Variations in S-adenosylmethionine, S-adenosylhomocysteine and adenosine concentrations in rat liver

The hepatic concentrations of S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH) and adenosine (Ado) in the rat were examined diurnally and as a function of fasting. Ado concentrations increased continuously throughout the fasting period; concentrations after 2 days of fasting were 7.5-fold higher than control values. Diurnally, the concentration of Ado was highest during the light hours. SAM and the ratio of SAM/SAH were reduced greater than 50% due to fasting and exhibited a significant daily rhythm which appeared to be related to dietary methionine availability. Hepatic SAM concentrations decreased continuously during the light hours and increased during the dark period to levels 7.3-fold greater than the lowest light values. The concentration of SAH was altered in a similar fashion yet to a much lesser degree such that the ratio of SAM/SAH paralleled the changes in the concentration of SAM. The SAM/SAH ratio exhibited a 4.5-fold difference between the peak and nadir values.