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PubMedDate not supplied

Characterization in vitro of interaction of human apolipoprotein E-free high density lipoprotein with human hepatocytes.

Characterization of the interaction of iodinated apolipoprotein (apo) E-free high density lipoprotein (HDL) with cultured human hepatocytes provides evidence for a saturable, Ca2(+)-independent, high affinity binding site with an apparent km value of 20 micrograms/ml of apolipoprotein. Nitrated HDL and low density lipoprotein (LDL) did not compete for the binding of HDL, in contrast to very low density lipoprotein (VLDL). It is suggested that VLDL competition is exerted by the presence of apo Cs. Degradation of HDL was relatively low and in some cases not detectable. In cases where degradation was found, inhibitors of the lysosomal pathway of protein degradation had no effect, while LDL degradation was inhibited more than 80%. In the presence of 10 microM of monensin, the cell-association of HDL was unaffected, but the degradation was inhibited by 30%. Under similar conditions, LDL association was inhibited by 40% and LDL degradation, by 90%. Incubation of human hepatocytes with fluorescently labeled HDL (Dil-HDL) revealed (in contrast to Dil-LDL) mainly strong membrane-bound fluorescence and hardly any labeling of small intracellular vesicles. It is concluded that human hepatocytes possess a specific high affinity site for human HDL with recognition properties similar to those described earlier on rat hepatocytes. No evidence that the binding of HDL is actively coupled to uptake and lysosomal degradation could be obtained, indicating that binding of LDL and HDL to human hepatocytes is coupled differently to intracellular pathways.

Ammonium Chloride↗

PubMed1994

Adsorption of fibrinogen and some other proteins from blood plasma at a variety of solid surfaces.

Enzyme linked immunosorbent assay (ELISA) was used for the estimation of protein adsorption from blood plasma at some model solid surfaces. The majority of those surfaces were made in the wells of microtiterplates of polystyrene commonly used for ELISA purposes. Three of the model surfaces were made by radio frequency plasma discharge polymerization (RFPD) of the microtiterplates of polystyrene. The monomers we used were diaminocyclohexane, hexamethylenedisiloxane, and acrylic acid. Other surfaces investigated were: unmodified polystyrene, oxidized polystyrene, hydrophilic silicon oxide, and methylized silicon oxide. Two substances, Tween and bovine serum albumin (BSA), for the prevention of unintended adsorption of ELISA conjugate were also tested and the BSA method was found to be superior for this kind of investigation. Human blood plasma at different dilutions was incubated in the surface-modified microtiterplates followed by incubation of rabbit antibodies against fibrinogen (FG), fibronectin (FN), human serum albumin (HSA), complement factor 3 (C3), and immunoglobulin G (IgG). Visualization of bound antibodies was then made by standard ELISA procedure. At low blood plasma concentrations (plasma dil 1/1000), anti-IgG and anti-HSA were detected at high levels at the majority of surfaces. At high blood plasma concentration (plasma dil 1/10), anti-FG dominated at most surfaces. ELISA activity of FN and C3 were low at most of the surfaces at both plasma concentrations. An 'optimum' plasma dilution for the detection of surface bound FG (the Vroman effect) was not found with the use of the ELISA on any of the surfaces except for the silicon oxide surface. This is in contrast to findings by others who had used isotope-labelled fibrinogen diluted in plasma. However, 'false' Vroman effects occurred if nonionic surfactant was used for the prevention of unspecific binding in the ELISA.

Adsorption↗

PubMed1989

Transplacental or enteral transfer of maternal immunization-induced antibody protects suckling rats from type III group B streptococcal infection.

