic effect of adaptation was equally pronounced in all cases Adaptation prevented stress-induced exhaustion of brain beta-endorphine presumably by its accumulation in adrenal glands and resulted in the accumulation of dopamine, 5-hydroxytryptamine and 5-hydroxyindolacetic acid in brain structures These data naturally lead to the assumption that central mechanisms play the main role in the antiarrhythmic effect of adaptation to intermittent hypoxia on ischemic arrhythmias, while mechanisms occurring at the level of heart play the main role in the protective effect of the same adaptation against reperfusion arrhythmias

Effects of modified respiratory rhythm on heart rate variability during active orthostatic load.

Abstract: The experiments were carried out to study the influence (a) of 3 different respiratory frequencies (0.12, 0.20 and 0.35 Hz) on heart rate power spectra during orthostatic load with special reference to the peak frequency of mid-frequency heart rate fluctuations, and (b) of variation in respiratory depth on this peak frequency in supine position. The peak frequency of mid-frequency heart rate fluctuations was shifted to lower frequency values in response to orthostasis despite the constant respiratory frequency for either posture. No differences in peak frequency were observed between respiratory frequencies of 0.20 and 0.35 Hz in both supine and standing position and between the two extreme patterns of respiratory depth. We suggest that the shift of the peak frequency of mid-frequency heart rate fluctuations to the lower end of the heart rate power spectrum during orthostasis represents an original effect independent of depth and frequency of respiration.

Preparation and validation of implantable electrodes for the measurement of oxygen and glucose.

Abstract: In realizing the continuous measurement of pO2 and glucose concentration in the subcutaneous tissue, miniaturized electrochemical oxygen- and enzyme glucose sensors, based on modified Clark-type electrodes for transient implantation, were developed and investigated. The electrodes were prepared by means of sequential dipping procedures in glucose oxidase and in different polymer solutions at well-defined environmental conditions in an incubator. By means of combining a hydrophobic membrane with a glucose permeable area and a hydrophilic membrane in the case of the glucose sensor, linearity of the glucose dependent electrode signal up to greater than 20 mmol/l could be achieved. After subcutaneous implantation in the neck of dogs, the enzyme sensor is able to follow glucose profiles in the normo- and in the hyperglycaemic range, e.g. as caused by oral glucose loads. Looking for the difference in sensitivity of the enzyme sensor measured in vitro and calculated from in vivo data, the influence of potential nonspecific, interfering substances in vivo such as urea, amino acids, electrolytes, and albumin was estimated.

In vitro measurements with electrocatalytic glucose sensor in blood.

Abstract: The principle of measurement with electrocatalytic glucose sensor is based on the direct electrochemical oxidation of glucose at an active and membrane-covered noble metal electrode. The objective is to measure glucose in the range of diffusion limiting current, since the glucose concentration in front of the membrane is proportional to the oxidative current. The determination of glucose concentration is realized by considering the electrode processes taking place at different potentials, and by measuring the impedance of the electrode/membrane system using the conventional three-electrode arrangement. Performance and long-term stability of the sensor are mainly dependent on the properties of the membrane and on the poisoning reactions at the electrode. Using this method, measurements were carried out in defibrinated sheep blood at 37 degrees C. After reproducible in vitro measurements could be made with the sensor over up to 3 weeks with an error of 20%, experiments were conducted in sheep using an extracorporeal circulation system. The correlation between the electrode signal and the glucose concentration in blood could be confirmed during glucose tolerance tests.

Behaviour of EMG-parameters and conduction velocity in contractions with different muscle temperatures.

Abstract: In the study the effect of changing muscle temperature on EMG-parameters and muscular conduction velocity was investigated for ambient temperatures of 0, 10, 20, 30, 40 degrees C. With temperatures below 20 degrees C a striking diminution of EMG-amplitudes was observed despite nearly unchanged mechanical capability. The decrease in mean frequency of surface EMG was related directly to changes in conduction velocity during cooling of the muscle whereas in fatiguing muscle contractions the mean frequency seemed to be also affected by other mechanisms.

Cerebral ischemia in the developing primate fetus.

