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Topic:In Vitro Research

In vitro research involving horses refers to the study of equine cells, tissues, or biological molecules outside their normal biological context, typically in controlled laboratory environments. This research approach allows scientists to investigate cellular processes, molecular interactions, and the effects of various treatments without the ethical and logistical complexities of in vivo studies. In vitro studies contribute to understanding equine physiology, pathology, and pharmacology by providing insights into cellular responses to pathogens, drugs, and other stimuli. This page compiles peer-reviewed research studies and scholarly articles that explore various in vitro methodologies and their applications in equine science, including cell culture techniques, molecular assays, and drug efficacy testing.
Equine coronavirus induces apoptosis in cultured cells.
Veterinary microbiology    December 5, 2007   Volume 129, Issue 3-4 390-395 doi: 10.1016/j.vetmic.2007.11.034
Suzuki K, Matsui Y, Miura Y, Sentsui H.Equine coronavirus (ECoV) was first isolated from a diarrheic foal and was found genetically similar to group II coronaviruses. However, its pathological characteristics were not adequately investigated. In our preliminary in vitro investigation, ECoV-induced cell death was observed in bovine kidney-derived MDBK cells. Based on this finding, we investigated whether the ECoV-induced CPE was apoptosis. Following ECoV infection, MDBK cells showed morphological changes such as cell rounding and detachment from the culture surface. Moreover, syncytium formation was observed as the other type of cyt...
Equine infectious anemia virus entry occurs through clathrin-mediated endocytosis.
Journal of virology    December 5, 2007   Volume 82, Issue 4 1628-1637 doi: 10.1128/JVI.01754-07
Brindley MA, Maury W.Entry of wild-type lentivirus equine infectious anemia virus (EIAV) into cells requires a low-pH step. This low-pH constraint implicates endocytosis in EIAV entry. To identify the endocytic pathway involved in EIAV entry, we examined the entry requirements for EIAV into two different cells: equine dermal (ED) cells and primary equine endothelial cells. We investigated the entry mechanism of several strains of EIAV and found that both macrophage-tropic and tissue culture-adapted strains utilize clathrin-coated pits for entry. In contrast, a superinfecting strain of EIAV, EIAV(vMA-1c), utilizes ...
Modeling trophoblast differentiation using equine chorionic girdle vesicles.
Placenta    December 3, 2007   Volume 29, Issue 2 158-169 doi: 10.1016/j.placenta.2007.10.005
de Mestre AM, Bacon SJ, Costa CC, Leadbeater JC, Noronha LE, Stewart F, Antczak DF.The chorionic girdle of the equine conceptus is comprised of specialized trophoblast cells which, at day 36-38 of equine pregnancy, gain an invasive phenotype and invade the endometrium to form endometrial cups. Studies of equine endometrial cups remain difficult to perform because of the invasive techniques required to obtain cup tissue and because sampling requires termination of the pregnancy. In this study we developed a system to model trophoblast differentiation and trophoblast-immune interactions in vitro and in vivo. We utilized a method of culturing chorionic girdle pieces in serum-fr...
Lactobacillus hayakitensis sp. nov., isolated from intestines of healthy thoroughbreds.
International journal of systematic and evolutionary microbiology    December 1, 2007   Volume 57, Issue Pt 12 2836-2839 doi: 10.1099/ijs.0.65135-0
Morita H, Shiratori C, Murakami M, Takami H, Kato Y, Endo A, Nakajima F, Takagi M, Akita H, Okada S, Masaoka T.Two strains, KBL13(T) and GBL13, were isolated as one of intestinal lactobacilli from the faecal specimens from different thoroughbreds of the same farm where they were born in Hokkaido, Japan. They were Gram-positive, facultatively anaerobic, catalase-negative, non-spore-forming and non-motile rods. KBL13(T) and GBL13 homofermentatively metabolize glucose, and produce lactate as the sole final product from glucose. The 16S rRNA gene sequence, DNA-DNA hybridization, DNA G+C content and biochemical characterization indicated that these two strains, KBL13(T) and GBL13, belong to the same species...
Analysis of factor VIII mediated suppression of lentiviral vector titres.
