Abstract
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 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.