Abstract: The common carotid arteries and jugular veins of fetuses of dated rhesus monkey pregnancies were ligated at different times during the last 2/3's of gestation. Fetuses that survived were delivered surgically at term and their brains examined pathologically. The findings obtained demonstrated the following principles: 1. Production of ischemia of the anterior cerebral circulation by bilateral ligation of the common carotid arteries and jugular veins prior to the end of the first half of gestation (82 days) produced brain abnormalities in all instances. 2. Ligation of the common carotid arteries and jugular veins during the middle 1/3 of gestation (55-110 days) produced 1) extensive focal tissue destruction restricted to the ischemic territory in 6 of 12 fetuses and 2) abnormal brain development in 3 of 12 fetuses. 3. Ligation of the common carotid arteries and jugular veins early during the middle 1/3 of gestation favored the occurrence of cerebral dysgenesis or brain malformation while late during the middle 1/3 it favored focal tissue destruction. In the earlier cases of blood vessel ligation the focal tissue destruction resembled hydranencephaly. 4. Production of ischemia of the anterior cerebral circulation by ligation of the common carotid arteries and jugular veins during the last 1/3 of gestation (greater than 110 days) produced no gross or microscopic brain abnormalities.

Purification of cytochrome P-450 from n-hexadecane-grown Acinetobacter calcoaceticus.

Abstract: A convenient procedure for the purification of cytochrome P-450 from an n-alkane-assimilating strain of the bacterial species Acinetobacter calcoaceticus has been elaborated. The cytochrome P-450 of n-hexadecane-grown cells was found to be distributed in cell-free extracts among particulate and soluble subcellular fractions. For isolation, cytochrome P-450 was extracted from particulate fractions by addition of Triton X-100 to the buffer. Subsequently, purification to an apparently homogeneous state was achieved by chromatography on DEAE-cellulose, Sepharose CL-6B and hydroxylapatite cellulose. A Mr of 52,000, an isoelectric point of 4.7 and the amino acid composition were determined. The Soret bands of absolute absorption spectra showed maxima at 417 nm for the oxidized form, at 408 nm for the reduced form and at 448 nm for the carbon monoxide compound of the reduced cytochrome. Difference spectra with octylamine showed maxima at 432 nm and minima at 410 nm indicating the predominance of the low-spin state. Conversion to the high-spin state could not be obtained. The isolated cytochrome P-450 was stable in the presence of Triton X-100 under neutral pH conditions. Removal of the detergent or change of the pH to values higher than 8.0 or lower than 6.0 resulted in the destruction of the cytochrome P-450.

Evidence for intermittent radiobiological hypoxia in experimental tumour systems.

Abstract: This paper describes flow and static fluorescence cytometry techniques to visualize and quantitate acute radiobiological hypoxia resulting from transient fluctuation in tumour blood flow in experimental tumour systems. The application of these techniques in two murine tumour systems provides evidence that such hypoxia exists and reduces the effectiveness of single doses of radiation. Possible mechanisms for and implications of these findings are discussed.

Response of different mammary epithelial cell lines to a mammary derived growth inhibitor (MDGI).

Abstract: MDGI, a 14.5-KDa protein, is a chemically defined growth inhibitor, which we have purified from lactating bovine mammary gland and characterized biologically in a mouse Ehrlich ascites mammary tumour (EAT) short term suspension culture. It has now been tested for its inhibitory activity on proliferation of four malignant mammary epithelial cell lines of human and mouse origin and normal human mammary epithelial cells. In all experiments, cells were brought to quiescence by serum or growth factor deprivation. Using [3H]TdR pulse labelling the effect of MDGI was measured on the restimulation of proliferation after medium change. MaTu and T47 D, human malignant mammary epithelial cell lines, as well as the mouse malignant mammary epithelial cell line mMaCa 20177 could be inhibited, whereas the human malignant mammary epithelial cell line MCF7 showed a slight stimulation. MDGI showed no activity on the residual DNA synthesis of all cell lines after starvation. Normal human mammary epithelial cells (HMEC) of different passages could also be inhibited. Their responsiveness seemed to be dependent on the number of passages. Cells from high passages (10-14) showed a higher sensitivity, which is also about 10 times higher than that of the malignant cell lines. Furthermore, growth factors like insulin, epidermal growth factor (EGF) and fetal calf serum (FCS), known to be potent antagonists to the MDGI activity in the EAT and, in the case of insulin, also in the MaTu culture (shown in the present study), do not abolish the inhibitory activity of MDGI on HMEC cells. These results demonstrate that the inhibitory activity of MDGI is not exclusively restricted to EAT cells studied so far.