Gene therapy    November 29, 2007   Volume 15, Issue 4 289-297 doi: 10.1038/sj.gt.3303080
Radcliffe PA, Sion CJ, Wilkes FJ, Custard EJ, Beard GL, Kingsman SM, Mitrophanous KA.Effective gene therapy for haemophilia A necessitates a vector system that is not subject to a pre-existing immune response, has adequate coding capacity, gives long-term expression and preferably can target non-dividing cells. Vector systems based on lentiviruses such as equine infectious anaemia virus (EIAV) fulfil these criteria for the delivery of factor VIII (FVIII). We have found that B domain-deleted (BDD) FVIII protein inhibits functional viral particle production when co-expressed with the EIAV vector system. Although particle numbers (as measured by reverse transcriptase activity) ar...
A soluble secreted glycoprotein (eCLCA1) is overexpressed due to goblet cell hyperplasia and metaplasia in horses with recurrent airway obstruction.
Veterinary pathology    November 28, 2007   Volume 44, Issue 6 901-911 doi: 10.1354/vp.44-6-901
Range F, Mundhenk L, Gruber AD.The equine putative chloride channel protein eCLCA1 is thought to be critically involved in the pathogenesis of recurrent airway obstruction (RAO) via modulation of the hydration of airway mucins. A recent study revealed a strong increase of eCLCA1 messenger ribonucleic acid (mRNA) in the lungs of horses with RAO. In this study, eCLCA1 protein and mRNA expression were quantified in airway goblet cells of 9 horses affected with RAO and 9 control horses by using immunohistochemistry and laser microdissection followed by real-time quantitative reverse transcription polymerase chain reaction, resp...
Effects of oxygen exposure and gentamicin on stallion semen stored at 5 and 15 degrees C.
Reproduction in domestic animals = Zuchthygiene    November 27, 2007   Volume 43, Issue 3 261-266 doi: 10.1111/j.1439-0531.2007.00888.x
Price S, Aurich J, Davies-Morel M, Aurich C.This study was undertaken to investigate the effects of storage of stallion semen in a defined milk protein extender at 5 and 15 degrees C under either anaerobic or aerobic conditions, with or without addition of the antibiotic gentamicin. Semen samples were collected from eight fertile stallions and stored for 96 h (day 0-4) and assessed daily for motility, velocity and membrane integrity (viability) using a CASA system. Samples for bacteriology assessment were taken on day 2 of storage. No significant (p > 0.05) differences in motility, velocity or viability were observed between treatmen...
Tissue engineering: chondrocyte culture on type 1 collagen support. Cytohistological and immunohistochemical study.
Journal of tissue engineering and regenerative medicine    November 27, 2007   Volume 1, Issue 2 158-159 doi: 10.1002/term.15
Negri S, Fila C, Farinato S, Bellomi A, Pagliaro PP.The scope of our study is to evaluate the possibility of cultivating and expanding human chondrocytes and seeding them on pure equine type I collagen support. Our results show that human articular cartilaginous cells can multiply and grow on type I collagen substrate with production of extracellular matrix. This type of chondrocyte culture on a support can be used for repairing cartilaginous lesions since they show a correct morphology (evaluated by cytological and histological methods) and a suitable differentiation and phenotype as shown by Alcian PAS staining to indicate the presence of muc...
Development of an in vitro three dimensional loading-measurement system for long bone fixation under multiple loading conditions: a technical description.
Journal of orthopaedic surgery and research    November 24, 2007   Volume 2 21 doi: 10.1186/1749-799X-2-21
Janicek JC, Carson WL, Wilson DA.The purpose of this investigation was to design and verify the capabilities of an in vitro loading-measurement system that mimics in vivo unconstrained three dimensional (3D) relative motion between long bone ends, applies uniform load components over the entire length of a test specimen, and measures 3D relative motion between test segment ends to directly determine test segment construct stiffness free of errors due to potting-fixture-test machine finite stiffness.Intact equine cadaveric radius bones, which were subsequently osteotomized/ostectomized and instrumented with bone plates were su...
Development of a fluorescent-microsphere immunoassay for detection of antibodies specific to equine arteritis virus and comparison with the virus neutralization test.
Clinical and vaccine immunology : CVI    November 21, 2007   Volume 15, Issue 1 76-87 doi: 10.1128/CVI.00388-07
Go YY, Wong SJ, Branscum AJ, Demarest VL, Shuck KM, Vickers ML, Zhang J, McCollum WH, Timoney PJ, Balasuriya UB.The development and validation of a microsphere immunoassay (MIA) to detect equine antibodies to the major structural proteins of equine arteritis virus (EAV) are described. The assay development process was based on the cloning and expression of genes for full-length individual major structural proteins (GP5 amino acids 1 to 255 [GP5(1-255)], M(1-162), and N(1-110)), as well as partial sequences of these structural proteins (GP5(1-116), GP5(75-112), GP5(55-98), M(88-162), and N(1-69)) that constituted putative antigenic regions. Purified recombinant viral proteins expressed in Escherichia col...
