Showing papers by "Laval University published in 1988"

Early events of vesicular-arbuscular mycorrhiza formation on Ri T-DNA transformed roots

Abstract: An in vitro system using Ri T-DXA transformed roots and the vesicular-arbuscular mycorrhizal fungus Gigaspora margarita Becker & Hall has been developed to study the initial events of mycorrhiza formation. Sucrose, sodium and phosphorus were found to be critical components of the medium used to establish the dual culture. Using a single spore as inoculum it was consistently possible to obtain colonization of a preselected point on the root and to time the colonization process (within 5 days). Abundant viable and aseptic spores can be obtained. The system is especially appropriate for studying the triggering of the fungal biotrophy towards the root.

Efficient and portable combined random number generators

Abstract: In this paper we present an efficient way to combine two or more Multiplicative Linear Congruential Generators (MLCGs) and propose several new generators. The individual MLCGs, making up the proposed combined generators, satisfy stringent theoretical criteria for the quality of the sequence they produce (based on the Spectral Test) and are easy to implement in a portable way. The proposed simple combination method is new and produces a generator whose period is the least common multiple of the individual periods. Each proposed generator has been submitted to a comprehensive battery of statistical tests. We also describe portable implementations, using 16-bit or 32-bit integer arithmetic. The proposed generators have most of the beneficial properties of MLCGs. For example, each generator can be split into many independent generators and it is easy to skip a long subsequence of numbers without doing the work of generating them all.

Management Theory for Small Business: Attempts and Requirements

Abstract: This paper examines the attempts that have been made to develop theories of small business management. The discussion of various contributions is structured according to task environment, organizational configuration, managerial characteristics, success-failure issues, and growth issues. Conclusions are drawn about how well these attempts meet the requirements of good theory.

Inheritance of the amount and distribution of human body fat.

Abstract: Despite recent advances, controversy continues about the inheritance of the amount and distribution of body fat. We have studied the genetic and 'cultural' (nongenetic) transmission between generations of the body mass index, sum of six skinfold measurements, percentage of body fat, fat mass, fat-free mass, and two indicators of fat distribution. These data were obtained in 1698 members of 409 families, which included the following pairs of family members: spouses, (maximum number of pairs = 348), foster parent-adopted child (322), siblings by adoption (120), first-degree cousins (95), uncle/aunt-nephew/niece (88), parent-natural child (1239), full sibs (370), dizygotic twins (69), and monozygotic twins (87). The total transmissible variance ranged from about 40 percent for the amount of subcutaneous fat to 60 percent for the pattern of subcutaneous fat distribution. Biological inheritance accounted for only 5 percent of the variance for subcutaneous fat and the body mass index, but 20 to 30 percent for the percentage of body fat, fat mass, fat-free mass, and fat distribution. These data suggest that the amount of internal fat is influenced by heredity more than the amount of subcutaneous fat. Furthermore, we consistently found that nongenetic influences are quite important in determining the amount and distribution of body fat in the population. These estimates may differ in the subpopulation of obese individuals.

Discrete image theory for horizontal electric dipoles in a multilayered medium

Abstract: The paper deals with the evaluation of Sommerfeld integrals that appear in the rigorous analysis of radiating objects embedded in a layered medium. The discrete images of a horizontal electric dipole above or within a multilayered medium, can be obtained by numerically approximating the kernel in a Sommerfeld type integral, using a series of exponential functions with different complex coefficients. The distance limitation of the image theory expression is eliminated by cooperating the contribution of the surface waves. The validity of the image theory is examined by the method of numerical integration.

