Biomedical subjects
Publications and source records attributed to S K Sarkar.
Oral administration of water fraction of alcoholic extract of leaves of Vinca rosea (fam. apocynaeceae) led to marked lowering of blood glucose level in normal and streptozotocin induced diabetic rats. The hypoglycemic effect of the fraction was comparable with that of tolbutamide.
We have applied NMR microimaging at 9.4 T to detect metastatic deposits in the liver of nude mice noninvasively, using an animal model for metastatic colon cancer that mimics several aspects of the human disease. Images were obtained with a resolution of 100 x 100 x 900 microns and the tumor deposits were clearly distinguished from the normal liver tissue with excellent contrast. Comparison of NMR images with corresponding histologic sections indicates that lesions as small as 900 microns were detected.
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We have studied the effects of two diuretics, selective for renal cortical (furosemide) and inner medullary (vasopressin antagonist) water handling, in rat kidney at 1.5 T and find that furosemide completely dissipates the cortical-inner medullary T2 gradient whereas the vasopressin antagonist has little effect. This phenomenon appears to be related to changes in luminal water content. We also demonstrate the feasibility of obtaining live mouse kidney images with a resolution of 100 x 100 x 700 micrometers at 9.4 T.
To evaluate the potential of 9.4 T imaging in distinguishing normal and neoplastic tissues, we examined the progressive growth of human colon and prostate adenocarcinoma xenografts in nude mice. Images were obtained with a resolution of 100 X 100 X 650 micron, and tumors were clearly distinguished from normal tissue with high contrast. These results demonstrate the feasibility of detecting small human tumors in live nude mice with microscopic resolution at 9.4 T.
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We have prepared samples of (a) intact calvaria collagen (cross-linked and mineralized), (b) intact tendon collagen (cross-linked but not mineralized), and (c) reconstituted chick calvaria collagen (not cross-linked and not mineralized) containing [methyl-2H3]methionyl, [4,4-2H2]pyrrolidinyl, (4-fluorophenyl)alanyl, and [6-15N]lysyl residues. Using multinuclear magnetic resonance spectroscopy, we have investigated the molecular dynamics of the labeled amino acids. Guided by model compound studies, we reached the following conclusions regarding collagen side chain dynamics from our analysis of line shapes and relaxation rates. At 22 degrees C, imino residues in all samples have flexible rings with root mean square angular fluctuations in the 11-30 degree range. Nearly all labeled amino acid side chains reorient about at least two side chain single bonds. At temperatures below -30 degrees C, most of these side chain motions are absent in all the samples. Surprisingly, in contrast with results obtained for backbone motions, side chain motions are only marginally more hindered in mineralized samples as compared with nonmineralized samples, a result we discuss with reference to collagen-mineral interactions. We also discuss the possible relationship between collagen dynamics and function.
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A 76-year-old on long-term Lasix and Pyrogastrone presented with stridor. This became worse with local irritation, e.g. on coughing or during indirect laryngoscopy. Indirect laryngoscopy showed a narrow glottis with an otherwise normal larynx. Blood investigation showed a low serum potassium with a raised bicarbonate level, and a serum calcium level just within the acceptable normal range. A diagnosis of laryngospasm secondary to drug-induced hypokalaemic alkalosis was made. This was treated with the withdrawal of the above drugs and supplementing potassium orally.
The Superior Mesenteric Artery (SMA) syndrome was the underlying cause of severe gastrointestinal symptoms in a patient with recurrent pregnancy loss. Following a surgical transposition of the duodenum, two normal pregnancies were carried to term. This is the first report of the SMA syndrome in pregnancy, to our knowledge.
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We have determined the amplitude of nanosecond fluctuations of the collagen azimuthal orientation in intact tissues and reconstituted fibers from an analysis of 13C NMR relaxation data. We have labeled intact rat calvaria and tibia collagen (mineralized and cross-linked), intact rat tail tendon and demineralized bone collagen (cross-linked), and reconstituted lathyritic (non-cross-linked) chick calvaria collagen with [2-13C]glycine. This label was chosen because one-third of the amino acid residues in collagen are glycine and because the 1H-13C dipolar coupling is the dominant relaxation mechanism. Spin-lattice relaxation times (T1) and nuclear Overhauser enhancements were measured at 15.09 and 62.98 MHz at 22 and -35 degrees C. The measured NMR parameters have been analyzed by using a dynamic model in which the azimuthal orientation of the molecule fluctuates as a consequence of reorientation about the axis of the triple helix. We have shown that if root mean square fluctuations in the azimuthal orientations are small, gamma rms much less than 1 rad, the correlation function decays with a single correlation time tau and T1 depends only upon tau and gamma rms and not the detailed model of motion. Our analysis shows that, at 22 degrees C, tau is in the 1-5-ns range for all samples and gamma rms is 10 degrees, 9 degrees, and 5.5 degrees for the non-cross-linked, cross-linked, and mineralized samples, respectively. At -35 degrees C, gamma rms is less than 3 degrees for all samples. These results show that mineral and low temperature significantly restrict the amplitude of nanosecond motions of the collagen backbone.(ABSTRACT TRUNCATED AT 250 WORDS)
Forty patients with undiagnosed pleural effusions were investigated by pleuroscopy, using a fiberoptic bronchoscope. Pleural biopsies diagnostic of tuberculosis were obtained in 17 cases, and in 12 of these tubercle bacilli were cultured from the pleural fluid. Pleural biopsy at thoracoscopy is superior to the percutaneous intercostal route and for this purpose the fiberoptic bronchoscope is preferable to the rigid thoracoscope.