Circulatory effects of oxygen radicals.

Abstract: Oxygen radicals have vasoactive properties. The hypoxanthine-xanthine oxidase system generates oxygen radicals. This system relaxes isolated constricted ductus rings from fetal lambs and constricts the pulmonary circulation of adult pigs. Since catalase, and not superoxide dismutase, inhibits the effect of the hypoxanthine-xanthine oxidase system, we believe the effect is caused by the hydroxyl radical. The hydroxyl radical stimulates prostaglandin synthesis in the vessel wall and high concentrations of prostanoids can be measured after hypoxanthine-xanthine oxidase exposure. Indomethacin inhibits the vasoactive effects of the hypoxanthine-xanthine oxidase system. We believe the hypoxanthine-xanthine oxidase system plays an important role in regulating the normal circulation.

Energy state, glycolytic intermediates and mitochondrial function in the liver during reversible and irreversible endotoxin shock.

Abstract: Metabolites of the energy and carbohydrate metabolism and mitochondrial function in the liver were compared in rats with reversible as well as with irreversible shock. 6 h after induction of shock there was a close correlation between the severity of shock and the energy state of the liver. Only rats with irreversible shock showed a marked deterioration in parameters of the adenylate system, whereas in animals with reversible shock the energy state remained at control levels. Liver glycogen and glucose stores declined similarly in all shocked rats. The capacity of isolated liver mitochondria to produce ATP did not essentially differ in reversible and irreversible shock. Further investigations should consider the intracellular environment in evaluating the mitochondrial function in vivo during endotoxin shock.

Changes of the neuronal structure produced by prolonged hypobaric hypoxia in infant rats.

Abstract: Structural parameters of neuronal circuits were studied in rats exposed to aerogenic hypoxia during the postnatal development. In 18-day-old experimental animals pyramidal cells of the hippocampal CA1 area had less branches of the apical dendrites. These branches were shorter with lower dendritic spine density. Myelinated axons in the corpus callosum were less frequent. In electron-microscopic picture the mean section area of myelinated axons was lower, the myelin sheets were thinner and consisted of less myelin layers. Synapses in the II. layer of the somatosensoric cortex had more often flat pre-synaptic dense projections, smaller width between pre- and post-synaptic densities and thinner post-synaptic densities.

Temperature effects on isometric contractions of slow and fast twitch muscles of various rodents--dependence on fibre type composition: a comparative study.

Abstract: The influence of temperature (range 15-37 degrees C) on the isometric contractions of the slow twitch soleus (SOL) and the fast twitch extensor digitorum longus (EDL) muscles of mice, rats and guinea pigs were investigated in vitro. Cooling of the bathing solution prolonged the time parameters of single twitches and tetanic contractions in a non-linear manner in both muscle types of all animals. In muscles containing predominately fast twitch fibres like the EDL of all animals cooling was followed by an increase of the single twitch tension (cold potentiation) with a maximum of 160-180% at about 20 degrees C. The influence of a decrease of the temperature on the twitch tension was different in the SOL of the three animals. In SOL of mice (containing about 50% slow twitch fibres) the twitch tension was virtually unchanged, in SOL of rats (about 70% slow twitch fibres) a moderate cold depression and in SOL of guinea pigs (composed by slow twitch fibres only) a strong cold depression was observed. The maximum tetanic tension decreased progressively on cooling in all muscles and independently of their fibre type composition. Cooling increased the twitch-tetanus-ratio in fast twitch and decreased it in pure slow twitch muscles. It is concluded that the temperature dependence of the single twitch and the twitch-tetanus-ratio can be used as a physiological measure of the fibre type composition of a given muscle.

Production and characterization of four monoclonal antibodies specific for human interferon-alpha-1 and -alpha-2.