Biliary Epithelial and Hepatocytic Cell Lineage Relationships in Embryonic Rat Liver as Determined by the Differential Expression of Cytokeratins, α-Fetoprotein, Albumin, and Cell Surface-exposed Components

Abstract: The differentiation patterns of epithelial cells in fetal rat liver were analyzed in situ and in primary culture by indirect immunofluorescence microscopy using polyvalent and monoclonal antibodies directed against cytokeratins with molecular weights of 55,000 (CK55), 52,000 (CK52), and 39,000 (CK39) and against vimentin, albumin, alpha-fetoprotein, and surface-exposed components of bile ductular cells (BDS7) and hepatocytes (HES6). The anti-CK52 antibody, which reacted with biliary ductal cells in the liver of adult rats (Germain et al., Cancer Res., 45:673, 1985; Germain et al., Cancer Res., 48: 368-378, 1988), stained essentially all of the epithelial cells of embryonic day 12 (E12) rat liver. The anti-BDS7 antibody reacted with a few cell foci, which enlarged and became more numerous at later developmental ages. At E12 essentially all of the cells were positive for albumin and alpha-fetoprotein but did not express HES6. In fact HES6 was not detected until E15 in cells with the morphology of immature hepatocytes. By E18 staining with anti-HES6 reached the level of that observed on adult rat hepatocytes. Liver cells isolated from E12 rats were seeded on fibronectin-treated dishes and their response to various combinations of growth- and differentiation-promoting factors was evaluated with respect to their capacity to express either the hepatocytic or the bile ductular phenotype. In medium supplemented with serum, insulin, dexamethasone, and dimethyl sulfoxide, the E12 cells were capable of differentiating in culture to mimic over a 6-day period the sequential phenotypic changes which occur in vivo during normal hepatoontogeny, namely the loss of CK52 and the appearance of HES6. In contrast, the addition of sodium butyrate to the above supplement mixture resulted in the massive expression of BDS7. To further assess the developmental potential of fetal rat liver cells toward the biliary epithelial cell lineage, the in vitro assay was performed using cells isolated from livers of E18 rats and also from 2-day-old (P2) and P14 rats. While a slight expression of BDS7 was induced in cell culture from E18 liver, essentially no expression was observed in cells from postnatal livers. These findings strongly suggest that the emerging hepatic tissue in rat embryo is composed of bipotential progenitor epithelial cells that are capable of differentiating along either the hepatocytic or biliary epithelial cell lineage. These observations constitute a clear demonstration of the plasticity of liver differentiation and also provide a striking example of environmental influences on liver progenitor cell differentiation.

Ciprofloxacin: chemistry, mechanism of action, resistance, antimicrobial spectrum, pharmacokinetics, clinical trials, and adverse reactions.

Abstract: Ciprofloxacin, considered a benchmark when comparing new fluoroquinolones, shares with these agents a common mechanism of action: inhibition of DNA gyrase. While ciprofloxacin demonstrated a fairly good activity against gram-positive bacteria, it is against gram-negative organisms that it proved to be more potent than other fluoroquinolones. It is the most active quinolone against Pseudomonas aeruginosa, with MIC90s on the order of 0.5 micrograms/ml. When given orally, ciprofloxacin exhibited 70% bioavailability and attained peak serum levels ranging between 1.5 and 2.9 micrograms/ml after a single 500-mg dose. Nineteen percent of an oral dose was excreted as metabolites in both urine and feces. In most cases, body fluids and tissue concentrations equaled or exceeded those in concurrent serum samples. In clinical trials, oral and intravenous ciprofloxacin yielded similar clinical and bacteriologic results compared to standard therapy in a wide array of systemic infections, including lower and upper urinary tract infections; gonococcal urethritis; skin, skin structure, and bone infections; and respiratory tract and gastrointestinal tract infections. Major benefits with the oral form of this quinolone are expected in chronic pyelonephritis and bone infections, and in pulmonary exacerbations in patients with cystic fibrosis. Emergence of ciprofloxacin-resistant microorganisms has been noted in clinical practice, primarily Pseudomonas aeruginosa and Staphylococcus aureus. The most frequent side effects are related to the gastrointestinal tract; but attention should be given to adverse central nervous system effects.

The glandular odontogenic cyst: an apparent entity

Abstract: This article reports 8 examples of a rare cyst of the jaws that appears to be a distinct entity and which we have named glandular odontogenic cyst because of its unusual histopathological features. This lesion occurs over a wide age range in both sexes, tends to recur, and may become very large. However, one example in this series remained small over a period of 9 years; another, somewhat atypical example, was associated with an ameloblastoma.

Estimation of the contribution of the various energy systems during maximal work of short duration.

