256 Brain Research, 229 (1981) 256-259 Elsevier/North-Holland Biomedical Press Age dependent changes in the methylation of rat brain phospholipids FULTON T. CREWS, GABRIELLA CALDERINI, ANTONIO BATTISTELLA and GINO TOFFANO Department of Pharmacology, The Universityof Florida Medical School, Gainesville, FL 32610 (U.S.A.) and ( G.C., A.B. and G.T.) Fidia Research Laboratories, Albano Terme (Italy) (Accepted August 20th, 1981) Ke.v words: aging -- brain -- phospholipid methylation Phospholipid methyltransferase I and II enzymes methylate phosphatidylethanolamine three times to form phosphatidylcholine. The activity of these two enzymes was determined in synaptosome- enriched fractions from rats 1, 3, 7, 15 and 21 months old. The activity of phospholipid methyltrans- ferase I was significantly greater in 7-, 15- and 21-month-old rats than in 1- and 3-month-old rats. In contrast, the activity of phospholipid methyltransferase II did not change with age. These changes in methyltransferase activity with increasing age may be related to changes in fl-receptor function with increasing age. The methylation of phospholipids is involved in the activation of a number of different receptors including the fl-adrenergic receptor where it has been shown to affect both the number of receptor binding sites 6 and the activation of adenylate cyclase 3. In rat brain there is an age dependent decrease in the number of fl-adrenergic receptor binding sites a,5. We investigated the changes in the methylation of phos- pholipids in rat brain with age to determine if these changes could explain the alterations in fl-adrenergic receptors. In the present studies we report an age dependent increase in the activity of phospholipid methyltransferase I (PMT I) ac- tivity, the rate-limiting enzyme in phospholipid methylations. In contrast, there was no age dependent change in the activity of phospholipid methyltransferase II (PMT II). The increase in PMT I activity with increasing age could represent an attempt to com- pensate for losses in fl receptor responsiveness due to a decreased number of receptors. Sprague-Dawley rats were maintained on a restricted diet of 30 mg of Altromin pellets/day in order to minimize differences in body weight. Rats presenting visible tumors were discarded. Animals of various ages were sacrificed by decapitation, a mid- line sagittal section was made and one-half of the brain was rapidly frozen on dry-ice. On the day of the assay samples were thawed and homogenized in 5 ml 10 °/o sucrose, 5 mM Tris-HC1 buffer, pH 7.4. The P2 pellet or synaptosome-enriched fraction was prepared and used for the assay of phospholipid methyltransferase I (PMT I) and phospholipid methyltransferase II (PMT II). PMT I and PMT II were assayed as described previously I except that 10 ~ trichloroacetic acid was not neutralized. Briefly, 0006-8993/81/0000-0000/$02.75 © Elsevier/North-Holland Biomedical Press