Inge N. Bojesen

Structure of fluorobenzene

Abstract The microwave spectra of four ring-substituted fluorobenzenes have been measured and the molecular structure of fluorobenzene has been determined by the substitution method from the data so obtained in combination with earlier published data for deuterated fluorobenzenes. The result shows a small shortening of the two C-C bonds nearest fluorine, while the rest of the molecule is practically like benzene. The C-F bond length is 1.35 A, as in vinyl fluoride.

Quantitative and qualitative analyses of isolated lipid droplets from interstitial cells in renal papillae from various species

The lipid droplets of renal papillae homogenates from four different species were obtained by ultracentrifugation. Ca. 80–98% of the lipids (triglycerides, phospholipids, free fatty acids, and cholesterol esters) consist of triglycerides. The triglycerides were fractionated by argentation thin layer chromatography and each fraction characterized by gas liquid chromatography. No fraction contained any unique triglyceride. The fatty acid composition of the total triglycerides, as analyzed by gas liquid chromatography and ozonolysis, differed markedly from the fatty acid composition of the corresponding plasma triglycerides. The papillary triglycerides were characterized by higher concentrations of stearic acid, arachidic acid, and polyunsaturated acids with 20 or more carbon atoms. Particularly interesting was the presence in the lipid droplets of docosa-7,10,13,16-tetraenoic acid. This acid has been shown to be a major component in the cholesterol ester fraction of rat and canine adrenal lipids. In the papillary triglycerides, this acid accounted for 7%, 15%, and more than 20% of the total fatty acids in the dog, rat, and rabbit, respectively. The pig differs from these three species in having only ca. 1% of this acid. These observations suggest that the interstitial cells produce these triglycerides. This production could occur either by a transacylation from phospholipids and cholesterol esters and by a de novo synthesis from locally produced fatty acids. The possibility that the triglyceride production may be involved in a control of the prostaglandin production of the renal medulla is discussed.

Evaluation of the chemical parameters of four systems of radioimmunological assay

An iterative indirect model fitting (IIMF) procedure has been designed to evaluate antibody binding capacities and ligand affinities of fairly simple RIA systems. The information is provided by one or more series of standard equilibrium assays, the mass of tracer ligand, the residual fraction of free ligand which contaminates measured bound fractions, and the chemical purity of the tracer. The procedure uses theoretical models which describe systems with one or two antibodies with identical or different affinities towards the hot and the cold ligands. The tracer may be the purified radioactive ligand or a mixture of the hot and the cold ligands with the cold species as the major component. The theoretical models corresponding to two antibody systems are simplified and only strictly valid within limited ranges of ligand concentrations. The chemical parameters of both antibodies may in suitable cases be estimated by two runs of assays with different doses of antiserum and tracer. The IIMF procedure involves the computation of the regression line of a dose function for which the dependent variable is the model derived bound fraction over the measured bound fraction multiplied by the dose. Two tallies are combined of which the statistics of means of replicates being on the regression line has a higher priority than the minimal deviation of the slope of the regression line from 1. The procedure is applied to three RIA systems using carbon adsorption of the free ligand: prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha) and angiotensin 1 (Ang. 1), and to one using antibody precipitation-arginine vasopressin (AVP). The consistency of the results was tested by repeated runs of standards or by varying the concentrations of the reactants and the temperature.

In vitro and in vivo synthesis of long-chain fatty acids from [1-14C]acetate in the renal papillae of rats

1. The relationship between the rate of [1-14C] acetate incorporation into the fatty acids of renal papillary lipids and the acetate concentration in the medium has been measured. 2. [1-14C] acetate was incorporated mainly into fatty acids of phospholipids and triacylglycerols. Only a few per cent of the radioactivity was found in the free fatty acid fraction. 3. The major part of the [1-14C] acetate was found to be incorporated by a chain elongation of prevalent fatty acids. The major component of the poly-unsaturated fatty acids in triacylglycerols and the major product of fatty acid synthesis from [1-14C] acetate in vitro was demonstrated by mass spectrometry to be docosa-7,10,13,16-tetraenoic acid. 4. The radioactivity of docosa-7,10,13,16-tetraenoic acid accounted for 40% of total radioactivity in triacylglycerol fatty acids (lipid droplet fraction) and 20% of total radioactivity in membrane phospholipid fatty acids.

In vitro and in vivo lipogenesis of the rat renal papillae from glucose.

The rate of [14C]glucose incorportion into rat renal papillary glycerolipids has been studied. Glucose is incorported mainly into the glycerol moiety of these lipids. 74 and 93% of the activity incorporated into triacylglycerols in vitro and in vivo, respectively, was present in the glycerol backbone. In phospholipids it was 82 and 96%, respectively. The fatty acid synthesis from [14C]glucose was similar to that from [14C]acetate. In accordance with previous experiments with [14C]acetate the papillary tissue was found to have a high capacity for chain elongation of preexisting fatty acids with the major product being cis-7,10,13,16-docosatetraenoic acid (chain elongated arachidonic acid). The in vitro and in vivo turnover rates of papillary glycerolipids can be calculated. A half-life of 25 h can be estimated for membrane phospholipids and less than 11 h for lipid droplet triacylglycerols. These appreciably high rates of turnover are discussed in relation to membrane turnover in renal papillae from rats in different physiological states and to variation in number of lipid droplets of papillary interstitial cells reported by others.

