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Biomedical subjects

S Rapoport

Publications and source records attributed to S Rapoport.

At least 19 recordsLinked to original sources
PubMed1997

No evidence for direct incorporation of esterified palmitic acid from plasma into brain lipids of awake adult rat.

Awake adult rats were given a solution of [9,10-3H]palmitate ([3H]PAM) by gavage. The appearance of radiolabel in plasma lipid fractions was monitored by thin-layer chromatography at fixed intervals thereafter. At 2 h, the rats were killed by microwave irradiation and radioactivity in whole brain and individual brain phospholipids was determined. In plasma, esterified [3H]PAM was mainly associated with triglyceride, phospholipid, and cholesterol ester. Radioactivity appeared to a larger extent in triglyceride than in unesterified fatty acid, suggesting that unesterified [3H]PAM in plasma was largely due to release from esterified [3H]PAM by lipoprotein lipase hydrolysis. Brain radioactivity could be accounted for entirely by incorporation of unesterified plasma [3H]PAM. Esterified [3H]PAM in chylomicrons or lipoproteins was calculated to make no measurable contribution using a published value for the incorporation coefficient of [3H]PAM into brain in the evaluation. These results suggest that ingested palmitic acid (PAM) in adult rats enters blood as esterified triglyceride within chylomicrons and lipoproteins and, in part, eventually is converted to circulating unesterified PAM. It is the circulating unesterified PAM that is incorporated into brain from blood, whereas esterified PAM within plasma chlomicrons and lipoproteins makes no measurable direct contribution.

Administration, Oral↗
PubMed1994

Telehygiene system for preventive chronopharmacology in space.

A remote computerized health care (telehygiene) system for space travel includes monitoring devices and pharmaceuticals aimed at the optimization of health and the environment. Early risk indicators are provided by dynamic characteristics of rhythms of several frequencies describing variation inside the physiologic range. These rhythm characteristics, assessed as one goes, can be updated and compacted as data accumulate by the use of chronobiologic software that resolves anticipated components of lower and lower frequency, thus providing summaries of data at intervals of differing length. At any time, harbingers of risk, including characteristics of circannual rhythms, can be retrieved in an instant. On their basis, early preventive action can be instituted for risk lowering and for delivery of timed treatment when needed. Preventive or curative health care in space and terrestrial spin-offs are the more effective the more of the chronome (time-structure) is resolved.

Aerospace Medicine↗
PubMed1990

Chromosomal protein HMG-14 gene maps to the Down syndrome region of human chromosome 21 and is overexpressed in mouse trisomy 16.

The gene for human high-mobility-group (HMG) chromosomal protein HMG-14 is located in region 21q22.3, a region associated with the pathogenesis of Down syndrome, one of the most prevalent human birth defects. The expression of this gene is analyzed in mouse embryos that are trisomic in chromosome 16 and are considered to be an animal model for Down syndrome. RNA blot-hybridization analysis and detailed analysis of HMG-14 protein levels indicate that mouse trisomy 16 embryos have approximately 1.5 times more HMG-14 mRNA and protein than their normal littermates, suggesting a direct gene dosage effect. The HMG-14 gene may be an additional marker for the Down syndrome. Chromosomal protein HMG-14 is a nucleosomal binding protein that may confer distinct properties to the chromatin structure of transcriptionally active genes and therefore may be a contributing factor in the etiology of the syndrome.

Animals↗
PubMed1989

Superior sulcus tumors: the role of imaging.

Advances in the treatment of stage 0 to III superior sulcus tumors mandate greater accuracy in establishing tissue diagnosis, assessing tumor extent, and staging. Currently, this is best accomplished by a combination of PA chest radiography, MRI, and needle biopsy. MRI is superior to other single imaging modalities for the overall assessment of local tumor extent, bone invasion, mediastinal invasion, and perhaps in the future, determining radiosensitivity. In patients with superior sulcus tumors, evaluation of the brain, liver, and skeleton for metastases may be advisable prior to treatment with preoperative radiation and radical surgical resection.

Diagnostic Imaging↗
PubMed1988

Brachial plexus: correlation of MR imaging with CT and pathologic findings.

