Changes of tissue water proton relaxation rates during early phases of chemical carcinogenesis.

Water proton spin lattice relaxation rate (T1) was determined on tissues of rats experiencing early phases of chemical carcinogenesis. Rats were fed a fast acting carcinogen, 3'-methyldimethylaminoazobenzene, and a slower acting carcinogen, 2-acetylaminofluorene, for up to 4 weeks. T1 of blood serum and liver tissue was significantly higher than those of controls after 4 weeks of 3'-methyldimethylaminoazobenzene feeding. This was not the case for 2-acetylaminofluorene. The blood serum T1 increase reflected the onset of liver nodulation (assumed to be preneoplastic). Liver T1 values increased as the degree of nodulation increased. Blood serum T1 correlated inversely with protein content and directly with water content. Liver T1 values correlated with water content, but this was not true for spleen T1 values. Spleen T1 values were significantly lower than controls at the earliest sampling date for each carcinogen: one week for 3'-methyldimethylaminoazobenzene and 4 weeks for 2-acetylaminofluorene. The spleen T1 decrease paralleled an increase of iron detectable by electron spin resonance in this tissue. Spleen T1 decreases are probably not unique to chemical carcinogenesis.