Fatty Acid Composition and Depot Function of Lipid Droplet Triacylglycerols in Renomedullary Interstitial Cells

Although the renin—angiotensin system is known to play an important role in renal hypertension, data have accumulated suggesting that a renal factor besides this system and besides sodium balance is responsible for blood pressure regulation. The question of whether this factor is a vasopressor or a vasdepressor substance has been much discussed. Several lines of evidence have been presented to support the theory that it has a hypotensive action. The theory that hypertension could result from a deficiency of such a vasodepressor substance has recently been supported by studies of Dietz et al. (1978) on the reversibility of experimental renal hypertension.

Sterol biosynthesis in vitro of rat renal inner medulla

Abstract In vitro studies of lipid production of rat renal papillae with [2-14C]acetate or [2-14C]mevalonate have shown that sterologenesis is an important part of the total lipogenesis in this tissue. However, only a very small amount of labelled cholesterol could be detected in the sterol fraction. The lipid extract of tissue slices was directly subjected to thin-layer chromatography or reversed-phase column chromatography. The purified sterols were analyzed by radio gas-liquid chromatography on three different stationary phases, argentation thin-layer chromatography and digitonin thin-layer chromatography. By these techniques it was demonstrated that nearly all the sterol radioactivity could be accounted for by 4,4,14α-trimethyl-5α-cholesta-8,24-dien-3β-ol (lanosterol) and three sterols, which were slightly more hydrophilic than cholesterol. Two of these sterols had the same chromatographic mobilities as cholesta-5,24-dien-3β-ol (desmosterol) and 5α-cholest-7-en-3β-ol (lathosterol), respectively. The third compound, which accounted for the largest fraction of the radioactivity in the sterol fraction, could be tentatively identified as 5α-cholesta-7,24-dien-3β-ol.

Exchange efflux of [3H]palmitate from human red cell ghosts to bovine serum albumin in buffer. Effects of medium volume and concentration of bovine serum albumin

[3H]Palmitate, PA, exchange efflux kinetics is recorded from human erythrocyte ghosts to buffer with bovine serum albumin, BSA, at 0 degrees C. The effects have been investigated of three medium/ghost volume ratios: 36, 80 and 500, of six BSA concentrations, [BSA]: 0.01, 0.02, 0.05, 0.2, 1 and 2% (1.5, 3.0, 7.5, 30, 150 and 300 microM) and of various v, molar ratios of palmitate to BSA, between 0.15 and 0.94. Data are analyzed in terms of a virtually closed three-compartment model. In theory, the tracer efflux is biexponential and the rate coefficients differ at least 20 fold [1]. The efflux rate at 2% BSA is monoexponential beyond our resolution time of about 1 s, but nearly biexponential at or below 0.2% BSA with a well-defined smallest-rate coefficient beta. beta depends strongly on [BSA] but is remarkably v independent. The medium/ghost volume ratio has no effect on beta when [BSA] > or = 0.2%, although beta measured at 2% BSA is almost 2-fold higher than at 0.2%. This suggests the presence of an unstirred layer, USL. According to our model, the observations are understood quantitatively on basis of our previously published dissociation rate constants of the PA-BSA complex, as well as PA equilibrium bindings to ghost membranes (Bojesen, I.N. and Bojesen, E. (1991) Biochim. Biophys. Acta 1069, 297-307). Essentially, beta is theoretically a function of two terms, one comprising the membrane transport parameters and the other the medium-dependent variables. Most important is the clearance with respect to monomer concentration adjacent to the membrane. The clearance is calculated on basis of quasi-stationary diffusion in USL. The data are compatible with a planar USL of 6 microns depth and with the same area as a ghost but not with a spherical USL.

Glycerolipid formation and PGE2 and PGF2α production of rat renal papillae in vitro, the effects of urea

The glycerolipid production by rat renal papillary slices varied inversely with the urea concentration (0-1660 mM) whether the production was measured as labelling of the glycerol backbone from glucose or as incorporation of labelled arachidonic acid and palmitic acid. The rate of phospholipid formation was most dependent on medium urea concentrations in the range between 0 and 1100 mM. The production of prostaglandins PGE2 and PGF2 alpha, measured radioimmunologically or by an isotope derivative method was in the same range inversely related to the production of glycerolipids and chain elongations. The effect of urea on prostaglandin formation is probably indirectly caused by the inhibition of the phospholipid formation and chain elongation, since the effect was abolished by 1% defatted albumin in the medium. The data suggest that the level of free arachidonic acid within the cells is controlled to an important extent by glycerolipid formation and chain elongation.

The influence of urea on lipogenesis in renal papillae of rats

The osmolality has been determined for the papillary interstitial fluids obtained from the isolated papillae of rats in different states of water balance. Hypertonic buffers for in vitro experiments were prepared by addition of urea to regular Krebs-Ringer phosphate buffers (340 mosmol/kg H2O) since urea is the most changeable solute of the renal papillary tissue in response to external influences. The effect of such hypertonic buffers on papillary lipogenesis was very pronounced. The fatty acid synthesis from acetate decreased by a factor of 7–9 in response to increased osmolality from 340 to 1370 mosmol/kg H2O. In the physiological range of osmolalities (500–1800 mosmol/kg H2O), the de novo synthesis of papillary glycerolipids from glucose decreased by a factor of ca. 5. A possible specific inhibitory effect of hypertonic buffers on the pentose phosphate cycle was studied with a negative result. It is concluded that the addition of urea causes a decrease of total energy metabolism in the tissue.