Abstract: The aim of this experiment was to estimate the relative contribution of the various energy delivery systems during maximal exercise tests of short duration. Twenty-five males were submitted to a VO2max test and 10-, 30-, and 90-s maximal ergocycle tests. Expiratory gases were collected with a Douglas bag during the entire 30-s test and continuously monitored with an open-circuit system during the 90-s test. Estimates of the phosphagenic component represented approximately 55%-60% of the energy expenditure during the 10-s work performance. Results of the 30-s test indicated that the relative contributions of the energy systems were 23%, 49%, and 28% for the phosphagenic, glycolytic, and oxidative pathways, respectively. For the 90-s test, these estimates were 12%, 42%, and 46% for the three metabolic systems. The highest contribution of each system during the 90-s was obtained from 5 to 15 s for the phosphagenic component, from 16 to 30 s for the glycolytic, and from 61 to 75 s for the aerobic energy systems. During the 90-s test, VO2max was reached after approximately 60 s. It is concluded that the 30 and 90 s are not strictly anaerobic although they all have a large anaerobic component.

Androgens inhibit basal and estrogen-induced cell proliferation in the ZR-75-1 human breast cancer cell line

Abstract: This study describes the inhibitory effect of 5 alpha-dihydrotestosterone (5 alpha-DHT) and its precursors testosterone (T) and androst-4-ene-3,17-dione (delta 4-DIONE) on the growth of the estrogen-sensitive human breast cancer cell line ZR-75-1. In the absence of estrogens, cell proliferation measured after a 12-day incubation period was 50-60% inhibited by maximal concentrations of 5 alpha-DHT, T, or delta 4-DIONE with half-maximal effects (IC50 values) observed at 0.10, 0.15 and 15 nM, respectively. This growth inhibition by androgens was due to an increase in generation time and a lowering of the saturation density of cell cultures. The antiestrogen LY156758 (300 nM) induced 25-30% inhibition of basal cell growth, its effect being additive to that of 5 alpha-DHT. The mitogenic effect of 1 nM estradiol (E2) was completely inhibited by increasing concentrations of 5 alpha-DHT with a potency (IC50 = 0.10 nM) similar to that measured when the androgen was used alone. E2 had a more rapid effect on cell proliferation than 5 alpha-DHT, the latter requiring at least 5 to 6 days to exert significant growth inhibition. As found in the absence of estrogens, maximal inhibition of cell proliferation in the presence of E2 was achieved by the combination of the antiestrogen and 5 alpha-DHT. Supraphysiological concentrations of E2 (up to 1 microM) were needed to completely reverse the growth inhibitory effect of a submaximal concentration of 5 alpha-DHT (1 nM). The antiproliferative effect of androgens was competitively reversed by the antiandrogen hydroxyflutamide, thus indicating an androgen receptor-mediated mechanism. The present data suggest the potential benefits of an androgen-antiestrogen combination therapy in the endocrine management of breast cancer.

Basal forebrain cholinergic and noncholinergic projections to the thalamus and brainstem in cats and monkeys