Diagnostic real-time PCR assay for the quantitative detection of Theileria equi from equine blood samples.
Veterinary parasitology    November 17, 2007   Volume 151, Issue 2-4 158-163 doi: 10.1016/j.vetpar.2007.10.023
Kim CM, Blanco LB, Alhassan A, Iseki H, Yokoyama N, Xuan X, Igarashi I.We developed a TaqMan real-time polymerase chain reaction (PCR) assay for the quantitative detection of Theileria equi from the in vitro-cultured parasite and field blood samples collected from horses living in Ghana and Brazil. The detection limit for the assay was determined to be 1.5 parasites/microl per sample, and the quantitative capacity was demonstrated using the in vitro-cultured parasite. For field applications, the real-time PCR assay was compared to a previously established nested PCR assay used as the gold standard for the real-time PCR assay. Of 65 field blood samples, 46 samples...
Expression of cell-surface antigens and embryonic stem cell pluripotency genes in equine blastocysts.
Stem cells and development    November 15, 2007   Volume 16, Issue 5 789-796 doi: 10.1089/scd.2007.0032
Guest DJ, Allen WR.Embryonic stem-like (ES-like) cells have now been derived from the inner cell mass (ICM) of horse embryos at the blastocyst stage. Because they have been shown to express cell-surface antigens found in both human and mouse ES cells, the present study investigated gene expression patterns in day-7 horse blastocysts from which the horse ES-like cells had been derived originally. The genes studied included Oct-4, stage-specific embryonic antigen-1 (SSEA-1), SSEA-3, SSEA-4, tumor rejection antigen-1-60 (TRA-1-60), TRA-1-81, and alkaline phosphatase activity, and whereas all three of the SSEA antig...
Differential anti-inflammatory and chondroprotective effects of simulated digests of indomethacin and an herbal composite (Mobility) in a cartilage explant model of articular inflammation.
Journal of veterinary pharmacology and therapeutics    November 10, 2007   Volume 30, Issue 6 523-533 doi: 10.1111/j.1365-2885.2007.00905.x
Pearson W, Orth MW, Lindinger MI.Herbs are an increasingly popular treatment option for horses with cartilage inflammation, despite a relative paucity of research demonstrating efficacy. The research objective was to evaluate the differential anti-inflammatory and chondroprotective efficacy of a simulated digest of indomethacin and a commercially available herbal product in a cartilage model of osteoarthritis. Cartilage explant was integrated with simulated digestion of indomethacin and the herbal product in order to account, at least in part, for the actions of major digestive enzymes and pH. The resulting digests were ultra...
Histomonas meleagridis (Parabasala, Trichomonadea, Monocercomonadidae): presence of natural agglutinins in horse serum.
Parasitology research    November 9, 2007   Volume 102, Issue 3 365-369 doi: 10.1007/s00436-007-0770-x
Hu J, Brooks M, Fuller AL, Armstrong P, McDougald LR.Cultured Histomonas meleagridis cells were readily agglutinated in vitro by horse serum at concentrations as low as 5%, although clumping was more rapid and prominent at 15% or higher. For observation of clumping, the cultured organisms were washed twice in Hanks balanced solution (HBSS) by centrifugation (1,000 x g for 15 min) and filtered through glass wool. The test sera were added and the mixture incubated in a Petri plate or 24-well culture plates at r.t. for 15-30 min. Formation of clumps was time- and concentration-dependent. Gentle agitation hindered agglutination at low serum concentr...
Monoclonal antibodies against the nucleocapsid proteins of henipaviruses: production, epitope mapping and application in immunohistochemistry.
