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Biomedical subjects

G Arvidson

Publications and source records attributed to G Arvidson.

At least 37 records · Page 2Linked to original sources
PubMed1982

Molecular organization in the liquid--crystalline phases of lecithin--sodium cholate-water systems studied by nuclear magnetic resonance.

The molecular organization in the hexagonal and lamellar phases of the ternary systems lecithin--sodium cholate--water has been investigated by using a variety of nuclear magnetic resonance techniques. The main findings and conclusions are the following: (i) When calculated on a mole fraction basis, the phase equilibria are insensitive to changes in the alkyl chains of the lecithin. (ii) When incorporated into a lecithin bilayer, cholate exerts a strong perturbation on the lecithin alkyl chain order, giving a large decrease of the order parameters. (iii) This decrease of the order occurs since the average cross-sectional area per alkyl chain increases probably as a result of cholate placing itself flat on the bilayer surface. (iv) The diffusion of lecithin molecules is approximately equally rapid in the lamellar and hexagonal phases. (v) The hexagonal phase is formed by rodlike aggregates with the polar groups at the surface of the rods and with a continuous hydrocarbon core. The rods are not formed by stacking disklike mixed micelles. (vi) With the interpretations of the molecular packing and the phase structures, the observed phase equilibria are in good agreement with current theories of the factors that govern phase behavior in amphiphile--water systems.

Chemical Phenomena↗
PubMed1982

Lysolecithin as a modifier of induced pinocytosis in Amoeba proteus.

Lysolecithin was found to modify cation-induced pinocytosis in Amoeba proteus. It is shown here that lysolecithin (LPC) in the concentration range of 10(-15) to 10(-10) g/ml has the same effect on Na+ -induced pinocytosis as cAMP and a pinocytosis regulating factor (PRF) which is secreted by the amoeba. Thus, LPC activated Na+-induced pinocytosis in starved amoebae and decreased the sensitivity to the inducer in normal cells. Pinocytosis depressed by treatment with EGTA or dibucaine became normal upon addition of LPC to the inducer. These effects were also obtained with lysolecithin isolated from the amoeba. It is suggested that PRF and amoeba LPC may be closely related and that phospholipase activity of the amoeba may regulate its capacity for pinocytosis.

Amoeba↗
PubMed1982

The insulin-releasing activity of the tropical plant momordica charantia.

An aqueous extract from the unripe fruits of the tropical plant Momordica charantia was found to be a potent stimulator of insulin release from beta-cell-rich pancreatic islets isolated from obese-hyperglycemic mice. The stimulation of insulin release was partially reversible. It differed from that of D-glucose and other commonly employed insulin secretagogues in not being suppressed by L-epinephrine and in even being potentiated by the removal of Ca2+. This anomalous behaviour was not associated with general effects on the metabolism of the beta-cells as indicated by an unaltered oxidation of D-glucose. Studies of 45Ca fluxes suggest that the insulin-releasing action is the result of perturbations of membrane functions. In support for the idea of direct effects on membrane lipids, the action of the extract was found to mimic that of saponin in inhibiting the Ca2+/H+ exchange mediated by the ionophore A23187 in isolated chromaffin granules and release Ca2+ from preloaded liposomes.

Animals↗
PubMed1982

Cold enhanced secretion of a pinocytosis-regulating factor in Amoeba proteus.

Low temperature inhibited preferentially pinocytosis induced by Na+ and Na+-like inducers, a category of inducers which are particularly dependent on the concentration of Ca++ that means susceptible to blockade by EGTA, La+++, or high Ca++. Coldness inhibited Na+-induced pinocytosis more effectively in cells from a calcium deficient medium than in normal cells and the inhibition was abolished by Ca++. In normally fed cells, a period of coldness prevented the subsequent induction of pinocytosis by Na+. This block was of the same type as that observed when the concentration of Ca++ was increased in the medium of normal cells kept at room temperature. In contrast, starved cells responded to coldness by an increased capacity for pinocytosis. These effects lasted for several hours after the cells had been rewarmed and were mediated by a cell-derived soluble factor, PRF, pinocytosis regulating factor. Solubility characteristics indicated that PRF is a lipid. Ca++, low pH, and low temperature stimulated accumulation of the factor in the medium. Preincubation with PRF or addition of PRF to the inducer stimulated pinocytosis in starved or Ca++-deficient cells and reduced the sensitivity to Na+-like inducers in normal cells. The amount of PRF secreted from cold cells was sufficient to cause the Ca++-like blockade of pinocytosis in the cold, the diminished pinocytotic activity after a cold period and the activating effect of coldness on starved cells. PRF appears to be an important physiological regulator of the capacity for pinocytosis in the amoeba.

