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Biomedical subjects

T S Tenforde

Publications and source records attributed to T S Tenforde.

At least 37 records · Page 2Linked to original sources
PubMed1983

Bioelectric properties of frog sciatic nerves during exposure to stationary magnetic fields.

The bioelectric properties of frog sciatic nerves have been measured during exposure to homogeneous, stationary magnetic fields. The action potential amplitude, conduction velocity, absolute refractory period and relative refractory period were found to be unaffected by a continuous 4-h exposure to perpendicular or parallel 2.0 T (1 T equal 10(4) G) magnetic fields. These parameters also remained unchanged during a 1-h post-exposure period. The conduction velocity was similarly found to be unchanged when the field was applied continuously for 17 h. Exposure of sciatic nerves to a 1.0-T field led to no alteration in the threshold for neural excitation. The absence of magnetic field effects on nerve electrical activity observed in the present experiments contrasts with the positive findings reported previously by other investigators. These discrepancies may be attributable to an inadequate control of ambient temperature in the earlier studies.

Action Potentials↗
PubMed1983

Differing electrical surface charge and transplantation properties of genetically variant sublines of the TA3 murine adenocarcinoma tumor.

Comparative measurements have been made of the transplantation and electrical surface charge properties of the near-diploid TA3-Ha ascites tumor and a new hypotetraploid ascites subline designated TA3-L. The negative surface charge density and the density of electrophoretically detectable sialic acid residues were determined to be twice as great for TA3-L as TA3-Ha cells. The two TA3 sublines were found to have identical growth properties in isogeneic mice and to exhibit progressive growth in three allogeneic strains of mice. The lethal tumor cell inoculum in allogeneic mice was lower in all cases for the TA3-L cells. From a comparison of several TA3 ascites tumor sublines, it can be concluded that their transplantability into allogeneic strains of mice is correlated with the density of negative surface charge but is independent of the degree of tumor aneuploidy.

Adenocarcinoma↗
PubMed1981

Alterations in the rat electrocardiogram induced by stationary magnetic fields.

A field strength dependent increase in the amplitude of the T-wave signal in the rat electrocardiogram (ECG) was observed during exposure to homogeneous, stationary magnetic fields. For 24 adult Sprague-Dawley and Buffalo rats of both sexes, the T-wave amplitude was found to increase by an average of 408% in a 2.0 Tesla (1 Tesla - 10(4) Gauss) field. No significant magnetically induced changes were observed in other components of the ECG record, including the P wave and the QRS complex. The minimum field level at which augmentation of the T wave could be detected was 0.3 Tesla. The magnetically induced increase in T-wave amplitude occurred instantaneously, and was immediately reversible after exposure to fields as high as 2.0 Tesla. No abnormalities in any component of the ECG record, including the T wave, were noted during a period of 3 weeks following cessation of a continuous 5-h exposure of rats to a 1.5-Tesla field. The heart rate and breathing rate of adult rats were not altered during, or subsequent to, application of fields up to 2.0 Tesla. The effect of animal orientation within the field was tested using juvenile rats 3-14 days old. The maximum increase in T-wave amplitude was observed when subjects were placed with the long axis of the body perpendicular to the lines of magnetic induction. These experimental observations, as well as theoretical considerations, suggest that augmentation of the signal amplitude in the T-wave segment of the ECG may result from a superimposed electrical potential generated by aortic blood flow in the presence of a stationary magnetic field.

Age Factors↗
PubMed1981

Misonidazole enhancement of radiation-induced growth delay in rat rhabdomyosarcoma tumours exposed to accelerated carbon and neon ions.

The response of a rat rhabdomyosarcoma tumour was assessed by measurements of radiation-induced growth delay resulting from administration of the hypoxic cell sensitizer misonidazole in combination with single and fractionated doses of X-rays and charged-particle radiation. Enhancement ratios of 1.8--2.1 were obtained following single doses of misonidazole (500 mg/kg i.p.) and 225 kV X-rays. Single doses of misonidazole with either carbon-ion or neon-ion radiation in the 4 cm extended-peak ionization region led to enhancement ratios of 1.2--1.3. When combined misonidazole (300 mg/kg i.p.) and X-ray treatments were given in four daily fractions, the enhancement ratios decreased to 1.2--1.5. However, a four-fraction schedule using either carbon-ion or neon-ion radiation in combination with misonidazole gave enhancement ratios of 1.1--1.3, which are similar to the values obtained for single-dose schedules with the sensitizer and charged-particle radiation.