Deficiency of maternal group B streptococcal (GBS) type-specific IgG increases neonatal susceptibility to GBS infection. We asked if immunization-induced maternal type III GBS opsonic antibody transferred prenatally (via placenta) or postnatally (via breast milk) would affect suckling rat survival after GBS infection. Pregnant immunized dams with type III GBS opsonic antibody (20 through 320 dil-1) and nonimmunized dams without GBS antibody were matched (n = 16). Half of each litter was cross-suckled to a matching dam creating four pup groups with different exposure to maternal type III GBS opsonic antibody: none, postnatal, prenatal, and combined (pre- and postnatal). After infection with type III GBS, group survival (n) was 41% (51), 66% (47), 98% (43), and 98% (47), respectively. Type III GBS opsonic antibody in surviving pups was directly related to their immunized dam's antibody either postnatally (R = 0.85), prenatally (R = 0.84), or combined (R = 0.81). Pups exposed postnatally to high titers (80 to 320 dilution-1) of type III GBS opsonic antibody survived more often than those exposed to low titers (20 to 40 dil-1) (p less than 0.03). Immunization-induced maternal type III GBS opsonic antibody is transferred pre- and postnatally and results in improved neonatal survival after GBS infection. Survival of pups exposed to postnatal antibody appears related to the concentration of maternal type III GBS opsonic antibody. Breast milk with high titers of GBS type-specific antibody may modify the course of GBS infection. GBS vaccines and strategies could be tested in this model.

Animals↗

PubMed1992

Growth and targeting of subplate axons and establishment of major cortical pathways.

In the developing mammalian neocortex, the first postmitotic neurons form the "preplate" superficial to the neuroepithelium. The preplate is later split into a marginal zone (layer 1) and subplate by cortical plate neurons that form layers 2-6. Cortical efferent axons from layers 5 and 6 and cortical afferent axons from thalamus pass between cortex and subcortical structures through the internal capsule. Here, we identify in rats the axonal populations that establish the internal capsule, and characterize the potential role of subplate axons in the development of cortical efferent and afferent projections. The early growth of cortical efferent and afferent axons was studied using 1-1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil) as an anterograde and retrograde tracer in aldehyde-fixed brains of embryonic rats. Cortical axons first enter the nascent internal capsule on embryonic day (E) 14 and originate from lateral and anterior cortex; axons from posterior cortex extend rostrally but do not yet exit cortex. The labeled axons, tipped by growth cones with complex morphologies, take a pathway deep to the preplate. Preplate neurons extend these early cortical efferents, based on the developmental stage of the cortex, and on their location and morphology. Most of these cells later occupy the subplate. Cortical plate neurons extend axons into the internal capsule by E16. En route to the internal capsule, cortical plate axons take the same path as the earlier-growing preplate axons, through the intermediate zone deep to subplate. Subplate axons reach thalamus by E16; the first cortical plate axons enter thalamus about a day later. Thalamic axons enter cortex by E16, prior to other cortical afferents. On E15, both preplate and thalamic axons reach the midpoint of the internal capsule. To determine the subcortical distribution of subplate axons, we used Dil as a retrograde tracer in aldehyde-fixed brains and fast blue and rhodamine-B-isothiocyanate as in vivo retrograde markers in neonatal rats. Tracers were injected into the superior colliculus, the principal midbrain target of layer 5 neurons, at times before, during, and after the arrival of cortical axons, or into the subcortical pathway of primary layer 5 axons at two points, the cerebral peduncle caudal to the internal capsule, and the pyramidal decussation at the junction of the hindbrain and spinal cord, at times shortly after the passing of cortical axons. In every case, the labeled neurons are confined to layer 5; subplate neurons are not labeled.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMedDate not supplied

The effect of Dilazep on F10 cells in vitro.

Experiments on F10 cell growth, colony ability, cell adhesion and ultramorphology at SEM have been performed. The effect of Dilazep (DIL) has been compared with that of well known modulating agents such as Flunarizine (FLU) and Verapamil (VER) on cells cultured in high Ca++ medium (HCM) and in low calcium medium (LCM). While in HCM there is no difference among the three drugs, FLU and VER had a stronger effect on cell growth inhibition in LCM. Cell adhesion to the growth substratum, evaluated by the technique of spontaneous detachment in culture medium, is reduced in DIL treated cells in comparison to the controls.

