Paramagnetic changes during development of DMBA-induced mammary tumours in Sprague-Dawley rats

Paramagnetic changes occurring during development of mammary tumours in Sprague--Dawley rats induced by the chemical DMBA were studied using electron spin resonance. A two-fold increase in free-radical signal intensity was observed at the time of appearance of the tumour. The free radical concentration remained elevated to this level throughout the experiment. This change is different from the gradual decrease reported for frozen ESR samples in other experimental tumour systems and from the pattern reported for lyophilised samples. A gradual increase in the concentration of Mn2+ was also observed. A high frequency (35 GHz) ESR spectrometer was used which enabled us to study the small amount of tissue available from small tumours and normal breast tissue. Quantitative histological analysis of the samples after ESR study indicated that the ESR signal in the normal tissues could not be attributed to any particular cell type, including glandular cells. The increase observed in the tumour appeared to be due to an increased concentration of paramagnetic species in the tumour cells. Most of the tumours were adenocarcinomas but several benign adenomas were also observed. The ESR signals in the benign tumours were indistinguishable from those of the malignant tumours.