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Biomedical subjects

V Natarajan

Publications and source records attributed to V Natarajan.

At least 145 records · Page 8Linked to original sources
PubMed1981

Alterations of inositol lipid metabolism of rat sciatic nerve in streptozotocin-induced diabetes.

The composition and metabolism of rat sciatic nerve phospholipids were studied 20 weeks after induction of chronic diabetes by intraperitoneal injection of streptozotocin (50 mg/kg). On a wet weight basis the nerves from the diabetic animals showed a 7% decrease in total phospholipid from that of controls and a relative decrease in phosphatidylinositol. Incubations of isolated sciatic nerves of diabetic rats in a medium containing [33P]orthophosphate gave decreased labeling of phosphatidylinositol and substantial changes in the labeling pattern of phosphatidylinositol phosphate and 4,5-bisphosphate from that of controls. The ratio of label in these polyphosphoinositides decreased from 2.5 for normal nerve to about 1.0 for diabetic nerve within a 2-h incubation period. These metabolic alterations were not observed in acutely diabetic animals 5 days after streptozotocin (100 mg/kg) administration. Because polyphosphoinositides may be involved in the control of membrane permeability during axonal conduction, alterations in their relative amounts or turnover rates could be related to the physiological changes of early diabetic neuropathy.

Animals↗
PubMed1980

Accumulation of N-acylethanolamine glycerophospholipids in infarcted myocardium.

A new phospholipid was detected in the infarcted areas of canine myocardium 24 h after ligation of the left descending branch of the coronary artery. Both the central and peripheral areas of the infarct contained significant amounts of this lipid (4-6& of lipid phosphorus), but it was not present in the apparently normal portions of the same tissue. The lipid was isolated and characterized by its infrared spectrum, by chemical degradation and by comparison with synthetic and semi-synthetic standards. It was identified as a mixture of N-acylethanolamine glycerophospholipids consisting of diacyl-, alk-1-enylacyl- and alkylacylglycerol species. The N-acyl groups were mainly 16 : 0 and 18 : 0 with smaller proportions of 18 : 1 and 18 : 2. The relative decrease of ethanolamine glycerophospholipids in the infarcated areas and the similarity in their molecular species suggests a percursor-product relationship between these phospholipids.

Animals↗
PubMed1980

Structure and metabolism of phospholipids in bovine epididymal spermatozoa.

Lipid analysis of bovine epididymal spermatozoa showed relatively large amounts of alkylacyl- and alk-1-enylacylglycerols in their choline and ethanol-amine phospholipids and alkylacylglycerol as the major constituent of a glycolipid tentatively identified as a monogalactosyl sulfate. The ether lipids exhibited remarkably simple molecular structures, i.e., the phospholipids had only 16:0 as alkyl and alk-1-enyl groups and their constituent fatty acids were almost exclusively 22:5 (n-6) and 22:6 (n-3). The glycolipid had mainly 16:0 as both alkyl and acyl moieties. In contrast, the diacyl choline and ethanolamine phosphoglycerides exhibited a much more complex fatty acid composition. 1,2-Diacylglycerols were the major nonpolar glycerolipid class and their acyl groups consisted almost exclusively of 14:0, 16:0 and 18:0. Labeled glycerol and dihydroxyacetone added to the incubation medium were readily incorporated into sperm lipids under both aerobic and anaerobic conditions. In each case, diacylcholine phosphoglycerides, diacylglycerols and phosphatidic acid were the major labeled lipids. Distribution of label among the molecular species of diacylglycerols and choline phosphoglycerides resembled somewhat their natural abundance. No radioactivity was found in alkylacyl or alk-1-enylacyl glycerolipids. The ether lipids may provide stable structural components of sperm membrane while the diacyl analogs undergo degradation and resynthesis.

Animals↗
PubMed1980

Interstitial hyperosmolarity may cause axis cylinder shrinkage in streptozotocin diabetic nerve.

Maximal conduction velocity values of nerves of diabetic rats 20 weeks after streptozotocin intoxication were found to be intermediate between those of onset-control and those of end-control groups. The abnormality of conduction velocity of the streptozotocin group might therefore be attributed to a failure of maturation. Detailed electron microscopic morphometry of myelinated fibers (MFs) indicates that more than lack of maturation is involved. Whereas the number of lamellae and the perimeter of axis cylinders of myelinated fibers of the three study groups suggested that growth continues, cross-sectional area of the axis cylinders of the streptozotocin group was smaller than those of either control group. Scored evaluation of fiber shape and the measured index of circularity, which related perimeter and transverse axis cylinder area, also indicated that a selective shrinkage of axis cylinders had occurred. This selective alteration in size and shape of axis cylinders is identical to that described after hyperosmolar fixation. Compared with that of controls, the serum of streptozotocin rats is hyperosmolar. It would seem reasonable to attribute the axis cylinder changes to shrinkage. Whether an additional maturational effect is operative as well cannot be resolved from our data.

