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Biomedical subjects

K Hecht

Publications and source records attributed to K Hecht.

At least 19 recordsLinked to original sources
PubMed1992

The evaluation of biological efficiency of electromagnetic fields generated by implanted radiotelemetric transmitters used in space research on animals.

The study was carried out in 50 male rats abdominally implanted with biotelemetric systems (BTS) or mock-up. The animals were provided with 12/12 light/dark schedule during 6-week experiment. The electromagnetic field (EMF) frequency was 455 kHz, magnetic induction near transducer was about 10(-2) mT. Circadian rhythm of the body temperature and locomotor activity was controlled in course of the experiment. The latter been finished, some tissues and the blood of the animals have been sampled to test corticosterone, testosterone, T3, T4 level in serum with radioimmunoassay and membrane permeability for Ca2+, Na+, K(+)-ATPase activity and charge changes in liver microsomes was detected. The probable ways of the EMF influence on whole body are discussed.

Animals↗
PubMed1991

[Relationship between insomnia and arterial hypotension].

The relations between insomnia and blood pressure were investigated in 151 patients (56 men and 95 women). It was found that 37.1% of the patients were normotensive, whereas 31.8% suffered from arterial hypertension and 31.1% from arterial hypotension. There was practically no difference between normotensives and hypertensives in respect of disturbed behavioral patterns of sleep, but an entirely different picture was presented by the arterial hypotensives. Characteristic features of hypotonic insomnias were (mostly in women) prolonged time before falling asleep, frequent awakening at night associated with tachycardia and long-lasting increased excitability, starting difficulties in the morning, depressive conditions, compulsive yawning and falling asleep during daytime, tiredness, lack of "drive" and reduced physical and mental efficiency. This pattern of signs and symptoms was enhanced by hypnotics and tranquilisers. During sleep blood pressures down to 50/35 Torr were measured. It is assumed that the low blood pressure results in hypoxic and hypoglycaemic conditions in the brain. Spontaneous awakening is considered to be an emergency reaction triggered by the deficient cerebral blood flow.

Adult↗
PubMed1990

Extracellular Ca2(+)-dependent inducible alkaline phosphatase from extremely halophilic archaebacterium Haloarcula marismortui.

When starved of inorganic phosphate, the extremely halophilic archaebacterium Haloarcula marismortui produces the enzyme alkaline phosphatase and secretes it to the medium. This inducible extracellular enzyme is a glycoprotein whose subunit molecular mass is 160 kDa, as estimated by sodium dodecyl sulfate-gel electrophoresis. The native form of the enzyme is heterogeneous and composed of multiple oligomeric forms. The enzymatic activity of the halophilic alkaline phosphatase is maximal at pH 8.5, and the enzyme is inhibited by phosphate. Unlike most alkaline phosphatases, the halobacterial enzyme requires Ca2+ and not Zn2+ ions for its activity. Both calcium ions (in the millimolar range) and NaCl (in the molar range) are required for the stability of the enzyme.

Alkaline Phosphatase↗
PubMed1990

Lactate dehydrogenase from the extreme halophilic archaebacterium Halobacterium marismortui.

D-Lactate dehydrogenase from the extreme halophilic archaebacterium Halobacterium marismortui has been partially purified by ammonium-sulfate fractionation, hydrophobic and ion exchange chromatography. Catalytic activity of the enzyme requires salt concentrations beyond 1M NaCl: optimum conditions are 4M NaCl or KCl, pH 6-8, 50 degrees C. Michaelis constants for NADH and pyruvate under optimum conditions of enzymatic activity are 0.070 and 4.5mM, respectively. As for other bacterial D-specific lactate dehydrogenases, fructose 1,6-bisphosphate and divalent cations (Mg2+, Mn2+) do not affect the catalytic activity of the enzyme. As shown by gel-filtration and ultracentrifugal analysis, the enzyme under the conditions of the enzyme assay is a dimer with a subunit molecular mass close to 36 kDa. At low salt concentrations (less than 1M), as well as high concentrations of chaotropic solvent components and low pH, the enzyme undergoes reversible deactivation, dissociation and denaturation. The temperature dependence of the enzymatic activity shows non-linear Arrhenius behavior with activation energies of the order of 90 and 25 kJ/mol at temperatures below and beyond ca. 30 degrees C. In the presence of high salt, the enzyme exhibits exceptional thermal stability; denaturation only occurs at temperatures beyond 55 degrees C. The half-time of deactivation at 70 and 75 degrees C is 300 and 15 min, respectively. Maximum stability is observed at pH 7.5-9.0.

Archaea↗
PubMed1989

Catalytic properties of thermophilic lactate dehydrogenase and halophilic malate dehydrogenase at high temperature and low water activity.

Thermophilic lactate dehydrogenases from Thermotoga maritima and Bacillus stearothermophilus are stable up to temperature limits close to the optimum growth temperature of their parent organisms. Their catalytic properties are anomalous in that Km shows a drastic increase with increasing temperature. At low temperatures, the effect levels off. Extreme halophilic malate dehydrogenase from Halobacterium marismortui exhibits a similar anomaly. Increasing salt concentration (NaCl) leads to an optimum curve for Km, oxaloacctate while Km, NADH remains constant. Previous claims that the activity of halophilic malate dehydrogenase shows a maximum at 1.25 M NaCl are caused by limiting substrate concentration; at substrate saturation, specific activity of halophilic malate dehydrogenase reaches a constant value at ionic strengths I greater than or equal to 1 M. Non-halophilic (mitochondrial) malate dehydrogenase shows Km characteristics similar to those observed for the halophilic enzyme. The drastic decrease in specific activity of the mitochondrial enzyme at elevated salt concentrations is caused by the salt-induced increase in rigidity of the enzyme, rather than gross structural changes.

