[The effect of gamma irradiation on the strain W of Tetrahymena pyriformis]. / Vplyv gama-ziarenia na Tetrahymena pyriformis kmen W.

It the present study the effects of gamma-radiation at doses of 102.1 Gy-1,633.4 Gy were investigated as exerted on the protozoan Tetrahymena pyriformis W strain. An investigation of lethality showed that all irradiated cells survived after the doses of 102.1 Gy and 204.2 Gy, When the doses of 408.4 and 816.7 Gy were applied, 60.6% and 8.8%, resp., of irradiated cells survived. Not a cell survived the dose of 1,633.4 Gy. The effects of gamma-radiation on the generation time of Tetrahymena pyriformis are shown in Tab. II. A markedly longer generation time than in the control was observed if the radiation doses made 408.4 and 816.7 Gy. There were no significant changes there when the effects of irradiated incubation media on the growth of nonirradiated cells of the W strain of Tetrahymena pyriformis were investigated. The results confirmed the relatively high radioresistance of the Tetrahymena protozoon with respect to gamma-radiation; this protozoan is a suitable biological model for a study of the effects of various kinds of ionizing radiation at the level of both cell and population.

Influence of acute hypoxia upon brilliant cresyl blue-induced disintegration of erythrocytes in rabbits and cats.

The disintegration of erythrocytes by brilliant cresyl blue was studied in rabbits and cats during two hypoxic periods resulting in apnoea which was followed by artificial ventilation and recovery. The rate of erythrocyte disintegration was measured after 2 hours' incubation in isotonic NaCl or Krebs-Ringer solution plus brilliant cresyl blue (0.5 mmol.l-1). Significant increases of disintegration rates were found in rabbits during recovery in both incubation solutions. Erythrocytes in cats seemed to be more resistant to acute hypoxia, as their disintegration rate rose only in isotonic NaCl solution, and that only transiently. Brilliant cresyl blue--induced erythrocyte disintegration in cats did not differ from the control values during 10 min of spontaneous breathing after the first and the second period of hypoxia in the isotonic NaCl solution, but it was significantly lower in Krebs-Ringer solution. The possible factors influencing the erythrocyte disintegration rate in acute hypoxia are discussed.

Anti-hypoxic potency of cerebroprotective drugs studied in a model of acute reversible respiratory failure.

The protective efficacy of pentoxiphylline, piracetam, and dihydroergotoxine against abrupt hypoxia was tested in a model of acute reversible respiratory failure, where repeated apnoeic attacks were induced by inhalation in repeated hypoxic exposures was reduced in control as well as in dihydroergotoxine-treated animals, it was increased after pentoxiphylline, and was not changed after piracetam. Repeated N2 inhalations reduced the duration of apnoea required for the development of mydriasis in all control cats. There were, however, no such reductions of the apnoeic interval in animals of the three groups treated with cerebroprotective drugs. The ratio between the total duration of hypoxia (hypoxic hyperventilation plus apnoea) and the time of recovery of breathing was significantly higher in the pentoxiphylline-treated animals already during the first hypoxic attack after drug application when compared both to the control and the dihydroergotoxine-treated animals. After piracetam the difference was apparent in the last hypoxic attack only. The model of acute reversible respiratory failure with apnoeic episodes induced repeatedly seems to be useful for testing some properties of cerebroprotective drugs during abrupt hypoxia.

[Use of sheep erythrocytes and plasma for the determination of neuroparalytic substances in vitro]. / Vyuzitie baraních erytrocytov a plazmy na stanovenie nervovoparalytických látok in vitro.

A simple method of the determination of nerve-paralytic substances is presented, based on the use of ram erythrocytes and plasma with the determination of cholinesterase inhibition. Dichlorvos administered at the rate of 94.64 ng per litre induced 50% inhibition of acetylcholinesterase in the erythrocytes; administration of dichlorvos at the rate of 243.82 ng per litre caused a 50% inhibition of butyrylcholinesterase in the plasma.

[A biological method for the determination of mycotoxins--Tetrahymena pyriformis]. / Biologická metóda na stanovenie mykotoxínov--Tetrahymena pyriformis.

The toxic action of selected mycotoxins on a biological subject was tested in the protozoan Tetrahymena pyriformis. The following toxins were tested: toxin T-2 at doses from 1.52 micrograms to 100.0 mg per litre of medium, ochratoxin A at doses from 12.21 micrograms to 800.0 mg per litre of medium, and rubratoxin B at doses from 12.21 micrograms to 800.0 mg per litre of medium. In toxin T-2 the LD100 was found to be about 390.63 micrograms and LD50 about 48.83 micrograms per litre of medium. In ochratoxin A the LD100 was about 25.0 mg and LD50 about 3.13 mg per litre of medium. In rubratoxin B the LD100 was about 200.0 mg and LD50 about 25.0 mg per litre of medium.