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Biomedical subjects

B A Berkowitz

Publications and source records attributed to B A Berkowitz.

At least 55 records · Page 3Linked to original sources
PubMed1991

Blood-retinal barrier breakdown investigated by real-time magnetic resonance imaging after gadolinium-diethylenetriaminepentaacetic acid injection.

Recent magnetic resonance imaging (MRI) studies show that gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) entry into the vitreous space can be used as a qualitative marker of blood-retinal barrier (BRB) disruption. To determine if a more quantitative measurement of BRB breakdown could be obtained, the utility of acquiring real-time, T1-weighted proton images was studied after Gd-DTPA injection. Two days before the MRI experiment, panretinal photocoagulation was done. The mean signal intensity over selected regions-of-interest (ROI) in the vitreous and anterior chamber was followed before and after (0, 10, 20, 30, 45, and 60 min) Gd-DTPA injection (1.0 mmol/kg, intravenously). At every laser power setting used in this study (0, 200, 400, 600, and 800 mW), the change in the mean signal intensity could be approximated by a simple exponential equation. However, the time constants determined for these curves were too imprecise to be useful as correlates between laser power and BRB breakdown. The slope of the line fit to the data in the first 20 min postinjection (ie, an initial-rate analysis) was a more precise correlate between BRB breakdown and laser power. This slope represented the rate of change in mean signal intensity in the ROI as a result of the entry of Gd-DTPA, and it was called the "leakiness" parameter. The leakiness parameter reflected changes in the permeability surface area product of the BRB if the blood flow and the Gd-DTPA arterial concentration immediately after injection were approximately the same between animals.

Animals↗
PubMed1991

Oxygen kinetics in the vitreous substitute perfluorotributylamine: a 19F NMR study in vivo.

Perfluorocarbon (PFC) vitreous substitutes yielded promising results in the surgical management of retinal detachments. This success is due primarily to their physical properties. However, oxygen kinetics in PFC in vivo have not been investigated. The oxygen flux in the vitreous substitute perfluorotributylamine (FTBA) was assessed in the rabbit eye by monitoring the partial oxygen pressure (PO2) in real-time using Fluorine-19 nuclear magnetic resonance spectroscopy (19F NMR) The spin-lattice relaxation rate (T1)-1 of the CF3 resonance of FTBA is a rapid and sensitive index of PO2. T1-derived PO2 from the FTBA-filled rabbit eye was followed at regular time intervals under different oxygenation protocols. In the first series of experiments, FTBA in the vitreous space was oxygenated by ventilating the rabbit with a mixture of 95% O2 and 5% CO2. The oxygen uptake profile could be approximated by a simple exponential function with a time constant of 159 +/- 110 min (mean +/- SD, n = 3). A more reproducible correlate was obtained by performing an initial rate analysis on the first hour of ventilation with high oxygen levels. This analysis showed that the rate of increase in FTBA PO2 was 2.34 +/- 0.67 mm Hg/min (mean +/- SD, r2 = 0.99, n = 7). After the animal was removed from the 95% O2/5% CO2 gas and was ventilated with room air, the oxygen clearance profile could be approximated in all cases by a single exponential with a time constant of 59.8 +/- 9.6 min (mean +/- SD, n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

In vivo metabolism of 3-deoxy-3-fluoro-D-glucose.

