PubMed Health⌕ Search

Biomedical subjects

T C Orton

Publications and source records attributed to T C Orton.

9 recordsLinked to original sources
PubMed1992

Proto-oncogene activation in liver tumors of hepatocarcinogenesis-resistant strains of mice.

Activation of the ras family of oncogenes occurs frequently in liver tumors of the B6C3F1 mouse, a strain which is highly sensitive to hepatocarcinogenesis. Many other mouse strains are much more resistant to hepatocarcinogenesis; the aim of this study was to determine the frequency and pattern of oncogene activation in spontaneous and chemically induced liver tumors of three such strains, the C57BL/6J, the C57BL/6 x DBA/2 F1 hybrid (B6D2F1) and the C57BL/6 x Balb/c F1 hybrid (B6BCF1). The C57BL/6, DBA/2 and Balb/c strains are all relatively resistant to spontaneous hepatocarcinogenesis (1.5-3.6% of animals develop liver tumors in 2 years); with regard to chemically induced hepatocarcinogenesis the Balb/c is highly resistant, the C57BL/6 has low susceptibility and the DBA/2 has low to moderate susceptibility. The nude mouse tumorigenicity assay was used to search for activated oncogenes in 15 C57BL/6J liver tumors induced by a single neonatal dose of vinyl carbamate (VC, 0.15 mumol/g body weight). Three tumors contained H-ras genes activated by point mutations at codon 61 and one contained a non-ras oncogene. The polymerase chain reaction and allele-specific oligonucleotide hybridization were used to study H-ras mutations in spontaneous and VC-induced tumors from all three strains of mice. The frequency of H-ras codon 61 mutations in tumors induced by 0.15 mumol/g body weight VC in the C57BL/6J mouse (5/37) was similar to that in spontaneous tumors (2/9); surprisingly, tumors induced by a lower dose of VC (0.03 mumol/g body weight) had a higher frequency of H-ras mutations (12/28). The frequencies of H-ras activation detected in VC (0.03 mumol/g body weight)-induced tumors from the two F1 hybrids studied differed markedly. Only one VC-induced B6BCF1 tumor contained a mutated H-ras gene (1/10), whereas the majority of B6D2F1 tumors contained such mutations (23/33). Several spontaneous B6D2F1 liver tumors contained H-ras codon 61 mutations (6/15). Thus, H-ras activation frequency does not determine susceptibility to hepatocarcinogenesis in inbred mice and their F1 hybrids, since a relatively high frequency of H-ras mutations was observed in two resistant strains and a low frequency was found in the other strain.

3T3 Cells↗
PubMed1992

Point mutation analysis of ras genes in spontaneous and chemically induced C57Bl/10J mouse liver tumours.

The high incidence and profile of ras gene mutations reported in spontaneous and chemically induced liver tumours of the B6C3F1 mouse provides a potential means of determining in vivo genotoxicity and its relevance to carcinogenicity. We analysed spontaneous and chemically induced [with 4-amino-biphenyl (ABP), 2-acetylaminofluorene (AAF) and diethylnitrosamine (DEN)] hepatocellular tumours of the C57Bl/10J mouse for H-ras, K-ras and N-ras gene mutations to see if mutational analysis of the ras genes could be useful for such a determination in this strain. Regions of DNA spanning codons 12, 13 and 61 of the ras genes were amplified from formalin fixed liver tumour sections using the polymerase chain reaction. Mutations were detected using allele specific oligonucleotide probing and confirmed by sequencing. We have found that there are few ras mutations in either spontaneous or chemically induced liver tumours in the C57Bl/10J mouse. Out of 25 spontaneous tumours two contained an A to T transversion and one contained an A to G transition in base 2 of H-ras codon 61 and two contained a G to A transition in base 2 of K-ras codon 13 (the K-ras mutations were only faintly detectable and may be present in a subpopulation of the tumour cells). In the case of the 18 ABP induced tumours one contained a C to A transversion in base 1 of H-ras codon 61, and one contained an A to T transversion in base 2 of H-ras codon 61 and one contained a G to C transversion in base 1 of K-ras codon 13. One C to A transversion in base 1 of H-ras codon 61 was detected out of eight AAF induced tumours. Of the 25 DEN induced tumours, one contained an A to G transition and one contained an A to C transversion in base 2 of H-ras codon 61. The data indicate that at least in hepatocellular tumours of the C57Bl/10J strain and using chronic dosing regimes the ras genes do not represent markers for in vivo genotoxic activity.

2-Acetylaminofluorene↗
PubMed1991

Hepatocarcinogenic effect of vinyl carbamate in the C57Bl/10J strain mouse.

