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Biomedical subjects

I Tamir

Publications and source records attributed to I Tamir.

At least 73 records · Page 4Linked to original sources
PubMed1979

Dependence of the conformation of the polar head groups of phosphatidylcholine on its packing in bilayers. Nuclear magnetic resonance studies on the effect of the binding of lanthanide ions.

Proton magnetic resonance spectra of vesicles of various sizes composed of egg phosphatidylcholine (PC) with varying concentrations of cholesterol differed in the apparent line width of the signal of the methylene protons of PC (delta v1/2). They also varied in the extent of lanthanide-induced shifts of the 31P and 1H NMR signals of the corresponding nuclei of the polar head groups located on the outer surface of the vesicles (delta delta). The differences in the lanthanide-induced shifts of the 31P signals are fully accounted for by the ratio between the externally added lanthanide and the number of PC head groups available for interaction with the lanthanide ions. This was not the case ofr the changes in the 1H NMR spectra. Here delta delta decreased with increasing delta v1/2, suggesting that the packing of the PC paraffinic chaings in the bilayer affects the conformation of the polar head groups; tightening of the packing probably results in a more extended conformation of the head groups. This conclusion is also supported by the larger effect lanthanides have on the 1H chemical shift of the choline head groups on the outer surface of small unilamellar vesicles as compared to groups on the inner, tighter packed layer.

Chemical Phenomena↗
PubMed1979

Dynamics and composition of serum lipids in hyperlipoproteinemias.

The microviscosity of serum lipids in patients with hyperlipoproteinemia and normal donors was determined by monitoring the degree of fluorescence polarization of the fluorescent probe 1,6-diphenyl-1,3,5-hexatrine (DPH). Determination of serum lipids--serum total cholesterol, serum triglycerides, and serum phospholipids--revealed that an increase in the ratio of cholesterol/triglyceride + phospholipid is accompanied by an increase in the degree of fluorescence polarization and an increase in the microviscosity values. Similar results were obtained with sonicated liposomes prepared from serum lipids extracts. This correlation between dynamics and composition of serum lipids was further supported by results obtained with an artificial model system of sonicated lipids dispersions. The results have shown that high microviscosity values are characteristic in patients with high levels of serum cholesterol, and that low microviscosity values are characteristic in patients with high levels of serum triglycerides. It is suggested therefore that this technique may serve as a basis for a rapid screening test for hyperlipoproteinemias.

Adult↗
PubMed1979

Distribution of high density and other lipoproteins in selected LRC prevalence study populations: a brief survey.

Selected lipid and lipoprotein data from the Lipid Research Clinics (LRC) Prevalence Study are presented, with particular emphasis given to high-density lipoprotein (HDL) values. Cross-sectional age- and sex-specific mean values are shown for 7007 white participants in the ten North American LRCs. Comparisons are drawn for males and females (including the pediatric group) and for females using or not using sex hormones. The US-USSR Collaborative Program is summarized, and selected comparisons are noted for the Soviet and United States samples.

Adolescent↗
PubMed1979

Plasma lipids, lipoproteins, and blood pressure in female adolescents using oral contraceptives.

Comparative profiles are reported for plasma lipids and lipoproteins, blood pressure, smoking, and selected socioeconomic variables for females less than 20 years of age using oral contraceptives and for pair-matched non-users from the Lipid Research Clinics Prevalence Study. About 5% of adolescent females reported OC use; they had significantly higher levels of plasma total cholesterol, triglyceride, and high-density lipoprotein-cholesterol than did the non-users. Significantly more non-users of OC belonged to households of the lowest occupational status; no differences in OC usage by educational status of the head of household were discernible. Of the OC users, 58% were classified as current smokers, as compared with 23% of the non-OC users.

Adolescent↗
PubMed1979

The effect of vitamin E administration to pregnant women, on the concentration of linoleic acid in adipose tissue of the newborns.

The composition of various lipids were measured in ten healthy newborns of mothers who were treated with 100 mg vitamin E per day, starting in the 35th week of pregnancy. The maternal serum vitamin E levels following the treatment (1.10 +/- 0.49 mg/dl) showed no increase as compared to the pretreatment values (1.06 +/- 0.38 mg/dl). There was no significant difference in serum vitamin E levels in those newborns whose mothers were treated--(0.19 +/- 0.12 mg/dl) as compared to 10 newborns whose mothers were not treated with vitamin E (0.13 +/- 0.07 mg/dl). However, there was a striking increase in the relative concentration of linoleic acid in the adipose tissue to those newborns whose mothers were treated (9.4%--versus--4.1%).

Adipose Tissue↗
PubMed1978

Increase in platelet aggregation following a rise in plasma free fatty acids.

Platelet aggregation was studied following intravenous injection of heparin to nine healthy adults. Heparin is known to produce an increase in the concentration of free fatty acids (FFA) within 10 minutes of intravenous injection. A significant correlation was found between the intensity of primary platelet aggregation and changes in plasma FFA levels. No correlation was found between plasma FFA levels and the intensity of secondary platelet aggregation.

Fatty Acids, Nonesterified↗
PubMed1978

Serum lipid concentration in newborns from various ethnic groups in Israel.