Abstract: The projections of basal forebrain neurons to the thalamus and the brainstem were investigated in cats and primates by using retrograde transport techniques and choline acetyltransferase (ChAT) immunohistochemistry. In a first series of experiments, the lectin wheat germ-agglutinin conjugated with horseradish peroxidase (WGA-HRP) was injected into all major sensory, motor, intralaminar, and reticular (RE) thalamic nuclei of cats and into the mediodorsal (MD) and pulvinar-lateroposterior thalamic nuclei of macaque monkeys. In cats numerous neurons of the vertical and horizontal limbs of the diagonal band nucleus and the substantia innominata (SI), including its rostromedial portion termed the ventral pallidum (VP), were retrogradely labeled after WGA-HRP injections in the rostral pole of the RE complex, the MD, and anteroventral/anteromedial (AV/AM) thalamic nuclei. Fewer retrogradely labeled cells were observed in the same areas after injections in the ventromedial (VM) thalamic nucleus, and none or very few after other thalamic injections. After RE, MD, and AV/AM injections, 7-20% of all retrogradely labeled cells in the basal forebrain were also ChAT positive, while none of the retrogradely labeled neurons following VM injections displayed ChAT immunoreactivity. The basal forebrain projection to the MD nucleus was shown to arise principally from VP in both cats and macaque monkeys. In a second series of experiments performed in cats, injections of WGA-HRP in the brainstem peribrachial (PB) area comprising the pedunculopontine nucleus led to retrograde labeling of a moderate number of neurons in the lateral part of the VP, SI, and preoptic area (POA), only a few of which displayed ChAT immunoreactivity. In addition, a large number of retrogradely labeled cells were observed in the bed nuclei of the anterior commissure and stria terminalis after PB injections. In a third series of experiments, the use of the retrograde double-labeling method with fluorescent tracers in squirrel monkeys allowed us to identify a significant number of basal forebrain neurons sending axon collaterals to both the RE thalamic nucleus and PB brainstem area, while no double-labeled neurons were disclosed after injections confined to the ventral anterior/ventral lateral (VA/VL) thalamic nuclei and PB area or following injections in the cerebral cortex and PB area. Our findings reveal the existence of cholinergic and noncholinergic basal forebrain projections to the thalamus and the brainstem in both cats and macaque monkeys. We suggest that these projections may play a crucial role in the control of thalamic functions in mammals.

A comparison of the Fishbein and Ajzen and the Triandis attitudinal models for the prediction of exercise intention and behavior.

Abstract: The main purpose of the study was to compare the efficiency of the Fishbein and Ajzen and the Triandis models to predict (1) the intention to participate regularly in some physical activities during free time within a 3-week period and (2) the exercise behavior within these 3 weeks among a group of 166 subjects, aged 22 to 65 years. Our results show that the Triandis model was as efficient as the Fishbein and Ajzen model in predicting the exercise behavior. However, the results obtained from the Triandis model demonstrate the importance of the habit of exercising in predicting the exercise behavior. Moreover, the Triandis model was superior to the Fishbein and Ajzen model in explaining behavioral intention. Of particular interest was the salience of the affective, social, and personal belief components of the Triandis model. In addition, from a practical perspective, this comparative study showed that (1) to exercise regularly is perceived as hard work, and (2) individuals believe that it is their own responsibility to exercise or not to exercise.

Androgenic activity of dehydroepiandrosterone and androstenedione in the rat ventral prostate

Abstract: In order to assess the androgenic potency of physiological plasma concentrations of the adrenal steroids dehydroepiandrosterone (DHEA) and androstenedione (delta 4-dione) in the rat prostate, these two steroids were released from Silastic tubings of appropriate length and size in castrated male rats. Implants of DHEA led to plasma levels of DHEA and 5-androsten-3 beta,17 beta-diol covering the range of concentrations found in adult men while no significant change was observed in plasma levels of delta 4-dione, testosterone and dihydrotestosterone (DHT). delta 4-Dione implants, on the other hand, led to a parallel increase in plasma delta 4-dione and testosterone levels at all doses used while plasma DHT only increased at supraphysiological doses of delta 4-dione. At plasma concentrations comparable to those found in adult men; delta 4-dione (0.8 ng/ml) and DHEA (3.4 ng/ml) stimulated prostate weight 3.7- and 2.1-fold, respectively. In the same groups, prostatic DHT levels were elevated at 4.48 +/- 0.05 and 2.70 +/- 0.73 ng/g tissue, respectively. A close parallelism was observed between prostatic DHT levels and prostatic weight in all groups. The present data show that in the rat, a species having no significant secretion of adrenal androgens, plasma concentrations of DHEA and delta 4-dione maintained within the range of those found in adult men are efficiently converted into DHT and act as potent androgenic stimuli in prostatic tissue. The castrated rat bearing Silastic implants releasing constant and predetermined amounts of adrenal steroids offers a good model to study the recently identified role of adrenal steroids in peripheral tissues.