The genotoxic carcinogen vinyl carbamate was dosed to C57Bl/10J strain mice for 35 weeks, and the study terminated after week 59. A main study group of 55 males and 50 females was dosed 6 mg/kg vinyl carbamate once weekly by intraperitoneal injection, whilst a reference group of 10 animals/sex were kept undosed. From week 39 onwards there was a high incidence of mortality, which was often associated with acute internal abdominal hemorrhage. Mice of both sexes killed from 34 weeks onwards frequently showed macroscopic evidence of blood-filled, cyst-like structures in the liver. Upon histopathological examination widespread peliosis hepatis was observed with frequent progression to hemangiomata and hemangiosarcomata. Trabecular hepatocellular carcinomata were also apparent, often within the same liver sections and invariably associated with peliosis hepatis. As a consequence of its tumor burden, the liver often showed hepatocyte atrophy, fibrosis, and coagulation necrosis. A small number of livers revealed hepatocellular adenomata and altered hepatocyte foci.

Animals↗
PubMed1990

Effect of tumour promoters and non-genotoxic carcinogens on terminal differentiation and proliferation in mouse teratoma XB2 cells cultured in low calcium medium.

XB2 cells, a teratocarcinoma derived cell line of keratinocyte lineage, have been shown to proliferate and differentiate in low calcium medium (0.03 mM Ca2+) at a density of 500 cells/9.6 cm2 without the need for fibroblast feeder layers or conditioned medium. The degree of differentiation can be assessed by measurements of keratin production and stratification of colonies of cells. Both of these parameters, as well as the proliferative capacity of the cells, can be altered by treatment of the cultures with various promoting agents and non-genotoxic carcinogens. Treatment with teleocidin and 12-O-tetradecanoyl phorbol-13-acetate induced large increases in proliferation, stratification and keratinization; mezerein-treated cells showed increased stratification at higher doses; butylated hydroxyanisole treatment resulted in hyperkeratinization and hyperstratification to lower levels than that seen with the phorbol-ester-like promoters; butylated hydroxytoluene had purely hyperproliferative effects. We suggest that this culture system may provide a useful model for studies of the mechanism of promotion and non-genotoxic carcinogenesis in epithelial tissues.

Animals↗
PubMed1975

The pharmacodynamics of 5-hydroxytryptamine uptake and metabolism by the isolated perfused rabbit lung.

We have investigated the dynamics for the removal of 5-hydroxytryptamine (5-HT) from the circulation using the isolated perfused rabbit lung. 5-HT was removed from the circulation at a constant rate and metabolized completely to 5-hydroxyindoleacetic acid which effluxed from the lung into the circulation. Two methods were developed to determine the constant rate of removal of 5-HT: (1) the constant rate is equal to the difference between the 5-HT concentration flowing into the lung and the 5-HT concentration in the effluent times the flow rate and (2) extrapolation of the rate of appearance of radioactivity in the effluent to zero time. With these methods, we have confirmed the 5-HT is removed by the lung by a carrier-mediated Na+-dependent transport system. Studies of transport systems in perfused organs required an adequate supply of the chemical to the lung. Supply rates less than removal rate will result in erroneous measurements of the constant removal rate. The relationships between the rate of removal, perfusate concentration and perfusion rate were analyzed.

Animals↗
PubMedDate not supplied

A study of the dynamics of imipramine accumulation in the isolated perfused rabbit lung.

An isolated perfused rabbit lung preparation (IPL) was used to study the uptake, accumulation, and efflux of the tricyclic amine imipramine (IMIP). The rate of IMIP uptake into the IPL was resolved into two exponential components (rates 1 and 2 of uptake). The initial velocities for these uptake components were linearly related to the concentration of IMIP in the perfusate (Cp). This linear relationship indicates that IMIP accumulated in the IPL by diffusion and/or binding. The steady-state accumulation of IMIP was obtained by integration of the exponential expression relating the rate of IMIP uptake to time. The amount of IMIP accumulated at steady state by rate 1 was linearly related to Cp, whereas the amount of IMIP accumulated at steady state by rate 2 was saturable with respect to Cp. These steady-state data are in agreement with the steady-state accumulation data previously reported from experiments with the recirculating blood-perfused rabbit lung. In the absence of IMIP in the perfusate. IMIP that had previously accumulated in the IPL effluxed from the lung at three rates (t1/2 = 18 sec, 58 sec, and 8.25 min), which indicates that accumulated IMIP was in at least three pools in the lung. In addition, a noneffluxable pool was detected which was not the result of irreversible binding to tissue.ated in pools 1 and 2 by rate 1 of uptake. The IMIP in pool 3 and in the noneffluxable pool was accumulated in the IPL by rate 2 of uptake. Efflux pool 3 and the IMIP accumulated at a steady state by rate 2 of uptake were resolved by a Hofstee plot into a biphasic curve indicating two types of binding sites. The noneffluxable pool of IMIP in the IPL was saturable with increasing Cp and represented approximately 30% of the IMIP accumulated by rate 2 into pool 3. Rate 2 of uptake, pool 3, and particularly the noneffluxable pool of IMIP in the IPL are possibly responsible for the accumulation and persistence of Imip in the lung as seen in whole body distribution studies. The physicochemical properties of IMIP and other compounds known to be accumulated in lung tissue are discussed in relation to the possible involvement of lung phospholipids and the compartmentalization of IMIP in the concentric lamellar organelles of the lung.

Animals↗