Animals↗
PubMed1980

The sequential alterations of endoneurial cholesterol and fatty acid in Wallerian degeneration and regeneration.

The endoneurial nonpolar lipids were serially examined throughout Wallerian degeneration and regeneration. Following nerve crush in the rat, the endoneurial content of cholesterol falls and cholesteryl ester content rises dramatically. The maximal alteration of this ratio corresponds reasonably well with events of myelin ovoid dissolution to sudanophilic amorphous lipids. Thereafter, as regenerative events overshadow degenerative events the ratio is slowly restored toward normal. The increased cholesteryl esters are probably synthesized within endoneurium from free fatty acids which become available when myelin is degraded. The endoneurial free fatty acid content presumably represents the net effect of phospholipid degradation, cholesterol esterification, cholesteryl ester hydrolysis, and fascicular entry and exit. Free fatty acids become significantly elevated by 12 days, probably reach a peak between 16 and 60 days, and thereafter return to normal with fiber regeneration. The fatty acid composition of cholesteryl esters from crushed nerves is markedly different from those of normal sciatic nerves. The altered fatty acid composition of cholesteryl esters from myelin suggests that both synthesis and hydrolysis exhibit substrate specificity toward chain length and unsaturation, with oleate being the most favored substrate.

Animals↗
PubMed1979

Purification and properties of valyl-tRNA synthetase from Mycobacterium smegmatis.

Valyl-tRNA synthetase from Mycobacterium smegmatis has been purified over 1200-fold by conventional techniques as well as affinity chromatography on valyl-aminohexyl Sepharose columns. The purified preparation is homogeneous by electrophoretic and immunologic criteria. The enzyme is a tetramer of approximate molecular weight of 120,000, composed of a single type of subunit. The synthetase exhibited maximal activity between 35--40 degrees C and pH 6.8--7.0. The pure enzyme though stable for several months below 0 degrees C, loses activity completely at 70 degrees C, for 1 min. The enzyme showed normal Michaelis-Menten kinetic behaviour in the total aminoacylation reaction with Km values of 1.25 microM, 0.1 mM and 1.0 microM for valine, ATP and tRNA, respectively, but the kinetic response deviated from the above pattern in the partial (activation) reaction. Based on these findings, the existence of the enzyme in two molecular forms, modulated by substrate concentration has been suggested; of these, only one may be active in the total reaction, while both forms may function in the phophosphate exchange reaction.

Amino Acyl-tRNA Synthetases↗
PubMed1977

1-Docosanol and other long chain primary alcohols in developing rat brain.

Long chain alcohols were detected in developing rat brain at ages ranging from 5 to 40 days. They were at their highest level of 0.0109% of the total lipids at the age of 10 days and decreased to 0.0036% at the age of 40 days. They consited mainly of hexadecanol, octadecanol, octadecenol, eicosanol, docosanol, and tetracosanol. The fact that substantial amounts of fatty alcohols having more than 20 carbon atoms were present in myelinating rat brain indicated a chain length specificity in their utilization for 0'alkyl and 0'alk-1-enyl glycerolipid biosynthesis.

Aging↗
PubMed1977

Chain length specificity in the utilization of long chain alcohols for ether lipid biosynthesis in rat brain.

A mixture of cis-9[1(-14)C] octadecenol and [1(-14)C] docosanol was injected into the brains of 19-day-old rats, and incorporation of radioactivity into brain lipids was determined after 3, 12, and 24 hr. Both alcohols were metabolized by the brain but at different rates; each was oxidized to the corresponding fatty acid, but oleic acid was more readily incorporated into polar lipids. Substantial amounts of radioactivity were incorporated into 18:1 alkyl and alk-1-enyl moieties of the ethanolamine phosphoglycerides and into 18:1 alkyl moieties of the choline phosphoglycerides. Even after the disappearance of the 18:1 alcohol from the substrate mixture (12 hr), the 22:0 alcohol was not used to any measurable extent for alkyl and alk-1-enylglycerol formation.

Animals↗