Specific properties of epithelial and stromal cells from the endometrium of cows

Abstract: Epithelial and stromal cells were isolated from endometrium of cyclic heifers by enzymic dispersion. These cells exhibited specific morphological and functional properties. Epithelial cells appeared cuboidal or columnal and showed contact inhibition as they reached confluence. Stromal cells were fibroblast-like and enlarged at the time of confluence after which they overgrew in multiple layers. The presence of specific receptors for PGE-2 and beta-adrenergic catecholamines (isoproterenol) was estimated by activation of adenylate cyclase. Stromal cells had more adenylate cyclase activity (P less than 0.01) than did epithelial cells before (basal) and after stimulation with guanosine triphosphate (GTP) and PGE-2. However, epithelial cells were much more responsive to isoproterenol (P less than 0.01). Treatment of cultured cells with indomethacin to block PG synthesis increased the sensitivity and maximal response to PGE-2 in stromal (P less than 0.01) but not in epithelial (P greater than 0.1) cells. The latter result suggested autologous desensitization of the PGE-2 response resulting from synthesis of PGs in cultured cells. Both cell types synthesized PGs in culture: PGF-2 alpha was synthesized in greater quantity in epithelial than in stromal cells (P less than 0.05) while stromal cells synthesized more PGE-2 than did epithelial cells (P less than 0.001). Endometrial cells separated in this way should prove useful for study of their specific role in the processes of implantation and maternal recognition of pregnancy.

Identification of sterol acceptors that stimulate cholesterol efflux from human spermatozoa during in vitro capacitation.

Abstract: The nature of cholesterol-binding proteins acting upon human spermatozoa during in vitro capacitation was determined by measuring the efflux of [3H]cholesterol and of [3H]cholesteryl sulfate from labeled spermatozoa. Efflux of [3H]sterols was stimulated when the labeled gametes were incubated in Ham's F-10 medium supplemented with female serum or follicular fluid. Upon centrifugation of capacitated spermatozoa and application of the supernatant to density-gradient ultracentrifugation for lipoprotein analysis, both [3H]cholesterol and [3H]cholesteryl sulfate were found to be carried by very-low-density lipoproteins (VLDL), low-density lipoproteins (VLDL), high-density lipoproteins (HDL), as well as the albumin fraction (d > 1.21) in serum. When the capacitation medium was supplemented with follicular fluid, the [3H]sterols were bound to HDL's and to the albumin fraction; when the latter fraction was analysed by molecular sieve chromatography, 60–70% of the radioactivity eluted in fractions with a mean molecular weight corresponding to that of human serum albumin. Sperm cholesterol efflux was also stimulated when serum or follicular fluid was added to a simplified medium (50 mM Tris-HCl, 0.56% NaCl, pH 7.8); efflux of [3H]cholesterol from labeled gametes progressed in a time-dependent manner, but was low in the absence of serum components. The [3H]cholesterol/cholesterol ratios were higher in the albumin and HDL fractions, indicating some degree of specificity of these sterol acceptors. It was observed that follicular fluid albumin has a [3H]sterol binding capacity that is 2—3-fold higher than that of serum albumin. Commercial human serum albumin also promoted sperm cholesterol efflux. These results provide new information concerning those components of follicular fluid which may play a role in human sperm capacitation and provide further support for the concept that loss of cholesterol from the sperm plasma membrane is an important component of the capacitation process.

Importance of physical and biological settlement cues used at different spatial scales by the larvae of Semibalanus balanoides

Abstract: The settling cues used by larvae of Semibalanus balanoides (L.) were examined at large (1 m), medium (1 mm), and small (<300 μm) spatial scales, corresponding roughly to choices made during broad and close exploration and final inspection within the settling zone. The experiments were carried out at two locations in Canada in May and June 1984. Samples of substratum surfaces from above (n=87 sites unselected by cyprids) and below (n=84 sites selected by cyprids) the upper limit of the barnacle zone were characterized according to 13 quantitative and semi-quantitative variables (diatom cover, macroalgae, detritus) using scanning electron microscopy (SEM). The data were analysed using a stepwise logistic regression. At the large scale, the presence of an alga (Urospora wormskjoldii Mertens) in the upper uncolonized zone and a diatom (Achnantes parvula Kutzing) within the settling zone are potential settlement cues. At the medium scale in the settling zone, larvae select clean sites, devoid of detritus and diatoms or on which detrital matter, when present, is of finer texture than on the unchosen sites within the settling zone. At the smallest scale (<300 μm, equal to the average maximum width of the larvae), we tested the hypothesis that the larva seeks optimal microheterogeneity (presumably providing good adhesion). Microheterogeneity of the surface was measured immediately under the larva, around the settling organs, the antennules. Our results show that such surface microheterogeneity is significantly greater and the vertical center of gravity of the surface significantly lower on the sites selected by the cyprids than on the unselected contiguous sites. Fractal measurements carried out on selected and contiguous unselected surfaces indicate that larvae discriminate microheterogeneity levels below a step length of 35 μm, a value approximately the size of the diameter of the antennular discs (40 μm), which are used to explore the substratum and attach.

