PubMed Health⌕ Search

Biomedical subjects

K Avramova

Publications and source records attributed to K Avramova.

10 recordsLinked to original sources
PubMed2006

Polymer chains in a soft nanotube: a Monte Carlo study.

We study the equilibrium properties of flexible polymer chains confined in a soft tube by means of extensive Monte Carlo simulations. The tube wall is that of a single sheet six-coordinated self-avoiding tethered membrane. Our study assumes that there is no adsorption of the chain on the wall. By varying the length N of the polymer and the tube diameter D we examine the variation of the polymer gyration radius Rg and diffusion coefficient Ddiff in soft and rigid tubes of identical diameter and compare them to scaling theory predictions. We find that the swollen region of the soft tube surrounding the chain exhibits a cigarlike cylindrical shape for sufficiently narrow tubes with D<<Rg. The observed scaling of static conformational properties with chain length N and tube diameter D follows the predictions of scaling theory and displays no significant difference between soft and rigid tubes. The Brownian dynamics of the polymer diffusion in a rigid tube is found to slow down in a tube with soft walls by an amount which depends on the Rg/D ratio albeit the relaxation time tau(parallel) for diffusive motion along the tube still scales as tau(parallel) proportional, N3.

Journal Article↗
PubMed1985

The experimental obesity by high-fat feeding--a model for evaluation of the biological value of fats.

The experimental obesity by high-fat feeding of rats, introduced after weaning, was found to be a suitable model for evaluation of the biological value of nutritional fats with different fatty acid composition: butter (group B), lard (L), partially hydrogenated oil (H), lard + sunflower oil 2:1 (LS). The differences in the fatty acid composition of these regimens affect: the efficiency in creating the model of obesity; the hormonal pattern of blood plasma; some metabolic pathways in liver and adipose tissue (especially in group H); the fatty acid composition of some structural, reserve and transport lipids; some biological tests indicative of membrane's phospholipid and fatty acid composition, i.e. the rate of platelets aggregation. A special attention should be paid to the striking differences in the cellularity and morphogenesis of adipose tissue in group B (hyperplastic obesity) in comparison with all other high-fat groups (hypertrophic obesity), irrespective of the identical energy and protein content of the diets. Thus, the early administration of a diet with butterfat (50% of energy) promoted a model of hyperplastic obesity, while the isocaloric diet with lard + sunflower oil caused a hypertrophic type of obesity. The authors have proved the regenerating capacity of the periepididymal fat pad in adult rats after partial lipectomy. The relative contribution of endogenic and exogenic (nutritional) factors in this process is discussed and the modifications in the cellularity of adipose tissue on these conditions are evaluated.

Adipose Tissue↗
PubMed1985

[Cholesterol ester-composition of the adrenal glands of rats in various fat-rich diet regimes].

Cells of adrenal cortex (AC) contain in about 80-90% cholesterol esters (CE), related to total cholesterol. It is assumed, that dietary fats can influence the composition of CE and hydrolytic activity of AC, leading to disorders in steroid biosynthesis. Results are presented about fatty acid composition of CE of AC from rats, fed with a fat rich diet containing different dietary fats. 5 groups and 2 subgroups of male rats at the age of 11 months were investigated: group K--control; group Oil--sunflower oil + lard; group Sch--lard; group Bu--butter; group Hy--hydrogenated oil: Every 5 animals from groups Oil and Bu were treated with dehydroepiandrosterone. Lipids of AC were extracted and analyzed chromatographically. The content of CE and other lipid classes did not differ among experimental groups and control. Differences in fatty acid composition of AC--CE, however, reflect the composition of dietary fats. Trans-isomers were detected by Ag+-thin layer chromatography. It can be assumed, that physiological barrier against trans-isomers is low. Possibly fat rich diets inhibits utilization of linoleic acid, leading to a deficit of arachidonic acid, which influences prostaglandin synthesis and causes disorders in steroid biosynthesis. Hormone treated animals showed minor differences in fatty acid composition of CE in AC in comparison to control. The results outline, that fat-rich diets with different dietary fats influence the composition of CE in AC.