Recent studies have demonstrated that 3-deoxy-3-fluoro-D-glucose (3-FG) is metabolized to 3-deoxy-3-fluoro-D-sorbitol (3-FS), via aldose reductase, and 3-deoxy-3-fluoro-D-fructose (3-FF), via the sorbitol dehydrogenase reaction with 3-FS, in rat cerebral tissue (Kwee, I. L., Nakada, T., and Card, P. J. (1987) J. Neurochem. 49, 428-433). However, the biochemistry of 3-FG in other mammalian organs has not been investigated making the application of 3-FG as a metabolic tracer uncertain. To address this issue we investigated 3-FG metabolism and distribution in isolated cell lines and in rabbit tissues in vivo with 19F NMR and gas chromatography-mass spectrometry. In general, the production of 3-FS is well correlated with the known distribution of aldose reductase in all the systems studied. Further metabolism of 3-FS to 3-FF was verified to occur in cerebral tissue. Surprisingly, two new fluorinated compounds were found in the liver and kidney cortex. These compounds are identified as 3-deoxy-3-fluoro-D-gluconic acid, which is produced via glucose dehydrogenase activity on 3-FG, and 3-deoxy-3-fluoro-D-gluconate-6-phosphate. Based on enzyme studies, it is argued that the 3-deoxy-3-fluoro-D-gluconate-6-phosphate is derived directly from 3-deoxy-3-fluoro-D-gluconic acid and not as a product of pentose phosphate activity. Direct oxidation and reduction are the major metabolic routes of 3-FG, not metabolism through glycolysis or the pentose phosphate shunt. Thus, 3-FG metabolism coupled with 19F NMR appears to be very useful for monitoring aldose reductase and glucose dehydrogenase activity in vivo.

Aldehyde Reductase↗
PubMed1990

NMR spectral analysis of kinetic data using natural lineshapes.

An automated rapid data analysis scheme for NMR spectroscopy time course studies is presented. This method uses a high signal-to-noise reference spectrum collected at the beginning of a time course as a lineshape model to analyze subsequent low signal-to-noise data collected with higher time resolution. The method is fast (approximately 1 s to evaluate two peaks in a 2K spectrum) and easily implemented on NMR spectrometer computers. An application of this method to spectroscopic studies on the heart is provided.

Humans↗
PubMed1990

Renal distribution and metabolism of [2H9]choline. A 2H NMR and MRI study.

Trimethylamines are required as substrates in the biosynthesis of a number of important molecules in the cell. Herein, we describe the use of choline, deuterated in its 9 methyl positions, as an NMR label for following the distribution and metabolism of methyl groups after intravenous choline infusion. Deuterium (2H) NMR spectroscopy of the rabbit kidney in vivo revealed a linear uptake of infused choline that was directly proportional to the rate of infusion. The sensitivity limit for the spectroscopic studies in vivo was in the order of 100 microM for a 2 min data collection. After the infusion, 2H NMR imaging of the kidney in vivo demonstrated high trimethylamine concentrations in both the cortex and inner medulla but not in the outer medulla. The inner medullary fraction, however, was more labile to diuresis induced by furosemide. Companion high resolution 2H NMR studies of extracts revealed a cortex betaine/choline concentration ratio of 0.69 +/- 0.05 (mean +/- SEM, n = 3) before furosemide administration. Following furosemide infusion, the cortex betaine/choline concentration ratio was 3 +/- 1 (n = 6). Thus, 2H renal images following furosemide treatment can be interpreted as metabolic maps of betaine distribution. In addition, extraction studies revealed high concentrations of labelled choline and betaine in the liver. These data demonstrate that 2H-labelled choline is an effective marker of choline methyl metabolism in vivo and should provide a unique tool for the investigation of this important substrate.

Animals↗
PubMed1990

Sodium-23 nuclear magnetic resonance imaging of the rabbit kidney in vivo.

The mechanism by which the mammalian kidney generates a concentration gradient of sodium from cortex to papilla is still not entirely understood. Studies of how the kidney as an organ generates this gradient have been hampered by the lack of a noninvasive method for monitoring the intrarenal sodium distribution. Herein, we demonstrate the value of sodium-23 nuclear magnetic resonance (23Na-NMR) imaging to nondestructively assess the intrarenal sodium distribution. 23Na-NMR images were obtained from a surgically exposed kidney preparation that showed the two-dimensional distribution of sodium in the rabbit kidney. In the antidiuretic kidney this gradient resulted in papillary sodium concentrations that were approximately threefold higher than cortical values. Serial 23Na-NMR images obtained during saline infusion demonstrated the kinetics by which the sodium gradient increases with diuresis. The half-time for 23Na washout of the medulla of the kidney was approximately 6 min with this protocol. In addition, a three-dimensional data set of the sodium distribution of the kidney was obtained with voxel dimensions of 1.5 mm3 by use of a three-dimensional 23Na-NMR imaging technique. Without surgical exposure, 23Na-NMR images of the rabbit kidney were collected under completely noninvasive conditions by use of a surface coil. The 23Na-NMR signal from the kidney was easily detected; however, to obtain images of comparable signal-to-noise ratio to the surgically exposed kidney, spatial and temporal resolution were significantly reduced.