Amoeba↗
PubMed1981

Effect of cholesterol in membranes. Pulsed nuclear magnetic resonance measurements of lipid lateral diffusion.

Lateral diffusion coefficients of lipids in a bilayer can be measured directly in a macroscopically aligned sample by use of a pulsed NMR method with pulsed magnetic field gradients [Lindblom, G., & Wennerström, H. (1977) Biophys. Chem. 6, 167]. This technique has been utilized to investigate the influence of cholesterol on the lipid diffusion of egg yolk lecithin, palmitoyloleoyllecithin, and dioleoyllecithin. It is found that cholesterol has a very small effect on the phospholipid diffusion. On the other hand, cholesterol has a great influence on the molecular ordering in the bilayer and on the lipid phase structure. It is therefore suggested that cholesterol exerts its dominant effect on the lipid membrane stability.

Cholesterol↗
PubMed1978

Lipid metabolism in the vitamin-B12-deprived rat.

Rats were deprived of vitamin B12 in order to study the effect of this deprivation on the metabolism of lipids in the liver and the nervous system. Serum vitamin B12 concentrations of 102.7 and 78 pg/ml were found at sacrifice after 5 and 6 months, respectively. Neurological testing failed to reveal signs of neuropathy. The total liver lipids were decreased in the vitamin-B12-deprived animals, but no changes were detected in the lipid concentration or in the phospholipid composition of the nervous system. Some animals were given propionate, and in these, contrary to expectations, pentadecanoic acid and heptadecanoic acid were found in smaller amounts in the liver triglycerides of the vitamin B12-deprived rats than in the control rats. This could be due to the inhibitory effect of methylmalonyl CoA on fatty-acid synthesis, demonstrated by others in vitro.

Animals↗
PubMed1977

Deuteron nuclear magnetic resonance studies of phase equilibria in a lecithin-water system.

Water deuteron NMR spectra have been studied for the system dipalmitoyllecithin (DPL)-heavy water (D2O) at different compositions and temperatures. From an analysis of the spectra in terms of quadrupole splittings, a phase diagram has been constructed for the temperature range 25-60 degrees C and the composition range 4-15 mol of D2O/mol of DPL. Evidence is given that the "pretransition" observed by differential scanning calorimetry is caused by a crossing of a three-phase line. Strong support for a specific hydration of about 11 water molecules per lecithin molecule in the phase between the pretransition and main transition is also found.

Deuterium↗
PubMed1976

Lecithin translational diffusion studied by pulsed nuclear magnetic resonance.

The translational diffusion coefficient of egg yolk and dilauroyl lecithin in optically isotropic phases containing sodium cholate has been measured using the pulsed NMR magnetic field gradient method. After a correction for geometrical factors the measured diffusion coefficient is found to agree well with previous determinations in phospholipid systems. The experimental data imply that the cubic mesophase of the lecithin-sodium cholate-water system contains continuous lipid aggregates. A possible model of the arrangement of the different amphiphile molecules in the cubic phase is discussed.

Diffusion↗
PubMed1976

Changes in amniotic fluid phospholipids on treatment with glucocorticoids to prevent respiratory distress syndrome.

Amniotic fluid was obtained by transabdominal amniocentesis in 51 women in the 29th-36th week of pregnancy. The lecithin/sphingomyelin ratio was determined. In 28 patients,the ratio was less than 2.2. Beta-methasone was given for three days to 14 of them; the rest served as controls. On the fourth day, a second amniocentesis was performed on all patients. The lecithin/sphingomyelin ratio rose to a value greater than 2.2 in 4 of the patients in the betamethasone-treated group and in one of the controls. The percentage of palmitic acid in the lecithin increased concomitantly with increasing lecithin/sphingomyelin ratio. These results suggest that glucocorticoid induced acceleration of fetal pulmonary maturation may be reflected in the amniotic fluid as changes in its phospholipid composition. The lecithin/sphingomyelin ratio was found to be greater than 2.2 in 23 patients at the first amniocentesis. In such cases treatment with glucocorticoids can be avoided.