Thirty-two patients with symptoms referable to the brachial plexus were evaluated with magnetic resonance (MR) imaging. Sixteen patients had undergone concurrent computed tomography (CT). MR imaging demonstrated normal findings in 16, 12 neoplasms, three cases of trauma, and one case of possible neural edema. Of the 16 patients with normal findings on MR images, eight had CT scans that were also normal. In one patient, MR images showed that the "mass" seen on CT was actually a tortuous blood vessel. In six of the 12 cases of neoplasm in which CT scans were available, MR imaging revealed more extensive disease. In the other six cases of tumor, MR imaging provided sufficient clinical information to obviate the need for CT or any other imaging modality. MR imaging provided definitive diagnoses in the three cases of trauma without further imaging. In one patient with paresthesia, MR imaging showed high signal intensity of the nerves on T2-weighted images, which was compatible with neural edema. A concurrent CT scan was normal.

Brachial Plexus↗
PubMed1988

Nonpalpable testes in young boys: evaluation with MR imaging.

A prospective evaluation of magnetic resonance (MR) imaging for localization of a nonpalpable testis was performed in 24 boys aged 11 months to 6 years. Definitive surgical follow-up was obtained for 15 nonpalpable testes in 14 patients who form the basis of this study. MR imaging correctly indicated the unilateral absence of a testis in six of seven patients prospectively and all seven patients retrospectively. Surgically localized undescended testes were identified with MR imaging in five of eight cases prospectively and seven of eight cases retrospectively. Like scrotal testes, undescended testes were hypointense to fat on sequences with a short repetition time (TR) and echo time (TE) in all cases, and hyperintense or isointense to fat on long TR/TE sequences in all but two cases. Inguinal testes were located along the course of a linear low-signal-intensity structure that extended to the scrotum, which may represent the remnant of the gubernaculum testis. A low-signal-intensity band through the testis, presumably the mediastinum testis, was seen in five of the undescended testes. Although MR imaging can often be used to localize a nonpalpable testis, currently MR is not sensitive enough to allow complete exclusion of the diagnosis of an undescended testis; thus failure to localize a testis with MR imaging should not defer laparoscopy or surgical exploration when indicated.

Child, Preschool↗
PubMed1987

Venous clots: evaluation with MR imaging.

In vitro and in vivo studies were performed to determine the proton relaxation and imaging characteristics of static blood and acute and organized clot in canine jugular veins. In vivo, it was found that two inversion recovery sequences using a short inversion time (100 msec) demonstrated better differentiation of signal intensity of intravascular clot from surrounding soft tissues than did standard T1- and T2-weighted sequences. In vitro, quantitative measurements showed marked reduction of both T1 and T2 relaxation time of acute clot compared with stagnant blood. In addition, the T1 relaxation time, and to a lesser extent the T2 relaxation time, shortened as the clot aged, indicating a potential role for magnetic resonance imaging in determining the age of venous thrombi.

Animals↗
PubMed1987

Normal brachial plexus: MR imaging.

Magnetic resonance (MR) imaging of the brachial plexus was performed in the axial, coronal, and sagittal planes in seven volunteers. Normal structures were delineated by comparison with axial and sagittal cadaver sections and with gross dissection. Differentiation of soft tissues with MR imaging enabled the brachial plexus to be defined from surrounding muscle and vascular structures. Multiplanar imaging demonstrated anatomic detail not previously demonstrated with other radiologic modalities and provided excellent delineation of the components of the brachial plexus from the ventral rami to the peripheral nerve branches.

Adult↗
PubMed1987

Assessment of the permeability of the blood-retinal barrier in hypertensive rats.

We assessed the permeability surface area products at the blood-retinal barrier and blood-brain barrier to sucrose (molecular weight, 340) and microperoxidase (molecular weight, 2000) following acute hypertension induced by metaraminol in Wistar-Kyoto rats (controls) and during chronic hypertension in spontaneously hypertensive rats. In acute hypertension, the permeability surface area product for sucrose was increased at the blood-retinal barrier and at the blood-brain barrier over control values (p less than 0.02), and the vessels became leaky to microperoxidase. In chronic hypertension, the permeability of the blood-retinal barrier to sucrose was increased over that in control animals (p less than 0.02), whereas the permeability of the blood-brain barrier was unaffected. Neither barrier leaked microperoxidase. These results indicate that the blood-brain barrier and the blood-retinal barrier are similarly affected in acute hypertension and that in chronic hypertension, the blood-brain barrier is unaffected whereas the blood-retinal barrier is rendered more permeable to small, but not large, solutes.

Acute Disease↗
PubMed1987

Permeability changes in blood-retinal barrier of galactosemic rats are prevented by aldose reductase inhibitors.