Archives of virology    November 5, 2007   Volume 153, Issue 2 273-281 doi: 10.1007/s00705-007-1079-x
Xiao C, Liu Y, Jiang Y, Magoffin DE, Guo H, Xuan H, Wang G, Wang LF, Tu C.Four monoclonal antibodies (mAbs) were generated by immunizing BALB/C mice with recombinant nucleocapsid protein (N) of Nipah virus (NiV) and Hendra virus (HeV) expressed in E. coli. Two mAbs each were obtained for the HeV N and NiV N, respectively. All four mAbs displayed specific reactivity with the recombinant N proteins of both viruses by western blot, which was further confirmed by immunofluorescent antibody assay using fixed insect cells infected with recombinant baculoviruses expressing either the HeV or NiV N protein. Epitope mapping using a 12-mer random peptide phage display library ...
Detection of “apoptosis-like” changes during the cryopreservation process in equine sperm.
Journal of andrology    October 31, 2007   Volume 29, Issue 2 213-221 doi: 10.2164/jandrol.107.003640
Ortega-Ferrusola C, Sotillo-Galán Y, Varela-Fernández E, Gallardo-Bolaños JM, Muriel A, González-Fernández L, Tapia JA, Peña FJ.The kinematics of the appearance of apoptotic markers was studied by flow cytometry and immunoblot assays in equine spermatozoa subjected to freezing and thawing. Caspase activity, low mitochondrial membrane potential, and increases in sperm membrane permeability were observed in all of the phases of the cryopreservation procedure. Freezing and thawing caused an increase in membrane permeability and changes in the pattern of caspase activity; decreases in mitochondrial membrane potential were observed after centrifugation and cooling to 4 degrees C and after freezing and thawing. It is propose...
The equine TLR4/MD-2 complex mediates recognition of lipopolysaccharide from Rhodobacter sphaeroides as an agonist.
Journal of endotoxin research    October 25, 2007   Volume 13, Issue 4 235-242 doi: 10.1177/0968051907083193
Lohmann KL, Vandenplas ML, Barton MH, Bryant CE, Moore JN.Lipopolysaccharide (LPS) antagonists inhibit the response of inflammatory cells to LPS, presumably by competitive inhibition, and may be of therapeutic value in the treatment of endotoxemia and sepsis. The inhibitory effects of some LPS antagonists are restricted to certain host species, however, as the same molecules can have significant endotoxic activity in other species. This species-specific recognition appears to be mediated by Toll-like receptor 4 (TLR4) and/or MD-2. We have shown previously that LPS from Rhodobacter sphaeroides ( RsLPS) is an LPS antagonist in human cells but an agonis...
Characterization of monoclonal antibodies to equine interleukin-10 and detection of T regulatory 1 cells in horses.
Veterinary immunology and immunopathology    October 24, 2007   Volume 122, Issue 1-2 57-64 doi: 10.1016/j.vetimm.2007.10.012
Wagner B, Hillegas JM, Brinker DR, Horohov DW, Antczak DF.Interleukin-10 (IL-10) terminates inflammatory immune responses and inhibits activation and effector functions of T-cells, monocytes, macrophages and dendritic cells. IL-10 has also been found to be a key cytokine expressed by subpopulations of regulatory T-cells. In this report, we describe the generation and characterization of three monoclonal antibodies (mAbs) to equine IL-10. The antibodies were found to be specific for equine IL-10 using different recombinant equine cytokine/IgG fusion proteins. Two of the anti-equine IL-10 mAbs were selected for ELISA to detect secreted IL-10 in superna...
Effects of unfractionated and fractionated heparins on myeloperoxidase activity and interactions with endothelial cells: possible effects on the pathophysiology of equine laminitis.
Veterinary journal (London, England : 1997)    October 17, 2007   Volume 178, Issue 1 62-69 doi: 10.1016/j.tvjl.2007.08.033
de la Rebière G, Franck T, Deby-Dupont G, Salciccia A, Grulke S, Péters F, Serteyn D.As heparins are sometimes used to prevent equine laminitis, the interactions between equine neutrophil myeloperoxidase (MPO), unfractionated (UFH) and fractionated low molecular weight (LMWH) heparins and digital endothelium have been investigated. The effects of the heparins on purified equine MPO activity were tested by immunocapture followed by enzymatic detection. Endothelium-MPO interactions were assessed by measuring total and active MPO uptake by arterial and venous digital endothelial cells in culture with or without the addition of heparins. A dose-dependent MPO inhibition by UFH and ...
Equine umbilical cord blood contains a population of stem cells that express Oct4 and differentiate into mesodermal and endodermal cell types.