Animals↗
PubMed1989

Endothelial thromboxane receptors: biochemical characterization and functional implications.

We have identified thromboxane specific receptors in membrane preparations of bovine pulmonary artery endothelial cells using a potent thromboxane specific antagonist, [125I]-PTA-OH in a binding assay. The binding was specific and saturable. Neither thromboxane B2, prostaglandin D2 nor prostaglandin F2 alpha displaced the ligand (0.1 nM) at concentrations up to 10 microM. However, binding was displaced by IPTA-OH greater than SQ29548 greater than U46619. In addition, we observed that thromboxane mimetic U46619 significantly lowered the basal production of prostacyclin and also markedly suppressed bradykinin-stimulated prostacyclin released by endothelial cells. We propose that an important biological effect of thromboxane on vascular endothelial cells may be the suppression of prostacyclin production.

Animals↗
PubMed1989

Improvement in 31P NMR signal-to-noise for ATP in vivo using homonuclear decoupling.

The efficiency of 31P homonuclear decoupling in vivo is demonstrated. In low-field clinical situations, when JPP is equal to or greater than delta v, significant improvements in the precision of measuring the ATP resonance area can be expected upon decoupling due to the increase in signal-to-noise produced upon collapse of the J coupling. The sensitivity loss due to time sharing between the decoupler and receiver is discussed.

Adenosine Diphosphate↗
PubMed1989

What is the relationship between the endothelium derived relaxant factor and nitric oxide?

Nitric oxide gas in solution (NO) relaxes blood vessels with similar actions and pharmacodynamics as the endothelium derived relaxant factor (EDRF) and has been proposed to be a component of the materials released from stimulated endothelial cells. Certain data however suggest that EDRF and NO may not be identical. In some non-vascular smooth muscles, NO and EDRF exhibit markedly different pharmacologic profiles. Furthermore the interaction of EDRF and NO with anion exchange resins differ. The hypothesis that EDRF is identical to nitric oxide gas in solution or a nitrogen oxide containing compound is discussed.

Animals↗
PubMed1989

Ultrastructure of an arterial lesion induced in rats by fenoldopam mesylate, a dopaminergic vasodilator.

Fenoldopam mesylate (FM) is a dopaminergic vasodilator with demonstrated efficacy and a favourable safety profile in hypertensive and congestive heart failure patients. FM produced a novel arterial lesion in renal and splanchnic arteries of rats, but not dogs or monkeys. The studies reported here were undertaken to investigate the ultrastructure of the arterial lesion induced in rats by FM in an attempt to shed light on its pathogenesis. Rats were infused intravenously with FM, either 50 micrograms/kg/min for 1 or 4 h, or 5 or 100 micrograms/kg/min for 24 h. Control rats were infused for 4 or 24 h with vehicle alone. Perfusion-fixed tissue from the stomach and pancreas of control and drug-treated rats was examined by transmission electron microscopy. No arterial lesions were seen in rats infused with the drug for 1 or 4 h, or in control rats. All drug-treated rats infused with 5 or 100 micrograms/kg/min of FM for 24 h had lesions in subserosal gastric arteries and interlobular pancreatic arteries. In areas of mild arterial damage, medial smooth muscle cells contained intracytoplasmic pseudovacuoles, autophagic vacuoles, and electron-dense, myofilamentous inclusions. More severe lesions were characterized by overt medial necrosis and haemorrhage. The endothelium of affected arteries was invariably intact, except in areas of severe medial damage. The internal elastic lamina and connective tissue elements within the arterial wall were unaffected. These findings suggest that medial smooth muscle cells are the primary site of damage caused by fenoldopam mesylate in splanchnic arteries of the rat. This iatrogenic arterial lesion could provide an interesting model to study the response of medial smooth muscle to pharmacologically mediated injury.

Animals↗
PubMed1988

DHFR coamplification of t-PA in DHFR+ bovine endothelial cells: in vitro characterization of the purified serine protease.

