1H MR visible lipids in colon tissue from normal and carcinogen-treated rats

Metabolic characteristics of colon mucosa, submucosa, muscularis and tumour specimens from four control (n = 105) and nine carcinogen (azoxymethane)-treated (n = 91) Sprague-Dawley rats were investigated by ex vivo 1H MRS. Ninety-seven per cent of pure mucosa samples (n = 59) yielded spectra with narrow lipid resonances (chemical shift delta of -(CH2)n-, 1.3 ppm; linewidth at half-height v1/2, 30-50 Hz). Eighty-two per cent of control mucosa samples with histologically proven submucosa contamination (n = 11) and 46% of control cross-sections (containing mucosa, submucosa and muscularis; n = 57) yielded spectra with broad lipid resonances (delta-(CH2)n-, 1.5 ppm; v1/2, 80-100 Hz) identical to those of adipose tissue surrounding rat colon. Thirty per cent of tumour samples (n = 10) yielded spectra with narrow lipid resonances while 70% contained no significant amount of MR visible lipids. We conclude that (i) lipids giving rise to broad resonances are in the heterogeneously distributed adipocytes of submucosa, (ii) lipids giving rise to narrow resonances are within the mucosa in an unknown structural environment, and (iii) the type and distribution of lipids in human and rat colon are similar. Tumours contained significantly more taurine than pure control mucosa (n = 15; p < 0.004) and pure mucosa containing aberrant crypt foci (putative preneoplasm, n = 36; p < 0.002). Our results suggest that the rat colon is a good model for 1H MR investigations of human colon carcinogenesis.