Animals↗

PubMed1990

Bidirectional fluorescent labelling techniques for the developing and regenerating visual system.

Fluorescent dyes like RITC or Dil (282) are convenient and highly efficient labelling substances for investigating developing and regenerating neurons. Either dye can be taken up by cell bodies and transported in an anterograde direction, resulting in a complete outlining of the axons and their growth cones. Additionally the dyes can be transported in a retrograde direction, resulting in labelling on the cell bodies and their dendrites. These dyes have several features in common, for instance their poor solubility in aqueous buffers, the absence of neurotoxicity and the long time persistence in the filled neurons. Dil can in particular be used for the staining of neurons post-mortem. These dyes have also been used to address several questions concerning fiber growth and pathfinding during embryogenesis of the visual system, and during the period of axonal regeneration of adult retinofugal fibers.

Animals↗

PubMed1990

Specific routing of retinal ganglion cell axons at the mammalian optic chiasm during embryonic development.

During development of the mammalian CNS, axons encounter multiple pathway choices on their way to central target structures. A major pathway branch point in the visual system occurs at the optic chiasm, where retinal ganglion cell axons may either enter the ipsilateral or the contralateral optic tract. To investigate whether embryonic mouse retinal ganglion cell axons, upon reaching the optic chiasm, selectively grow into the correct pathway, developing retinal ganglion cells were retrogradely labeled using either 1,1'-dioctadecyl- 3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil) or fluorescent microspheres placed into the optic tract on one side. The distribution of ipsilaterally and contralaterally projecting ganglion cells in the embryo was then examined and compared to that of the adult animal. Results show that axon routing at the chiasm is already extremely adult-like as early as embryonic day 15 (E15), shortly after retinal axons arrive at the chiasm. [Retinal ganglion cell neurogenesis = E11-E18 (Drager, 1985); birth = E21.] Throughout the development of this pathway, routing errors are infrequent and are on the order of only about 3-8/1000 retinal ganglion cells. Thus, embryonic retinal ganglion cell axons do not project randomly at the optic chiasm but instead appear to be highly specific in their choice of pathway. To learn how correct pathway choices are made, retinal axons were retrogradely labeled with Dil and their trajectories at the optic chiasm were reconstructed. Results show that ipsilaterally and contralaterally projecting axons are highly intermixed as they enter the chiasm region but selectively grow into the correct pathway. For example, a contralaterally projecting axon near the entrance of the ipsilateral optic tract will turn and bypass this pathway and grow towards the midline to head into the contralateral optic tract. Similarly, axons far away from the ipsilateral optic tract frequently turn abruptly at right angles to enter the ipsilateral tract, directly crossing over contralaterally projecting axons heading to the opposite side. The sorting out of intermixed ipsilaterally and contralaterally projecting retinal axons into the appropriate optic tracts strongly suggests the presence of specific guidance cues at the optic chiasm during embryonic development. Together, results from this study demonstrate that the pattern of axon projection at the adult mammalian optic chiasm is gradually built upon a highly specific pattern of axon routing laid down early during development.

Animals↗

PubMed1987

Effects of Ca2+ agonist and antagonists on cytosolic free Ca2+ concentration: studies on Ca2+ channels in rat parotid cells.

1. Effects of Ca2+ agonist and antagonists on cytosolic free Ca2+ concentration [( Ca2+]i)were studied using quin2. 2. Nicardipine (NIC), diltiazem (DIL) and verapamil (VER) had no effect on the rise in [Ca2+]i evoked by carbachol. Methoxamine-elevated [Ca2+]i was inhibited by VER but not by NIC and DIL. 3. All Ca2+ antagonists tested produced a decline of [Ca2+]i elevated by isoproterenol to the resting level. 4. The addition of 30 mM K+ gradually elevated [Ca2+]i in normal and Ca2+-free media, but it did not increase 45Ca2+ uptake into cells. BAY K 8644 did not increase [Ca2+]i. 5. We suggest that voltage-sensitive Ca2+ channels are lacking and that at least 2 distinct receptor-operated Ca2+ channels exist in rat parotid cells.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1989

[Analysis of binding and absorption of native and modified low density lipoproteins by human liver cells in primary culture].