High-level expression of human tissue-type plasminogen activator was accomplished in endothelial cells by a novel approach to dihydrofolate reductase (DHFR) coamplification in DHFR+ cells. A tripartite mammalian expression vector coding for DHFR, neomycin phosphotransferase, and the t-PA gene was introduced into bovine endothelial cells by transfection and selection for G418 resistance. Upon methotrexate selection of these transformants, we obtained endothelial cells that had amplified the plasmid-encoded DHFR and t-PA genes. As a result, cell lines were isolated that efficiently produced t-PA (greater than 4 pg/cell.day). This t-PA was purified and compared with recombinant t-PA produced in Chinese hamster ovary cells. These two t-PA samples differed in carbohydrate composition, and amounts of 530 and 527 amino acid forms but had similar in vitro activity.

Animals↗
PubMed1988

Comparative pharmacology of endothelium-derived relaxing factor and nitric oxide.

The present study was designed to characterize endothelium-derived relaxing factor (EDRF) and nitric oxide (NO) by employing both biological and chemical methods. EDRF was released by the calcium ionophore A23187 from cultured bovine pulmonary artery endothelium (BPAE) grown on microcarrier beads and then superfused in a cell column. The maximum relaxations induced by EDRF (83%) or NO (79%) on phenylephrine (PE)-contracted rabbit aorta were similar. In contrast, EDRF was only half as potent as NO in relaxing the KCl-contracted rabbit aorta. EDRF induced a concentration-dependent relaxation of both PE-contracted rabbit aorta and histamine-contracted guinea pig aorta that was accompanied by a marked elevation in cyclic GMP levels. However, EDRF was vascular selective and did not relax or increase cyclic GMP levels of the histamine-contracted taenia coli of either species. NO was not vascular selective and relaxed both aorta and taenia coli and also markedly increased cyclic GMP levels in each. NO also relaxed dog femoral artery and gastrointestinal smooth muscle preparation of the lower esophageal sphincter, whereas EDRF only relaxed the femoral artery. Experiments were also performed describing the actions of a series of different resins: anion exchange resins (NH2/NH, AG-1), cation exchange resin (-COOH), reversed phase resin (C18) and hemoglobin-agarose on EDRF- or NO-induced relaxation. NH2/NH, AG-1 and hemoglobin-agarose resins inhibited EDRF-induced relaxation, but -COOH and C18 did not. The inhibition was dependent on the amount of resin employed. NO-induced relaxation was blocked only by hemoglobin-agarose but by none of the other resins.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Characterization and function of bradykinin receptors in vascular endothelial cells.

One of many important roles of the naturally occurring nonapeptide bradykinin (BK) is the modulation of vascular tone. As endothelial cells may play vital roles in the physiology of vascular tissues, it is important to understand the interaction of this peptide with endothelial cells. By using radiolabeled BK we have demonstrated for the first time BK specific binding sites in membranes of bovine pulmonary artery endothelial cells. There are two types of receptors shown in binding assay: one with a saturable, high-affinity binding (Kd = 1.28 +/- 0.21 nM, maximum binding = 111.4 +/- 12.0 fmol/mg) and the other with not readily saturable, low-affinity binding. The activation of BK receptors on bovine pulmonary artery endothelial cells is assessed by two functional assays, namely, the release of endothelium-derived relaxing factor and the elevation of cytosolic calcium. The characteristics of the BK receptors in both binding and functional assays indicate that the high-affinity binding is to B2 receptors and the low-affinity binding is to B1 receptors on the cells. Thus, high-affinity binding is blocked by B2 antagonists, D-Arg[Hyp3, thienylalanine5,8,D-Phe7]-BK and [thienylalanine5,8, D-Phe7]-BK and low-affinity binding is blocked by B1 antagonist des-Arg9[Leu8]-BK. The elevation of intracellular calcium and the release of endothelium-derived relaxing factor in response to BK in endothelial cells is predominately through B2 receptor activation. The ability to subtype BK receptors in endothelial cells may facilitate the understanding of the vascular functions of BK and the potential design of drugs to regulate these functions.

Animals↗