Influence of substratum heterogeneity and settled barnacle density on the settlement of cypris larvae

Abstract: On the Atlantic coast of Canada, Semibalanus balanoides (L.) is widely distributed in the mid-intertidal zone, whereas in the Gulf of St. Lawrence, this species is mostly limited to crevices. We tested the hypothesis of regional differences in microhabitat selection by barnacle larvae at settlement in 1984 and 1985 at St. Andrews, New Brunswick, Canada. Since larvae settle in microhabitats already colonized by adults, the relative influence of settled barnacle density and of different scales of substratum heterogeneity on settlement were evaluated experimentally at Capucins, Quebec, (Gulf of St. Lawrence) and at St. Andrews, New Brunswick (Atlantic coast). On a large scale (>10 cm deep crevices) of heterogeneity, results show that, in the Gulf, cypris larvae settled nearly exclusively (93%) in natural crevices rather than on adjacent horizontal surfaces. On the Atlantic coast, settlement was more important outside than inside of crevices, when the substrata were either natural or artificial. This result is unique and contrasts sharply with all known reports on barnacle settlement in relation to surface contour. The influence of barnacle density on settlement was greater than that of large scale heterogeneity. On a small scale (<1.5 cm deep cracks), the presence of conspecifics had a stronger effect on settlement than heterogeneity in both regions. Field observations showed a relationship between larval settlement density and percentage of adult cover. Settlement increased up to 22 or 30% (Gulf and Atlantic coast) of adult cover and decreased afterwards. The results confirm the hypothesis of larval selection for cryptic habitats in the Gulf and the opposite behaviour (preferences for horizontal surfaces) on the Atlantic coast. This microhabitat selection is apparent at large scales of heterogeneity, whereas at small scales, the presence of conspecifics is the predominant factor.

The nature and role of learning in the orientation and migratory behavior of fishes

Abstract: Fish migration may be viewed as the product of two processes; the selection and tracking of optimal environmental conditions through time and space, and the use of predictive information about environmental structure to bias movements towards a goal. The establishment and maintenance of directional bias is based on the interaction of experience and instinct. The preoccupation of much fish orientation research with innate fixed patterns of behavior on one hand and hydrodynamics on the other has led us to underestimate the possibility that orientation is a flexible process relying on developmental sequences, calibration of the motor-sensory interaction based on experience and the learning of environmental pattern. Evidence illustrating how experience and learning may influence the direction of movement and how the goal is recognized is presented according to two general categories: (a) imprinting and early experience and (b), spatial learning, including the social transmission of migratory routes and directions. In the first category, the olfactory hypothesis of salmon homing is briefly reviewed and new data presented describing olfactory imprinting in Atlantic salmon,Salmo salar. In the second category, evidence is presented demonstrating the modifiability of sun-compass orientation and the ability of some fish species to learn the spatial distribution of landmarks. The role of social transmission in the migration of coral reef fishes is reviewed. The possible role of these learning phenomena in the formation of familiar area maps, route-based and location-based navigation and the critical distance factor is considered. The relationship between life history and the nature of learning in migratory orientation is discussed

Gambling behaviors among high school students in the Quebec area

Abstract: A sample of 1,612 adolescents from nine different high schools in the region of Quebec city completed a questionnaire developed by Lesieur and Klein (1987) concerning their gambling behavior. Seventy-six percent had gambled once in their lifetime, 65% placed a bet in the last year and 24% gambled at least once a week. Of those who had gambled, 5.6% wanted to stop playing but reported they were unable to do so, while 1.7% were considered to be pathological gamblers. Practical and social implications of these results are discussed.