The binding and uptake of native low density lipoproteins (LDL) and malondialdehyde treated (MDA) LDL by human hepatocytes in primary culture has been analyzed. Indirect immunofluorescent technique and lipoproteins labeled with fluorescent dye 3.3 dioctadecylindocarbocyanine (Dil) were used. Practically all culture cells have binding sites for native LDL which visualized in a form of separate granules on the cell surface. The binding sites for MDA LDL were found only on some (5%) cells culture that differed from hepatocytes in shape and size. Like other cells of culture hepatocytes internalized native Dil-LDL and acquired brightly specific fluorescence.

Binding Sites↗

PubMed1989

Characterization of two factors enhancing choline acetyltransferase activity in cultures of purified rat motoneurons.

Motoneurons from E14 rat embryos have been retrogradely labeled with the carbocyanine derivative dil and purified 12-fold by centrifugation on a density gradient made of Nycodenz, as assessed by the increase in CAT activity per cell and in the percentage of dil-labeled cells. A 20- to 36-fold purification was achieved by the microdissection of the labeled lumbar motor columns followed by density-gradient centrifugation. Motoneurons were then purified to near homogeneity by fluorescence-activated cell sorting. In certain experiments, motoneurons were purified by a novel cell-sorting procedure that only uses light-scatter parameters and does not necessitate retrograde labeling. In cultures of motoneurons enriched by centrifugation, muscle-conditioned media (CM) had only a marginal effect on the overall neuronal survival but increased up to 10-fold the number of labeled motoneurons surviving after 7 d in culture. CAT activity per culture was quantitatively stimulated to the same extent, suggesting that the increase in CAT activity caused by CM mostly reflected better survival of motoneurons. In cultures of motoneurons purified by cell sorting, CM increased both survival and CAT expression per motoneuron. We have partially purified 2 factors from CM that stimulate CAT activity per motoneuron 2- to 3-fold without affecting their survival. One of these factors is probably identical to the factor involved in the cholinergic/noradrenergic choice of sympathetic neurons (Fukada, 1985).

Animals↗

PubMed1985

Similar mechanism of various lupus anticoagulants.

Potent lupus inhibitors from various patients were mixed with platelet free normal plasma and were compared in activated partial thromboplastin time (APTT), dilute prothrombin time (dil. PT), kaolin clotting time (KCT), contact product clotting time (CPCT), and Russell viper venom clotting time (RVVCT) tests. In the last three tests platelets and platelet lipid substitutes were avoided to enhance the sensitivities of these tests for the lupus anticoagulant. Correlations between the KCT and the other tests were mostly good, indicating that different lupus inhibitors functioned by a similar mechanism. There was no significant trend between particular clinical symptoms and individual coagulation test combinations. The KCT was found to be the most sensitive test for the lupus inhibitor, followed by the CPCT, RVVCT, dil. PT and APTT tests. Activated platelets tended to correct the APTT lupus inhibitor defect in all except the strongest inhibitor cases.

Blood Coagulation Disorders↗

PubMed1994

N-type Ca2+ channels are located on somata, dendrites, and a subpopulation of dendritic spines on live hippocampal pyramidal neurons.