Animals↗
PubMed1980

Assessment of tumour response in a rat rhabdomyosarcoma.

A rhabdomyosarcoma in a WAG/Rij rat with capacity for colony growth after tumour excision and enzymatic dissociation has been used to study response to high and low LET radiation. End points are tumor volume response, TCD50/180, clonogenic capability after tumour irradiation in situ, and in vitro cell survival after irradiation in both the well-oxygenated and the hypoxic conditions. Experience has shown that sublines with different growth rates, radiosensitivity and plating efficiency can arise from the same frozen stock. The conclusions that can be drawn from an analysis of the data obtained to date are as follows: 1. There is no correlation between the doubling times of our two cell lines growing in culture and in the animal. 2. RBE values obtained from growth delay and from TCD50 end points are in fair agreement. 3. Cell survival curves obtained after in situ irradiation show the cells to be more radioresistant than cells irradiated in suspension in vitro. 4. RBE values for cell survival after in situ irradiation compare favourably with those obtained both for tumour growth delay and in vitro cell survival. 5. Not enough is known at present about radiation-altered cell kinetics to develop a self-consistent model of tumour response after irradiation.

Animals↗
PubMed1978

Inhibition of adenocarcinoma TA3 ascites tumor growth by rifamycin derivatives.

A growth inhibitory effect on adenocarcinoma TA3 ascites tumors in LAF1/J mice resulted from the repeated IP administration of subtoxic doses of 3 rifamycin derivatives: rifampicin (Rif)1, dimethylbenzyldesmethylrifampicin (DMB), and rifazone-82 (R-82). A high-viscosity methylcellulose vehicle was found to be essential for obtaining a uniform drug suspension and a significant antitumor effect by the least water soluble derivatives, DMB and R-82. The more hydrophilic derivative, Rif, was found to have a comparable growth inhibitory effect on TA3 cells when prepared in 0.9% NaCl solution with or without added methylcellulose. Oral or SC drug injections did not have an antitumor effect. The results of this study point to the importance of vehicle and route of administration in chemotherapy trials with these compounds.

Adenocarcinoma↗
PubMed1975

Carbodiimide enhancement of complement-dependent antibody-mediated tumor cell lysis in vitro and antitumor activity in vivo.

The water-soluble carbodiimide salt 1-ethyl-3-(3'-dimethylaminopropyl)carbodiimide. HCl (EDCI-HCl) has been shown to increase the complement-dependent lysis of cultured mouse neuroblastoma C1300 cells by two types of antibody: (1) natural antibodies in the sera of normal (nonimmunized) rabbits, and (b) serum antibodies from snygeneic tumor-bearing A/HeJ mice. In the latter case, both the level of serum antibodies and the extent of carbodiimide enhancement of immune lysis were demonstrated in vitro to be substantially greater with sera from mice bearing 21-day-old tumors relative to 4-day-old tumors. The carbodiimide EDCI-HCl has also been found to increase the complement-dependent lysis of cultured TA3 carcinoma cells by serum antibodies from isogeneic LAF1/J mice bearing ascites tumors in advanced stages of growth. Finally, it has been shown that EDCI-HCl exerts an antitumor activity in vivo that is significantly greater against 21-day-old than against 4-day-old neuroblastoma c1300 tumors. The increase in EDCI-HCl activity with tumor age is contrary to the response that would be expected if this drug were serving as an antimetabolite. This is evidenced by data showing that the antimetabolite 6-thioguanine is most effective against young rapidly growing neuroblastoma C1300 tumors. The correlation between carbodiimide antitumor activity and host production of cytotoxic antibodies suggests that EDCI-HCl may operate in vivo by an immunological mechanism comparalbe to that demonstrated in vitro.

Adenocarcinoma↗