Abstract: Four monoclonal antibodies against HuIFN-alpha-1 and -alpha-2 were produced by the lymphocyte hybridoma technique. The screening for monoclonal anti-IFN antibodies was performed by two different procedures permitting the detection of neutralizing and non-neutralizing antibodies. The first antibody screening in the supernatants of hybridoma clones was carried out by an immunodot ELISA using a novel chromogen, 2-bromo-1-naphthol, for the immunoperoxidase reaction. The second screening was performed with a solid-phase bioassay. The monoclonal antibodies IIG11 and IVH2 react specifically with HuIFN-alpha-1 independently of its origin, natural or recombinant. The mAb IIG11 recognizes also an epitope on a 27 kDa interferon, probably HuIFN-alpha-8. The mAb IIG7 binds to HuIFN-alpha-2 only, whereas the mAb IIB2 binds to HuIFN-alpha-2 and also to the 27 kDa interferon and to a 25 kDa interferon, not yet further characterized. These antibodies can be used successfully for immunopurification as well as for quantification of the corresponding interferons.

Reduction of tumour blood flow by vasoactive drugs: a role in cancer therapy.

Abstract: The potential use of tumour blood flow reductions, induced by the vasodilator hydralazine, in cancer therapy are described. Data obtained in experimental tumour systems indicate that with appropriate scheduling and drug combinations, hydralazine can increase the therapeutic effectiveness of certain chemotherapeutic agents whether used alone or in combination with other modalities such as radiation or hyperthermia.

Interindividual variability of isometric endurance with regard to the endurance performance limit for static work.

Abstract: In literature there are doubts concerning the 15% MVC (maximal voluntary contraction) level and invariability of isometric endurance, as described by ROHMERT (1962) as a "biologische Konstante". Therefore, 3 experimental sets using different levels of relative loads from approximately 2.9% (individual weight of forearm) to 50% MVC and different holding times (up to 1 hr) were performed concerning elbow flexion and knee extension. Measurements of the times until exhaustion and muscular fatigue (EMG) underlined the great variability of the holding times and showed that the mean endurance performance limit for isometric exercise lies neither at the 15% MVC level nor can it be used as a "biologische Konstante". The muscle fibre composition is discussed as the main reason for the observed variability.

Hypoxic brain and heart injury thresholds in piglets.

Abstract: Both heart and brain are at risk for damage from asphyxia. However, these 2 organs' relative injury-thresholds have remained poorly defined. The present study using 16 anesthetized newborn piglets attempts to separate brain and heart damaging exposures from those that leave these organs unaffected. The hypoxic exposure (mean PaO2 = 3.6 +/- 0.6 kPa (27 mmHg) lasted for an average duration of 40 minutes and was associated with hypotension less than 4.7 kPa (35 mmHg) MABP. For brain damage assessment, 9 piglets that survived greater than 12 hours following resuscitation permitting histologic evaluation were used. For heart outcome assessment, those piglets that developed a postexposure, secondary hypotension to less than 4.7 kPa (35 mmHg) were compared to those without excluding 3 with uncertain cause of death. BRAIN-RESULTS: Six piglets remained brain intact while 3 exhibited brain edema and diffuse neuronal damage. The damaged animals' exposures differed from those that remained brain intact in sustaining significantly lower lowest MABPs (1.6 +/- 0.1 vs 3.3 +/- 0.4 kPa (12 vs 25 mmHg] and longer durations of MABP below 3.3 kPa (25 mmHg): 6 vs 1 min. and below 2.7 kPa (20 mmHg): 4 vs 0 min. HEART-RESULTS: Six of 13 animals developed marked delayed post-exposure hypotension requiring 5 to be killed prior to complete cardiovascular collapse. The only significant difference observed during exposure differentiating the two outcome groups (blood pressure maintenance vs cardiogenic shock) was the latter's more marked systemic acidosis (lowest mean arterial blood pH: 6.61 +/- 0.10 vs 6.91 +/- 0.10). These results suggest the brain is at risk for damage during hypoxia only when accompanied by an extreme lowering of blood pressure and the heart when accompanied by a severe acidosis. Further, the heart and brain need not both be damaged by the same hypoxic exposure. Contrary to common belief, the brain is not readily damaged from hypoxia alone absent marked circulatory changes.

On-line determination of anaerobic threshold with rms-EMG.