In the nervous system the influx of Ca2+ orchestrates multiple biochemical and electrical events essential for development and function. A major route for Ca2+ entry is through voltage-dependent calcium channels (VDCCs). It is becoming increasingly clear that the precise contribution VDCCs make to neuronal function depends not only upon their specific electrophysiological properties but also on their distribution over the nerve cell surface. One location where the presence of VDCCs may be critical is the dendritic spine, a structure known to be the major site of excitatory synaptic input. On spines, VDCCs are hypothesized to play an essential role in signal processing, learning, and memory. However, direct evidence for the presence of VDCCs on spines is lacking. Attempts to examine the distribution of VDCCs, or indeed any other components, on spines have been hampered since the size of many spines is close to the limits of resolution of conventional light microscopy. Using a new, biologically active, fluorescein conjugate of omega-conotoxin (Fl-omega-CgTx), a selective blocker of N-type VDCCs, and confocal microscopy, we have mapped the distributions of N-type VDCCs on live CA1 neurons in rat hippocampal slices. VDCCs were found on somata, throughout the dendritic arbor, and on dendritic spines in all hippocampal subfields. A comparison of three-dimensional reconstructions of structures labeled by Fl-omega-CgTx with those outlined by 1,1-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (Dil) or Lucifer yellow confirmed the presence of N-type VDCCs on dendritic spines. However, spine frequency on dendrites labeled with Fl-omega-CgTx was much lower than the spine frequency on dendrites labeled with Lucifer yellow or Dil, suggesting that some spines lack N-type VDCCs. These results offer the first direct evidence for the localization of any voltage-dependent channel on dendritic spines. The presence of N-type VDCCs on dendrites and their spines argues that these channels may participate in the generation of active Ca2+ conductances in distal dendrites, and is consistent with a role for spines as specialized compartments for concentrating Ca2+.

Animals↗

PubMed1995

Modular organization of the pontine nuclei: dendritic fields of identified pontine projection neurons in the rat respect the borders of cortical afferent fields.

Cortical afferents transferring information destined for the cerebellum terminate in the pontine nuclei (PN) in a divergent and patchy fashion. We investigated whether the form of dendritic fields of pontine projection neurons which are postsynaptic to the cortical afferents are related to this patchy pattern. To this end we used a triple combination of (1) retrograde labeling (injection of Fluorogold into the brachium pontis), (2) anterograde labeling [injection of Dil into cortical areas A17 and Sml(forelimb)], and (3) subsequent intracellular fills of identified projection neurons (Lucifer yellow) in slightly fixed slices of pontine brainstem. In 64 projection neurons whose somata were located within 160 microns of the border defined by cortical afferent fields, most of the dendritic trees were found to respect the border. Strikingly, proximal dendrites which were oriented toward the border often bent in order to avoid the boundary. This observation was supported by a quantitative analysis. It revealed that overlap areas of dendritic fields with the neighboring compartment were significantly smaller than those of hypothetical, radially organized dendritic fields of the same size, indicating that the dendritic fields are indeed confined to single compartments. In a second series of experiments, double injections of the anterograde tracers Dil and DiAsp into adjacent sites within one cortical area (A17 or Sml) were made in order to test if the topology of the cortical map is preserved within individual pontine compartments. This, however, does not seem to be the case, since the terminal fields displayed a complex pattern of overlap and nonoverlap rather than a consistent shift of terminal fields expected in the case of preserved topology. The results of the present study are consistent with the view that pontine modules independently process information from different parts of individual cortical areas. We suggest that this characteristic property of the corticopontine projection system might be the morphological basis of the well established fact that somatotopically continuous sensory maps in the cortex are transformed into maps at the level of the cerebellar cortex, showing a fractured somatotopy.

Afferent Pathways↗

PubMed1995

The first retinal axons and their microenvironment in zebrafish: cryptic pioneers and the pretract.

The initial development of the optic tract was studied with light and electron microscopy in the zebrafish (Danio rerio). Intraocular injections of the fluorescent marker, 1,1'-dioctadecyl-3,3,3',3' tetramethylindocarbocyanine perchlorate (dil), labeled retinal axons and growth cones anterogradely, and injections of dil into the optic chiasm labeled retinal ganglion cells retrogradely. Labeled tissue was photoconverted and examined electron microscopically. The ventronasal retinal quadrant produced the first growth cones. They were the first growth cones in the optic stalk. The leading retinal growth cones, typically 4-10 in number, advanced alongside the tract of the postoptic commissure but rarely sent filopodia into it and never wrapped its axons. Instead, the retinal growth cones followed a pretract, a subpial region that was morphologically distinct from its surroundings and extended out in front of the leading growth cones, presaging the optic tract. Thus, the retinal growth cones, previously thought to be followers of preexisting axons, are actually cryptic pioneers whose proximity to the earlier axons masks their pioneering nature. We suggest that cryptic pioneers and pretracts are probably common elsewhere in the nervous system.

