S-adenosylmethionine, S-adenosylhomocysteine and adenosine system. Age-dependent availability in rat brain.

The changes in activity of N-methyltransferase 1 and [3H]-S-adenosylhomocysteine binding were determined in cortical membranes preparations from newborn and 1-, 2- and 10-month-old rats. These parameters were significantly higher: +130 and 200%, respectively, in 1-day compared to 2-month-old rats (adult). With maturation, S-adenosylmethionine levels decreased (-24%) whereas adenosine levels increased gradually from 0.17 to 6.10 nmol/mg protein in forebrain or whole brain between 1-day and 10-month-old rats. The ontogenesis of adenosine receptors was studied. The A2 receptors were not detectable at 1 day. For A1 receptors, Kd and Bmax increased with age while for A2 receptors Kd and Bmax were similar between 9 days and 2 months of age.