Serum cholesterol was determined in the cord blood of 438 newborns and repeated on venous samples from the same infants at the ages of 6 and 18 months. Of 36 infants who were originally defined as hypercholesterolemic, 28 had normal values by the age of six months. The prevalence of hypercholesterolemia at birth was 8%. No differences were noted among the five ethnic groups examined. The results suggest that serum cholesterol level at birth is of limited value for the early detection of familial hypercholesterolemia.

Cholesterol↗
PubMed1977

Oxidation of methyl derivatives of pteridin-4-one, lumazine and related pteridines by bovine milk xanthine oxidase.

1. Pteridin-4-ones, methylated at nitrogen or carbon, N-methylated lumazines and related oxopteridines were studied as substrates of a highly purified bovine milk xanthine oxidase (xanthine : oxygen oxidoreductase, EC 1.2.3.2). 2. The enzyme can oxidise at high rates both uncharged and anionic substrates. Variation of enzymic activity with pH is mainly due to pH-dependent changes in the active enzymic center. 3. Milk xanthine oxidases at different stages of purification convert pteridin-4-one into the 4,7-dione (compound 13 in this article). 4. Methylation at C-6 in the pyrazine moiety enhances enzymic attack at C-2 in the pyrimidine ring. N-Methylation may increase or reduce rates of oxidation. 5. For oxidation at C-2, the most favorable form of the substrate bears a double bond at C(2) = N(3). Attack at C-7 is enhanced strongly in structures bearing a double bond at C(6) = C(7). 6. In general, pteridines react with xanthine oxidase as non-hydrated molecules. However, oxidation of 8-methyllumazine at C-7 may take place by dehydrogenation of the 7-CHOH group of the covalently hydrated molecule.

Animals↗
PubMed1976

Further observations on familial hypobetaliproteinaemia.

A family with hypobetalipoproteinaemia with 10 affected members is described. In six patients low density lipoprotein cholesterol (LDL-c) concentrations were about 10 % of normal. In four LDL-c was reduced to about 50 % of normal; these four patients probably represent the "intermediate" form of hypobetalipoproteinaemia. This variation in total cholesterol concentration and LDL-c among the affected individuals of the same family could reflect differences of expression in a single aberrant gene or additive expression of a gene at a second locus.

Abetalipoproteinemia↗
PubMed1975

The amniotic fluid foam test, L/S ratio, and total phospholipids in the evaluation of fetal lung maturity.

The results of the L/S ratio, TPL (total phospholipids) concentration, and the FT (foam test) from 126 amniotic fluid samples (105 of which were obtained less than 48 hours before delivery) between weeks 26 and 43 of gestation were compared in evaluating fetal lung maturity. A perfect correlation between an L/S ratio of 2 or more and TPL of 2.8 mg./100 ml. or more and pulmonary maturity was found. L/S ratio of 1.4 or less and TPL of 1.5 mg./100 ml. or less were associated in all cases with RDS. The intermediate zone between these values, where pulmonary maturity could not be predicted, contained 3.8 per cent of the cases when L/S ratio is evaluated compared to 21.9 per cent by TPL assessment. The intermediate and positive FT were associated in all cases with fetal lung maturity and mature values of L/S ratio and TPL; the negative FT cases (36 out of 105) were associated with a wide range of TPL and L/S ratio values including immature, intermediate, and mature values. No RDS occurred in cases in which the FT was positive or intermediate. It is concluded that the FT is highly valuable as a screening test. If positive or intermediate, the risk of RDS is very small; when negative, the sample should be subjected to chemical analysis.

Amniotic Fluid↗
PubMed1975

Changes in amniotic fluid lecithin-sphingomyelin ratio following maternal dexamethasone administration.

The effect of dexamethasone on amniotic fluid lecithin-sphingomyelin (L/S) ratio was measured in 15 fetuses of 34 weeks or less of gestation. Six of the patients presented with premature rupture of the membranes. A rise in the L/S ratio is mature levels (two or more) was observed 24 hours to 11 days after the start of treatment in 12 patients. In 2 patients (one second twin and one anencephalic fetus), no rise in L/S ratio occurred. Of 12 cases whch ended in premature delivery (29 to 35 weeks) only one infant, a second twin delivered at the thirtieth week with a posttreatment L/S ration o1.4 weighing 1,240 grams, developed severe respiratory distress syndrome and died. Tt is suggested that dexamethasome accelerates fetal lung maturation by increasing surfactant synthesis or release, and this may be achieved as early as the twenty-eighth week of pregnancy.

Amniotic Fluid↗
PubMed1975

Serum lipids in patients with psoriasis.

In 13 patients with psoriasis a lower total cholesterol (TC) concentration was found compared to healthy controls of the same population. No differences in the concentration of serum triglyceride (TG) or phospholipids (PL) were detected between these two groups. In the same patients, serum triglyceride fatty acid analyses showed a reduced concentration of linoleic acid and a raised level of palmitoleic and myristic acids. No differences were detected in the major phospholipid fractions. The increase in plasma free fatty acids (FFA) following intravenous heparin was comparable in the psoriatic patient and in the controls. It is concluded that no basic abnormality of serum lipids exists and that the changes described were due to a selective loss via the scales or due to malabsorption.

Adult↗