Adrenal Cortex↗
PubMed1982

[Biochemical characteristic of arteriosclerosis and obesity in the industrial and agricultural complex of Burgas].

The following indices were determined in 444 subjects (healthy, patients with various forms of atherosclerosis and obese subjects) with the study of a representative population group from IAC--Burgas: total cholesterol, cholesterol in beta-lipoproteins, lecithin, cholesterol-lecithin index, total fats, beta-lipoproteins, esterified fatty acids and uric acid. The biochemical syndrome of atherosclerosis is characterized by moderate (and not ebigatorily in each case) increase of lipid indices and uric acid in serum. The hyperlipidmic syndrome is more frequent and better manisfested in the patients with obesity. That syndrome in the patients with body overweight could be considered to increase the risk of early atherosclerotic complications.

Adult↗
PubMed1975

[Changes in the liver transport of bile pigments in certain forms of jaundice under the influence of novobiocin and luminal].

The novobiocin and luminal test application increases the possibilities to differentiate premicrosome from postmicrosome jaundice and extends the knowledge on hyperbilirubinemia pathobiochemistry. Novobiocin (an antibiotic) inhibits the conjugation and glucuronidizing of bile pigments. Accordingly, the novobiocin test is strongly positive in any premicrosome jaundice form--Gilberts's disease, posthepatitis hyperbilirubinemia (PHHB) and hemolytic jaundice. It is negative in hepatocellular and hepatocanalicular jaundice, and in Dubin-Johnson's syndrome. In premicrosome jaundice with fluctuating bilirubinemia and normal bilirubin level at the time of examination, the novobiocin test may bring about manifestation of a latent or temporary compensated defect which proves to be most helpful in diagnosing. It is assumed that hemolytic jaundice is caused, apart from bile pigments hyperproduction, also by concomitant disorders in the intrahepatal transport of bile pigments. The latter hypothesis is corroborated by the data of the study. The luminal test is likewise markedly positive in premicrosome jaundice, and negative--in chronic hepatocellular and hepatocanalicular jaundice. In some instances with slight defect in the intrahepatal transport of pigments, the luminal test accounts for normalization of bilirubinemia and of the direct to total bilirubin ratio. The test is moderately positive in the syndrome of Dubin-Johnson. The latter fact supports the hypothesis that luminal, alongside the effect on transport mechanisms, exerts influence on bile pigments excretion also.

Bile↗
PubMed1975

[Study of liver glucuronidase function in indirect hyperbilirubinemia and liver cirrhosis].

A discussion is made of the basic peculiarties and differences in the clinico-laboratory profile in various forms of pre- and postmicrosome jaundice. The importance of direct to total bilirubin ratio, and of quantitative bilirubin and urobilinogen bodies' determination in the urine is stressed. Bile pigments conjugation by the hepatic cells and free bilirubin conversion to glucuronose may be also assayed by resorting to some additional tests. The test with N-acetyl-paraaminophenol (NAPA) provides for an indirect assessment of the liver's glucuronidase function and has a good informative value. It is optimally characterized by the percentage of free (non-conjugated) NAPA with respect to the total. The latter indicator is normal in chronic hepatitis and in Dubin-Johnson's syndrome, and is at the uppermost normal limit in hepatic cirrhosis and cholestatic jaundice. It is strongly increased (in the average three times with respect to normal values) in Gilbert's disease and posthepatitis hyperbilirubinemia (PHHB). It affords some information on the severity of the defect in transport of bile pigments in the mentioned affections. In hemolytic jaundice a normal percentage of free NAPA is usually found. Glucuronose conversion of bilirubin hardly plays an essential role in the pathogenesis of hyperbilirubinemia i the listed above diseases. This is also confirmed by the NAPA test, performed subsequent to novobiocin loading. The percentare of free NAPA under the conditions just outlined is furthermore increased in Gilbert's disease and PHHB, while in hemolytic jaundice it remains within normal limits. In Gibert's disease and PHHB, a strongly pronounced delay in the excretion of substances is noted. Not infrequently, a similar disorder is also observed in hepatic cirrhosis. It is interpreted as an expression of an overall disturbance in hepatic blood flow and function of the heavily affected hepatic parenchyma.

Acetaminophen↗