Table 1 shows the blood chemistry of the rats used. Aspartame administration, either chronic or acute (NC, NA groups), did not result in significant changes in plasma composition of the rats. In the cirrhotic rats, groups CC and CA, the plasma chemistry was deeply altered. The liver cytology (data not presented) together with altered transaminase levels and plasma chemistry showed that the CC and CA rats were affected by liver cirrhosis. The rats with cirrhosis showed lower urea, albumin and, especially, triacylglycerol levels than the controls. Aspartame administration resulted in no changes in plasma chemistry in normal rats.

Figure 1 shows the radioactivity found in several tissues of rats receiving a single oral dose of labelled aspartame. Liver, blood plasma and kidneys showed the higher radioactivity levels, in the range of 0. 1-0.4 % in each gram of fresh tissue of the dose administered. Since the dose given to each rat was 10 mg, of which a 10.5 % corresponded to methanol (i.e. I mg), 1/1000th of the dose given was just I µg, which means that 0. I% of the dose per gram of tissue was equivalent to 1 µgof methanol/ formic acid/ formaldehyde (= 31 mnol = I ppm). Liver, thus, contained between 1 and 3.7 ppm of label, while plasma and kidneys maintained very stable levels of about 2 ppm, following administration of a single dose. Chronic administration of aspartame (NC group) resulted in a higher yield of label after the last administration, as observed when comparing the data for 6 hours, ranging from 130-140 % of the value obtained in the single NA group. A fairly conservative estimate may indicate that the daily incorporation of aspartame carbon was in the range between 2 and 4 ppm for liver tissue, i.e. after 11 days the accumulation may be up to 30 ppm. In the cirrhotic rats, the pattern of label distribution was quite similar to that of healthy rats. In general, the amount of radioactivity in liver and kidney was lower, but higher in WAT than in normal-liver rats.

 The counting of radioactivity in plasma after acid precipitation of protein (which would set free formic acid and methanol, but not formaldehyde) gave a yield of less ffim 2 % of total label in the supernatant, i.e. practically all the radioactivity in the plasma at 6 hours was bound to protein. The same experiment done with liver gave a yield of 20-23 % of the label in the supernatant, the rest bound to protein and nucleic acids. The form of the time-course of label present in liver agrees with this finding, since there is a certain decay of label present in that organ with time from a peak at 60 min. This same pattern can be found in several other tissues (brown adipose tissue, muscle, brain and eye), but in the end, a significant part of the label can be assumed to be retained bound to protein.

 The specific radioactivity of liver RNA, DNA and protein in the rats treated with very high specific activity labelled aspartame are presented in Table 2. Despite considerable variability in the individual data, RNA showed lower specific activity than DNA and protein had the higher values per mg. The data are also expressed as a ratio of altered versus total structural unit (nucleotide / amino acid), i.e. units incorporating one of the labelled carbons derived from aspartame versus total nucleotides or amino acids. This ratio was obtained by dividing the specific activity found by that of the aspartame in the gavage. The ratios obtained show that the uniformity between protein and DNA was higher than when expressed per unit of weight. Cirrhotic rats showed high liver specific activities, in the same general range as the normal rats did. Roughly, the liver contained about one quarter of its label in "soluble" form, 2/3 in protein and less than 10% in nucleic acids, with a higher share in DNA than in RNA.

 Figure 2 depicts the distribution of label in two thin layer chromatograins, the first showing the label distribution of DNA hydrolysates, from the rats receiving high specific activity aspartame, and the second, run under the same conditions, depicts the location of labelled adenine, guanine and thymine spots. In the DNA hydrolysate, the radioactivity present in the adenine, guanine and thymine spots was nil, since the label was present in another different and distinct spot, which was assumed to correspond to the adduct products of meffimol-derived carbon and DNA constitutive bases. The Rf values for the bases and the adduct were quite different: adduct 0.05/0.0 (first run/second run), guanine 0.10/0.22, adenine 0.40/0.43, thymine 0.57/0.49.

 The separation through HPLC of the labelled fractions in the DNA hydrolysate resulted in three main peaks, eluting at 7.65, 11.94 and 12.86 min. Thymine eluted at 8.95 min, guanine at 9.42 min and adenine at 12.28 min under the same conditions.

 Figure 3 shows the distribution of radioactivity in three thin layer chromatography plates. The first plate shows the label distribution obtained after processing the product of plasma protein hydrolysis from rats treated with high specific activity labelled aspartame. The second plate shows the results of an albumin sample exposed to labelled formaldehyde and ran in parallel with the other samples.