Abstract: 1. On-line monitoring of surface rms-EMG for detecting the anaerobic threshold during a cycle ergometer test was evaluated and compared with blood lactate and ventilatory parameters in 12 healthy icehockey players. 2. Dislinearity of increase in blood lactate level, ventilatory parameters and myoelectrical activity was observed at the mean work level of 300 (range 270-330) watts in each case. 3. The linearity disappeared at the same time in the rms-EMG-load ratio in working quadriceps and gastrocnemius muscles while also in nonworking frontalis muscle a change in EMG level was noticed. 4. The break point in rms-EMG did not correlate with the changes in skin humidity and temperature. No change was observed in spectral properties of the myoelectrical signals. 5. The rms-EMG follow-up is easier to perform than measurements of blood lactate and ventilatory parameters in the determination of anaerobic threshold.

Protein stabilization by blocking the native unfolding nucleus.

Abstract: Studies on the thermal inactivation of immobilized enzymes result in a novel conception of protein stabilization. The native protein molecule is suggested to be characterized by a specific structural region where the unfolding process starts. Accordingly, enzyme stabilization by immobilization is the result of blocking this unfolding nucleus.

The influence of suspension hypokinesia on contractile properties of slow and fast twitch muscles of young growing and adult rats.

Abstract: The influence of the lack of the gravity force on contractile properties of the slow-twitch soleus (SOL) and the fast-twitch extensor digitorum longus (EDL) muscles was investigated in 3 week or 6-month-old rats suspended by their tail. In both groups suspension hypokinesia (SH) lasting 3 weeks or longer leads to a marked decrease of the mass and of the mean cross-sectional area of the SOL. The SOL of suspended animals shows decreased contraction and half-relaxation times and a lower tension of the single twitch, a decreased maximum tetanic force output, an increased fusion frequency and a decreased tetanus-half-rise time. The force developed per unit cross-sectional area and the twitch-tetanus ratio are unchanged. The atrophy and the changes in contractile properties are more pronounced in young developing rats than in adult ones. The SOL of suspended young rats does not develop into a slow-twitch muscle and shows a posttetanic potentiation and a cooling potentiation of the single twitch, properties observed in fast-twitch muscles only. In comparison to controls SH has no influence on the wet weight, mean cross-sectional area, and contractile properties of the EDL of young or adult rats. The data presented here and supported by histochemical and biochemical results demonstrates the importance of the gravity force for slow-twitch muscles especially during development.

Studies of lipid peroxidation in isolated rat heart mitochondria.

Abstract: Peroxidation in isolated, functionally intact rat heart mitochondria was induced by iron/ascorbate or ADP-iron/NAD(P)H. Compared to liver mitochondria, MDA formation was very low and lipohydroperoxides not detected. The NADPH-mediated peroxidation which generally resulted in somewhat higher MDA levels was accompanied by an increasing inhibition of ADP-stimulated respiration. The active respiration was sensitively inhibited at very early stages of MDA formation, whereas in the same period the CAT-insensitive respiration exhibited almost no response at all. It was demonstrated that the decrease in active respiration correlated with the time for half-maximum MDA formation. No considerable degradation of major mitochondrial phospholipids was observed during two hours of incubation. It was not until after complete inhibition of respiration and onset of enhanced MDA formation that cardiolipin, phosphatidylethanolamine and, later, phosphatidylcholine were diminished.

On the release of glycogen phosphorylase from heart muscle: effect of substrate depletion, ischemia and of imipramine.

Abstract: The release of glycogen phosphorylase from isolated, perfused rabbit heart was studied after substrate depletion and after global ischemia. The assayed efflux of the enzyme was found to be not only related to alterations in membrane integrity but also to the amount of glycogen in the injured heart tissue. The differential efflux profile of phosphorylase as a constituent of the sarcoplasmic reticulum-glycogenolysis complex in cardiac cells in comparison to cytosolic creatine kinase was found to be more pronounced employing K+-arrested, hypothermically perfused hearts exposed to imipramine (0.4 to 0.6 mM), known for altering specifically membrane integrity. Under these conditions only a rise in the release of creatine kinase occurs, whereas both glycogen content and the efflux of phosphorylase remains uneffected. It is suggested that the metabolical dependence of phosphorylase efflux from the injured heart muscle is of importance for its high sensitivity being a marker of acute heart infarction.