Aging↗

PubMed1995

Long aboral projections of Dogiel type II, AH neurons within the myenteric plexus of the guinea pig small intestine.

Enteric AH neurons, with multipolar Dogiel type II morphology, project around the circumference of the intestine to myenteric ganglia, the submucosa and mucosa. Using retrograde labeling in vitro, intracellular recording, dye filling and immunohistochemistry, the projections of these neurons along the intestine were studied. When the retrograde tracer, Dil, was applied to the myenteric plexus, labeled nerve cell bodies were located up to 111 mm orally but only 13 mm aborally, demonstrating a marked difference in the lengths of projections up and down the small intestine. Of labeled nerve cell bodies located 2-110 mm orally, 43% had Dogiel type II morphology and of these, 70% were immunoreactive for calbindin, a calcium binding protein exclusive to Dogiel type II neurons. Intracellular filling with neurobiotin revealed several long circumferentially directed nerve fibers and short, filamentous dendrites; thus these were "dendritic" Dogiel type II neurons. This class accounts for approximately 3-4% of all myenteric neurons, and about 10% of all Dogiel type II neurons. Intracellular recordings revealed AH cell characteristics, with long afterhyperpolarizations following their action potentials, pronounced slow excitatory synaptic inputs and a lack of fast excitatory synaptic inputs. Antidromic action potentials could be evoked from the Dil application site in some cells, confirming their aboral projection. This is the first account of a major aboral projection of AH/Dogiel type II neurons and suggests an important role in aborally directed reflexes in the intestine.

Action Potentials↗

PubMed1994

Reversal effects of several Ca(2+)-entry blockers, neuroleptics and local anaesthetics on P-glycoprotein-mediated vincristine resistance of L1210/VCR mouse leukaemic cell line.

The ability of several Ca(2+)-entry blockers, neuroleptics and local anaesthetics to depress the P-glycoprotein-mediated resistance to vincristine was studied in vitro using the L1210/VCR cell line. This cell line was obtained by long-term adaptation of the L1210 mouse leukaemic cell line on vincristine and showed an overexpression of P-glycoprotein and accompanying multidrug resistance (MDR) which was defined as a cell resistance to several cytostatics such as vincristine, vinblastine and actinomycin D. Efficiency of the drugs applied to reverse this resistance was as follows: for Ca(2+)-entry blockers: verapamil (VER) > or = galopamil (GAL) > flunarizine (FLU) >> diltiazem (DIL) > nimodipine (NIM) > or = nifedipine (NIM); for neuroleptics: trifluoperazine (TFP) > chlorpromazine (CHP) > thioridazine (TRD) > perphenazine (PER); for local anaesthetics: carbanilate-Ca7 > cinchocaine (CIN) >> carbanilate-Ca3 > articaine (ART) > carbanilate CAO > lidocaine (LID). Quaternary cabanilate derivatives (Ca7Q and Ca3Q) with permanent positive charge were found to be unable to reverse the vincristine resistance of L1210/VCR cells. No reasonable correlation between the ability of calcium-entry blockers (DIL, VER, GAL, NIF, NIM and FLU) to reduce the viability of L1210/VCR cells growing in the medium supplemented with vincristine and their reported affinity to the L-type of calcium channel was observed. On the other hand, significant positive correlations were observed between both the inhibitory action of local anaesthetics on propagation of action potential in rat sciatic nerve and the ability of drugs to interact with calmodulin and the ability of the respective drug to reverse the resistance of L1210 cells to vincristine.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1994

Axons of early generated neurons in cingulate cortex pioneer the corpus callosum.