Permeability-surface-area products (PA) for sucrose at the blood-retinal barrier (BRB) were determined with quantitative in vivo techniques and compared in control rats, rats fed a 50% galactosemic diet, and rats fed a diet containing both galactose and the aldose reductase inhibitor sorbinil. The mean PA +/- SE for controls was 0.656 x 10(-5) +/- 0.13 ml.g-1.s-1 and increased by approximately 500% in galactose-fed animals to 3.13 x 10(-5) +/- 0.32 ml.g-1.s-1. Animals fed both galactose and sorbinil showed no significant difference from control animals (P greater than .05), with a PA of 0.91 x 10(-5) +/- 0.22 ml.g-1.s-1. No breach in the BRB to horseradish peroxidase was detected in any of the groups. These results demonstrate an increased permeability at the BRB to small molecules in galactosemic rats that is prevented by an aldose reductase inhibitor. This suggests that the retinal capillary basement membrane thickening seen in galactosemic rats is associated with an increased permeability of the BRB and that aldose reductase is implicated in its pathogenesis.

Aldehyde Reductase↗
PubMed1987

Effect of substrate heat-denaturation on ATP- and ubiquitin-dependent proteolysis.

The susceptibility of human serum albumin (HSA) to degradation by the ATP- and ubiquitin-dependent proteolytic system is enhanced by heat-denaturation. The steady-state levels of formed ubiquitin conjugates, however, are equal with denatured and native HSA. In contrast, both the hemin sensitive Pi release and proteolysis with native HSA are less than one fourth of that with denatured HSA. The rate limiting step for the degradation of HSA by the ATP- and ubiquitin-dependent proteolytic system must be beyond the ubiquitin conjugation steps. Differences concerning the effects of heat denaturation of mitochondria-containing stroma and HSA on ATP- and ubiquitin-dependent proteolysis are discussed.

Adenosine Triphosphate↗
PubMed1986

Hydroperoxyfatty acids inactivate the reticulocyte lipoxygenase independently of a hydroperoxidase reaction.

From a comparison of 9Ds-HPODE and 13Ls-HPODE and their methyl esters as substrates and inactivating agents of reticulocyte lipoxygenase it is concluded that the compounds inactivate the enzyme independently of any hydroperoxidase reaction. The protective effect of 4-nitrocatechol indicates the formation of Fe(III) complexes of the enzyme with the hydroperoxyfatty acid compounds prior to inactivation.

Anaerobiosis↗
PubMed1986

The stoichiometry of oxygen uptake and conjugated diene formation during the dioxygenation of linoleic acid by the pure reticulocyte lipoxygenase. Evidence for aerobic hydroperoxidase activity.

Simultaneous measurements of oxygen uptake and conjugated diene formation (increase in the absorbance at 234 nm) during the dioxygenation of linoleic acid by the pure reticulocyte lipoxygenase gave a nearly theoretical stoichiometry of 1.1 in a temperature range from 5 to 30 degrees C and a wide range of concentrations of both oxygen and linoleic acid. At low concentrations of either oxygen or linoleic acid or both, secondary processes occurred such as linoleic acid-supported lipohydroperoxidase reactions leading to the disappearance of conjugated dienes and to the formation of oxodienes, linoleic acid dimers and epoxyhydroxy derivatives. Under these conditions marked deviations of the stoichiometry between oxygen uptake and conjugated diene formation appeared. The formation of conjugated oxodienoic fatty acids absorbing at 285 nm occurred only under conditions of high concentrations of linoleic acid and limiting oxygen supply. The results indicate that lipohydroperoxidase reactions catalyzed by the pure reticulocyte lipoxygenase do not only take place under strictly anaerobic conditions but also under conditions of limiting concentrations of either linoleic acid or oxygen or both.

Aerobiosis↗
PubMed1986

Kinetics of 125I-ubiquitin conjugation with and liberation from rabbit reticulocyte stroma.

The breakdown of mitochondria-containing stroma of rabbit reticulocytes is an ATP- and ubiquitin-dependent process and there is no evidence for an ATP-dependent but ubiquitin-independent proteolysis in these cells. The ubiquitin conjugate formation with heat-denatured stroma proteins is about one-fifth of that with native stroma. In reticulocytes there exist two mechanisms of ubiquitin liberation from its conjugates with stroma proteins: an ATP-dependent and hemin-resistant release of ubiquitin, which is assumed to be the first step in the degradation of ubiquitin conjugates by the protease system, and a release of ubiquitin catalyzed by an isopeptidase activity.

Adenosine Triphosphate↗
PubMed1986

The management of drop attacks.

From the preceding it is evident that drop attacks can result from a myriad of causes. As in all situations, the patient's history and the clinical picture are the most important factors in arriving at the appropriate diagnosis. However, understanding the neurophysiologic basis of posture should prove significantly helpful in this endeavor.

Aged↗