Amniotic Fluid↗
PubMed1976

Effect of cortisone and acth on the phospholipids of human amniotic fluid and lung tissue in early gestation.

Fifteen physically healthy women who received permission for legal abortion on sociomedical grounds in the second trimester of pregnancy were given either cortisone acetate per os or adrenocorticotrophic hormone (ACTH) intramuscularyly for 3 days previous to hysterotomy. Eight other patients served as controls. The phospholipid composition of amniotic fluid, fetal lung washings, and lung tissue was analyzed. In the cortisone group there was a significant increase in the proportion of palmitic acid in the lung tissue lecithins linked to a corresponding decrease in the oleic acid. A similar tendency was observed in the ACTH group, but the changes were not significant. The investigation suggests that the human fetal lung already at this early stage of development is capable of responding to the action of cortisone by a relative increase in the synthesis of dipalmitoyllecithin.

Adrenocorticotropic Hormone↗
PubMed1975

Effect of cortisol on human fetal lung in organ culture: a biochemical, electron-microscopic and autoradiographic study.

Human fetal lung tissue obtained during the second trimester was cultured as organ culture with or without cortisol. The effect of cortisol on the phospholipid metabolism, as related to the appearance of osmiophilic lamellar bodies and the localisation of newly incorporated choline, was studied. In cortisol-treated explants, the concentration of saturated lecithins and the incorporation of (Me-3H)-choline into saturated lecithins increases significantly concomitantly with an increased number of osmiophilic lamellar bodies. The labelled choline is predominantly associated with these bodies. The obtained results indicate that cortisol accelerates the synthesis of pulmonary surfactant in the human fetal lung as early as in the second trimester.

Body Height↗
PubMed1975

Proton NMR bandshape studies of lamellar liquid crystals and gel phases containing lecithins and cholesterol.

Proton NMR spectra for gel and liquid crystalline samples, composed of dimyristoyl and/or dipalmitoyl lecithin, cholesterol and water, can be consistently interpreted in terms of mesophase symmetry and molecular diffusion according to a model proposed by Wennerstrom (Wennerstrom, H. (1973) Chem. Phys. Lett. 18, 41-44). It is shown by computer simulation that the characteristic "super-lorentzian" bandshape of the lamellar mesophase can be described by the superposition of three gaussian curves. The NMR signal of the gel phase can be simulated by the superposition of two gaussian curves with widths at half height of 2.5 kHz and 19 kHz. An upper limit of the lateral diffusion coefficient of the lecithin molecules in the gel phase is calculated to be about 5-10(-15) m-2/s. It is therefore concluded that the static intermolecular dipolar couplings average to zero in the lamellar mesophase. An estimation of the order parameter of the liquid crystalline phase is made from experimental data and a calculated "rigid lattice" linewidth. A two phase system is shown to exist in the temperature range 28-34 degrees C for a mesophase of a mixture of dimyristoyl and dipalmitoyl lecithin. The presence of cholesterol results in enhanced lateral diffusion of the lecithin molecules at temperatures below the Chapman transition point.

Binding Sites↗
PubMed1975

Cortisol-induced accumulation of phospholipids in organ culture of human fetal lung.

Lungs obtained from human fetuses with a gestational age of 17, 19, and 24 weeks were cultured as organ culture for 6 days with or without cortisol. The total phospholipid content per milligram protein in the explants incubated with cortisol increased by 56-81 per cent compared with the controls. Lecithin accounted for 62-69 per cent of the phospholipid increment in the cortisol-treated explants, whereas only 44.2 per cent of the total phospholipids in the control incubations consisted of lecithin. Cortisol increased the incorporation of [Me-3H]choline into lecithin by 118-224 per cent. The investigation shows that the human fetal lung, quite early in gestation, is capable of responding to the action of glucocorticoids by accumulating phospholipids.

Choline↗
PubMed1975

Surfactant studies in the fetal and neonatal foal.

Phospholipids in embryonic lung tissue, pulmonary washings and amniotic fluid were measured to study the development of lyng surfactant in the horse. A significant increase in the concentration of total phospholipids in lung tissue and a concomitant rise in the amount of dipalmitoyl lecithin in amniotic fluid between 100 and 150 days of gestation indicated the initial formation of surfactant in the fetal lung during this period.

Amniotic Fluid↗