The internal capsule and corpus callosum are the two major efferent axonal pathways of the mammalian neocortex. Previous studies have shown that the first cortical axons to grow through the internal capsule, the pathway from cortex to its subcortical targets, are extended by subplate neurons, which are the earliest generated neurons in the neocortex. Here, we characterize the origin of the first axons to project through the other major efferent pathway of the cortex, the midline corpus callosum, which connects the two cortical hemispheres. Using anterograde Dil tracing, we show that cortical axons first cross the midline through the nascent corpus callosum at E17. Retrograde Dil labeling from medial cortex at E18 reveals that these axons originate from a discrete group of neurons in medial (presumptive cingulate) cortex. These early callosal cells have complex morphologies with highly branched dendrites and later appear to take on a pyramidal form characteristic of callosal neurons in deep layers of cingulate cortex. 3H-thymidine birthdating demonstrates that these cells are predominantly generated on E14, making them among the earliest generated neurons in this cortical region. Injections of retrograde tracers in one cortical hemisphere at late embryonic or early postnatal ages result in substantial numbers of neurons labeled in the ipsilateral subplate, but only a few neurons labeled in the contralateral subplate. Thus, subplate neurons do not pioneer or ever project in significant numbers through the corpus callosum. We conclude that the two major efferent pathways from cortex, the corpus callosum and the internal capsule, are pioneered by developmentally and spatially distinct populations of early generated cortical neurons.

Aging↗

PubMed1990

Polychlorinated biphenyls increase fatty acid desaturation in the proliferating endoplasmic reticulum of pigeon and rat livers.

1. Polychlorinated biphenyls (PCB) are abundant and persistent pollutants in the ecosystem. Commercial mixtures (e.g. Aroclor 1254) can contain up to 80 different isomers and congeners, many of which accumulate in biological systems by the ingestion of PCB-contaminated lipid components of food chains. 2. Commercial mixtures of PCB induce, in hepatic microsomal membranes in vivo, a variety of different forms of the cytochrome P-450 components of enzyme systems involved in the metabolism of drugs and other xenobiotics, and can also induce the proliferation of this membrane. Since these microsomal enzyme systems share a number of the requirements of microsomal fatty acid desaturases, we have investigated whether the induction by PCB in vivo of cytochrome-P-450-linked enzymes in the proliferating hepatic microsomal membrane of the pigeon and the rat is accompanied by increased proportions of polyunsaturated fatty acids in this membrane. 3. The most striking changes observed 120 h after treating pigeons and rats with 1.5 mmol Aroclor 1254/kg body mass were 2.2-fold and 1.6-fold increases, respectively, in the proportion of arachidonic acid in the hepatic microsomal membrane. When the effects of this treatment on the proliferation of this membrane and increase in liver mass are taken into account, the amount of arachidonic acid in the total microsomal membrane of pigeon and rat livers increased 6.7-fold and 1.9-fold, respectively. 4. These changes were accompanied by very significant increases in pigeons and rats of the concentration of hepatic microsomal cytochrome P-450, and in the activity in microsomal protein of a wide range of cytochrome P-450-dependent enzyme involved in the metabolism of drugs and other xenobiotics. 5. This effect of PCB, of increasing in vivo the degree of unsaturation of fatty acids of hepatic microsomal membrane, appears to be a novel finding, and does not seem to have been investigated for other drugs and xenobiotics. Preliminary results have shown that the effect is accompanied by substantial increases in the total activity of delta 6 and delta 5 microsomal fatty acid desaturases converting 18:2 (9, 12) (linoleic acid) to 20:4 (5, 8, 11, 14) (arachidonic acid) [Borlakoglu, J.T., Dils, R.R., Edwards-Webb, J.D. & Walker, C.H. (1988) Biochem. Soc. Trans. 16, 1072]. 6. It is postulated that there is a significant link between increased fatty acid desaturation and the induction of cytochrome-P-450-linked enzymes, and this is discussed in terms of the mechanisms involved in the metabolism of foreign compounds.

Animals↗