Promotion of Growth and Differentiation of Rat Ductular Oval Cells in Primary Culture

Abstract: Oval cells emerging in rat liver at the early period of 3-methyl-4-dimethylaminoazobenzene treatment constitute a mixed epithelial cell compartment with respect to α-fetoprotein (AFP) and cytokeratin differential expression, and include a subpopulation which exhibits a phenotype intermediate between ductular cells and hepatocytes (Germain et al. , Cancer Res., 45: 673–681, 1985). In the present study we have examined the developmental potential of ductular oval cells in primary culture and after in vivo transfer. The use of monoclonal and polyclonal antibodies directed against cytokeratins of M r 39,000 (CK39), 52,000 (CK52), and 55,000 (CK55) and vimentin, and also monoclonal antibodies against exposed surface components of oval cells (BDS7) and normal hepatocytes (HES6) allowed us to establish the ductular phenotype of the oval cells. A highly enriched preparation of oval cells was obtained by perfusion/digestion of the liver with collagenase, treatment of the cell suspension with trypsin and DNase, selective removal of hepatocytes by panning using the anti-HES6 antibody, and cell separation by isopyknic centrifugation in a Percoll gradient. The procedure yielded about 8 × 107 cells, of which 95% expressed CK39, CK52, and BDS7, 84% γ-glutamyl transpeptidase, and 5% albumin and AFP. The primary response of cultured oval cells to various combinations of growth and differentiation promoting factors was evaluated with respect to their capacity to initiate DNA synthesis as measured by [3H]thymidine labeling from day 1 to 3, and/or to produce albumin and AFP and express tyrosine aminotransferase. Culture in the presence of either serum or clot blood extract resulted in a low proliferative activity with less than 5% of the nuclei being labeled. Over a 5-day period, fusion of a large portion of the oval cells led to multinucleated cells. When the cells were cultured in the presence of an elaborate combination of supplements [minimum essential medium containing 1 mm pyruvate, 0.2 mm aspartate, 0.2 mm serine, 1 mm tyrosine, 1 mm proline, 1 mm phenylalanine and supplemented with 20% clot blood extract, 10 ng/ml oxidized bile acids, 17 µm bilirubin, 10 ng/ml cholera toxin, 1 µm dexamethasone, 2.5 µg/ml insulin, 50 mm β-mercaptoethanol, and 5 µg/ml transferrin (medium MX)], the labeling index increased to around 30% and the level of cell fusion greatly decreased. The addition of dimethyl sulfoxide further enhanced the initiation of DNA synthesis, while sodium butyrate acted as an inhibitor. Cell morphology varied depending on the combinations of factors used. Most of the oval cells still expressed the three cytokeratins, BDS7, γ-glutamyl transpeptidase, and some vimentin after 5 days in culture. Culture in medium MX in the absence of sodium butyrate resulted in the emergence of a small subpopulation of BDS7 negative/γ-glutamyl transpeptidase positive fusiform cells, which by day 5 constituted a distinct epithelial cell population that expressed CK39 and vimentin and which could be subcultured. The addition of dimethyl sulfoxide or sodium butyrate at day 1 in the presence of dexamethasone differentially modified the phenotype of the ductular oval cells cultured in growth factor-supplemented medium. Of major interest was the finding that the presence of sodium butyrate and dexamethasone led to a massive production of albumin over a 3-day period and a progressive induction of tyrosine aminotransferase activity. Fourteen days after the injection of freshly isolated oval cells into the fat pads of syngeneic rats, the cells were arranged as clusters similar to bile ductular structures. These findings indicate that oval cells isolated from 3-methyl-4-dimethylaminoazobenzene-treated rat liver which exhibit the phenotypic characteristics of bile ductular epithelial cells after in vivo transfer, produce albumin, cease AFP production, and express tyrosine aminotransferase activity in primary mass culture, properties of facultative hepatocytic precursors.