Heretofore the complexity of natural abundance spectra has precluded the use of 13C NMR to detect cis peptide bonds in proteins. We have incorporated [4-13C]proline into chicken calvaria collagen and report here well-resolved C gamma signals, arising from cis and trans X-Pro and X-Hyp peptide bonds (where X is any amino acid residue) in the 13C NMR spectrum of the thermally unfolded protein. Measurement of 13C signal areas shows that 16% of the X-Pro and 8% of X-Hyp bonds are cis in the unfolded collagen. These results strongly support the conclusion drawn from kinetic studies that cis-trans isomerization of peptide bonds is the rate-limiting step in helix propagation after nucleation. Our method can be applied to other proteins as well and should aid in testing the generality of the hypothesis of Brandts, Halvorson, and Brennan that cis-trans isomerization is the rate-limiting step in protein folding when proline is present.
The molecular dynamics of the collagen backbone in intact connective tissues has been elucidated using 13C line shape analysis. Since one-third of the amino acid residues in collagen are glycines, we have labeled: (a) reconstituted lathrytic (uncross-linked) chick calvaria collagen fibrils; (b) rat tail tendon (cross-linked); and (c) rat calvaria (cross-linked and mineralized) collagen with [1-13C]glycine. The proton-enhanced and normal 90 degrees - t proton-decoupled spectrum of each collagen sample shows an asymmetric chemical shift powder pattern for the glycine carbonyl carbon. The powder line width, delta, (delta = sigma zz - sigma xx) at 22 degrees C for the uncross-linked reconstituted collagen fibril is 108 ppm, whereas the maximum value of delta (140 ppm) is observed for the cross-linked and mineralized collagen fibrils in rat calvaria. The powder line widths for the cross-linked fibrils in tail tendons and demineralized calvaria are 124 and 120 ppm, respectively. However, since the same line shape and line width (145 ppm) are observed for all samples at -35 degrees C, the difference in delta values observed at room temperature is attributed to differences in molecular mobility of collagen in various samples. The line shapes are analyzed using a dynamic model in which azimuthal orientation of the collagen backbone is assumed to fluctuate as a consequence of reorientation about the helix axis. The observed line shapes are sensitive to motions having correlation times less than approximately 10(-4) s and the analysis provides the values of the root mean square fluctuation in azimuthal angle, gamma rms, due to such motions. It is found that gamma rms equals 41 degrees, 33 degrees, and 14 degrees for the uncross-linked, cross-linked, and mineralized collagens, respectively. These results provide the first information about the extent that cross-linking and mineralization restrict molecular motion in collagen.
13C- and 2H-labelled amino acids have been incorporated into elastin and collagen and rotational correlation times of the labelled sites have been derived from an analysis of nuclear magnetic resonance relaxation parameters and line-shapes. The elastin experiments were designed to discriminate between the various models that have been proposed to account for the rubber-like elasticity of elastin. The correlation times of carbonyl carbons of the elastin backbone show that elastin chains are very flexible at the molecular level. In addition, the molecular dynamics and viscoelastic behaviour of elastin are well correlated over a wide range of temperatures and solvents. These results all support the rubber-like network model of elastin structure. The collagen experiments were designed to investigate the intermolecular interactions between molecules in collagen fibres. Correlation times of labelled sites in the collagen backbone and side-chains show that substantial flexibility, especially of the side-chains, takes place in reconstituted (non-cross-linked) collagen fibrils. Therefore, the interactions between side-chains that presumably direct and stabilize the fibrillar assembly take place in fluid domains. The molecular flexibility is not affected by the presence of cross-links but is absent when the collagen is mineralized.
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