Catalysis↗
PubMed1987

Prevention of stress-induced involution of the thymus in rats by substance P (SP1-11) and its N-terminal fragment SP1-4.

Selye found that in response to different stressors the body reacts with a characteristic stress syndrome: adrenal enlargement, gastrointestinal ulcera, and thymicolymphatic involution. In this paper we demonstrate that i.p. injected Substance P (SP) can prevent stress-induced involution of thymus in Wistar rats. This protecting effect on the immune system of SP, in addition to the "normalizing" effects of this peptide on stress-induced disorders in vegetative and central functions first described by Oehme and co-workers and Hecht and co-workers is a new hint to the function of SP as an "anti-stress" agent. The mode of action of the anti-stress effect of SP in adrenals as well as in the thymus is discussed. It is suggested that the anti-stress effect of SP1-11 and its N-terminal fragment SP1-4 is mediated by specific receptors in adrenals and/or thymus which are different from the so called SP-P and SP-E receptors.

Adrenal Glands↗
PubMed1987

[Comparison of the effects of DSIP and SP 1-11 on stress-induced chronic sleep disorders in rats].

In the present paper the effects of substance P (SP1-11, Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-MetNH2) and delta sleep inducing peptide (DSIP, Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu) to normalize the deprivation of sleep in chronically stressed rats with hyposomnia were investigated. The results indicated that SP1-11 is more potent than DSIP in rats with stress-induced hyposomnia. Different effects were found in the duration of sleep, the percentage of sleep phases compared to wake phases, the rhythm of sleep phases and the time periods of sleep-cycles. Based on the present results both the common and differences in the mode of action were discussed.

Animals↗
PubMed1987

Relationship of substance P to catecholamines, stress, and hypertension.

This paper presents results on the function of the adrenal medulla, especially the influence of substance P (SP) on the cholinergic-adrenergic interaction. Interconnections between the function of SP and its role in the development and maintenance of hypertension as well as its role in stress and adaptation are investigated. Substance P acts only in situations with an increased nervous activity, for example, after stress-induced activation of the pituitary-adrenal and sympathetic-adrenal axis. Substance P normalizes stress-induced disorders by maintaining homeostasis in the catecholamine system. The basis of the antistress effect is the modulation of both biosynthesis and release of catecholamines in the adrenals. The homeostasis effect of SP, as well as the antistress effect do not require the complete sequence of the molecule. The N-terminal SP fragment is fully active and has no side effects.

Adrenal Glands↗
PubMed1986

Behavioural changes in adult rats produced by early postnatal maternal deprivation and treatment with choline chloride.

Rats deprived temporarily of maternal contact and nutrition from the 3rd to 14th day of life showed decreased emotionality and poor memory capacity when tested in adulthood. Simultaneous administration of choline chloride, an acetylcholine precursor, in neonatal life permanently increased the emotionality and restored memory capacity to levels of control animals. However, no effect was demonstrated when choline chloride administration occurred after the deprivation period. The results of this study reveal that the effects on later behaviour appear to be dependent on the timing of choline chloride exposure in early life. Profound and long-lasting abnormalities in brain function produced by early postnatal maternal deprivation can be attenuated by correcting abnormal acetylcholine levels during brain development. Hence, acetylcholine can be considered as an important, environment-dependent local organizer of the brain.

Acetylcholine↗
PubMed1986

The cell surface glycoprotein of Halobacterium halobium. Physico-chemical characterization in the absence and presence of salt.

The cell surface glycoprotein of Halobacterium halobium is soluble in dilute buffer at neutral pH. At low counterion concentrations, the protein is monomeric (Ms,D = 209 kDa) and exhibits the characteristics of a highly charged polyelectrolyte. Evidence obtained from intrinsic fluorescence and far-UV circular dichroism shows that the monomer at low salt loses both its native conformation and its inherent tendency to form high molecular mass assemblies. In 4M NaCl, 25 mM KCl, and in the presence of divalent ions (greater than or equal to 50mM Mg2+ or Ca2+), association to well-defined assemblies of up to approximately 4 X 10(6) Da occurs. At low Mg2+ concentration and in the presence of Ba2+, a wide size-distribution of aggregates is observed. The assembly pattern of the protein may be correlated with salt-dependent alterations in the morphology of the bacterium.

Buffers↗
PubMed1986

[The role of the N-terminal of the substance P molecule in its action in stress-related behavioral and blood pressure disorders].

Substance P and the N-terminal sequences SP1-9, SP1-7, SP1-4 and SP1-2 were investigated in their action on stress related alterations in blood pressure behaviour, stress related disturbances in conditioned reflex learning behaviour, alterations in the endogenous opioid system and on the blood pressure behaviour of spontaneously hypertensive rats. In addition the occurrence of vegetative effects such as acute hypertension and histamine release from mast cells were investigated. The results of this work show that N- and C-terminal sequences of the Substance P molecule differ in their actions. Whereas the vegetative effects decrease if the SP molecule is shortened from the C to the N-terminus the "antistress effect" of the Substance P molecule remains unchanged. Whereas the N-terminal tetrapeptide SP1-4 can be considered "essential" for the "antistress effect", the C-terminal pentapeptide of SP is considered to be the "essential sequence" for the vegetative effects. These results will open new possibilities for the synthesis of selectively acting SP-agonists.

Animals↗