Implications of methionine and S-adenosylmethionine for the brain function

We have studied the effect of S-adenosylmethionine (SAM) on tail flick latency in the rat. We also studied the effect of methionine the immediate precursor of SAM. Administration of methionine to the rat increases brain SAM, but little is known about its behavioral effects. Long-Evans rats were given SAM and methionine orally at different doses and tail-flick latency was measured at various times. Both methionine and SAM increased tail-flick latency, but methionine did so at a lower dose. A biochemical study showed that methionine was more effective than SAM in raising brain SAM probably because it is transported better into brain. The biochemical measurements were not consistent with the idea that the effects of SAM and methionine were mediated by an increase in brain 5-HT.Folate deficiency can lower brain SAM levels and cause depression. Thus, methionine, which raises brain SAM, may overcome the effects of folate deficiency. Seven day food records were done by 26 psychiatric outpatients who were stable on lithium treatment. Eight patients had mean daily folate intakes below those recommended. Some of those with low folate intake had high methionine intake consistent with the idea that methionine could substitute metabolically for folate deficiency. Daily methionine intakes ranged from 13 to 304% of the recommended intake. As methionine had behavioral effects in the rat at doses much less than the daily dietary intake this raises the question of whether varying daily intakes of methionine in humans have behavioral implications. (Abstract shortened by UMI.