Journal of cellular physiology    October 12, 2007   Volume 215, Issue 2 329-336 doi: 10.1002/jcp.21312
Reed SA, Johnson SE.Mesenchymal stem cells (MSCs) offer promise as therapeutic aids in the repair of tendon, ligament, and bone damage suffered by sport horses. The objective of the study was to identify and characterize stem-like cells from newborn foal umbilical cord blood (UCB). UCB was collected and MSC isolated using human reagents. The cells exhibit a fibroblast-like morphology and express the stem cell markers Oct4, SSEA-1, Tra1-60 and Tra1-81. Culture of the cells in tissue-specific differentiation media leads to the formation of cell types characteristic of mesodermal and endodermal origins. Chondrogenic...
Heterophile antibodies in horse plasma interfering in an enzyme-linked immunosorbent assay.
Veterinary research communications    October 10, 2007   Volume 31 Suppl 1 165-168 doi: 10.1007/s11259-007-0023-6
Borromeo V, Berrini A, Gaggioli D, Secchi C.No abstract available
A comparison of equine and bovine sera as sources of lipopolysaccharide-binding protein activity in equine monocytes incubated with lipopolysaccharide.
Veterinary immunology and immunopathology    October 10, 2007   Volume 121, Issue 3-4 275-280 doi: 10.1016/j.vetimm.2007.10.002
Figueiredo MD, Salter CE, Hurley DJ, Moore JN.Lipopolysaccharide-binding protein (LBP) is an acute phase protein that binds the lipid A moiety of lipopolysaccharide (LPS) and transfers LPS monomers to soluble CD14 in plasma or membrane bound CD14 on mononuclear phagocytes. The result of these interactions is activation of the TLR4 receptor complex, and the synthesis and release of inflammatory mediators. Inclusion of LBP in cellular assays increases the sensitivity of cells expressing CD14 to LPS. Therefore, the objectives of this study were to (1) compare differentially treated sera from cattle and horses as sources of LBP activity using...
Establishment of a novel equine cell line for isolation and propagation of equine herpesviruses.
The Journal of veterinary medical science    October 6, 2007   Volume 69, Issue 9 989-991 doi: 10.1292/jvms.69.989
Maeda K, Yasumoto S, Tsuruda A, Andoh K, Kai K, Otoi T, Matsumura T.In the present study, an equine-derived cell line was established by transfecting primary fetal horse kidney (FHK) cells with expression plasmid encoding simian virus 40 (SV40) large T antigen and then cloning them by limiting dilution. The cloned cell line, named FHK-Tcl3, grew well and could be propagated over 30 times by splitting them 1:3. Equine herpesvirus (EHV)-1 and EHV-4 replicated well in FHK-Tcl3. EHV-2 and EHV-4 were isolated from samples collected from horses in the field using FHK-Tcl3, and EHV-3 also propagated in FHK-Tcl3. These results indicated that this novel cell line, FHK-...
In vitro susceptibility patterns of fungi associated with keratomycosis in horses of the northeastern United States: 68 cases (1987-2006).
Journal of the American Veterinary Medical Association    October 6, 2007   Volume 231, Issue 7 1086-1091 doi: 10.2460/javma.231.7.1086
Ledbetter EC, Patten VH, Scarlett JM, Vermeylen FM.To determine in vitro susceptibility patterns of fungi associated with keratomycosis in horses in the northeastern United States and compare those patterns with results of studies from other geographic regions. Methods: Retrospective case series. Methods: 68 horses with keratomycosis. Methods: Medical records of horses with a clinical diagnosis of keratomycosis, positive results of corneal fungal cultures, and susceptibility data were reviewed from the years 1987 to 2006. Fungal identification and in vitro antifungal susceptibility test results were recorded. The percentage of susceptible isol...
Molecular characterization and chromosomal assignment of equine cartilage derived retinoic acid sensitive protein (CD-RAP)/melanoma inhibitory activity (MIA).
Gene    October 5, 2007   Volume 407, Issue 1-2 98-104 doi: 10.1016/j.gene.2007.09.022
Berg LC, Mata X, Thomsen PD.Cartilage-derived retinoic acid sensitive protein (CD-RAP) also known as melanoma inhibitory activity (MIA) has already been established as a marker for chondrocyte differentiation and a number of cancerous conditions in humans. Studies have also shown that CD-RAP/MIA is a potential marker of joint disease. The objective of this study was to characterize the equine CD-RAP/MIA gene and thus make it available as a marker in cartilage research and clinical studies. Gene analysis revealed that the equine gene (GenBank accession no. EF679787) consists of four exons and three introns, and the homolo...
