RESUMO
Effect of pre- and post-irradiation hyperthermia on the induction of gene conversion (non-reciprocal recombination) in diploid yeast cells was investigated. Post irradiation heat treatment does not significantly modify the frequency of gene conversion. Both low-level (51 degrees C-10 min) and lethal (51 degrees C, 40 min) pre irradiation heat treatments enhanced the gene conversion frequency by 17-49%. There was no quantitative correlation between the observed enhancement and the radiation dose. These results suggest that hyperthermia given prior to radiation not only sensitizes the cells to killing but also increases their convertogenic response. It has been suggested that recombination may be involved in carcinogenesis and tumour promotion. Based on these observations along with other reports, wherein hyperthermia was shown to modify the carcinogenic effects in animals as well as the genetic effects of radiation in vitro, it is possible to suggest that hyperthermia may have a potential to increase the second primary cancers, especially in long term survivors. Certain differences in the mechanism of interaction between radiation and heat in the pre- irradiation and post irradiation modalities appear likely.