Serine incorporation into phospholipids in vivo and serine phosphoglyceride metabolic transformations in cerebral areas from adult and aged rats.

Serine phosphoglycerides (SPG) in the nervous tissue are synthesized by base-exchange reaction. SPG may be decarboxylated and converted into ethanolamine phosphoglycerides (EPG). This latter reaction may be followed in turn by several enzymatic reactions leading to choline phosphoglycerides (CPG) via three successive methylations. These metabolic pathways are important for several reasons and their contribution to membrane phospholipid renewal has been clearly demonstrated. Base-exchange is the only metabolic route to synthesize SPG; it was therefore possible to test this pathway in vivo by injecting labeled serine. Serine incorporation into phosphoglycerides was reduced in cortex and hippocampus from aged rat brain as compared to adult, while no change in the SPG successive metabolic transformation was found. Based on both the results presented herein and previous ones obtained in vitro the authors suggest that the reduced serine incorporation may be due to reduced uptake into cells from aged animals. This finding leads to the conclusion that the above mechanisms for partial renewal of the phospholipid molecule may play an important role in the brain structure of aged animals.