Dynamics of sperm DNA fragmentation in domestic animals II. The stallion.
Theriogenology    October 4, 2007   Volume 68, Issue 9 1240-1250 doi: 10.1016/j.theriogenology.2007.08.029
López-Fernández C, Crespo F, Arroyo F, Fernández JL, Arana P, Johnston SD, Gosálvez J.The mixed success of equine artificial insemination programs using chilled and frozen-thawed semen is most likely associated with the variable response of the sperm cell to the preservation process and the fact that stallions are not selected on the basis of reproductive performance. We propose that the traditional indicators of sperm viability do not fully account for male factor infertility in the stallion and that knowledge of sperm DNA damage in the original semen sample and during semen processing may provide a more informed explanation of an individual stallion's reproductive potential. ...
Analysis of Venezuelan equine encephalitis virus capsid protein function in the inhibition of cellular transcription.
Journal of virology    October 3, 2007   Volume 81, Issue 24 13552-13565 doi: 10.1128/JVI.01576-07
Garmashova N, Atasheva S, Kang W, Weaver SC, Frolova E, Frolov I.The encephalitogenic New World alphaviruses, including Venezuelan (VEEV), eastern (EEEV), and western equine encephalitis viruses, constitute a continuing public health threat in the United States. They circulate in Central, South, and North America and have the ability to cause fatal disease in humans and in horses and other domestic animals. We recently demonstrated that these viruses have developed the ability to interfere with cellular transcription and use it as a means of downregulating a cellular antiviral response. The results of the present study suggest that the N-terminal, approxima...
Increased immunogenicity of a DNA-launched Venezuelan equine encephalitis virus-based replicon DNA vaccine.
Journal of virology    October 3, 2007   Volume 81, Issue 24 13412-13423 doi: 10.1128/JVI.01799-07
Ljungberg K, Whitmore AC, Fluet ME, Moran TP, Shabman RS, Collier ML, Kraus AA, Thompson JM, Montefiori DC, Beard C, Johnston RE.A novel genetic vaccine that is based on a Venezuelan equine encephalitis virus (VEE) replicon launched from plasmid DNA is described. The plasmid encodes a VEE replicon under the transcriptional control of the cytomegalovirus immediate-early promoter (VEE DNA). The VEE DNA consistently expressed 3- to 15-fold more green fluorescent protein in vitro than did a conventional DNA vaccine. Furthermore, transfection with the DNA-launched VEE replicon induced apoptosis and type I interferon production. Inoculation of mice with VEE DNA encoding human immunodeficiency virus type 1 gp160 significantly ...
Direct stimulation of the oxidative activity of isolated equine neutrophils by TNF-alpha and IL-1beta.
Veterinary immunology and immunopathology    October 2, 2007   Volume 121, Issue 1-2 101-106 doi: 10.1016/j.vetimm.2007.09.006
Benbarek H, Deby-Dupont G, Deby C, Serteyn D.The capacity of the two cytokines TNF-alpha and IL-1beta to directly stimulate the oxidative activity of polymorphonuclear neutrophils remains debated. The purpose of this study was to verify if a direct stimulation of equine neutrophils by TNF-alpha and IL-1beta was possible. Equine neutrophils were isolated from blood by discontinuous density gradient centrifugation. The cell viability after isolation was >98%. The neutrophils were used at 1.25 x 10(6) cells by assay, immediately after isolation. The oxidative activity of neutrophils was measured by luminol- or lucigenin-enhanced chemilumine...
The presence of 19-norandrostenedione and its sulphate form in yolk-sac fluid of the early equine conceptus.
The Journal of steroid biochemistry and molecular biology    September 29, 2007   Volume 108, Issue 1-2 149-154 doi: 10.1016/j.jsbmb.2007.09.021
Raeside JI, Christie HL.C(18) neutral steroid formation by cytochrome P450 aromatase has been recorded for several equine and porcine tissues. High activity of P450 aromatase is reflected in the quantities of estrogens in yolk-sac (y-s) fluid of early equine conceptuses. In a previous study of y-s fluid we detected large amounts of androgens by radioimmunoassay (RIA), using an antiserum for androstenedione (A(4)). Here, we report that RIA, following chromatography, gave tentative identification of the major peak as norandrostenedione (19-norA) not as A(4). Furthermore, even greater quantities of 19-norA seemed to be ...